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Braking thoughts. A sanity check of sorts.

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Braking thoughts. A sanity check of sorts.

Old 02-24-21, 11:05 AM
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bakerjw
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Braking thoughts. A sanity check of sorts.

I know that brakes have been the topic of discussions in the past but my searches didn't find too much in the way of recent discussions. Some of the products that I am considering have been around for quite a while. Anyway, we are on the verge of getting our new custom road tandem built and delivered. When I say built, I mean that Doug Curtiss at Curtlo Cycles is preparing to be build the frame and I will assemble on it once it is in hand.


Lolly, our mountain tandem, shown below, was also built by Doug and I completed the build with my list of components. With Lolly, I used TRP Spyke brakes with larger disks. As you can see, the rear rotor is like a 220mm. Fully loaded with gear, food and water on our Tour Divide Ride a couple of years back, Lolly weighed in at around 90#. The Spyke brakes and rotors were solid as can could be regardless of load or descent and as the captain, I couldn't be happier.


With the new build, brakes are a topic of discussion and although not necessarily up in the air just a thought rattling around in my head.

We are going to be running a Shimano 105 3x10 drivetrain which has readily available components.

My initial thoughts are to go with TRP Spyre calipers and a 203mm rotor in front with another large one in the rear. The build will also have a caliper mount on the rear in case I would ever want to mount a supplemental rim brake.

The wheels will be built on Onxy hubs and Sun Ringel Rhyno Lite rims as I've never had any trouble with them and they can utilize rim braking.


Just looking for thoughts.



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Old 02-24-21, 05:45 PM
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A lot of people are using these. They are cable actuated hydraulic which give a little more stopping power then the Spyres . We have the Spyres on our Co-Motion which work well but most folks building customs are using the Hy/Rd's.
https://trpcycling.com/product/hyrd/
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Old 02-24-21, 06:05 PM
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Is it photographic distortion or is the front wheel/tire of your MTB tandem smaller than the rear? I too find mechanical discs up to the job. I've never seen a rotor (or adapter) larger than 203mm! We ride loaded all the time but we don't tour that way. When running f/r discs, convention has the bigger rotor up front. I would not use a caliper brake as a supplemental. If it was my bike I would use the caliper (dual pivot side-pull?) as the MAIN rear brake and use the large disc as a drag brake on a thumbshifter control. I would keep the thumbshifter on my bars and learn to use the drag to modify speed not just on long downgrades. Good rotors and pads can be pushed very hard. A single disc and caliper are more than adequate main braking with, or without, supplemental thermal mass from a 203 or larger rotor. Enjoy.
Edit: Yes, the HyRd's are well regarded. Have not tried them but would not hesitate.

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Old 02-24-21, 06:55 PM
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Uhm, disc brakes do not work well as drag brakes. they are not designed for continuous use. The advantage of having a rear disc brake and rear caliper brake is to alternate use to manage heat, not to use one as a drag brake. If you really need a drag brake get a drum.

as for the Spyres, we have used them, as well as TRP hybrids, and full hydraulic.

in order I would prefer full hydraulic, then hybrid then the mechanical spyres.

the hybrids are nice, and a big upgrade from pure cable actuated. But if you can do a full hydraulic setup it is definitely better in raw stopping power, and modulation.

additionally, give the much greater volume of fluid in the full hydraulic setup, the risk of boiling fluid should be lower than In the hybrids which have a small amount of fluid.
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Old 02-24-21, 11:21 PM
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Originally Posted by merlinextraligh View Post
Uhm, disc brakes do not work well as drag brakes. they are not designed for continuous use. The advantage of having a rear disc brake and rear caliper brake is to alternate use to manage heat, not to use one as a drag brake. If you really need a drag brake get a drum.

as for the Spyres, we have used them, as well as TRP hybrids, and full hydraulic.

in order I would prefer full hydraulic, then hybrid then the mechanical spyres.

the hybrids are nice, and a big upgrade from pure cable actuated. But if you can do a full hydraulic setup it is definitely better in raw stopping power, and modulation.

additionally, give the much greater volume of fluid in the full hydraulic setup, the risk of boiling fluid should be lower than In the hybrids which have a small amount of fluid.
I won't argue that a 203mm disc is not an Arai drum, but it is a lot better than most people realize. It's not a best practice, but it is done, and given the scenario being presented, it seemed the better idea than figuring how to 'alternate' between a caliper rear and disk rear. Do people really rig that up? I would be curious how that works in practice. Thing is, drum brakes are no longer easily available. It would be taking a step backwards, I think to try and work one into a modern braking picture.

