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Braking thoughts. A sanity check of sorts.

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Braking thoughts. A sanity check of sorts.

Old 03-11-21, 12:59 AM
  #26  
LV2TNDM
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Originally Posted by DangerousDanR View Post
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.
From what I understand, you are nowhere near "running out of range" with a 10psi "overpressure" in road tires. I understand blowoff pressure is determined by inflating a tire on an industry-standard hook-bead rim and inflated. Blowoff pressure is divided in two to determine "max pressure" for the tire. So, a tire with a 120 max pressure rating will blow off at 240psi.* This safety margin of 100% makes sense. Bicycles do regularly heat up rims, so the tire should be able to withstand pressure increases by heat, per the PV=nRT relationship.

A friend of mine, captain of a 400 lb team regularly exceeded his road tire's max pressure by 20 to 30 pounds. He did this for years without any negative incidents or problems.

I'm pretty sure 10psi over max on a road tire isn't anything to worry about. Then again, on a tandem with rim heating a potential problem, DON'T EVER DO THIS!!!! (Thanks Lawyer Bob for requiring me to say this!)

*Unfortunately, I still have not been able to confirm this by finding legitimate sources on the subject. I had just heard this "in the bike industry." So I guess I owe it to myself and everyone else to actually track this down before stating it as fact. Something to work on. Unless someone here can confirm or deny this; I'm all ears!

EDIT: Well, that wasn't THAT hard! Shoulda consulted master Sheldon from the get-go! He says:
"The lawyers want the number kept conservatively low, in case the tire gets mounted on a defective or otherwise loose-fitting rim. They commonly shoot for half of the real blow-off pressure."
(https://www.sheldonbrown.com/tires.html#pressure)

So there we are. From the cycling god's mouth. Don't think any more citation is necessary!

Last edited by LV2TNDM; 03-11-21 at 01:30 AM.
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Old 03-11-21, 03:04 AM
  #27  
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I've had heat problems with rim brakes: velox rim tape came loose or plastic ones got hard and because of that small tears appear which causes a whole in the inner tube.
But if u ride on the flat and in dry conditions rim brakes are fine and more bomb proof, the maintenance is easy and the cost is low. Always carry spare break pads on a tandem.

Last edited by longpete; 03-11-21 at 03:27 AM.
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Old 03-11-21, 02:07 PM
  #28  
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Originally Posted by LV2TNDM View Post
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.)
The leverage means less force at the brake lever, not less energy. Moving the Earth with Archimedes' lever wouldn't require any less energy than moving it by hand. The lever would allow you to apply only a little force over a very long distance to input the same energy. Likewise no matter how hard you have to squeeze the lever, stopping a tandem of a given mass over a given time from a certain velocity requires the same amount of kinetic energy to be converted. More mechanical advantage probably allows for MORE heat to be put into the system, as you can potentially create more friction at the rotor/pad interface for a given hand strength. That's why you can haul the big bike down to a stop quicker with a larger rotor. A rotor with more mass would absorb more heat before reaching a given temperature, and a rotor with a larger surface area would cool faster. A Shimano Freeza rotor with cooling fins should stay cooler than an identically sized rotor without the cooling fins because it has more surface area, but the mechanical advantage is the same. I still don't see how adding mechanical advantage results in less heat going into the brakes.
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Old 03-13-21, 09:50 AM
  #29  
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any thoughts on which pads manage heat better, resin or sintered, we have ice tech 203 rotors with resin pads that suffer on the long steep descents. We are off on tour soon so would like to improve heat management if possible
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Old 03-13-21, 10:38 AM
  #30  
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Originally Posted by headasunder View Post
any thoughts on which pads manage heat better, resin or sintered, we have ice tech 203 rotors with resin pads that suffer on the long steep descents. We are off on tour soon so would like to improve heat management if possible
i use resin front brake, sintered rear(more heat, risk fading) with 22 disk
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Old 03-13-21, 05:02 PM
  #31  
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Originally Posted by Alcanbrad View Post
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
ok, I have redone the calculation to include the additional energy from gravity on a 10% slope during the time it takes to stop the bike. I assume a constant braking force of 500 N (from values on-line) and include an extra term for the wind force. The initial velocity is 45 mph. The wind force is 200 N at 20 m/s (45 mph), and reduces with the square of velocity. For a total mass of 210 kg, the total energy needed to stop the bike is 56,000 J.

