swamptandem
02-14-12, 11:26 AM
http://www.bikerumor.com/2012/02/14/road-bike-disc-brakes-are-coming-but-will-they-work/#more-39660
Tandem Cycling - Good info on disc brakes
Bikeforums.net is a forum about nothing but bikes. Our community can help you find information about hard-to-find and localized information like bicycle tours, specialties like where in your area to have your recumbent bike serviced, or what are the best bicycle tires and seats for the activities you use your bike for.coldfeet
02-14-12, 12:29 PM
I would call it "interesting" info.
Going all weight weenie on your braking surfaces is a bit chancy. I was interested to read that bit from the Shimano guy about how much braking force you can get from a road front wheel. I currently ride a BB7 on the front of my old tourer, but it's my Winter bike so I don't expect to run into the same problem, but I will inspect the disc surface before I next ride to see how it's doing.
Going all weight weenie on your braking surfaces is a bit chancy. I was interested to read that bit from the Shimano guy about how much braking force you can get from a road front wheel. I currently ride a BB7 on the front of my old tourer, but it's my Winter bike so I don't expect to run into the same problem, but I will inspect the disc surface before I next ride to see how it's doing.
wheelspeed
02-14-12, 07:31 PM
I think the author mislabeled the article. He had very light weight disc brakes that are meant for conditions in which you barely need brakes, and took them down a big steep asphalt road. Then, with undersized brakes, he did the worst thing and held them on for a long time, letting them build up heat. That disk brake "failure" is as much a failure as if he wrote an article after his cyclocross knobby tires slipped on an asphalt road, causing him to crash.
It was interesting to read the mfr's comments about the challenges of introducing disk brakes to road bikes, but I wish one of them called him out on his ignorance of using an undersized brake on a steep downhill road. :-)
It was interesting to read the mfr's comments about the challenges of introducing disk brakes to road bikes, but I wish one of them called him out on his ignorance of using an undersized brake on a steep downhill road. :-)
Chris_W
02-15-12, 02:15 AM
There is some excellent information in this article from informed experts in the field about the problems associated with putting disc brakes on road bikes (and problems with disc brakes in general). Getting such candid, open, and informative comments from Shimano, Magura, Tektro, and Hayes is almost unheard of these days, and it makes fascinating reading. A lot of the issues raised apply even more so to tandem bikes than to single bikes. Here is a summary of my impressions and things that I learned from reading the article.
Looking again at the Avid BB7 in light of this article
Fortunately, most road-tandem disk brake setups avoid many of the possible causes of the author's incident, given that the standard setup is an Avid BB7 with a 203 mm rotor. First, there is no hydraulic fluid to boil with the mechanical, cable brakes. Second, the large and heavy rotors should dissapate heat reasonably well. Third, brake pad size was mentioned as being an important factor, and the BB7 brakes have decent-sized pads that are larger than those on many regular (single-piston) MTB disc brakes. I'm assuming that dual-pistons would not be possible with cable brakes, so a bigger pad may not be possible.
This all suggests why Avid have not launched a lightweight version of the BB7: It sounds like this would introduce far too many performance compromises - most of us would be best to stick with the current BB7 even if there was a lighter version offered. I've never liked hydraulic brakes purely from a maintenance point of view, when coupled with the fact that the BB7 brakes that I've got on a couple of bikes work so well means that I cannot see the point of having the hassle of hydraulics. This article has taught me about another major downside of hydraulic brakes, the potential of boiling the fluid all too easily, and now I'm even more strongly against them.
I'm therefore not sure that the Avid BB7 can be improved upon by much in terms of it's braking functionality and reliability; it is already very close to the ultimate disc brake for all-purpose riding. My only small gripes with the BB7 is that it protrudes from the frame/fork too much, causing excessive interference with fenders and racks and the pads could be made easier to change (I've worked on other disc brakes that are better on both of these criteria).
Analysis of author's incident
I am not surprised that the author's set-up, designed for CX use and then further tuned to reduce weight, failed in this situation. However, I am a little surprised at how quickly this happened. Looking at the posted graphs, the time from the start of the downhill (2:36:40) until the point he marked just before the brakes failed totally and the speed started to shoot up (2:38:11) was 1 minute 30 seconds! His speed was climbing steadily from 20 to 30 mph during this time, so the distance cannot have been much more than 0.5 miles (1 km)! You can see in the photo at the top of the article that this is not a big guy, so the weight was certainly not extreme. Even given his terrible braking technique, I would have expected the brakes to last for more than 1 km, so this is very revealing.
It would be nice to see results of controlled studies showing how the factors mentioned in the article: rotor size, rotor mass, pad size, hydraulic vs cable operation, etc., affect failure times. The manufacturers obviously have data on such things, and this is what their responses are partly based on, but it would be nice to see the actual numbers.
Future of disc brakes on road bikes
There are a lot of journalists and regular cyclists who are getting excited about the idea of disc brakes on road bikes. It is fascinating to read that many of the major manufacturers have significant reservations on the topic.
Looking again at the Avid BB7 in light of this article
Fortunately, most road-tandem disk brake setups avoid many of the possible causes of the author's incident, given that the standard setup is an Avid BB7 with a 203 mm rotor. First, there is no hydraulic fluid to boil with the mechanical, cable brakes. Second, the large and heavy rotors should dissapate heat reasonably well. Third, brake pad size was mentioned as being an important factor, and the BB7 brakes have decent-sized pads that are larger than those on many regular (single-piston) MTB disc brakes. I'm assuming that dual-pistons would not be possible with cable brakes, so a bigger pad may not be possible.
This all suggests why Avid have not launched a lightweight version of the BB7: It sounds like this would introduce far too many performance compromises - most of us would be best to stick with the current BB7 even if there was a lighter version offered. I've never liked hydraulic brakes purely from a maintenance point of view, when coupled with the fact that the BB7 brakes that I've got on a couple of bikes work so well means that I cannot see the point of having the hassle of hydraulics. This article has taught me about another major downside of hydraulic brakes, the potential of boiling the fluid all too easily, and now I'm even more strongly against them.
I'm therefore not sure that the Avid BB7 can be improved upon by much in terms of it's braking functionality and reliability; it is already very close to the ultimate disc brake for all-purpose riding. My only small gripes with the BB7 is that it protrudes from the frame/fork too much, causing excessive interference with fenders and racks and the pads could be made easier to change (I've worked on other disc brakes that are better on both of these criteria).
Analysis of author's incident
I am not surprised that the author's set-up, designed for CX use and then further tuned to reduce weight, failed in this situation. However, I am a little surprised at how quickly this happened. Looking at the posted graphs, the time from the start of the downhill (2:36:40) until the point he marked just before the brakes failed totally and the speed started to shoot up (2:38:11) was 1 minute 30 seconds! His speed was climbing steadily from 20 to 30 mph during this time, so the distance cannot have been much more than 0.5 miles (1 km)! You can see in the photo at the top of the article that this is not a big guy, so the weight was certainly not extreme. Even given his terrible braking technique, I would have expected the brakes to last for more than 1 km, so this is very revealing.
It would be nice to see results of controlled studies showing how the factors mentioned in the article: rotor size, rotor mass, pad size, hydraulic vs cable operation, etc., affect failure times. The manufacturers obviously have data on such things, and this is what their responses are partly based on, but it would be nice to see the actual numbers.
Future of disc brakes on road bikes
There are a lot of journalists and regular cyclists who are getting excited about the idea of disc brakes on road bikes. It is fascinating to read that many of the major manufacturers have significant reservations on the topic.
swamptandem
02-15-12, 05:26 AM
I think it was mostly rider error with this guys crash. However I would not use that brake setup on a road bike or tandem.
I also learned at a very early age (16yrs) that you "stab" brakes, never ride them. My friends taught me this when we used to race our sports cars down Mt. Lemon in Tucson, AZ. I've applied that knowledge to braking ever since.
I did learn from the article that the brake fluid can boil. Didn't know that part of it.
As for the Ashima rotors, my wife and both have them on our MTBs (intended use) and they work great. Also very light weight.
Bottom line: poor braking technique is most likely to cause you problems with any brake setup on any type of vehicle. Poor technique and an inferior brake system will almost certainly hurt you. Tandem captains have to be "good" on the brakes!
I also learned at a very early age (16yrs) that you "stab" brakes, never ride them. My friends taught me this when we used to race our sports cars down Mt. Lemon in Tucson, AZ. I've applied that knowledge to braking ever since.
I did learn from the article that the brake fluid can boil. Didn't know that part of it.
As for the Ashima rotors, my wife and both have them on our MTBs (intended use) and they work great. Also very light weight.
Bottom line: poor braking technique is most likely to cause you problems with any brake setup on any type of vehicle. Poor technique and an inferior brake system will almost certainly hurt you. Tandem captains have to be "good" on the brakes!
TandemGeek
02-15-12, 06:50 AM
Hopefully folks with tandems will draw on the experience of road and off-road tandem teams who have been using disc brakes on tandems as long-back as the mid-90s. There's a wealth of information out there on mechanical, hydraulic and hybrid systems that have been used -- successfully and less than successfully -- on road and off-road tandems.