The main reason why no one has bothered to manufacture a replacement for the Arai drum is that a front/rear pair of 203mm high performance (think Icetech) rotors gripped by modern calipers offers immense performance. And, as the o.p. knows, bigger rotors than 203mm exist, even if I personally have never seen any. Given that, I don't see the need for a caliper at all. I I should have just not mentioned using the disc as a drag. Consider it retracted. And I also agree with the technology/performance ranking you listed, but didn't have time earlier to go into it. A full hydraulic offers a significant advantage over mechanical actuation, the greater fluid volume is neither here nor there IMO because the heat path through the brake lines isn't the most efficient. The long cable run to the rear brake introduces a lot of mechanical friction, even when a lot of the run is exposed. Sticking calipers and/or sluggish action at the rear caliper is eliminated with a hydraulic connection between brake lever and caliper. Prices are coming down all the time on full hydraulics. Brakes that used to cost $600/pr. are now half that. Worth considering.

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Old 02-25-21, 05:50 AM
  #6  
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I agree with Merlinextraligh on rank ordering choice. We too had TRP Spyres on our Co-Mo and while I loved them over caliper brakes, I found that the return spring on the rear caliper was not strong enough to overcome normal cable slack that you get over the long cable which required me to add a boost return spring which resolved that issue, however, I also found that I had to constantly futz with adjusting the pad spacing. I imagine that the HYRD version would mitigate the latter. Last year I upgraded to full hydraulic and I'll never go back. Braking control and feel is like butter and I haven't had any adjustment futzing to contend with.

That said, I get it, outfitting hydraulic can be a challenge to find the right shifter/brifter's and dealing with fluid and bleeding issues poses some overhead and may limit transporting options..

Not being a braking expert I'll offer the following as nothing more than a point of view. I am sure others on the forum know better. Braking power and stopping power is stronger in the front. On half bikes, we tend to rely more on the rear brake so we don't endo over the bars. There is more cable loss in the longer cable run to rear so we tend to want to beef up the rear brakes. On a tandem, the chance of an endo is almost non-existent and you can (and most do) rely more on your front brake. You mention using a larger disc in the rear. What is behind this choice? Is it to beef up the rear braking force or to dissipate more heat? Either way, given what I am saying I would contend that the front would benefit more from a larger disc. We are a 400lb team and have 203mm discs front and back and have plenty of stopping power, we live and ride in a very hilly area but the longest desents are only a couple of miles so we don't have to worry about sustained braking issues.

In the end I am sure you will be happy with the Spyres and you will get perfectly acceptable braking performance with your current thinking. Going with a larger disc may limit sourcing it, but not insurmountable.
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Old 02-25-21, 06:17 AM
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I tried the TRP Hy/rd and of the 2 I purchased, 1 had sticking rotors. I felt it wasn't that good either. The feel is rather wonky with a lot of pull even before the brakes make contact with the rotors. I'm waiting for a Spyre to arrive and will compare that but otherwise I've found better results by finding new pads for my BB7s. I'm not super happy with them but I don't feel the Hy/rds are worth it.

I tend to tow around 70lbs on my rides but with few long/steep hills in my area I rarely encounter truly demanding braking scenarios.
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Old 02-28-21, 12:14 PM
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Saint Hydro is an option

We also had Hy/Rd brakes on shimano 203mm rotors, and they failed due to overheating on a longish downhill in traffic. The pistons never let go after that. had to remove that night after limping home.
We returned to the Spyre cable pull calipers, but the effort required to pull these is very difficult after a few minutes.
After a bit of internet research and concluding that our spare road Di2 hydro Brifters will work with Saint 4piston calipers. (I picked up XT/XTR front and rear derailleurs)
The saint hose has a long brass banjo fitting to help dissipate heat.
WIth the LARGE caliper and LARGE metallic pad with heat sinks, this combination works far better than I expected.
Finally, I changed the rotors over to Magura MDR-P e-bike full float 203 rotor. these don't warp nearly as much as standard rotors. so not much chattering after hard use.

