Brake heating
10-30-16, 08:26 AM
#51
Senior Member
We live in Switzerland and ride our tandem in the Alps a lot and have taken it to several other mountainous locations. We've nearly always had 3 brakes on the bike, a mix of disc brakes and rim brakes, although the exact models and combinations have evolved over 8 years. I'm happy descending pretty fast and use the best braking techniques I can, alternating between the three brakes as much as possible. However, we've done many extreme descents in the past, some averaging 10% for extended periods on narrow European roads. All descents that we've done in North America were a piece of cake compared to some of these due to the lesser gradients and wider roads over there, but I'm sure that we haven't tried the most extreme ones.
We've twice had inner tubes explode on the tandem due to overheating rims from excessive braking on descents; I don't believe the tire popped off of the rim on either occasion, it instead appeared that the inner tube material itself just failed due to heat before there was enough air pressure to separate the tire from the rim.
I've never overheated a tube on a single bike, but have been on rides with other people on single bikes and twice seen tubes fail due to rim heat on descents. I believe both were on steep descents in heavy fog with a reasonably heavy rider - a bad combination. I've also seen tubular tires roll off of friends' bikes due to the glue melting (Beloki's crash in the 2003 TDF was apparently caused by the same thing), and I've seen tubular tires shifting around the rim after the glue melted until the tire bulge up where the valve stopped it from going further. Fortunately, none of these resulted in serious injuries (except for Beloki).
We've also overheated a disc brake on the tandem to the point where it was barely braking and was smoking/steaming and smelling bad once we finally got the bike stopped during a very wet descent with full touring gear in New Zealand. On other occasions, a disc brake has started to fade but not too significantly, and the discs have been discolored and slightly warped at times (we've always used discs of between 200 and 220 mm diameter). We've only recently tried a disc brake with hydraulic fluid (we'd previous only used cable-actuated discs), and haven't yet managed to boil the fluid, but I've read reports that it is possible.
So, I've experienced nearly all types of brake overheating failures, most of which were on our tandem. I cannot say exactly which is more likely to happen given a certain standard degree of braking force, but I do know that a disc brake failing during a descent is less catastrophic than a tube failing, especially if you have one or two other brakes still working.
We've twice had inner tubes explode on the tandem due to overheating rims from excessive braking on descents; I don't believe the tire popped off of the rim on either occasion, it instead appeared that the inner tube material itself just failed due to heat before there was enough air pressure to separate the tire from the rim.
I've never overheated a tube on a single bike, but have been on rides with other people on single bikes and twice seen tubes fail due to rim heat on descents. I believe both were on steep descents in heavy fog with a reasonably heavy rider - a bad combination. I've also seen tubular tires roll off of friends' bikes due to the glue melting (Beloki's crash in the 2003 TDF was apparently caused by the same thing), and I've seen tubular tires shifting around the rim after the glue melted until the tire bulge up where the valve stopped it from going further. Fortunately, none of these resulted in serious injuries (except for Beloki).
We've also overheated a disc brake on the tandem to the point where it was barely braking and was smoking/steaming and smelling bad once we finally got the bike stopped during a very wet descent with full touring gear in New Zealand. On other occasions, a disc brake has started to fade but not too significantly, and the discs have been discolored and slightly warped at times (we've always used discs of between 200 and 220 mm diameter). We've only recently tried a disc brake with hydraulic fluid (we'd previous only used cable-actuated discs), and haven't yet managed to boil the fluid, but I've read reports that it is possible.
So, I've experienced nearly all types of brake overheating failures, most of which were on our tandem. I cannot say exactly which is more likely to happen given a certain standard degree of braking force, but I do know that a disc brake failing during a descent is less catastrophic than a tube failing, especially if you have one or two other brakes still working.
Wayne
10-30-16, 09:25 AM
#52
Newbie
...
Our personal preference for the past 40,000+ miles is Dura Ace sidepull front and and mini V-brake on the rear.
We are a rather light duo (sub 250 lbs total).
Have descended Kitt Peak in AZ (a 6%+ grade) and 11 miles long with lots of switchbacks in the late 1970s with Mafac cantis front and rear and NO 3rd brake. Worked great!...
Have also used the old drum brake setup and felt that for us, it was not necessary.
Just our experience and input. Your needs/wants may very from ours. Do what is good and comfortable for your team.
