swamptandem

https://www.bikerumor.com/2012/02/14/...rk/#more-39660

coldfeet

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.

wheelspeed

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. :-)

Chris_W

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.

swamptandem

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!

TandemGeek

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.

waynesulak

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.

https://www.bikeradar.com/news/articl...st-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

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.

rdtompki

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

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

There is another mechanical disc brake, the Bengal, 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. 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, and a positive report, but I've not seen the technical details of how it was done. TG has an informative blog post 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, whereas the Bengal is listed as 166 grams. Installed the weights would probably differ, but it looks not like much.

PMK

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

PK

PMK

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

DubT

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

akexpress 

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

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

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

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

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.

akexpress 

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 

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

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

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 

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

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