Regarding hydraulics, if anyone is running them they need to get up to speed on periodic maintenance requirements. Mineral Oil and DOT fluids both have their limits in terms of heat capacity, but DOT fluids demand more attention than Mineral Oil to ensure their heat capacity / resistance to boiling is maintained. Special, high-heat fluids like Motul 600 are prudent to use, but still demand nearly annual fluid changes to keep their high-heat capacity ratings.
Regarding hydraulics, if anyone is running them they need to get up to speed on periodic maintenance requirements. Mineral Oil and DOT fluids both have their limits in terms of heat capacity, but DOT fluids demand more attention than Mineral Oil to ensure their heat capacity / resistance to boiling is maintained. Special, high-heat fluids like Motul 600 are prudent to use, but still demand nearly annual fluid changes to keep their high-heat capacity ratings.
waynesulak
02-15-12, 08:52 AM
The lure of hydraulics is the great power transfer and modulation. Early reports from hydraulic rim brakes soon to be released appear to say that the weight will be slightly more than current double pivot calipers.
http://www.bikeradar.com/news/article/magura-rt8-tt-first-look-32961/
The idea of a rear hydraulic rim brake is very appealing to me especially since the fluid is physically much farther away from the friction and therefore should be less prone to boiling. Tire blow off would still be an issue of course so the stab and release method is still needed. For non mountain riders like us however a light rear hydraulic rim brake could greatly increase brake performance.
The article does make me wonder how many people replace their DOT brake fluid annually,
Wayne
http://www.bikeradar.com/news/article/magura-rt8-tt-first-look-32961/
The idea of a rear hydraulic rim brake is very appealing to me especially since the fluid is physically much farther away from the friction and therefore should be less prone to boiling. Tire blow off would still be an issue of course so the stab and release method is still needed. For non mountain riders like us however a light rear hydraulic rim brake could greatly increase brake performance.
The article does make me wonder how many people replace their DOT brake fluid annually,
Wayne
TandemGeek
02-15-12, 11:07 AM
The idea of a rear hydraulic rim brake is very appealing to me especially since the fluid is physically much farther away from the friction and therefore should be less prone to boiling.
Magura Hydraulic rim brakes were OEM on both Cannondale's RT3000 (Magura HS66) and MT3000 (Magura HS11) tandems back in the late 90's. We had a '98 Cannondale MT3000 that came with the HS11s.
Their downfall for road tandem use was lack of compatibility with integrated shifting, which became standard fare at the same time. One company came out with an aftermarket integrated shifting system for the hydralics, but they were a compromise at best.
Hydralics then were not lightweight by any stretch, but they were low maintenance in that they used Mineral Oil (which doesn't absorb water like DOT fluids) and had more stopping power than any other rim brake that has been offered before or since. In fact, they pretty needed brake stiffiners because they easily deflected the rear stays and even Cannondale's fairly massive Pepperoni forks under heavy brake input, moreso than any V-Brake.
http://gallery.mtbr.com/data/mtbr/500/Magura_HS66_NOS_2.JPG
Magura Hydraulic rim brakes were OEM on both Cannondale's RT3000 (Magura HS66) and MT3000 (Magura HS11) tandems back in the late 90's. We had a '98 Cannondale MT3000 that came with the HS11s.
Their downfall for road tandem use was lack of compatibility with integrated shifting, which became standard fare at the same time. One company came out with an aftermarket integrated shifting system for the hydralics, but they were a compromise at best.
Hydralics then were not lightweight by any stretch, but they were low maintenance in that they used Mineral Oil (which doesn't absorb water like DOT fluids) and had more stopping power than any other rim brake that has been offered before or since. In fact, they pretty needed brake stiffiners because they easily deflected the rear stays and even Cannondale's fairly massive Pepperoni forks under heavy brake input, moreso than any V-Brake.
http://gallery.mtbr.com/data/mtbr/500/Magura_HS66_NOS_2.JPG
rdtompki
02-15-12, 01:47 PM
It's incredible that only a 500' elevation drop would have resulted in failure. I've done one 2400' descent on my Volagi on a twisty, steep ranch road with no brake fade whatsoever. Total descent was more like 3000'. When I used the brakes, which was often, I used them hard, but let the bike run quite a bit. I'm 200 lbs so not a featherweight. But, I have cable-actuated discs. Obviously, I'm a big fan of discs.
when
02-15-12, 01:58 PM
I've heard of people riding their BB7s so hard on descents that the red adjustment knobs melted, but the brakes still worked fine. Oh wait, that was me. :)
Ritterview
02-15-12, 05:42 PM
I've heard of people riding their BB7s so hard on descents that the red adjustment knobs melted, but the brakes still worked fine. Oh wait, that was me. :)
There is another mechanical disc brake, the Bengal (http://www.bengalperformance.com.tw/products3659.html?ino=7), the MB700T version of which that Santana modifies and uses. It doesn't have any plastic bits, and it was found not to have as many problems on a challenging descent (http://www.bikeforums.net/showthread.php/759413-Tandems-on-Mt-Ventoux?highlight=Mt+Ventoux). Of course, it is usually paired with a 10" rotor, which must have greater heat capacity than the 8" rotors usually paired with BB7's.
I spoke with Tim at Santana all about brakes. He thinks the Bengal superior to the Avid BB7 (but that's what they said about the defunct Winzip, too).
The Santana/Bengal caliper could be installed on other tandems, but according to Tim at Santana, it needs to be attached as are Santana's onto the chainstay rather than the more common seatstay mount.
Akexpress has a mountain version of the Bengal on their Calfee (http://www.bikeforums.net/showthread.php/759413-Tandems-on-Mt-Ventoux?p=13196560&viewfull=1#post13196560), and a positive report (http://www.bikeforums.net/showthread.php/769717-Bengal-Brake-Update-from-Cycle-Oregon?p=13256101&highlight=#post13256101), but I've not seen the technical details of how it was done. TG has an informative blog post (http://tandemgeek.wordpress.com/2011/09/18/hot-disc-brake-news-or-news-about-overheated-disc-brakes-if-you-prefer/) about all this.
It would be interesting to have some more reports comparing the Avid BB7 to the Bengal MT700T on a tandem.
It doesn't appear that the Bengal would save any weight, FWIW. The Avid BB7 caliper reportedly weighs 155 grams (http://faqload.com/faqs/bicycle-components/brakes/avid-bb7-mechanical-disc-brake-weights), whereas the Bengal is listed as 166 grams (http://www.bengalperformance.com.tw/products3659.html?ino=7). Installed the weights would probably differ, but it looks not like much.
There is another mechanical disc brake, the Bengal (http://www.bengalperformance.com.tw/products3659.html?ino=7), the MB700T version of which that Santana modifies and uses. It doesn't have any plastic bits, and it was found not to have as many problems on a challenging descent (http://www.bikeforums.net/showthread.php/759413-Tandems-on-Mt-Ventoux?highlight=Mt+Ventoux). Of course, it is usually paired with a 10" rotor, which must have greater heat capacity than the 8" rotors usually paired with BB7's.
I spoke with Tim at Santana all about brakes. He thinks the Bengal superior to the Avid BB7 (but that's what they said about the defunct Winzip, too).
The Santana/Bengal caliper could be installed on other tandems, but according to Tim at Santana, it needs to be attached as are Santana's onto the chainstay rather than the more common seatstay mount.
Akexpress has a mountain version of the Bengal on their Calfee (http://www.bikeforums.net/showthread.php/759413-Tandems-on-Mt-Ventoux?p=13196560&viewfull=1#post13196560), and a positive report (http://www.bikeforums.net/showthread.php/769717-Bengal-Brake-Update-from-Cycle-Oregon?p=13256101&highlight=#post13256101), but I've not seen the technical details of how it was done. TG has an informative blog post (http://tandemgeek.wordpress.com/2011/09/18/hot-disc-brake-news-or-news-about-overheated-disc-brakes-if-you-prefer/) about all this.
It would be interesting to have some more reports comparing the Avid BB7 to the Bengal MT700T on a tandem.
It doesn't appear that the Bengal would save any weight, FWIW. The Avid BB7 caliper reportedly weighs 155 grams (http://faqload.com/faqs/bicycle-components/brakes/avid-bb7-mechanical-disc-brake-weights), whereas the Bengal is listed as 166 grams (http://www.bengalperformance.com.tw/products3659.html?ino=7). Installed the weights would probably differ, but it looks not like much.
PMK
02-15-12, 06:50 PM
FWIW, the Tandemgeek is stating the truth about fluid maintenance. If you run hydraulic brakes, buy the tools and learn how to bleed them, ensuring a solid lever feel. In regards to the Motul 600, yes it is very good stuff. I have never boiled it in the KTM. It has however had issues after sitting for a while. Not certain what happened, but something within the fluid congealed or solidified. This required me to disassemble those Brembos, front and rear, flush with iso alcohol, then brake cleaner. Reassembled and bled, all is fine. Same exact thing happened on a friends CRF450r. Maybe just too long between fluid replacement.
Magura rim brakes...If you have ever ridden a set that was properly aligned and setup, with a booster bridge, well these will stop if dry. You would almost believe the rim is being crushed. Hence the nickname "rim crushers".
Again, good info from the Tandemgeek:thumb:
PK
Magura rim brakes...If you have ever ridden a set that was properly aligned and setup, with a booster bridge, well these will stop if dry. You would almost believe the rim is being crushed. Hence the nickname "rim crushers".