For two wheels...
Rim brake heating: 56000/920/1.2 = 50 C (90 F) (tire pressure increases ~ 10psi)
Standard Disc brake heating: 56000/500/0.16 = 700 C (1300 F)
Hope disc at twice mass: 350 C (600 F).

The relevant disc mass is the band of steel at the caliper, not the entire disc. Unlike solid car discs, bike discs have holes in this band which reduced the mass by about half. The hope discs have smaller holes, so perhaps more than twice the mass of regular discs. From density of steel (8g/cc) and for 2 discs, I calculate 0.16 kg for regular disc. Steel retains 50% of its integrity at 1100 F, but probably 1300 F ruins pads. The rim mass is for our Ryde rims. The heat capacity of Al and Steel is 920 and 500 J/kg/C.
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Old 03-15-21, 09:27 AM
  #32  
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Originally Posted by bakerjw View Post
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.


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.
If you're investing in a custom tandem, it's not a good idea to skimp on brakes. The price difference between the Spyre and Hy/Rd is only about $40 per wheel, but the latter is more powerful due to the hydraulic calipers. if you're really confident about the Spyre, why bother with supplemental rim brake? Does any good quality mtn or road bike come with the Spyre?


The other advantage of using a disc-specific rim is that you can use wider aluminum rims (with minimal weight gain), or carbon rims. Wider rims and tires are more popular now because they provide more comfort without sacrificing rolling resistance. For example, it's common to see a high-end single road bike (eg, Giant TCR) with 25mm or 28mm tires. We use carbon rims with 28 & 32mm tires on our Calfee road tandem.


For even better braking, think about full hydraulic brakes (eg. Shimano Ultegra). Unfortunately, this option is more expensive because you have to use hydraulic shifters in in 2x11 drivetrain (eg. Ultegra ST-R8020). However, a 2x11 drivetrain will shift better than a 3x10, and a large cassette should allow you to handle steep climbs.
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Old 03-15-21, 10:13 AM
  #33  
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Originally Posted by LV2TNDM View Post
From what I understand, you are nowhere near "running out of range" with a 10psi "overpressure" in road tires. I understand blowoff pressure is determined by inflating a tire on an industry-standard hook-bead rim and inflated. Blowoff pressure is divided in two to determine "max pressure" for the tire. So, a tire with a 120 max pressure rating will blow off at 240psi.* This safety margin of 100% makes sense. Bicycles do regularly heat up rims, so the tire should be able to withstand pressure increases by heat, per the PV=nRT relationship.
Looking at rim heating purely from the influence on tire pressure ignores the reduction in tube and tire properties (yield strength, tensile strength, stiffness) as temperature goes up.

Softening of rim strips and kevlar tire beads occurs as the rim heats up. I've seen flats caused by softened velox rims strips.
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Old 03-15-21, 10:16 AM
  #34  
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Originally Posted by mtseymour View Post
For even better braking, think about full hydraulic brakes (eg. Shimano Ultegra). Unfortunately, this option is more expensive because you have to use hydraulic shifters in in 2x11 drivetrain (eg. Ultegra ST-R8020). However, a 2x11 drivetrain will shift better than a 3x10, and a large cassette should allow you to handle steep climbs.
The GRX groupset paired with an xd driver body (9t or 10t capable) gives an impressive gear range and offers hydraulic braking...but isn't cheap. Will also be interesting to see what the shimano di2 12 speed group set options are, supposedly coming out in 6 days.
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Old 03-15-21, 10:22 AM
  #35  
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Originally Posted by mtseymour View Post
Does any good quality mtn or road bike come with the Spyre?
All the higher-end Co-Motion tandems spec the Spyre, that was a good enough recommendation for us when were building our Macchiato.


Originally Posted by mtseymour View Post
The other advantage of using a disc-specific rim is that you can use wider aluminum rims (with minimal weight gain), or carbon rims. Wider rims and tires are more popular now because they provide more comfort without sacrificing rolling resistance. For example, it's common to see a high-end single road bike (eg, Giant TCR) with 25mm or 28mm tires. We use carbon rims with 28 & 32mm tires on our Calfee road tandem.
Bingo. Beside removing a potential braking failure mode, moving to disk brakes allowed us to use lightweight, chi-chi carbon wheels.
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Old 03-15-21, 12:26 PM
  #36  
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Originally Posted by diabloridr View Post
All the higher-end Co-Motion tandems spec the Spyre, that was a good enough recommendation for us when were building our Macchiato.
Keep in mind that manufacturers spec their bikes for their typical customer. A team will get good results with the Spyre if they're average weight (eg. not loaded touring), don't do steep or extended descents, and ride at moderate speeds. A heavier team riding on steep terrain should use more powerful brakes (eg. Hy/Rd or full hydraulic).

