Cycling and bicycle discussion forums. 
   Click here to join our community Log in to access your Control Panel  


Go Back   > >

Tandem Cycling A bicycle built for two. Want to find out more about this wonderful world of tandems? Check out this forum to talk with other tandem enthusiasts. Captains and stokers welcome!

User Tag List

Reply
 
Thread Tools Search this Thread
Old 10-30-16, 08:26 AM   #51
DubT
Senior Member
 
Join Date: Sep 2009
Location: Central Illinois
Bikes: Trek Speed Concept 9.9, 2011 Calfee Tetra Tandem
Posts: 1,087
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 16 Post(s)
Quote:
Originally Posted by Chris_W View Post
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.
Chris, do you have any experience with running tubeless tires on your tandems? I would think the lower air pressures and the lack of an inner tube would solve the overheating problem associated with rim brakes. What do you think?

Wayne
DubT is offline   Reply With Quote
Old 10-30-16, 09:25 AM   #52
joel1952
Junior Member
 
Join Date: Feb 2009
Bikes:
Posts: 9
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by zonatandem View Post
...
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
Ah, the weight is a big factor.

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.
joel1952 is offline   Reply With Quote
Old 10-30-16, 02:36 PM   #53
Chris_W
Likes to Ride Far
 
Chris_W's Avatar
 
Join Date: May 2007
Location: Switzerland
Bikes: road, commuter/tourer, hardtail MTB, touring tandem, cargo, folder
Posts: 2,262
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 15 Post(s)
Quote:
Originally Posted by DubT View Post
Chris, do you have any experience with running tubeless tires on your tandems? I would think the lower air pressures and the lack of an inner tube would solve the overheating problem associated with rim brakes. What do you think?

Wayne
You are probably correct, that would be an advantage of tubeless tires, but i haven't tried it. I've used tubeless tires on my single road bike for a while, but I've had mixed experiences with them so have given up on them because they are more hassle and haven't been immune to punctures for me. I only briefly used a tubeless tire on our tandem, but that was on a wheel that had no rim brake.

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.
Chris_W is offline   Reply With Quote
Old 11-06-16, 08:40 PM   #54
twocicle
Clipless in Coeur d'Alene
 
twocicle's Avatar
 
Join Date: Mar 2012
Location: Coeur d'Alene, Idaho
Bikes: Tandems: Calfee Dragonfly S&S, Fandango 29er Mtb; Singles: Specialized Tarmac SL4 S-Works, Specialized Stumpjumper FSR, plus other misc Road & Mtb.
Posts: 1,861
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 110 Post(s)
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.
twocicle is offline   Reply With Quote
Old 11-06-16, 11:29 PM   #55
Leisesturm
Senior Member
 
Join Date: Jul 2005
Bikes:
Posts: 3,107
Mentioned: 8 Post(s)
Tagged: 0 Thread(s)
Quoted: 671 Post(s)
Quote:
Originally Posted by DubT View Post
Chris, do you have any experience with running tubeless tires on your tandems? I would think the lower air pressures and the lack of an inner tube would solve the overheating problem associated with rim brakes. What do you think?

Wayne
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.
Leisesturm is offline   Reply With Quote
Old 11-07-16, 04:32 PM   #56
geoffs
Senior Member
 
geoffs's Avatar
 
Join Date: Sep 2004
Location: Sydney
Bikes: Co-Motion Mocha Co-pilot, Santana Sovereign, Seven Axiom SL, Seven Axiom SLX, Blom Track
Posts: 187
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 38 Post(s)
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.
geoffs is offline   Reply With Quote
Old 09-06-17, 07:08 AM   #57
Stick69
Senior Member
 
Join Date: Jan 2016
Location: Sacramento
Bikes: Trek 7.2 FX, Co-Motion Supremo
Posts: 179
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 23 Post(s)
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.
Stick69 is offline   Reply With Quote
Old 09-06-17, 07:25 AM   #58
oldacura
Senior Member
Thread Starter
 
oldacura's Avatar
 
Join Date: Nov 2006
Location: Lafayette, Colorado
Bikes: 1998 Co-Motion Co-Pilot, 2015 Calfee Tetra
Posts: 867
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 95 Post(s)
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.
oldacura is offline   Reply With Quote
Old 09-13-17, 08:27 PM   #59
pdlpsher
Senior Member
 
Join Date: Mar 2017
Location: Loveland CO
Bikes: 2017 Santana Ti700
Posts: 102
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 53 Post(s)
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/
pdlpsher is offline   Reply With Quote
Old 09-13-17, 09:03 PM   #60
FBinNY 
Senior Member
 
Join Date: Apr 2009
Location: New Rochelle, NY
Bikes: too many bikes from 1967 10s (5x2)Frejus to a Sumitomo Ti/Chorus aluminum 10s (10x2), plus one non-susp mtn bike I use as my commuter
Posts: 34,586
Mentioned: 92 Post(s)
Tagged: 1 Thread(s)
Quoted: 3122 Post(s)
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.
__________________
FB
Chain-L site

An ounce of diagnosis is worth a pound of cure.