Again, good info from the Tandemgeek:thumb:
PK
PMK
02-15-12, 06:56 PM
I read the linked article.
It was interesting but kind of made me not read it as close as I could have.
Maybe I missed it, but as I recall, this rider was dragging the brakes, realized he had a problem...never saw mention of where he released the brakes and tried to "pump them up" to gain a little bit of braking.
It is a bummer he crashed and got hurt. What would he have done if the bike had rim brakes and it began to drizzle or rain?
Let's call him lucky and use this as a poster child of what not to do.
PK
It was interesting but kind of made me not read it as close as I could have.
Maybe I missed it, but as I recall, this rider was dragging the brakes, realized he had a problem...never saw mention of where he released the brakes and tried to "pump them up" to gain a little bit of braking.
It is a bummer he crashed and got hurt. What would he have done if the bike had rim brakes and it began to drizzle or rain?
Let's call him lucky and use this as a poster child of what not to do.
PK
DubT
02-16-12, 09:52 AM
My thoughts on brakes for whatever they are worth. I have been riding and racing bicycles and motorcycles for years but have never descended a long mountain pass where I would need to use the brakes for an extended amount of time.
1. Our Calfee has 2 X 25 inch disc brakes on it right now, they are in the form of Topolino 700C wheels with aluminum rims that have machined braking surfaces.
2. With the Dura Ace calipers and Ultegra levers we have plenty of stopping power for use here in the relative flat Midwest.
3. It is my understanding that the most effective vehicle brake is the front brake.
4. Most of the tandems that I see on this forum that utilize a disc brake only have it on the rear, the exception being the Cannondale.
So from what I see the main reason for the use of a disc brake is to keep from melting carbon fiber rims on long descents. However it appears that you can melt the disc brake pads and components.
I am going to stay with caliper brakes and aluminum braking surfaces until something MUCH better comes along.
I see a need for some serious brake system testing on tandem bicycles. It would be a great project for someone to undertake. The main issue that I have heard about using caliper brakes on long descents is that they can produce enough heat to cause a tire to explode. It would be great to see some real data on this issue.
Wayne
1. Our Calfee has 2 X 25 inch disc brakes on it right now, they are in the form of Topolino 700C wheels with aluminum rims that have machined braking surfaces.
2. With the Dura Ace calipers and Ultegra levers we have plenty of stopping power for use here in the relative flat Midwest.
3. It is my understanding that the most effective vehicle brake is the front brake.
4. Most of the tandems that I see on this forum that utilize a disc brake only have it on the rear, the exception being the Cannondale.
So from what I see the main reason for the use of a disc brake is to keep from melting carbon fiber rims on long descents. However it appears that you can melt the disc brake pads and components.
I am going to stay with caliper brakes and aluminum braking surfaces until something MUCH better comes along.
I see a need for some serious brake system testing on tandem bicycles. It would be a great project for someone to undertake. The main issue that I have heard about using caliper brakes on long descents is that they can produce enough heat to cause a tire to explode. It would be great to see some real data on this issue.
Wayne
akexpress
02-16-12, 11:34 AM
As we are team that has had our Avid melt on Mt Ventoux last year I will not ever own a disc brake caliper with plaster parts again. Even though most times the knob can completely melt off and the brake still functions it is now subject to catastrophic failure. Our riding partners had that happen the next day. Someone suggested putting locktite on the adjuster however that defeats the adjustment process and probably only red is temperature tolerant enough to be of any good and you would not be able to adjust the pad. We now have about 3000 miles on a Bengal rear caliper with a number of long descents without incident. FWIW we are about 340# team weight. We are using a standard 203 mm disc. One concern I have is how much heat is transferred to the frame from the caliper. In that we have a carbon Calfee this is a question that I plan on asking at what point should I be concerned about resin failure on the frame. The comforting part about all this is the fact these issues are only present on exceptional mountain descents. We are planning on doing Cycle Oregon this year which has over 40,000 ft of climbing and descending so we will have another opportunity to test the Bengal.
Werkin
02-16-12, 02:28 PM
...am a little surprised at how quickly this happened. Looking at the posted graphs, the time from the start of the downhill (2:36:40) until the point he marked just before the brakes failed totally and the speed started to shoot up (2:38:11) was 1 minute 30 seconds! His speed was climbing steadily from 20 to 30 mph during this time, so the distance cannot have been much more than 0.5 miles (1 km)!...I would have expected the brakes to last for more than 1 km...fascinating to read that many of the major manufacturers have significant reservations on the topic.
I can gain 10mph downhill in less than 5 seconds. On the brakes for more than a minute is an eternity. Five hundred feet of drop over a half mile is an extreme decline. No surprise here.
Manufacturers reservations are about being able to sell a product (buyer acceptance), not about barriers to creating that road going product.
Replacing and/or bleeding a hydraulic brake system is no more hassle than lubing a chain.
Incompatible rotors were a contributing factor in the journalist's failure, but the biggie here was opening the hydraulic system and allowing air ingress. With the rotor cooked and the pads glazed there would have been a minor amount of brake power available if some lever travel was retained. I could further speculate about moisture content in the fluid, but no need to go further than the first apparent mistake. The failure victim had this to say "The brake fade that led to my accident is something I’ve experienced on my mountain bike on several occasions with multiple brands of brakes." This user has not learned from his previous experience.
I can gain 10mph downhill in less than 5 seconds. On the brakes for more than a minute is an eternity. Five hundred feet of drop over a half mile is an extreme decline. No surprise here.
Manufacturers reservations are about being able to sell a product (buyer acceptance), not about barriers to creating that road going product.
Replacing and/or bleeding a hydraulic brake system is no more hassle than lubing a chain.
Incompatible rotors were a contributing factor in the journalist's failure, but the biggie here was opening the hydraulic system and allowing air ingress. With the rotor cooked and the pads glazed there would have been a minor amount of brake power available if some lever travel was retained. I could further speculate about moisture content in the fluid, but no need to go further than the first apparent mistake. The failure victim had this to say "The brake fade that led to my accident is something I’ve experienced on my mountain bike on several occasions with multiple brands of brakes." This user has not learned from his previous experience.
Ritterview
02-16-12, 02:32 PM
We now have about 3000 miles on a Bengal rear caliper with a number of long descents without incident. ... We are using a standard 203 mm disc.
Thanks for responding to the thread, I was fixing to PM you!
I think that ther Bengal set up on your Calfee will be of interest, as it is a welcome development to have an additional choice of mechanical disc caliper aside from the Avid BB7. Would you please post a report of how it was set up? For example, the Model Bengal brake, the mount, cable routing, etc. Pics will be especially appreciated.
Tim at Santana told me the Bengal needed to be mounted on the chainstay, whereas the Calfee disc mount is more on the seatstay side. I doubt you had your carbon chainstay modified, so it must be on the Calfee mount, and Santana mistaken. Won't know, however, until you post the details!
Thanks for responding to the thread, I was fixing to PM you!
I think that ther Bengal set up on your Calfee will be of interest, as it is a welcome development to have an additional choice of mechanical disc caliper aside from the Avid BB7. Would you please post a report of how it was set up? For example, the Model Bengal brake, the mount, cable routing, etc. Pics will be especially appreciated.
Tim at Santana told me the Bengal needed to be mounted on the chainstay, whereas the Calfee disc mount is more on the seatstay side. I doubt you had your carbon chainstay modified, so it must be on the Calfee mount, and Santana mistaken. Won't know, however, until you post the details!
PMK
02-16-12, 02:50 PM
My thoughts on brakes for whatever they are worth. I have been riding and racing bicycles and motorcycles for years but have never descended a long mountain pass where I would need to use the brakes for an extended amount of time.
1. Our Calfee has 2 X 25 inch disc brakes on it right now, they are in the form of Topolino 700C wheels with aluminum rims that have machined braking surfaces.
2. With the Dura Ace calipers and Ultegra levers we have plenty of stopping power for use here in the relative flat Midwest.
3. It is my understanding that the most effective vehicle brake is the front brake.
4. Most of the tandems that I see on this forum that utilize a disc brake only have it on the rear, the exception being the Cannondale.
So from what I see the main reason for the use of a disc brake is to keep from melting carbon fiber rims on long descents. However it appears that you can melt the disc brake pads and components.
I am going to stay with caliper brakes and aluminum braking surfaces until something MUCH better comes along.
I see a need for some serious brake system testing on tandem bicycles. It would be a great project for someone to undertake. The main issue that I have heard about using caliper brakes on long descents is that they can produce enough heat to cause a tire to explode. It would be great to see some real data on this issue.
Wayne
I hear you, it is pretty darn flat in South Florida also. Yes your setup is fine for your location. Our Team In Training event a couple years ago had us riding around Lake Tahoe. Big difference from home. After seeing some videos posted here of the downhills in CA from USPS bike, and no doubt others...flat or not, discs or serious reliable brakes that allow confidence do have relevance.
Also consider, these discussions are talking about dry conditions. Not that you plan or want to ride in the wet, sometimes it happens.
My opinion for the little bit it is worth...if a team says they need disc brakes, and the captain knows how to use them, then enjoy. I surely will not be the one to say "no".