in summary- oversized calipers, oversized pads, over-designed rotors = confident braking for extended periods. Metallic pads don't seem to wear as fast as organics, nor do they "grab" instantly, so progressive stopping power.
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Old 03-04-21, 06:18 PM
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I used TRP HY/RD brakes on a gravel half-bike and would not use them again. They are finicky as can be. There are hacks to address the problem of the lever bottoming out, but I still had the problem. I switched to straight hydraulic and based on that experience would never put a HY/RD on a tandem. Our tandem has hydraulic discs as an add on, with 203 front rotor, and I can stop easily while pulling a trailer with 50 lbs.
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Old 03-05-21, 06:05 PM
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Originally Posted by Alcanbrad View Post
..... You mention using a larger disc in the rear. What is behind this choice? Is it to beef up the rear braking force or to dissipate more heat? Either way, given what I am saying I would contend that the front would benefit more from a larger disc. We are a 400lb team and have 203mm discs front and back and have plenty of stopping power, we live......
The larger disc offers several advantages:
A larger disc will have a little more heat capacity, but more importantly, much more surface area to dissipate heat.
A larger disc has more mechanical advantage, so will generate less heat during braking.
The additional mech. advantage offers better stopping power. However, I find this the least important of the advantages, as a 203mm rotor would easily exceed the rear tire's traction capacity.

The first two advantages I feel are the main reason to use a larger rotor. This SHOULD obviate the need for a rim brake. That said, a rim brake is a perfectly good additional heat sink to give the rotor and caliper time to cool. I'd do this if I had had issues with overheating on descents. Alternating between the two is a perfectly sensible idea. Or just rely on the disc brake and if things get dire, you have a bail out brake with full stopping power. That's win-win if you ask me!

Ok, back to the Co-Motion rebuild... that has an Aria drum that I just lovingly refreshed!!! I'm SO CLOSE to done!
To do:
Install computer. (Wanna track my miles from the very start.)
Install fresh tires & tubes (Co-Motion rim strips are BOMBER!)
Install chain
Final F & R derailleur adjustments
Install stoker bars.
Wrap handlebars (double wrap? Still deciding)
And TEST RIDE!!!
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Old 03-06-21, 06:36 AM
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A bit of perspective rim vs. disc braking…
Heat capacity: Al:920 J/kg/C, Steel: 500 J/kg/C
Mass heated: Rim: 0.6 kg, Disc: 0.08 kg

Kinetic energy of loaded tandem (220 kg) moving at 16 mph: 5400 J

Temperature increase in components to stop tandem
2 rims: 5400/920/1.2 = 5 C increase (9 F)
2 discs: 5400/500/0.16 = 68 C increase (120 F)

If the riders are smaller and without gear, disc brakes may be sufficient. However, rim heat capacity is far greater.
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Old 03-06-21, 07:15 AM
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Originally Posted by LV2TNDM View Post
The larger disc offers several advantages:
A larger disc will have a little more heat capacity, but more importantly, much more surface area to dissipate heat.
A larger disc has more mechanical advantage, so will generate less heat during braking.
The additional mech. advantage offers better stopping power. However, I find this the least important of the advantages, as a 203mm rotor would easily exceed the rear tire's traction capacity.
I haven't been in a science classroom in a very long time, but your second point doesn't make sense to me. Regardless of the mechanical advantage, a brake converts kinetic energy to heat energy. The only way the mechanical advantage could generate less heat in the pads/rotors during braking is if it sent the energy somewhere else in the system compared to a brake with less mechanical advantage. Am I missing something?
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Old 03-06-21, 10:59 AM
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Originally Posted by IPassGas View Post
A bit of perspective rim vs. disc braking…
Heat capacity: Al:920 J/kg/C, Steel: 500 J/kg/C
Mass heated: Rim: 0.6 kg, Disc: 0.08 kg

Kinetic energy of loaded tandem (220 kg) moving at 16 mph: 5400 J

Temperature increase in components to stop tandem
2 rims: 5400/920/1.2 = 5 C increase (9 F)
2 discs: 5400/500/0.16 = 68 C increase (120 F)

If the riders are smaller and without gear, disc brakes may be sufficient. However, rim heat capacity is far greater.
I agree that the physics show that the energy required to reduce the kinetic energy of the system to 0 that the mass of the disc will get a lot hotter than the rim, but shouldn't there be time and cooling component over time in the above equations? The rim and disc will cool after picking up heat from the pads while rotating around to the pads again. The same amount of energy is required to stop a given mass in 0 sec as is required in, say, 2 hours, but the final temperature of the rim and disc would be much different based on time.