Secondly, manufacturers have tight margins and must carefully spec each component to reach a target price. For example, Co-Motion's Ristretto Di2 single bike uses the Shimano 8070 hydraulic disc brake. If the Spyre was fully adequate, why spec the 8070? The answer is that it's worthwhile for an aggressive rider on the Ristretto to pay more for the extra degree of safely. Similarly, the Supremo has the option for hydraulic brake cable routing.
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Old 03-16-21, 01:17 AM
  #37  
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Originally Posted by Msteven View Post
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.
So you run shimano calipers and magura rotors any issues with pad clearance given the magura rotors are 0.2mm thicker. I'm underwhelmed with the icetech offering and would like to change the front out
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Old 03-18-21, 08:56 AM
  #38  
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Shimano + Magura

Originally Posted by headasunder View Post
So you run shimano calipers and magura rotors any issues with pad clearance given the magura rotors are 0.2mm thicker. I'm underwhelmed with the icetech offering and would like to change the front out
No issues at all. No noise when just riding flat. very little warping from heat. no loss of performance after heavy use with metallic pads.
Note that the only Magura product I have used is the MDR-P rotor.
Our total weight is probably 350 - 375 pounds.
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Old 03-25-21, 07:09 AM
  #39  
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Originally Posted by mtseymour View Post
If you're investing in a custom tandem, it's not a good idea to skimp on brakes. The price difference between the Spyre and Hy/Rd is only about $40 per wheel, but the latter is more powerful due to the hydraulic calipers. if you're really confident about the Spyre, why bother with supplemental rim brake? Does any good quality mtn or road bike come with the Spyre?
As fate would have it, the pound is over/under valued to our advantage against the dollar so a pair of HY/RD calipers delivered was around $200.00.

I was only considering the Spyre because the Spyke was absolutely rock solid on our mountain tandem (90# fully loaded) and they handled every descent on our Canada ride beautifully.

Our current road tandem, a chinese Giordanno viaggio, came as a triple (3x8 originally) and the drivetrain was updated as we grew with the bike. The 105 3x10 shifts flawlessly so I see no reason to change and buy all new components.

We currently have Sun Ringle rims and they've been flawless even with an occasional pothole. It happens. I'll likely go with their rims on this wheel build as well on a set of Onyx hubs. Onyx are pricey and weigh a bit more than others but again, Rock solid and the sprag clutch is amazing.
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Old 03-25-21, 09:23 AM
  #40  
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Originally Posted by bakerjw View Post
As fate would have it, the pound is over/under valued to our advantage against the dollar so a pair of HY/RD calipers delivered was around $200.00.

I was only considering the Spyre because the Spyke was absolutely rock solid on our mountain tandem (90# fully loaded) and they handled every descent on our Canada ride beautifully.
You should be carefully about comparing the braking on your mtn tandem to your new road tandem. My understanding is that your Tour Divide Ride was a long tour done mainly on wide dirt roads and Jeep trails with gradual grades (ie. non-technical mtn trails). You should look at your bike computer to look at peak and average speeds. A road tandem will easily reach speeds of 40mph (even on moderate grades), while your mtn tandem probably went much slower. A road tandem may also have to stop quickly to avoid cars and other hazards. We've raced and crashed our mtn tandem (with minor injuries), but definitely want to avoid any crash on our road tandem (cars & hard pavement).
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Old 03-26-21, 08:48 AM
  #41  
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Prior to taking our mountain tandem to the mountains, I ran larger front rings to give us a road feel (for trail use we run 22/36 up front) and a narrow rim on our hubs with 700Cx28 Gatorskins. We wanted to get used to how the Curtlo handled as it has a different feel to it and doing so on the road was the best way to do that. The brakes were much better than the rim brakes on our current road tandem.
None of that comes into play though since we have the HY/RD calipers ready to go when the new bike arrives.
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