Pedal on TWOgether!
Rudy and Kay/zonatandem
Our personal preference for the past 40,000+ miles is Dura Ace sidepull front and and mini V-brake on the rear.
We are a rather light duo (sub 250 lbs total).
Have descended Kitt Peak in AZ (a 6%+ grade) and 11 miles long with lots of switchbacks in the late 1970s with Mafac cantis front and rear and NO 3rd brake. Worked great!...
Have also used the old drum brake setup and felt that for us, it was not necessary.
Just our experience and input. Your needs/wants may very from ours. Do what is good and comfortable for your team.
Pedal on TWOgether!
Rudy and Kay/zonatandem
As a heavy(er) team 340 lbs, I tried using my cantilevers only on a straight 2 mile 8% desent. Used up 1/4 of the rubber!!!!!! One 3 minute descent...Very different from your decades long experience.
After that one time, I use the rear drum brake descending and only use the cantilevers under 7mph. Obviously there is no noticeable wear on the rubber cantilever pads. Furthermore, the friction materials on the drum "shoes" can take virtually any level of heat and pressure and show minimal wear after 3000 miles
My conclusion. F&R disc brake friction material will take the heat and pressure that rubber rim pads can not.
10-30-16, 02:36 PM
#53
Likes to Ride Far
At the moment, our two primary brakes, controlled by the captain, are disc brakes, so overheating rims should no longer be a problem. The third, back-up brake is now the rear rim brake that is controlled by the stoker, but it doesn't get much use except in really serious descents, so I think (hope) that there is almost no chance of us bursting a tube due to heat anymore.
11-06-16, 08:40 PM
#54
Clipless in Coeur d'Alene
Just a data point for comparison, I did the same hwy 9 descent (Saratoga, CA) yesterday on my single and although I thought I pushed it pretty good, my time was 1 minute/3mph slower than what we did on the tandem 2 weeks ago (and that was my first time down it).
Last edited by twocicle; 11-07-16 at 01:36 AM.
11-06-16, 11:29 PM
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I don't use or know much about tubeless bicycle tires but I wouldn't think that tubeless has any inherent advantage with respect to overheating. The problem is the small volume of a bicycle tire in very close thermal proximity to a rim that is being used as a brake radiator! You are going to have a problem if you put too much heat into either kind of tire. Disc or drum brakes that do not use the rim as the thermal sink are about the only way I can think to protect the tube (or tubeless) from overheating in a high stress situation.
11-07-16, 04:32 PM
#56
Full Member
For anyone interested in using carbon fibre rims and wants to know more about heat from rim braking etc,. This vlog is well worth a look. Raoul who is being interviewed is most probably Australia's best carbon fibre repairer
Last edited by geoffs; 09-07-17 at 05:37 PM.
09-06-17, 07:08 AM
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Careful riding could be a mistake ? The problem of slowing tandems on long downhills
Interesting article on heat generation during braking. The take-away is don't ride the brakes at what might initially appear to be a safe speed as this will maximize heat generation. Alternate between very slow for corners and free-wheel for straight sections. The second graph shows this visually.
Probably not news to most of you but for a beginner it is nice to see graphically that 15 to 20 mph may not be safe and a better strategy may be either 10 (if needed) or 35 but otherwise stay off the brakes.
Interesting article on heat generation during braking. The take-away is don't ride the brakes at what might initially appear to be a safe speed as this will maximize heat generation. Alternate between very slow for corners and free-wheel for straight sections. The second graph shows this visually.
Probably not news to most of you but for a beginner it is nice to see graphically that 15 to 20 mph may not be safe and a better strategy may be either 10 (if needed) or 35 but otherwise stay off the brakes.
09-06-17, 07:25 AM
#58
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Interesting article. This quantifies the effect and technique that we have adopted over many miles on our tandem. When doing a descent where we need to periodically slow down (like for switchbacks) we carry a lot of speed in the straight sections (and sit up to increase drag) and then brake heavily as we approach the switchback. This dumps a lot of energy to the air and allows us to go into the corners with relatively cool rims. If we were on a very steep road with close, frequent switchbacks (on a hot day) this might not work but we have never had a problem with brake heating on our many miles.
Thanks for the link.
Thanks for the link.