There would also need to be a slope and gravitational term in the equation.

I realize this is getting into the weeds and does not change your point, however, it would be interesting to have and equation that would allow us to plug in some real world scenarios to see where disc braking falls apart. Just throwing it out there to see if someone is game
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Old 03-06-21, 11:25 AM
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Yes, the weeds, you can apply corrections, but the vast difference will remain. Braking over a longer time will reduce the heat build up, or like us when riding with disc brake, stop to give time to let disc cool. My point was that the rim can take on a far greater heat load. Also, the rim is a much larger cooling surface. I feel that this important heat load capability is often ignored in the face of flashy new disc tech.
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Old 03-06-21, 01:39 PM
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According to Hope their 180 mm floating rotor has a mass of 146 grams and the 203 mm vented rotor at 288 grams. They also list their plain rotor at 142 grams for a 180 mm rotor. Not sure where you came up with 80 grams as the mass of a rotor, but you are off by at least a factor of 2 for a 200 mm rotor.

Also, I have seen a Hope 203 mm floating brake rotor glowing red, which puts them over 900 F. I have not had that issue again with the larger downhill calipers and a vented rotor.

Our load was more like 250 kg, and our speed more like 45 MPH. And we were on a 10% incline. Care to guess what that kind of energy input would have done to a rim brake? I didn't have a tire fail. And disc brakes work just fine with a rotor temperature below the boiling point of the brake fluid, say around 350 F for water saturated Castrol React fluid. Do you want a rim at 175F? And by the way, I change my fluid once a year so that boiling temperature is more like 500F.

Heat is conducted into the wheel hub and you don't account for that. I am sure that is greater than the heat conducted into the spokes on a rim brake. Also, some of the heat is carried away from the rotor into the caliper and the fluid, although engineers try to limit that because that is where brake failure comes from in disc brakes. Still, you are not making a valid comparison. Yes, disc brakes run at a higher temperature than rim brakes. What is your point? They are engineered to function at those temperatures. Have you seen any rim brake pads that were sintered metal?

I agree that disk brakes add drag when compared to rim brakes, and I am very happy with the rim brakes (Dura Ace, Campagnolo Record and SR) on my road bikes, but on a touring tandem we are willing to pay that penalty in exchange for brakes which work in the rain and the superior performance of a properly configured disc brake setup.

And finally, with the larger calipers and vented rotor the disc setup does an acceptable job of keeping speeds down to our comfort zone. Yes, they work just fine as a drag brake.
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Old 03-06-21, 04:05 PM
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Originally Posted by DangerousDanR View Post
According to Hope their 180 mm floating rotor has a mass of 146 grams and the 203 mm vented rotor at 288 grams. They also list their plain rotor at 142 grams for a 180 mm rotor. Not sure where you came up with 80 grams as the mass of a rotor, but you are off by at least a factor of 2 for a 200 mm rotor.

Also, I have seen a Hope 203 mm floating brake rotor glowing red, which puts them over 900 F. I have not had that issue again with the larger downhill calipers and a vented rotor.

Our load was more like 250 kg, and our speed more like 45 MPH. And we were on a 10% incline. Care to guess what that kind of energy input would have done to a rim brake? I didn't have a tire fail. And disc brakes work just fine with a rotor temperature below the boiling point of the brake fluid, say around 350 F for water saturated Castrol React fluid. Do you want a rim at 175F? And by the way, I change my fluid once a year so that boiling temperature is more like 500F.