PK
1. Our Calfee has 2 X 25 inch disc brakes on it right now, they are in the form of Topolino 700C wheels with aluminum rims that have machined braking surfaces.
2. With the Dura Ace calipers and Ultegra levers we have plenty of stopping power for use here in the relative flat Midwest.
3. It is my understanding that the most effective vehicle brake is the front brake.
4. Most of the tandems that I see on this forum that utilize a disc brake only have it on the rear, the exception being the Cannondale.
So from what I see the main reason for the use of a disc brake is to keep from melting carbon fiber rims on long descents. However it appears that you can melt the disc brake pads and components.
I am going to stay with caliper brakes and aluminum braking surfaces until something MUCH better comes along.
I see a need for some serious brake system testing on tandem bicycles. It would be a great project for someone to undertake. The main issue that I have heard about using caliper brakes on long descents is that they can produce enough heat to cause a tire to explode. It would be great to see some real data on this issue.
Wayne
I hear you, it is pretty darn flat in South Florida also. Yes your setup is fine for your location. Our Team In Training event a couple years ago had us riding around Lake Tahoe. Big difference from home. After seeing some videos posted here of the downhills in CA from USPS bike, and no doubt others...flat or not, discs or serious reliable brakes that allow confidence do have relevance.
Also consider, these discussions are talking about dry conditions. Not that you plan or want to ride in the wet, sometimes it happens.
My opinion for the little bit it is worth...if a team says they need disc brakes, and the captain knows how to use them, then enjoy. I surely will not be the one to say "no".
PK
when
02-16-12, 03:36 PM
It is interesting to note that the Bengal looks almost exactly like the Tektro Lyra, which is all metal. I do believe however that the Lyra does not have the additional set screw that retains the inner pad adjust however, to my knowledge Bengal is the only disc brake that does this. The Shimano mechanical discs do click-adjust, but I think the bearing surfaces are plastic.
Therefore, it would seem that the problem is that the inner pad adjust rattles out if the click adjust part melts. Therefore, it would seem to behoove users that want 100% reliability to put a lockwasher on the pad adjustment bolts.
As we are team that has had our Avid melt on Mt Ventoux last year I will not ever own a disc brake caliper with plaster parts again. Even though most times the knob can completely melt off and the brake still functions it is now subject to catastrophic failure. Our riding partners had that happen the next day. Someone suggested putting locktite on the adjuster however that defeats the adjustment process and probably only red is temperature tolerant enough to be of any good and you would not be able to adjust the pad. We now have about 3000 miles on a Bengal rear caliper with a number of long descents without incident. FWIW we are about 340# team weight. We are using a standard 203 mm disc. One concern I have is how much heat is transferred to the frame from the caliper. In that we have a carbon Calfee this is a question that I plan on asking at what point should I be concerned about resin failure on the frame. The comforting part about all this is the fact these issues are only present on exceptional mountain descents. We are planning on doing Cycle Oregon this year which has over 40,000 ft of climbing and descending so we will have another opportunity to test the Bengal.
Therefore, it would seem that the problem is that the inner pad adjust rattles out if the click adjust part melts. Therefore, it would seem to behoove users that want 100% reliability to put a lockwasher on the pad adjustment bolts.
As we are team that has had our Avid melt on Mt Ventoux last year I will not ever own a disc brake caliper with plaster parts again. Even though most times the knob can completely melt off and the brake still functions it is now subject to catastrophic failure. Our riding partners had that happen the next day. Someone suggested putting locktite on the adjuster however that defeats the adjustment process and probably only red is temperature tolerant enough to be of any good and you would not be able to adjust the pad. We now have about 3000 miles on a Bengal rear caliper with a number of long descents without incident. FWIW we are about 340# team weight. We are using a standard 203 mm disc. One concern I have is how much heat is transferred to the frame from the caliper. In that we have a carbon Calfee this is a question that I plan on asking at what point should I be concerned about resin failure on the frame. The comforting part about all this is the fact these issues are only present on exceptional mountain descents. We are planning on doing Cycle Oregon this year which has over 40,000 ft of climbing and descending so we will have another opportunity to test the Bengal.
akexpress
02-16-12, 04:11 PM
It is interesting to note that the Bengal looks almost exactly like the Tektro Lyra, which is all metal. I do believe however that the Lyra does not have the additional set screw that retains the inner pad adjust however, to my knowledge Bengal is the only disc brake that does this. The Shimano mechanical discs do click-adjust, but I think the bearing surfaces are plastic.
Therefore, it would seem that the problem is that the inner pad adjust rattles out if the click adjust part melts. Therefore, it would seem to behoove users that want 100% reliability to put a lockwasher on the pad adjustment bolts.
I don't think a lock washer is possible as the whole inner pad adjuster is threaded into the caliper body. When the plastic adjuster cap melts off the whole inner pad support can rotate out and fall out-at that point you have catastrophic failure.
Therefore, it would seem that the problem is that the inner pad adjust rattles out if the click adjust part melts. Therefore, it would seem to behoove users that want 100% reliability to put a lockwasher on the pad adjustment bolts.
I don't think a lock washer is possible as the whole inner pad adjuster is threaded into the caliper body. When the plastic adjuster cap melts off the whole inner pad support can rotate out and fall out-at that point you have catastrophic failure.
akexpress
02-16-12, 04:27 PM
Thanks for responding to the thread, I was fixing to PM you!
I think that ther Bengal set up on your Calfee will be of interest, as it is a welcome development to have an additional choice of mechanical disc caliper aside from the Avid BB7. Would you please post a report of how it was set up? For example, the Model Bengal brake, the mount, cable routing, etc. Pics will be especially appreciated.
Tim at Santana told me the Bengal needed to be mounted on the chainstay, whereas the Calfee disc mount is more on the seatstay side. I doubt you had your carbon chainstay modified, so it must be on the Calfee mount, and Santana mistaken. Won't know, however, until you post the details!
I will try and get some pictures of the mounted Bengal brake caliper. Right now the bike is packed in the cases for a trip to the Moab Skinny tire festival in 3 weeks. Snow bikes only right now here in Alaska. For both of the Calfee's that have replaced the Avids it was a direct bolt on replacement in the same adapter. I didn't have to change the cable or housing at all. It has a cable adjuster built into the body of the caliper. I am using an Avid 203mm disc. It takes a little longer to set up because it doesn't have the patented (Avid) conical washers to help center it, you have to do it manually. The only minor annoyance is it makes a little noise on very rough chip seal type of roads as I believe the magnetic pad retraction allows the pad to vibrate ever so slightly against the disc. It is very minor compared to the noise the Winzips make in the same condition. On any normal road this is not apparent. The model number is a M700T. Precision tandems now lists them on their website. I am convinced it is a standard M700 caliper with a tandem sticker on it.
I think that ther Bengal set up on your Calfee will be of interest, as it is a welcome development to have an additional choice of mechanical disc caliper aside from the Avid BB7. Would you please post a report of how it was set up? For example, the Model Bengal brake, the mount, cable routing, etc. Pics will be especially appreciated.
Tim at Santana told me the Bengal needed to be mounted on the chainstay, whereas the Calfee disc mount is more on the seatstay side. I doubt you had your carbon chainstay modified, so it must be on the Calfee mount, and Santana mistaken. Won't know, however, until you post the details!
I will try and get some pictures of the mounted Bengal brake caliper. Right now the bike is packed in the cases for a trip to the Moab Skinny tire festival in 3 weeks. Snow bikes only right now here in Alaska. For both of the Calfee's that have replaced the Avids it was a direct bolt on replacement in the same adapter. I didn't have to change the cable or housing at all. It has a cable adjuster built into the body of the caliper. I am using an Avid 203mm disc. It takes a little longer to set up because it doesn't have the patented (Avid) conical washers to help center it, you have to do it manually. The only minor annoyance is it makes a little noise on very rough chip seal type of roads as I believe the magnetic pad retraction allows the pad to vibrate ever so slightly against the disc. It is very minor compared to the noise the Winzips make in the same condition. On any normal road this is not apparent. The model number is a M700T. Precision tandems now lists them on their website. I am convinced it is a standard M700 caliper with a tandem sticker on it.
PMK
02-16-12, 06:09 PM
I don't think a lock washer is possible as the whole inner pad adjuster is threaded into the caliper body. When the plastic adjuster cap melts off the whole inner pad support can rotate out and fall out-at that point you have catastrophic failure.
I do not believe this is exactly accurate. I should pull a current version and older version caliper apart but don't really want to right now. If I recall correctly, melting the knobs will only allow the adjusters (inbd & otbd) to self adjust. There is no means to allow the entire assembly to unscrew and fall apart. If that were the case, fully unwinding the adjuster under normal conditions would disassemble the caliper. The caliper pad seats are a flanged setup, with the wide flange inside the threads of the caliper internals. It can only unwind until it bottoms. This is full clearance on the pads. Basically so far out of adjustment there are no brakes.
Regardless, still bad.
Loctite is softened with heat (propane torch), but is not practical since you would not have easy adjustability.
PK
I do not believe this is exactly accurate. I should pull a current version and older version caliper apart but don't really want to right now. If I recall correctly, melting the knobs will only allow the adjusters (inbd & otbd) to self adjust. There is no means to allow the entire assembly to unscrew and fall apart. If that were the case, fully unwinding the adjuster under normal conditions would disassemble the caliper. The caliper pad seats are a flanged setup, with the wide flange inside the threads of the caliper internals. It can only unwind until it bottoms. This is full clearance on the pads. Basically so far out of adjustment there are no brakes.