09-13-17, 08:27 PM
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I ran across this very good article today. This poor rider crashed while descending on a disk-equipped single bike! Thank goodness he's OK but he did learn some important lessons. The included industry opinions on disk brakes is quite interesting and informative.
https://www.bikerumor.com/2012/02/14...ill-they-work/
https://www.bikerumor.com/2012/02/14...ill-they-work/
09-13-17, 09:03 PM
#60
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Way back in post No.3 I made reference to the importance of using the "air brakes" we get near terminal velocity. The problem for tandems is that terminal velocity is higher, but the basic principles of braking still apply.
DO NOT USE BRAKES FOR STEADY DRAG. This is the surest way to heat them to failure, and is like accidentally leaving your parking brake partly set when driving. Instead let the bike roll and accelerate, controlling speed to the extent you can by maximizing your drag. Then before corners, or when the speed reaches your maximum comfort level, scrub off speed with a short hard braking cycle, then repeat the process.
Since air drag is proportional to the cube of speed, the much greater drag achieved at higher speed restrains your speed without heating the brakes. In many cases the terminal velocity is slow enough that you don't need to use the brakes at all, except to lower speed for cornering.
Personally, I try to mainly use the rear brake for speed control, saving the front as much as possible so it'll stay cool and be there, should I need it stop.
BTW- If I were ever to ride a tandem in true alpine conditions, and find braking to be an issue on descents, I'd improvise a drogue chute and deploy it at the top, and stow it later for future use. I have no data, but suspect that something as small as 3' or less in diameter would do the trick.
DO NOT USE BRAKES FOR STEADY DRAG. This is the surest way to heat them to failure, and is like accidentally leaving your parking brake partly set when driving. Instead let the bike roll and accelerate, controlling speed to the extent you can by maximizing your drag. Then before corners, or when the speed reaches your maximum comfort level, scrub off speed with a short hard braking cycle, then repeat the process.
Since air drag is proportional to the cube of speed, the much greater drag achieved at higher speed restrains your speed without heating the brakes. In many cases the terminal velocity is slow enough that you don't need to use the brakes at all, except to lower speed for cornering.
Personally, I try to mainly use the rear brake for speed control, saving the front as much as possible so it'll stay cool and be there, should I need it stop.
BTW- If I were ever to ride a tandem in true alpine conditions, and find braking to be an issue on descents, I'd improvise a drogue chute and deploy it at the top, and stow it later for future use. I have no data, but suspect that something as small as 3' or less in diameter would do the trick.
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09-13-17, 10:24 PM
#61
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We are friends with a team in which the stoker will hold her arms out straight in summer. In winter she unzips her jacket and holds that out as an air brake. The jacket is extremely effective. I don't advise that stokers deploy such a drag unless they are very experienced. Easy to be blown right off your saddle. The chute thing has been tried but is dangerous and likely to get entangled in running gear or objects along the road.
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09-13-17, 10:44 PM
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I believe that these would only be needed for the most extreme alpine descents where the combination of grade and corners would tax brakes to the limits.
Otherwise being comfortable at speeds nearer to terminal velocity is key, that or taking scenic photo ops off the bike from time.
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09-14-17, 12:05 AM
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I ran across this very good article today. This poor rider crashed while descending on a disk-equipped single bike! Thank goodness he's OK but he did learn some important lessons. The included industry opinions on disk brakes is quite interesting and informative.
https://www.bikerumor.com/2012/02/14...ill-they-work/
https://www.bikerumor.com/2012/02/14...ill-they-work/
By the author's own admission, the "Braking was handled by a first gen TRP Parabox clamping on Ashima’s new and ridiculously light Ai2 rotors. It’s important to note that the original Parabox is meant as a cyclocross brake system. The rear caliper and brake pads are smaller than the front, and the Ashima rotors are about as minimalist as you can get. In other words, they’re perfect for ‘cross where speeds are low and braking is rarely a life or death matter."
It's such a bad idea to use 1st-generation cable-actuated disc brake with a "ridiculously" light rotor (designed for cross-country rides) on a "very curvy, steep road" at 30-40 mph. It's like using lightweight wheels and being surprised that they crack on a fully-loaded touring bike.