Heat is conducted into the wheel hub and you don't account for that. I am sure that is greater than the heat conducted into the spokes on a rim brake. Also, some of the heat is carried away from the rotor into the caliper and the fluid, although engineers try to limit that because that is where brake failure comes from in disc brakes. Still, you are not making a valid comparison. Yes, disc brakes run at a higher temperature than rim brakes. What is your point? They are engineered to function at those temperatures. Have you seen any rim brake pads that were sintered metal?

I agree that disk brakes add drag when compared to rim brakes, and I am very happy with the rim brakes (Dura Ace, Campagnolo Record and SR) on my road bikes, but on a touring tandem we are willing to pay that penalty in exchange for brakes which work in the rain and the superior performance of a properly configured disc brake setup.

And finally, with the larger calipers and vented rotor the disc setup does an acceptable job of keeping speeds down to our comfort zone. Yes, they work just fine as a drag brake.
Yes, hydraulics are different, but the thread was discussing standard rotors. Steel is a poor heat conductor versus Al, so the mass relevant to the heat capacity is approximately just the outer disc mass. The floating rotor helps this, which was why they were introduced. But hydraulics are complicated for a touring/breakable bike.
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Old 03-06-21, 06:25 PM
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Originally Posted by IPassGas View Post
Yes, hydraulics are different, but the thread was discussing standard rotors. Steel is a poor heat conductor versus Al, so the mass relevant to the heat capacity is approximately just the outer disc mass. The floating rotor helps this, which was why they were introduced. But hydraulics are complicated for a touring/breakable bike.
When we fly with our Ritchey the brakes come off and are packed in plastic bags that prevent a leak (never have had that happen) from fouling anything else in the case. It is no more bother than dealing with cables on my solo Ritchey. It is maybe 5 minutes to install them. There are people who make quick connect fittings for the motorcycle racing world, and I have considered them, but they don't seem worth the cost at this time. Maybe if I switch to a drop bar bike I will get a set.

I have no personal experience with cable disc brakes because as much as I consider myself a bottom feeder, I am not a platypus which only eats the rotten muck at the bottom of the pond because it doesn't have gastric juice to digest real food. Cable disc brakes are about cost cutting, and they are a step too far for me.

Steel is not as good a conductor of heat as aluminum. And stainless steels are mostly rubbish. Carbon steel is a lot better, and I don't care about rust spots on a brake rotor.

But if carbon steel is not good enough, let's pretend that somebody makes a rotor with a steel working surface on an aluminum core. Hmmmm. If Shimano makes it , it is a mainline product. Now, just maybe, if they want better conductivity they could use the silver / aluminum alloy that Harley - Davidson used in their XR750 race bike engines. That stuff could frighten the devil. Wilwood makes coated aluminum rotors for cart racing and if I have any issues with the vented Hope rotor overheating I will talk to them about using one on the Ritchey.

Also, my memory of the reason for floating rotors was to reduce heat distortion by keeping the whole rotor closer to the same temperature, not to carry heat away. The vented Hope rotors and the Shimano IceTech rotors are both aimed at moving heat away from the rotor surface.
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Old 03-07-21, 08:47 AM
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ok, 250 kg = 550 lbs! We are tall and carry much gear/camping, but more like 460 with bike.
250 kg @ 45 mph = 49,000 J dissipated to stop.
Heat increases:
rims 49000/920/1.25 = 40 C (75 F)
From PV=nRT, the tire pressure increases by 10 psi, seems ok.

disc 49000/500/0.16 = 600 C (1100F).
The hope rotors are ~twice the mass of normal rotors, so ~300 C (550 F) increase, so doesn't melt. Perhaps piston seals can be compromised.

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Old 03-08-21, 10:21 AM
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What can I say. In my university days a lot of people would ask me if I played "Football." They were thinking lineman, not QB. The answer was "No", said in such a tone that they knew I did not care for that game.

At the time we saw red hot rotors I was around 280 pounds. Add Mrs. Dan, and a 40 pound bike, and our gear, and a lot of wool we had bought on Shetland, and we were well over 500. Loosing 50 pounds helped a lot, We have also gotten better at knowing what we need on our tour. And switching to the vented rotor was also a big help.