Regardless, still bad.
Loctite is softened with heat (propane torch), but is not practical since you would not have easy adjustability.
PK
PMK
02-16-12, 06:17 PM
One concern I have is how much heat is transferred to the frame from the caliper. In that we have a carbon Calfee this is a question that I plan on asking at what point should I be concerned about resin failure on the frame.
I have no real answer, the temp you would be looking for is a wet transition temp or something similar. This is all about how good (performance wise) the resin system is that Calfee uses. It might also be affected slightly by the temperature at which the resin system is cured.
It would be interesting to see how much heat these brakes generate. A simple test would be a typical day, typical hill, typical team, ride down the hill and have a friend take temp readings with an IR gun.
Not to poke fun at all of this, maybe we need a sensor on the caliper and an app for those using phones or a Garmin that has a brake overtemp warning light.
PK
I have no real answer, the temp you would be looking for is a wet transition temp or something similar. This is all about how good (performance wise) the resin system is that Calfee uses. It might also be affected slightly by the temperature at which the resin system is cured.
It would be interesting to see how much heat these brakes generate. A simple test would be a typical day, typical hill, typical team, ride down the hill and have a friend take temp readings with an IR gun.
Not to poke fun at all of this, maybe we need a sensor on the caliper and an app for those using phones or a Garmin that has a brake overtemp warning light.
PK
akexpress
02-16-12, 06:48 PM
I have no real answer, the temp you would be looking for is a wet transition temp or something similar. This is all about how good (performance wise) the resin system is that Calfee uses. It might also be affected slightly by the temperature at which the resin system is cured.
It would be interesting to see how much heat these brakes generate. A simple test would be a typical day, typical hill, typical team, ride down the hill and have a friend take temp readings with an IR gun.
Not to poke fun at all of this, maybe we need a sensor on the caliper and an app for those using phones or a Garmin that has a brake overtemp warning light.
PK
the typical day typical hill typical team is not the problem with any of these brakes It is the big bad hill, typical day, typical team that is the problem.
It would be interesting to see how much heat these brakes generate. A simple test would be a typical day, typical hill, typical team, ride down the hill and have a friend take temp readings with an IR gun.
Not to poke fun at all of this, maybe we need a sensor on the caliper and an app for those using phones or a Garmin that has a brake overtemp warning light.
PK
the typical day typical hill typical team is not the problem with any of these brakes It is the big bad hill, typical day, typical team that is the problem.
PMK
02-16-12, 06:57 PM
the typical day typical hill typical team is not the problem with any of these brakes It is the big bad hill, typical day, typical team that is the problem.
It was more of a test as opposed to a Kamikaze hope for the best...did you get the temp as they went flying by?, type thing.
100% I agree, it is the big hill typical team, typical day that creates the real concern.
Like they said on TV...be careful out there.
PK
It was more of a test as opposed to a Kamikaze hope for the best...did you get the temp as they went flying by?, type thing.
100% I agree, it is the big hill typical team, typical day that creates the real concern.
Like they said on TV...be careful out there.
PK
akexpress
02-16-12, 11:09 PM
PK I agree be careful and I have an IR temp gun and will try to get some temps on the brakes in a few weeks. I have enclosed some pictures of my avid that melted. It is hard to show but the inner adjusting pad is threaded into the body of the caliper. The post that is sticking out is attached to the red plastic adjusting ring which uses the dimpled ring on the the caliper to hold position as the inner pad is adjusted. If the plastic piece is gone there is nothing to stop the inner pad support from unscrewing it self out and falling completely out which in turn will let the inner pad fall out. This is what happened to our sister bikes brake the next day. On the second picture you can also see the discoloration of the body of the caliper itself due to the high heat it achieved.
237663237664
237661
237660237662
237663237664
237661
237660237662
PMK
02-17-12, 05:48 AM
I have two calipers here at home. One is a brand new spare BB7mtn. I also have a BB?road, the decal says BBDB / Avid / Road, came on our 2006 Co-Motion Roadster.
The designs are totally different. An obvious external difference is the BB7m has a Torx internal / hex external center on the adjuster, while the BBDB road has a blade to engage the plastic adjuster wheel.
The BB7m is as you described, yes if the plastic melts away, the entire pad adjuster is free to unwind and fall apart.
The road caliper, does NOT have threads cut through the body. The body is stepped, making a "stop" to prevent a total unwind of the adjuster.
After some research on the Avid parts breakdowns for later style road calipers. They are the same as a mountain except the internals are different for the different lever pulls.
Yes, this should have people take a lot of time to respect these brakes on long descents.
PK
237690237689237691237688237692
The designs are totally different. An obvious external difference is the BB7m has a Torx internal / hex external center on the adjuster, while the BBDB road has a blade to engage the plastic adjuster wheel.
The BB7m is as you described, yes if the plastic melts away, the entire pad adjuster is free to unwind and fall apart.
The road caliper, does NOT have threads cut through the body. The body is stepped, making a "stop" to prevent a total unwind of the adjuster.
After some research on the Avid parts breakdowns for later style road calipers. They are the same as a mountain except the internals are different for the different lever pulls.
Yes, this should have people take a lot of time to respect these brakes on long descents.
PK
237690237689237691237688237692
Bostic
02-17-12, 08:50 AM
Here is a comment from one of the Volagi founders. All of their bikes have disc brakes.
http://www.bikerumor.com/2012/02/14/road-bike-disc-brakes-are-coming-but-will-they-work/comment-page-2/#comment-88839
Thus far I have been very satisfied with the disc brake setup on our Cannondale RT2 riding around the usual areas of Silicon Valley. About the longest descents around here are HW9, 84 and eventually Mt. Diablo when we get stronger as a team. I have family in Reno and often climb both sides of Mt. Rose while visiting. The east side twists and turns upwards 16 miles from Reno to the summit while the west is a wide open 8 mile descent from the top to Incline Village. As a 285lb team I would hope that the disc brakes are much more effective than V brakes or calipers.
http://www.bikerumor.com/2012/02/14/road-bike-disc-brakes-are-coming-but-will-they-work/comment-page-2/#comment-88839
Thus far I have been very satisfied with the disc brake setup on our Cannondale RT2 riding around the usual areas of Silicon Valley. About the longest descents around here are HW9, 84 and eventually Mt. Diablo when we get stronger as a team. I have family in Reno and often climb both sides of Mt. Rose while visiting. The east side twists and turns upwards 16 miles from Reno to the summit while the west is a wide open 8 mile descent from the top to Incline Village. As a 285lb team I would hope that the disc brakes are much more effective than V brakes or calipers.
when
02-17-12, 09:15 AM
I don't think a lock washer is possible as the whole inner pad adjuster is threaded into the caliper body. When the plastic adjuster cap melts off the whole inner pad support can rotate out and fall out-at that point you have catastrophic failure.
I think it would also be possible to drill a hole and thread it for a setscrew from the side that retains the pad adjuster bolt. With a small enough setscrew it is doubtful you would compromise the structural integrity of the caliper at all.
I think it would also be possible to drill a hole and thread it for a setscrew from the side that retains the pad adjuster bolt. With a small enough setscrew it is doubtful you would compromise the structural integrity of the caliper at all.
PMK
02-17-12, 10:22 AM
I think it would also be possible to drill a hole and thread it for a setscrew from the side that retains the pad adjuster bolt. With a small enough setscrew it is doubtful you would compromise the structural integrity of the caliper at all.
There are no doubt many ways to prevent the adjuster from falling out.
The real task is one to improve the detent system from plastic to something more heat resistant. If the pad adjuster were to unwind even 1/2 turn, this is a big change in lever travel. Several turns could render the brake useless, with the disc now rubbing the caliper housing when the brake is applied.
I have not disassembled the actuator mechanism, while it does use a plastic knob, the detents are supplemented via a spring clip. The plastic knob is still important though.
PK
There are no doubt many ways to prevent the adjuster from falling out.
The real task is one to improve the detent system from plastic to something more heat resistant. If the pad adjuster were to unwind even 1/2 turn, this is a big change in lever travel. Several turns could render the brake useless, with the disc now rubbing the caliper housing when the brake is applied.
I have not disassembled the actuator mechanism, while it does use a plastic knob, the detents are supplemented via a spring clip. The plastic knob is still important though.
PK
Team Fab
02-24-12, 08:23 PM
Just my 2 cents.
Light weight rotors can fail as well. They can split along the spiders when they overheat.
Learned this one after a 5000 ft decent while riding La Ruta.
Light weight rotors can fail as well. They can split along the spiders when they overheat.
Learned this one after a 5000 ft decent while riding La Ruta.
Chris_W
02-25-12, 12:05 AM
Part 2 of this series of Bikerumor posts is now up, and contains responses from 6 top wheel manufacturers, see here (http://www.bikerumor.com/2012/02/23/disc-brakes-are-coming-to-road-bikes-but-what-about-wheels/). Interestingly, several of the companies believe that disc brakes are not appropriate for road racing - their weight and aerodynamic costs being too great compared to the braking benefits. Not much info in this one that is really related to tandems, but a good read anyway.