To compound the problem, the brakes were not properly installed. The Parabox is a clunky design that used two standard brake cables run from the road shifters to a pair of cylinder actuators on a hydraulic reservoir clamped to the steerer tube (under the stem). Exiting this unit are two hydraulic hoses that feed the calipers. By comparison, the current TRP Hy/Rd eliminated the hydraulic hoses by incorporating the hydraulic reservoir in the calipers. Since the Paradox used long hydraulic hoses, it's critical to properly bleed the fluid and eliminate air bubbles. Improper installation will make the brake fade badly ("the levers went to the bar"). The author installed the parts, cut the rear hose, and "chose to not use TRP’s stock rotors." He evidently didn't fully test the brakes before making a steep descent.
On top of these self-induced errors, the author used poor descending technique" "being my first time on this road, I kept light pressure on the levers, dragging my brakes to keep my speed around 30mph on a very curvy, steep road." The proper technique is to modulate the brakes (brake hard and release) using both the F & R calipers.
This article is really a cautionary tale about improperly using outdated technology. Even the author admitted that " I do not blame TRP or any other manufacturer for what happened. In hindsight, it was poor parts selection for the actual use. And perhaps I could have used better braking technique – brake hard, release, brake hard, release."
If you ignore this article, you'll get safe and powerful braking from modern designs like the Shimano R785, Shimano R9170 (with new flat mount), and Sram HRD disc brakes. Every top brand (Trek, Cannondale, Specialized, Pinarello, Cervelo, Giant, etc) now offer these disc brakes on their road bikes because they work really well. Caliper brakes are still a good choice if you value light weight and aerodynamics.
09-14-17, 09:57 AM
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It annoys me to see another reference to this out-dated article with a misleading headline. If you actually read the article, you'll see that the brake failure was due to poor part selection, shoddy installation, and unsafe braking technique.
By the author's own admission, the "Braking was handled by a first gen TRP Parabox clamping on Ashima’s new and ridiculously light Ai2 rotors. It’s important to note that the original Parabox is meant as a cyclocross brake system. The rear caliper and brake pads are smaller than the front, and the Ashima rotors are about as minimalist as you can get. In other words, they’re perfect for ‘cross where speeds are low and braking is rarely a life or death matter."
It's such a bad idea to use 1st-generation cable-actuated disc brake with a "ridiculously" light rotor (designed for cross-country rides) on a "very curvy, steep road" at 30-40 mph. It's like using lightweight wheels and being surprised that they crack on a fully-loaded touring bike.
To compound the problem, the brakes were not properly installed. The Parabox is a clunky design that used two standard brake cables run from the road shifters to a pair of cylinder actuators on a hydraulic reservoir clamped to the steerer tube (under the stem). Exiting this unit are two hydraulic hoses that feed the calipers. By comparison, the current TRP Hy/Rd eliminated the hydraulic hoses by incorporating the hydraulic reservoir in the calipers. Since the Paradox used long hydraulic hoses, it's critical to properly bleed the fluid and eliminate air bubbles. Improper installation will make the brake fade badly ("the levers went to the bar"). The author installed the parts, cut the rear hose, and "chose to not use TRP’s stock rotors." He evidently didn't fully test the brakes before making a steep descent.
On top of these self-induced errors, the author used poor descending technique" "being my first time on this road, I kept light pressure on the levers, dragging my brakes to keep my speed around 30mph on a very curvy, steep road." The proper technique is to modulate the brakes (brake hard and release) using both the F & R calipers.
This article is really a cautionary tale about improperly using outdated technology. Even the author admitted that " I do not blame TRP or any other manufacturer for what happened. In hindsight, it was poor parts selection for the actual use. And perhaps I could have used better braking technique – brake hard, release, brake hard, release."
If you ignore this article, you'll get safe and powerful braking from modern designs like the Shimano R785, Shimano R9170 (with new flat mount), and Sram HRD disc brakes. Every top brand (Trek, Cannondale, Specialized, Pinarello, Cervelo, Giant, etc) now offer these disc brakes on their road bikes because they work really well. Caliper brakes are still a good choice if you value light weight and aerodynamics.
By the author's own admission, the "Braking was handled by a first gen TRP Parabox clamping on Ashima’s new and ridiculously light Ai2 rotors. It’s important to note that the original Parabox is meant as a cyclocross brake system. The rear caliper and brake pads are smaller than the front, and the Ashima rotors are about as minimalist as you can get. In other words, they’re perfect for ‘cross where speeds are low and braking is rarely a life or death matter."