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Old 03-08-21, 02:08 PM
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Originally Posted by IPassGas View Post
ok, 250 kg = 550 lbs! We are tall and carry much gear/camping, but more like 460 with bike.
250 kg @ 45 mph = 49,000 J dissipated to stop.
Heat increases:
rims 49000/920/1.25 = 40 C (75 F)
From PV=nRT, the tire pressure increases by 10 psi, seems ok.
With a 75F increase in temperature, I'd look at softening of the tube or the rim stripe as possible failure mechanisms.
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Old 03-08-21, 02:56 PM
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Originally Posted by diabloridr View Post
With a 75F increase in temperature, I'd look at softening of the tube or the rim stripe as possible failure mechanisms.
The point is that the heat capacity of rims is greater than that of standard discs (by roughly a factor of 2). Rims brakes are better than standard disc brakes in this regard.
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Old 03-09-21, 10:37 AM
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Originally Posted by IPassGas View Post
The point is that the heat capacity of rims is greater than that of standard discs (by roughly a factor of 2). Rims brakes are better than standard disc brakes in this regard.
The point is that "the heat capacity of rims" is a fallacy.

For rim brakes, we should be looking at the heat capacity of the rim + tire + tube system.
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Old 03-10-21, 11:20 AM
  #23  
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Reading the OP's description of the new tandem it will be a disc brake bike. I am more than fine with rim brakes for a solo road bike. But when my wife was looking at a new solo bike in 2014-2015 I made sure that she got one with disc brakes. She mostly uses it for short trips to visit friends or go shopping. Disc brakes work better in the rain, and sometimes rain storms come in very fast here on the north plains.

My road bikes are all rim brakes. My MTBs are all disc brakes. Our tandem is disc. The only one that has had heat issues is the tandem, and that has been solved. For our bulk, MTB downhill brakes are, in my opinion, the best way to go. Lighter teams will probably have a different set of parameters, but even if my wife and I both got down to our ideal weight, we would be around 350 lbs. Add in the bike and gear for touring and we are in the 400 to 450 lbs. range.

Mine are Hope, SRAM, Formula, TRP, Trickstuff, and a whole lot more companies make very good downhill specific brakes. I prefer to use DoT 4 fluid because I know that I can get fluid anywhere that I am likely to travel without having to wait for it to be shipped to me. Others will prefer mineral oil fluids, used by companies such as Magura or Shimano. Drum drag brakes are mostly unavailable for new bikes. My setup as it sits today has been shown to work as both a drag brake to keep speeds below our tolerance level on descents, and as a fast stopper from high speeds.

If I am running my tires at the tire and rim manufacturer's upper limit for pressure (I do) and the PV=nRT thing pushes them up by 10 PSI I am running out of range. Probably safe, but not certified. I wouldn't want to have to stop on a steep downhill with a strong tailwind traveling 45 MPH with a rim brake bike.
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Old 03-11-21, 12:41 AM
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Originally Posted by Alan_F View Post
I haven't been in a science classroom in a very long time, but your second point doesn't make sense to me. Regardless of the mechanical advantage, a brake converts kinetic energy to heat energy. The only way the mechanical advantage could generate less heat in the pads/rotors during braking is if it sent the energy somewhere else in the system compared to a brake with less mechanical advantage. Am I missing something?
The leverage of a larger rotor means less energy. Remember, Archimedes said "If I had a lever long enough, I could lift the earth." In other words and for experiment's sake, if you had a REALLY large rotor (much larger than your wheel), you could easily stop your wheel with your fingers. Again, if the rotor were large enough. So a larger rotor will require less energy to stop. At least that's my interpretation! (Granted 20mm difference isn't much, but it's still something. That combined with additional surface area makes a difference.)
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Old 03-11-21, 12:44 AM
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Originally Posted by diabloridr View Post
The point is that "the heat capacity of rims" is a fallacy.

For rim brakes, we should be looking at the heat capacity of the rim + tire + tube system.
But I'd guess the heat capacity of the tire and tube are not of much value as they are really good insulators. They'd take forever to absorb all that heat. And then they wouldn't dissipate it very well either. The problem is the air in the tube overheats and blows out the tire before the tube and tire can absorb much heat. Descent tire blowouts happen pretty quickly. Otherwise, we'd see incidence of tires and inner tubes melting on tandems. Don't think this is the case, whereas melted carbon rims are indeed an issue.

Or perhaps I'm mistaken.
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