StanleyJ
02-26-12, 11:20 AM
So here I am in Hong Kong, land of not particularly tall mountains, but the descents are steep (occasionally 20~25% grade) and twisty. Average grade down 2000ft could average 12%... so I was quite chuffed (because I'm looking at a tandem purchase) that the British guys at Hope made the remote master cylinder V-Twin which drives the XC MTB X2 caliper:
http://www.hopetech.com/page.aspx?itemID=SPG343
So that'll work nicely with the brifters normally seen with road bikes. However, as the remote master cylinder appears to be based off "Race" series brake (rather than the "Tech"), that also infers that the V-Twin has a disc limit of 160mm. However, it also means the V-Twin should be able to drive the M4 "all mountain" calipers, which Hope confirmed in an email it would work and that "some point in the future", they'll offer this as a standard options.
This would then allow Hope's 183mm & 203mm rotors (fixed and floating) to be used, which I would think should be more than enough, considering Clyde-size 18 stone MTBers can drag Hope M4's with just 183mm rotors and have fade-free braking. Hope also can make custom sized rotors. I would hazard a guess they can go to the 255mm size which apparently Santana now offer as the only option as the rear disc brake rotor size?
http://www.hopetech.com/page.aspx?itemID=SPG343
So that'll work nicely with the brifters normally seen with road bikes. However, as the remote master cylinder appears to be based off "Race" series brake (rather than the "Tech"), that also infers that the V-Twin has a disc limit of 160mm. However, it also means the V-Twin should be able to drive the M4 "all mountain" calipers, which Hope confirmed in an email it would work and that "some point in the future", they'll offer this as a standard options.
This would then allow Hope's 183mm & 203mm rotors (fixed and floating) to be used, which I would think should be more than enough, considering Clyde-size 18 stone MTBers can drag Hope M4's with just 183mm rotors and have fade-free braking. Hope also can make custom sized rotors. I would hazard a guess they can go to the 255mm size which apparently Santana now offer as the only option as the rear disc brake rotor size?
Ritterview
02-26-12, 06:05 PM
This would then allow Hope's 183mm & 203mm rotors (fixed and floating) to be used, which I would think should be more than enough, considering Clyde-size 18 stone... Hope also can make custom sized rotors. I would hazard a guess they can go to the 255mm size which apparently Santana now offer as the only option as the rear disc brake rotor size?
The demand for rotors larger than 203 mm appears to be limited to tandems, and the numbers are there so small as to not command any rotor maker's respect. Santana has a proprietary deal with a company so to make the 255 mm rotor. Formula's 220 mm rotor is discontinued, but it is a nice size. i had to have the chainstay modified to make it fit.
The demand for rotors larger than 203 mm appears to be limited to tandems, and the numbers are there so small as to not command any rotor maker's respect. Santana has a proprietary deal with a company so to make the 255 mm rotor. Formula's 220 mm rotor is discontinued, but it is a nice size. i had to have the chainstay modified to make it fit.
CaptainHaddock
03-05-12, 10:13 PM
Hi PMK! I've kind of followed you over from the MTBR forums (same Captain Haddock here). I wanted to ask since you've taken the time to pull them apart, does it appear that one could swap the internals from a mountain BB7 into a road BB7?
Chris_W
03-06-12, 04:50 AM
AFAIK, the internals of the mountain and road Avid BB7 brakes are the same. It is only the actuation ratio of cable pull to pad movement that differs between them, so that they are compatible with different types of brake levers.
Interestingly, Shimano announced some new cable disc brakes last week designed for road and cyclocross use that should be available some time this summer. They do not appear to have any plastic parts, but it is not clear whether the pads are as big as on the BB7 or whether they are rated for use with large tandem-sized rotors and heat levels, but they might make an interesting alternative. The new Shimano brakes are claimed to have a lot lower profile than the old Shimano versions, and that is one problem that I have with the BB7's - they often get in the way of racks and fender stays; however, it is not clear how the new Shimano models will compare to the BB7 in this regard.
Interestingly, Shimano announced some new cable disc brakes last week designed for road and cyclocross use that should be available some time this summer. They do not appear to have any plastic parts, but it is not clear whether the pads are as big as on the BB7 or whether they are rated for use with large tandem-sized rotors and heat levels, but they might make an interesting alternative. The new Shimano brakes are claimed to have a lot lower profile than the old Shimano versions, and that is one problem that I have with the BB7's - they often get in the way of racks and fender stays; however, it is not clear how the new Shimano models will compare to the BB7 in this regard.
TandemGeek
03-06-12, 08:20 AM
There is another mechanical disc brake, the Bengal (http://www.bengalperformance.com.tw/products3659.html?ino=7), the MB700T version of which that Santana modifies and uses. It would be interesting to have some more reports comparing the Avid BB7 to the Bengal MT700T on a tandem.
FWIW: Mark Johnson from Precision Tandems just sent me a Bengal MB700T, a Bengal 203mm rear rotor adapter & a Bengal-provided 203mm rotor to test out on our Calfee. I will be updating my blog with a preliminary report and subsequent updates as we put some miles on the alternative disc caliper and the Bengal-provided 203mm rotor.
However, at first blush the Bengal appears to be a direct replacement for the Avid. Mind you, this is a dead-stock Bengal MB700T that Mark is sourcing from Bengal. The only difference I can see or detect between the one that was on the Santana Beyond we rode at Santana's Chattanooga Rally is the color (this one is black) and the lack of the word "Tandem" on the caliper body. I should have checked, but I believe the Bengal-spec'd rotor is a bit more robust than the Avid rotor we've been using.
Installation was exactly the same as the Avid. Bolt the calper to the adapter with two machine screws, then bolt the adapter to the frame's I.S. disc mount on the back of the rear drop-out. While the Bengal lacks Avid's Tri-Align™ Caliper Positioning System™, so long as your I.S. disc caliper mount is properly aligned with your frame the Bengal is also a no-brainer to set-up. The inboard adjuster is manipulated using a 5mm hex drive and has a small 1.5mm hex head-driven fixing screw that holds it in place once you have it adjusted. There's also a knurled cable stop / adjuster where the brake cable housing attaches to the caliper which is a bit more intiutive to use than the outboard adjuster knob on the Avid.
Performance out of the box is really quite excellent. No rotor rub or "chiming" (something we heard a lot of with the larger rotor on the Santana) and even without being seasoned, great stopping power with normal lever travel. I rode the brake a few times on our Sunday loop in an effort to bed-in the pads and season the rotor. Again, even without being fully broken-in we were able to lock the rear tire on the 8% grade going into our community using only the rear brake. Mind you, we're only about a 280lb team.
Again, no plastic parts are in evidence.
More details and photos will go on the blog as time permits.
In case anyone is curious, I believe Mark has an upcharge of $50 for the Bengal MB700T vs. an Avid BB7 in his various Disc Brake kits. It's hard to back into the actual cost of the Avid BB7 from a price sheet since Avid doesn't sell a BB7 with a 203mm rotor that you can bolt onto a tandem. You have to buy the stock BB7 Road, the mounting adapter and the 203mm rotor ala carte as well as a thread-on rotor adapter assuming you have a left-hand threaded rear hub. If you have a rear disc hub or already have the thread-on adapter, then you save a few bucks on the kit.
FWIW: Mark Johnson from Precision Tandems just sent me a Bengal MB700T, a Bengal 203mm rear rotor adapter & a Bengal-provided 203mm rotor to test out on our Calfee. I will be updating my blog with a preliminary report and subsequent updates as we put some miles on the alternative disc caliper and the Bengal-provided 203mm rotor.
However, at first blush the Bengal appears to be a direct replacement for the Avid. Mind you, this is a dead-stock Bengal MB700T that Mark is sourcing from Bengal. The only difference I can see or detect between the one that was on the Santana Beyond we rode at Santana's Chattanooga Rally is the color (this one is black) and the lack of the word "Tandem" on the caliper body. I should have checked, but I believe the Bengal-spec'd rotor is a bit more robust than the Avid rotor we've been using.
Installation was exactly the same as the Avid. Bolt the calper to the adapter with two machine screws, then bolt the adapter to the frame's I.S. disc mount on the back of the rear drop-out. While the Bengal lacks Avid's Tri-Align™ Caliper Positioning System™, so long as your I.S. disc caliper mount is properly aligned with your frame the Bengal is also a no-brainer to set-up. The inboard adjuster is manipulated using a 5mm hex drive and has a small 1.5mm hex head-driven fixing screw that holds it in place once you have it adjusted. There's also a knurled cable stop / adjuster where the brake cable housing attaches to the caliper which is a bit more intiutive to use than the outboard adjuster knob on the Avid.
Performance out of the box is really quite excellent. No rotor rub or "chiming" (something we heard a lot of with the larger rotor on the Santana) and even without being seasoned, great stopping power with normal lever travel. I rode the brake a few times on our Sunday loop in an effort to bed-in the pads and season the rotor. Again, even without being fully broken-in we were able to lock the rear tire on the 8% grade going into our community using only the rear brake. Mind you, we're only about a 280lb team.
Again, no plastic parts are in evidence.
More details and photos will go on the blog as time permits.