It's such a bad idea to use 1st-generation cable-actuated disc brake with a "ridiculously" light rotor (designed for cross-country rides) on a "very curvy, steep road" at 30-40 mph. It's like using lightweight wheels and being surprised that they crack on a fully-loaded touring bike.
To compound the problem, the brakes were not properly installed. The Parabox is a clunky design that used two standard brake cables run from the road shifters to a pair of cylinder actuators on a hydraulic reservoir clamped to the steerer tube (under the stem). Exiting this unit are two hydraulic hoses that feed the calipers. By comparison, the current TRP Hy/Rd eliminated the hydraulic hoses by incorporating the hydraulic reservoir in the calipers. Since the Paradox used long hydraulic hoses, it's critical to properly bleed the fluid and eliminate air bubbles. Improper installation will make the brake fade badly ("the levers went to the bar"). The author installed the parts, cut the rear hose, and "chose to not use TRP’s stock rotors." He evidently didn't fully test the brakes before making a steep descent.
On top of these self-induced errors, the author used poor descending technique" "being my first time on this road, I kept light pressure on the levers, dragging my brakes to keep my speed around 30mph on a very curvy, steep road." The proper technique is to modulate the brakes (brake hard and release) using both the F & R calipers.
This article is really a cautionary tale about improperly using outdated technology. Even the author admitted that " I do not blame TRP or any other manufacturer for what happened. In hindsight, it was poor parts selection for the actual use. And perhaps I could have used better braking technique – brake hard, release, brake hard, release."
If you ignore this article, you'll get safe and powerful braking from modern designs like the Shimano R785, Shimano R9170 (with new flat mount), and Sram HRD disc brakes. Every top brand (Trek, Cannondale, Specialized, Pinarello, Cervelo, Giant, etc) now offer these disc brakes on their road bikes because they work really well. Caliper brakes are still a good choice if you value light weight and aerodynamics.
You may agree or not agree with the info. presented in the article. It's unfortunate that you attacked me personally for putting out what you believe it's misleading information.
09-14-17, 01:16 PM
#65
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While road disc brakes continue to evolve and improve one thing won't change and that's brake fade from overheating.
That has nothing to do with the brake mechanism, and is purely a function of the amount of heat the rotor can take up and how fast it can cool. This is true for all brake rotors, including the rim with rim brakes.
The flip side is the amount of heat generated which is a function of weight, grade and speed.
The rider has some degree of control by tolerating higher speed where air brakes do more of the work, and by cycling the brakes to allow cooling intervals between short braking bursts.
But, when comparing brakes, it still boils down to the heat capacity and cooling speed of the rotor.
That has nothing to do with the brake mechanism, and is purely a function of the amount of heat the rotor can take up and how fast it can cool. This is true for all brake rotors, including the rim with rim brakes.
The flip side is the amount of heat generated which is a function of weight, grade and speed.
The rider has some degree of control by tolerating higher speed where air brakes do more of the work, and by cycling the brakes to allow cooling intervals between short braking bursts.
But, when comparing brakes, it still boils down to the heat capacity and cooling speed of the rotor.
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An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
09-15-17, 02:58 AM
#66
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We are a 300lb team and have blown tyres off rims (with rim brakes) twice. Both on fast technical descents.
I am not an overly cautious downhill, quite the opposite actually. Do not ride the brakes. But with steep grades and a number of tight corners you simply have to work the brakes hard.
I use discs now and haven't had any trouble.
Really with my wife on the back I don't like the idea of cornering downhill at speed and wondering if the tyre is going to stay on because of all the hard braking that I have also been doing.
Fortunately the two times we blew tyres were on straight bits and we managed to stay upright.
I am not an overly cautious downhill, quite the opposite actually. Do not ride the brakes. But with steep grades and a number of tight corners you simply have to work the brakes hard.
I use discs now and haven't had any trouble.
Really with my wife on the back I don't like the idea of cornering downhill at speed and wondering if the tyre is going to stay on because of all the hard braking that I have also been doing.
Fortunately the two times we blew tyres were on straight bits and we managed to stay upright.