“Never argue with an idiot. He will only bring you down to his level and beat you with experience.”, George Carlin

“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.

Last edited by FBinNY; 09-13-17 at 09:13 PM.
FBinNY is offline   Reply With Quote
Old 09-13-17, 10:24 PM   #61
Carbonfiberboy 
just another gosling
 
Carbonfiberboy's Avatar
 
Join Date: Feb 2007
Location: Everett, WA
Bikes: CoMo Speedster 2003, Trek 5200, CAAD 9, Fred 2004
Posts: 12,678
Mentioned: 39 Post(s)
Tagged: 0 Thread(s)
Quoted: 716 Post(s)
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.
__________________
Results matter
Carbonfiberboy is offline   Reply With Quote
Old 09-13-17, 10:44 PM   #62
FBinNY 
Senior Member
 
Join Date: Apr 2009
Location: New Rochelle, NY
Bikes: too many bikes from 1967 10s (5x2)Frejus to a Sumitomo Ti/Chorus aluminum 10s (10x2), plus one non-susp mtn bike I use as my commuter
Posts: 34,586
Mentioned: 92 Post(s)
Tagged: 1 Thread(s)
Quoted: 3122 Post(s)
Quote:
Originally Posted by Carbonfiberboy View Post
.... The chute thing has been tried but is dangerous and likely to get entangled in running gear or objects along the road.
I agree that the chute has problems, which is why I doubt we'd ever see a commercial version. But I think a small one can be used safely if designed and used intelligently. Alternately some kind of spoiler might be rigged to carrier legs and deployed as needed.

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.
__________________
FB
Chain-L site

An ounce of diagnosis is worth a pound of cure.

“Never argue with an idiot. He will only bring you down to his level and beat you with experience.”, George Carlin

“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.
FBinNY is offline   Reply With Quote
Old 09-14-17, 12:05 AM   #63
mtseymour
Senior Member
 
Join Date: Nov 2010
Location: Vancouver, BC
Bikes: 2014 Calfee Tetra, 2014 Norco Carbon Sight, 2016 Giant TCR
Posts: 329
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 75 Post(s)
Quote:
Originally Posted by pdlpsher View Post
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/
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.
mtseymour is offline   Reply With Quote
Old 09-14-17, 09:57 AM   #64
pdlpsher
Senior Member
 
Join Date: Mar 2017
Location: Loveland CO
Bikes: 2017 Santana Ti700
Posts: 102
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 53 Post(s)
Quote:
Originally Posted by mtseymour View Post
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.
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.
pdlpsher is offline   Reply With Quote
Old 09-14-17, 01:16 PM   #65
FBinNY 
Senior Member
 
Join Date: Apr 2009
Location: New Rochelle, NY
Bikes: too many bikes from 1967 10s (5x2)Frejus to a Sumitomo Ti/Chorus aluminum 10s (10x2), plus one non-susp mtn bike I use as my commuter
Posts: 34,586
Mentioned: 92 Post(s)
Tagged: 1 Thread(s)
Quoted: 3122 Post(s)
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.
__________________
FB
Chain-L site

An ounce of diagnosis is worth a pound of cure.

“Never argue with an idiot. He will only bring you down to his level and beat you with experience.”, George Carlin

“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.
FBinNY is offline   Reply With Quote
Old 09-15-17, 02:58 AM   #66
Dean V
Senior Member
 
Join Date: Oct 2009
Bikes:
Posts: 1,524
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 265 Post(s)
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.
Dean V is offline   Reply With Quote
Old 09-15-17, 10:14 AM   #67
Carbonfiberboy 
just another gosling
 
Carbonfiberboy's Avatar
 
Join Date: Feb 2007
Location: Everett, WA
Bikes: CoMo Speedster 2003, Trek 5200, CAAD 9, Fred 2004
Posts: 12,678
Mentioned: 39 Post(s)
Tagged: 0 Thread(s)
Quoted: 716 Post(s)
Quote:
Originally Posted by FBinNY View Post
<snip?
But, when comparing brakes, it still boils down to the heat capacity and cooling speed of the rotor.
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.
__________________
Results matter
Carbonfiberboy is offline   Reply With Quote
Old 09-15-17, 10:46 PM   #68
mtseymour
Senior Member
 
Join Date: Nov 2010
Location: Vancouver, BC
Bikes: 2014 Calfee Tetra, 2014 Norco Carbon Sight, 2016 Giant TCR
Posts: 329
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 75 Post(s)
Quote:
Originally Posted by pdlpsher View Post
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.
I offered detailed reasons why this article was not "very good" and didn't mean to attack you personally. I would appreciate it if you explain your reaction.