In case anyone is curious, I believe Mark has an upcharge of $50 for the Bengal MB700T vs. an Avid BB7 in his various Disc Brake kits. It's hard to back into the actual cost of the Avid BB7 from a price sheet since Avid doesn't sell a BB7 with a 203mm rotor that you can bolt onto a tandem. You have to buy the stock BB7 Road, the mounting adapter and the 203mm rotor ala carte as well as a thread-on rotor adapter assuming you have a left-hand threaded rear hub. If you have a rear disc hub or already have the thread-on adapter, then you save a few bucks on the kit.
Carbonfiberboy
03-06-12, 09:15 AM
There are problems with every system, for sure. A riding buddy had his front caliper cable come loose on a short steep bit. His rear disc quickly overheated and he could not stop the bike. He went off into the blackberries, no oncoming, very lucky. We've been able to descend steep windy bits even fully loaded with our rim brakes, but don't think we could handle steep windy long bits. If we're going into the unknown or the steep known, we put on the rear wheel with the drum.
TandemGeek
03-06-12, 03:23 PM
A riding buddy had his front caliper cable come loose on a short steep bit. His rear disc quickly overheated and he could not stop the bike. He went off into the blackberries,
.... and if he had the same thing happen with a rear caliper brake instead of a disc the difference would have been??? Just saying.
WRT to the front caliper brake cable coming loose, IMHO torque wrenches are way undervalued. Followed closely by periodic cable replacement.
.... and if he had the same thing happen with a rear caliper brake instead of a disc the difference would have been??? Just saying.
WRT to the front caliper brake cable coming loose, IMHO torque wrenches are way undervalued. Followed closely by periodic cable replacement.
oldacura
03-07-12, 08:08 AM
Interesting reading. I had no idea that the considerations to adapt disc brakes to road bikes were so involved: fork design, seat stay strength, wheel dish, spoke lacing, spoke types, etc. Is this a solution looking for a problem? We have descended most of the mountain passes in Colorado (some several times), Mt. Evans (highest paved road in N. America) and Haleakala in Hawaii with rim brakes and never had a problem. It sounds like the margin of error for discs is much smaller. Will manufacturers' liabilty concerns make this technology too expensive for wide acceptance?
Question: If you take 2 otherwise identical bikes, one optimized for rim brakes and one optimized for discs, which will be lighter?
Question: If you take 2 otherwise identical bikes, one optimized for rim brakes and one optimized for discs, which will be lighter?
TandemGeek
03-07-12, 11:12 AM
Supplemental brakes are a belt and suspenders approach that is only "needed" for certain heavy-brake use descent situations, e.g., larger teams, teams travelling fully loaded or anyone else venturing into steep grades who wants to either control their speed all the way down the descent or has a concern about over-using their rim brakes to the point where rim heating could cause a tire failure.
However, as you point out, there are just as many examples of teams who have tackled demanding descents with only rim brakes with zero problems as there are teams who have even had brake capacity issues on even not-so-epic grades.
While drum brakes have been the defacto drag brake for teams that needed the belt & suspenders, discs have always offered the possibility of having a somewhat lighter weight, less clunky-looking alternative.
- Early discs did not hold up well when used like a drum brake, but did well-enough for many teams that didn't put big demands on those discs, e.g., Hope mechanicals of the mid-90's vintage.
- Hydraulic discs were never a good choice for road tandems, and even Santana's much touted Formula hybrid struggled with heat.
- The Avid BB7 was mediocre at best early on when only the MTB version was available, necessitating some type of cable-pull modifier like a Travel Agent or BPB. The BB7 Road model addressed cable pull and has proven to be pretty reliable for folks looking to have something "better" than a rim-only rear brake. However, as noted from the Santana tour feedback provided by akexpress, still has some operational limits under extreme use.
- Santana's WinZip solved a few issues, but wasn't as user-friendly as the Avid and has now been replaced by the Bengal MB700T which looks to be a better mousetrap.
- Rotor diameter and robustness has been an issue, noting the 160mm rotors that work OK on single bikes are overwhelmed by the weight of a tandem where even 180mm rotors are too small. 203mm has become the benchmark that Avid used to qualify it's BB7 rotors for use on tandems as "primary brakes", noting that they do not approve nor recommend their use as a supplemental / drag brake: that's well outside their design limits. Santana has been spec'ing 10" rotors for their tandems and they seem to work well for most, but not for all: very thin, but large diameter rotors are hard to keep perfectly true.
So, where are we today? To your point, a tandem with disc brakes will be heavier and more expensive than a tandem with rim brakes; however, it's still lighter than a tandem with rim brakes and an Arai drum brake. A tandem with dual brakes will easily have far more braking / heat capacity than a tandem with rim brakes and is also unfazed by the weather. A tandem with rim brakes up front and a disc in back provides folks with the belt & suspenders who really are probably quite fine with dual rim brakes.
Lots of choices for consumers is always a good thing, so long as there is good information to support an informed decision. The latter tends to be the weakness, along with varying degrees of rider skill that will always lead to poor decisions regarding tandem brakes as well as problems with those brakes.
However, as you point out, there are just as many examples of teams who have tackled demanding descents with only rim brakes with zero problems as there are teams who have even had brake capacity issues on even not-so-epic grades.
While drum brakes have been the defacto drag brake for teams that needed the belt & suspenders, discs have always offered the possibility of having a somewhat lighter weight, less clunky-looking alternative.
- Early discs did not hold up well when used like a drum brake, but did well-enough for many teams that didn't put big demands on those discs, e.g., Hope mechanicals of the mid-90's vintage.
- Hydraulic discs were never a good choice for road tandems, and even Santana's much touted Formula hybrid struggled with heat.
- The Avid BB7 was mediocre at best early on when only the MTB version was available, necessitating some type of cable-pull modifier like a Travel Agent or BPB. The BB7 Road model addressed cable pull and has proven to be pretty reliable for folks looking to have something "better" than a rim-only rear brake. However, as noted from the Santana tour feedback provided by akexpress, still has some operational limits under extreme use.
- Santana's WinZip solved a few issues, but wasn't as user-friendly as the Avid and has now been replaced by the Bengal MB700T which looks to be a better mousetrap.
- Rotor diameter and robustness has been an issue, noting the 160mm rotors that work OK on single bikes are overwhelmed by the weight of a tandem where even 180mm rotors are too small. 203mm has become the benchmark that Avid used to qualify it's BB7 rotors for use on tandems as "primary brakes", noting that they do not approve nor recommend their use as a supplemental / drag brake: that's well outside their design limits. Santana has been spec'ing 10" rotors for their tandems and they seem to work well for most, but not for all: very thin, but large diameter rotors are hard to keep perfectly true.
So, where are we today? To your point, a tandem with disc brakes will be heavier and more expensive than a tandem with rim brakes; however, it's still lighter than a tandem with rim brakes and an Arai drum brake. A tandem with dual brakes will easily have far more braking / heat capacity than a tandem with rim brakes and is also unfazed by the weather. A tandem with rim brakes up front and a disc in back provides folks with the belt & suspenders who really are probably quite fine with dual rim brakes.
Lots of choices for consumers is always a good thing, so long as there is good information to support an informed decision. The latter tends to be the weakness, along with varying degrees of rider skill that will always lead to poor decisions regarding tandem brakes as well as problems with those brakes.
oldacura
03-07-12, 02:51 PM
I haven't really been paying attention to the disc brake discussion w/regard to tandems. Is the accepted technology for tandems mechanical (cable) or hydraulic (or both)?
TandemGeek
03-07-12, 03:10 PM
I haven't really been paying attention to the disc brake discussion w/regard to tandems. Is the accepted technology for tandems mechanical (cable) or hydraulic (or both)?
Road = Mechanical with at least 203mm rotors
Off-Road = Hydraulic preferred by most for techincal single track / Freeriding but, but Mechanical are typically "good enough" and more than adequate for double-track, fire roads and the like. Again, 203mm rotors.
Road = Mechanical with at least 203mm rotors
Off-Road = Hydraulic preferred by most for techincal single track / Freeriding but, but Mechanical are typically "good enough" and more than adequate for double-track, fire roads and the like. Again, 203mm rotors.
Carbonfiberboy
03-07-12, 03:54 PM
.... and if he had the same thing happen with a rear caliper brake instead of a disc the difference would have been??? Just saying.
WRT to the front caliper brake cable coming loose, IMHO torque wrenches are way undervalued. Followed closely by periodic cable replacement.Just sayin' that things can go wrong, and that even a BB7 couldn't lock the rear with that stoker or stop the bike, and that the disc failed from overheat very quickly since it has so little mass. I don't know if a rim brake could have stopped the bike or not. Not my Avids, for sure. I once blew a rear tube on that same bit when rim heat blew it right through the rim tape. It's a well-known spot around here where several cyclists have had notable crashes on their singles. I went to sturdier rim tape and have done that bit several times since. I think you and this forum have done a good job of pointing out that discs have incredible stopping power, but also have problems which might not be apparent to the new disc brake user. It's good to progressively test one's braking system.