09-15-17, 10:14 AM
#67
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Quite so. We haven't blown a tire off with rim brakes since we went to deep section aluminum rims. 285 lb. team. When we tour and weigh extra, plus are going into unknown terrain, I put on our spare rear wheel with the drum brake. That is a true drag brake which I can just leave on to keep the speed down.
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09-15-17, 10:46 PM
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Perhaps you don't ride enough to experience extreme conditions. I have overheated my 254mm disk brake. I experienced the same thing as the crashed rider...a complete loss of braking when vapors from the melted brake pads prevented pads to rotor contact. We are a lightweight team and I see plenty of tandems with rotors smaller than 254mm.
You may agree or not agree with the info. presented in the article. It's unfortunate that you attacked me personally for putting out what you believe it's misleading information.
You may agree or not agree with the info. presented in the article. It's unfortunate that you attacked me personally for putting out what you believe it's misleading information.
Since you brought it up, tandems are fun but don't really encounter "extreme" conditions. They're usually ridden in good weather, and on good roads that are not steeper than 12%. I've been riding singles and tandems for over 30 years, and find it more challenging to do a high speed group descent in a Gran Fondo (and hope that no does anything stupid like drop a water bottle), or make steep technical descents in an enduro mtn bike race while dodging other riders.
In my neighbourhood, there are many off-road descents of 20-30% (see photo). Some trails are too steep to walk, and poor braking (too much or too little) can lead to serious crashes. For these conditions, full-hydraulic disk brakes with 180mm (F) and 160mm (R) rotors are extremely effective and reliable. This kind of setup can easily handle Whistler's Top of the World trail (see Youtube video). It drops 740m over 5,600 km for an average grade of 13%, with there are few smooth or straight sections. Even for these conditions, it's rare to hear about hot rotors. So a modern hydraulic disks (Shimano R785, R9170) can easily get a tandem down an epic descent like Mt Ventoux, where the average grade is only 7% (w straight sections between switchbacks).
If you overheat 254mm rotors, it's likely that you're using BB7 or Bengal mechanical disk brakes with a single piston. These are obsolete designs without hydraulic brake's "mechanical advantage", dual pistons, and self-centering pads. Not surprisingly, you can't find mechanical disk brakes on good-quality single road or mtn bikes. If these brakes are not good enough for a single, why use them on a tandem? I also hope that you modulate your brake (squeeze and release) rather than use the rear disk as a drag brake to "save" the front caliper on steep descents.
09-16-17, 07:07 AM
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If you overheat 254mm rotors, it's likely that you're using BB7 or Bengal mechanical disk brakes with a single piston. These are obsolete designs without hydraulic brake's "mechanical advantage", dual pistons, and self-centering pads. Not surprisingly, you can't find mechanical disk brakes on good-quality single road or mtn bikes. If these brakes are not good enough for a single, why use them on a tandem? I also hope that you modulate your brake (squeeze and release) rather than use the rear disk as a drag brake to "save" the front caliper on steep descents.
If you overheat 254mm rotors, it's likely that you're using BB7 or Bengal mechanical disk brakes with a single piston. These are obsolete designs without hydraulic brake's "mechanical advantage", dual pistons, and self-centering pads. Not surprisingly, you can't find mechanical disk brakes on good-quality single road or mtn bikes. If these brakes are not good enough for a single, why use them on a tandem? I also hope that you modulate your brake (squeeze and release) rather than use the rear disk as a drag brake to "save" the front caliper on steep descents.
Last edited by marciero; 09-16-17 at 07:13 AM.
09-16-17, 07:12 AM
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We have been through a number of the brake systems out there after melting a BB7 on a descent of Mt Venteau a number of years ago. Since then HyRd hydraulic and Bengal , and melted a Ice tech disc with a Bengal on a 17% descent in Europe( we were not the only one whom melted one on the same descent). For the last few years we have been running R785 hydraulic dual discs with very good results. We are presently on a 14 day self supported tour of Vermont including most of the ski areas. Our Calfee is pretty heavy with all the gear and us and we recently did a 2 mile descent of 10-12% on one of the gap routes and the brakes did great although the rotors did get a bit noisey. The ceramic pistons I believe are a real key to heat management . Shimano recently announced 4 piston Xt brakes which should be compatible with the 785 levers and give even more braking power and will be a simple upgrade. I have not heard of any failures of these brakes. We are using Goodridge hoses for the long length necessary on a tandem with very good results. YRMV
09-17-17, 12:59 AM
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...hydro vs cable/mechanical, dual vs single-piston, self-centering, etc, have no affect on the ability to dissipate heat. Nor does the mechanical advantage of the brakes have any affect on ability to dissipate heat. The advantage of hydros is that they require less force at the lever to generate the same force at the pad/rotor interface. Rotors- size and design, and brake pads- material and design, are what determines the ability to dissipate heat.