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.
Attached Images
File Type: jpg North Shore.jpg (99.7 KB, 69 views)
mtseymour is offline   Reply With Quote
Old 09-16-17, 07:07 AM   #69
marciero
Senior Member
 
Join Date: Aug 2015
Bikes: 2005 CoMotion Speedster, 2014 Cannondale T2, various single bikes
Posts: 99
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 20 Post(s)
Quote:
Originally Posted by mtseymour View Post
...
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.
This conflates different things. The ability of a disc brake to dissipate heat is dependent on the actuation only to the extent that the different designs, materials, parts, and construction may have different heat dissipation properties. So for example, hydro vs cable/mechanical may differ due to plastic parts on one melting or the brake fluid on the hydros boiling, which cant happen with cable actuated. Other than that, 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.

Last edited by marciero; 09-16-17 at 07:13 AM.
marciero is offline   Reply With Quote
Old 09-16-17, 07:12 AM   #70
akexpress
Senior Member
 
Join Date: Nov 2007
Location: Anchorage, Ak
Bikes: Calfee Tetra tandem, Ventana ECDM 26, Ventana ECDM 29r, Orbea Orca, Santa Cruz Carbon 5010
Posts: 537
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 26 Post(s)
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
akexpress is offline   Reply With Quote
Old 09-17-17, 12:59 AM   #71
mtseymour
Senior Member
 
Join Date: Nov 2010
Location: Vancouver, BC
Bikes: 2014 Calfee Tetra, 2014 Norco Carbon Sight, 2016 Giant TCR
Posts: 329
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 75 Post(s)
Quote:
Originally Posted by marciero View Post
...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.
I disagree. The hydraulic brake's dual pistons, self-centering pads, and mechanical advantage all work together to provide superior heat dissipation.

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.
mtseymour is offline   Reply With Quote
Old 09-17-17, 02:20 AM   #72
Dean V
Senior Member
 
Join Date: Oct 2009
Bikes:
Posts: 1,524
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 265 Post(s)
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.
Dean V is offline   Reply With Quote
Old 09-17-17, 05:22 AM   #73
bwebel
Senior Member
 
Join Date: May 2014
Bikes:
Posts: 50
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 12 Post(s)
Quote:
Originally Posted by mtseymour View Post
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.
I suppose there's always one outlier, but I've bought two bikes worth of mechanical disk brakes (TRP spyres) since installing the SRAM hydraulic disks on one of our tandem. They hydraulics have a lighter lever feel, but otherwise I just haven't seen the overwhelming advantages that are being pointed to by proponents of them. Maybe the Shimano brakes are better? but I think I am too used the shifting action on SRAM and Campy to switch back to Shimano now.

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.
bwebel is offline   Reply With Quote
Old 09-17-17, 02:37 PM   #74
akexpress
Senior Member
 
Join Date: Nov 2007
Location: Anchorage, Ak
Bikes: Calfee Tetra tandem, Ventana ECDM 26, Ventana ECDM 29r, Orbea Orca, Santa Cruz Carbon 5010
Posts: 537
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 26 Post(s)
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 .
akexpress is offline   Reply With Quote
Old 09-17-17, 02:45 PM   #75
FBinNY 
Senior Member
 
Join Date: Apr 2009
Location: New Rochelle, NY
Bikes: too many bikes from 1967 10s (5x2)Frejus to a Sumitomo Ti/Chorus aluminum 10s (10x2), plus one non-susp mtn bike I use as my commuter
Posts: 34,586
Mentioned: 92 Post(s)
Tagged: 1 Thread(s)
Quoted: 3122 Post(s)
Quote:
Originally Posted by akexpress View Post
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. ....
You've identified the problem here. Skilled or knowledgeable riders don't have problems because they either avoid them with smart brake use, and/or manage the potential problem by stopping to cool brakes when needed.

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.
__________________
FB
Chain-L site

An ounce of diagnosis is worth a pound of cure.

“Never argue with an idiot. He will only bring you down to his level and beat you with experience.”, George Carlin

“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.
FBinNY is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off



All times are GMT -6. The time now is 06:43 AM.


 
  • Ask a Question
    get answers from real people!
Click to start entering your question.
I HAVE A QUESTION