WRT to the front caliper brake cable coming loose, IMHO torque wrenches are way undervalued. Followed closely by periodic cable replacement.Just sayin' that things can go wrong, and that even a BB7 couldn't lock the rear with that stoker or stop the bike, and that the disc failed from overheat very quickly since it has so little mass. I don't know if a rim brake could have stopped the bike or not. Not my Avids, for sure. I once blew a rear tube on that same bit when rim heat blew it right through the rim tape. It's a well-known spot around here where several cyclists have had notable crashes on their singles. I went to sturdier rim tape and have done that bit several times since. I think you and this forum have done a good job of pointing out that discs have incredible stopping power, but also have problems which might not be apparent to the new disc brake user. It's good to progressively test one's braking system.
PMK
03-08-12, 04:35 AM
Hi PMK! I've kind of followed you over from the MTBR forums (same Captain Haddock here). I wanted to ask since you've taken the time to pull them apart, does it appear that one could swap the internals from a mountain BB7 into a road BB7?
Captain, yes they can be converted, but why? I have never done that and honestly, would suspect the parts would cost as much as the entire replacement caliper assembly.
PK
Captain, yes they can be converted, but why? I have never done that and honestly, would suspect the parts would cost as much as the entire replacement caliper assembly.
PK
PMK
03-08-12, 04:45 AM
Without spiking a controversy, I want to send post a consideration for disc brakes. We have thousands of miles on Avid BB7 brakes on our three tandems. Regardless of whether on-road or off-road, the brakes are not 100% maintenance free.
The brakes stop very well for us, and yes I can see there can be some concerns of overheating them.
For me, I have found that wiping the disc with a rag dampened in Brakleen, Acetone or lacquer thinner, will remove any contaminants and allow effective simple high performing brakes. Obviously this also requires brake pads that are not saturated in spray on chain lube or fully contaminated by another means, plus not worn to the backing plates.
When the discs are "dirty" the braking distances extend, and the brakes lack feel.
Typically I decide to clean or not based on the ride. A big event on unknown terrain, they are cleaned, a local training ride by ourselves probably not.
FWIW, this is a simple 5 minute job.
It works for us, may not for you, but decided to place it up anyway.
PK
The brakes stop very well for us, and yes I can see there can be some concerns of overheating them.
For me, I have found that wiping the disc with a rag dampened in Brakleen, Acetone or lacquer thinner, will remove any contaminants and allow effective simple high performing brakes. Obviously this also requires brake pads that are not saturated in spray on chain lube or fully contaminated by another means, plus not worn to the backing plates.
When the discs are "dirty" the braking distances extend, and the brakes lack feel.
Typically I decide to clean or not based on the ride. A big event on unknown terrain, they are cleaned, a local training ride by ourselves probably not.
FWIW, this is a simple 5 minute job.
It works for us, may not for you, but decided to place it up anyway.
PK
PMK
03-08-12, 04:54 AM
Road = Mechanical with at least 203mm rotors
Off-Road = Hydraulic preferred by most for techincal single track / Freeriding but, but Mechanical are typically "good enough" and more than adequate for double-track, fire roads and the like. Again, 203mm rotors.
We run discs.
In regards to discs off-road, I am not sure of how they average for tandems that prefer hydraulic vs those with cables. Yes, many teams do ride hydraulics off-road. We have ridden the hydraulics off-road and found them good, we now run mechanicals on that Ventana. They stop fine also.
I prefer the Avids for the reason of keeping all the tandems the same and spares common. I have no problem with hanging on and squeezing the lever, possibly from growing up with drum brake MX racers. Others do complain the lever effort is more than they care for so in that instances, hydraulics are preferred.
PK
Off-Road = Hydraulic preferred by most for techincal single track / Freeriding but, but Mechanical are typically "good enough" and more than adequate for double-track, fire roads and the like. Again, 203mm rotors.
We run discs.
In regards to discs off-road, I am not sure of how they average for tandems that prefer hydraulic vs those with cables. Yes, many teams do ride hydraulics off-road. We have ridden the hydraulics off-road and found them good, we now run mechanicals on that Ventana. They stop fine also.
I prefer the Avids for the reason of keeping all the tandems the same and spares common. I have no problem with hanging on and squeezing the lever, possibly from growing up with drum brake MX racers. Others do complain the lever effort is more than they care for so in that instances, hydraulics are preferred.
PK
uspspro
03-20-12, 01:42 AM
Shimano is coming out with a couple new mechanical disc brake calipers for 2013. They look very nice.
I wonder if they will bolt to any existing 203mm adapters?
I wonder if they will bolt to any existing 203mm adapters?
Chris_W
03-20-12, 04:19 PM
I'm sure that the new Shimano mechanical disc brakes will bolt onto adaptors to use 203 mm rotors with them, there is no reason why they should not. My main questions about these new brakes is whether they can handle the heat of a tandem and the braking torque of the bigger rotors. Shimano have stated that one model is more designed for road use, I believe they are calling it the CX55, and one is more for cyclocross use, I believe the CX75. Does this mean that the CX75 is the minimalist, lightweight version that cannot handle long periods of extended braking? Does it mean that the model designed for road use will actually be up to tandem road use, or will it also be under-specced? I'd like to know more about the differences between the two models, including the size of the pads each one uses, and what rotor sizes Shimano recommend using on each. Hopefully all will become clearer closer to the vague launch date of "summer".
Ritterview
03-20-12, 04:43 PM
Shimano is coming out with a couple new mechanical disc brake calipers for 2013. They look very nice.
Googling....lessee....
NAHBS 2012: Shimano Unveils New CX75 Cyclocross Mechanical Disc Brake... Updated: More Specs, Exclusive Photos (http://www.cxmagazine.com/nahbs-2012-shimano-unveils-cx75-cyclocross-mechanical-disc-brake-cyclocross-gearing-wheels)
http://www.cxmagazine.com/wp-content/uploads/2012/03/BR-CX75_withRT-72-590x392.jpg
Shimano's new CX75 Cyclocross and Road Mechanical Disc Brake. Photo: Shimano
Update: Exclusive CX75 mechanical disc brake photos and specs added, price estimates for wheels updated.
As seen with the introduction of the CX70 cyclocross component group in 2011 (reviewed in Issue 16), the Japanese component giant Shimano has started to take cyclocross seriously, and today at the North American Handmade Bicycle Show (NAHBS) in Sacramento, the company has unveiled a new mechanical disc brake for cyclocross racers that is scheduled to be ready for this fall.
The CX75 disc brake is said to offer 30% more power and a 20% smaller profile than the R505 mechanical road disc brake (reviewed in Issue 15). The cable pull is optimized for the Super SLR STI shift and brake levers, and is to be paired with the RT81 Deore XT-level mechanical disc brake rotor. Shimano’s Dave Lawrence, road product manager, told Cyclocross Magazine that the new caliper will be approximately 160 grams per wheel, putting the brake close to Tektro’s 148 gram Lyra disc brake caliper and Avid’s 155 gram BB7 caliper...
[See article for very large, detailed photographs, so to look for plastic that will melt.]
Edit: Also interesting information on RD and cassette:
Cyclocrossers should also take note that Shimano is releasing wider-range capability to its Ultegra, 105 and Tiagra component groups. All short-cage rear derailleurs and the Ultegra medium cage rear derailleur will accept up to a 30 tooth rear cog, while the mid-cage rear 105 and Tiagra rear derailleurs will accept up to a 32 tooth cog. Of course, Shimano will also offer 12-30 tooth Ultegra cassettes to take advantage of the expanded range.
Googling....lessee....
NAHBS 2012: Shimano Unveils New CX75 Cyclocross Mechanical Disc Brake... Updated: More Specs, Exclusive Photos (http://www.cxmagazine.com/nahbs-2012-shimano-unveils-cx75-cyclocross-mechanical-disc-brake-cyclocross-gearing-wheels)
http://www.cxmagazine.com/wp-content/uploads/2012/03/BR-CX75_withRT-72-590x392.jpg
Shimano's new CX75 Cyclocross and Road Mechanical Disc Brake. Photo: Shimano
Update: Exclusive CX75 mechanical disc brake photos and specs added, price estimates for wheels updated.
As seen with the introduction of the CX70 cyclocross component group in 2011 (reviewed in Issue 16), the Japanese component giant Shimano has started to take cyclocross seriously, and today at the North American Handmade Bicycle Show (NAHBS) in Sacramento, the company has unveiled a new mechanical disc brake for cyclocross racers that is scheduled to be ready for this fall.
The CX75 disc brake is said to offer 30% more power and a 20% smaller profile than the R505 mechanical road disc brake (reviewed in Issue 15). The cable pull is optimized for the Super SLR STI shift and brake levers, and is to be paired with the RT81 Deore XT-level mechanical disc brake rotor. Shimano’s Dave Lawrence, road product manager, told Cyclocross Magazine that the new caliper will be approximately 160 grams per wheel, putting the brake close to Tektro’s 148 gram Lyra disc brake caliper and Avid’s 155 gram BB7 caliper...
[See article for very large, detailed photographs, so to look for plastic that will melt.]
Edit: Also interesting information on RD and cassette:
Cyclocrossers should also take note that Shimano is releasing wider-range capability to its Ultegra, 105 and Tiagra component groups. All short-cage rear derailleurs and the Ultegra medium cage rear derailleur will accept up to a 30 tooth rear cog, while the mid-cage rear 105 and Tiagra rear derailleurs will accept up to a 32 tooth cog. Of course, Shimano will also offer 12-30 tooth Ultegra cassettes to take advantage of the expanded range.