Mechanical disk brake (eg. BB7) uses a single piston to push the rotor against a fixed pad. Until the rotor is firmly pressed against the fixed pad, the piston is just generating more heat than braking force. The single piston continues to generate excess heat when it retracts from the fixed pad. On the other hand, a hydraulic disk brake has 2 pistons converging on the rotor. The 2 pistons slow down the rotor immediately, and releases the rotor without any excess heat. Since the hydraulic pistons are auto-centering, they're not affected by pad wear like the BB7.
Hydraulic systems use pistons of different diameter to achieve mechanical advantage (eg. hydraulic car jack). Hydraulic use the same principle to achieve more brake force in shorter time (eg. slow from 30 to 20 mph with shorter brake engagement). Less time on the brakes mean less heat build-up. Riders who try hydraulic brakes will soon learn that they can brake less and later (ie. go faster with more safety margin).
The hydraulic fluid, ceramic pistons, metal hydraulic line, and banjo also improve heat dissipation.
Their superior heat dissipation is borne out by the use of smaller rotors. On road bikes, 140mm rotors are common. For gravel bikes, some riders may use 160mm front rotors. For enduro or downhill mtn bikes, the typical setup is 180/160mm rotor (F&R). Heavier riders on demanding descents may go to 200/180mm rotors (F&R).
Tandems use 200 or 250mm rotors mainly to compensate for the inefficiencies of mechanical disk brakes. Teams who've converted to hydraulic disk brakes find that 180mm rotors (F&R) provide enough braking power and heat dissipation. A minor bonus is the smaller rotors and adapters are lighter. I doubt that anyone who's tried hydraulic disk brakes will go to mechanical disk brakes, which is why hydraulic disk brakes vastly outnumber the mechanicals.
09-17-17, 02:20 AM
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Actually the ceramic pistons are to stop heat dissipation. The design is for the heat to go from the pads to the heat sinks attached to them. The ceramic pistons stop the heat getting to the hydraulic fluid and main body of the caliper.
09-17-17, 05:22 AM
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We don't live in an area that particularly tests heat sink capability, but the one trip that we took to the mountains, we took a bike with spyres on them because of the difference in failure mode between cable and hydraulic disks. Boiling brake fluid and completely losing braking ability sounds like a pretty bad thing to me. We ride 203 rotors on both the cable and hydraulic systems, the extra bit of weight seems worth it to me for an extra margin of safety on the brakes.
09-17-17, 02:37 PM
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i would be interested in hearing from someone whom actually had boiling brake fluid and or complete brake failure. I think we have done a significant number of major decents in Europe, New Zealand and the US and never had complete brake failure on our hydraulic systems. The few times the brakes have gotten extremely noisey or started chattering we just stop and let them cool for a short period, we are not racing so the little time we stop for safety is of little concern. We were with a group of 8 tandems in New Zealand on a 17% descent and we all stopped at about the halfway point as everyone was smelling the pads and concerned, the one team with rim brakes had a stoker in tears as they could barely stop at that point. BTW we are 340# team for reference .
09-17-17, 02:45 PM
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i would be interested in hearing from someone whom actually had boiling brake fluid and or complete brake failure. I think we have done a significant number of major decents in Europe, New Zealand and the US and never had complete brake failure on our hydraulic systems. ....
Put 10 teams on the same alpine descent, and you'll see a spectrum of speeds and brake problems, running from "what's the issue", to (possibly) total brake fade. One may be tempted to draw conclusions based on the equipment, but I suspect the bigger factor would be rider skill.
That's the problem when working with limited data points and anecdotal evidence, there's simply not enough data to show patterns form which one might draw meaningful conclusions.
It's not about hardware, it's a software problem, meaning that which runs between the ears.
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An ounce of diagnosis is worth a pound of cure.
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