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  1. #1
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    Rotor warping

    Are you bigger guys warping rotors with the larger wheels?
    I'm running 160 Elixers and I always seem to be warping them, the front particularly...
    Think a bump up to 180 would help (I don't really need the added stopping power)
    Or is there a better rotor I can try?
    thanks

  2. #2
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    a bigger rotor will certainly help your problem

  3. #3
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    Also consider going with a rotor with a spider (I have the Magura Ventidisc and they've been fantastic). Avoid avid rotors - I went through several before I vowed never again to buy avid rotors.

  4. #4
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    Being a bigger dude, the larger rotors will help with the heat.
    "Those are some good humans."

  5. #5
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    Has nothing to do with wheel size. It's all about momentum being turned into heat. 29ers don't have any more momentum than little wheels, apart from being able to maintain higher speed due to lower rolling resistance and better traction.

    I'm running 215# these days, and 160mm rotors work fine for me. I hardly ever have issues with overheating the brakes, and I do ride a lot of steep stuff. If I'm riding in Tahoe with higher speeds on longer runs, I have to take it a bit easier. That only comes up like once every few years.

    That said, if you are overheating your brakes, a bigger rotor is the easiest fix, assuming your brake pads aren't the weakest link. I tried some of those cheapo ebay organic pads, and immediately I was smoking my brakes.

  6. #6
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    The only Avid rotors

    Ive found warped were the Roundagon rotors. Once i swapped um out to G2 160 and 185mm Cleansweeps everythings been Ok.

    There might also be something going on with the caliper alignment and pad wear that gives the impression that the rotor is warped.

  7. #7
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    Quote Originally Posted by pimpbot
    Has nothing to do with wheel size. It's all about momentum being turned into heat. 29ers don't have any more momentum than little wheels, apart from being able to maintain higher speed due to lower rolling resistance and better traction.
    Think about the physics. Make the example more extreme. 6" rotor on 20" wheel vs 6" rotor on 36" wheel. Don't you think the larger wheel will have more mechanical advantage and traction to over come the rotor than the small one? If it takes more energy to overcome the rotating larger wheel it will have the potential to create more heat at the brake. If you think a 29" wheel has no influence on potential for heat build up then you can't believe a 180 rotor will be any better than a 160. Same dif.
    Last edited by modifier; 12-20-2010 at 10:35 AM.
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  8. #8
    CB2
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    Stop riding so fast!

    Science question:
    Because of the larger circumference, a 29" wheel is actually rotating slower than a 26" wheel traveling the same speed. Would this slower rotation compensate to some degree for the added mass of the 29" wheel?

  9. #9
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    Quote Originally Posted by CB2
    Stop riding so fast!

    Science question:
    Because of the larger circumference, a 29" wheel is actually rotating slower than a 26" wheel traveling the same speed. Would this slower rotation compensate to some degree for the added mass of the 29" wheel?

    Speed is not the issue... trust me....

    Your question is hurting my brain....

  10. #10
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    Quote Originally Posted by CB2
    Stop riding so fast!

    Science question:
    Because of the larger circumference, a 29" wheel is actually rotating slower than a 26" wheel traveling the same speed. Would this slower rotation compensate to some degree for the added mass of the 29" wheel?
    It's not science....it's new math:

    2 riders leave the trail head at the same time.
    One rider is 160 lbs and riding a 26er
    One rider is 220 lbs and riding a 29er
    Who will warp their disc first?
    Who will bend their dics first?

  11. #11
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    Quote Originally Posted by modifier
    Think about the physics. Make the example more extreme. 6" rotor on 20" wheel vs 6" rotor vs 36" wheel. Don't you think the larger wheel will have more mechanical advantage and traction to over come the rotor than the small one? If it takes more energy to overcome the larger wheel it will have the potential to create more heat at the brake. If you think a 29" wheel has no influence on potential for heat build up then you can't believe a 180 rotor will be any better than a 160. Same dif.
    No. A specific amount of weight moving at a specific speed will have a specific amount of kinetic energy. Brakes turn that kinetic energy into heat energy. It doesn't matter how large or small the wheels are. The exact same amount of heat will be created in the rotors when you bring that weight to a stop.

    Anyways, larger rotors or rotors more tolerant of heat should solve your problem. Before springing for a size increase you might try Aztec rotors. They are thicker than most and have a lot of beef at the outer circumference. I have found to be very tolerant of heat and it will only cost you about $20.

  12. #12
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    Been running 160s and never warped a single rotor at 250.

  13. #13
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    Yep!

    Quote Originally Posted by CB2
    Stop riding so fast!

    Science question:
    Because of the larger circumference, a 29" wheel is actually rotating slower than a 26" wheel traveling the same speed. Would this slower rotation compensate to some degree for the added mass of the 29" wheel?
    For overheating issues, it's all about thermal capacity. Its about turning momentum into heat. Since the same amount of momentum is being converted to heat... apart from maybe a few pounds extra for a slightly heavier bike. That isn't really enough mass in the overall picture (rider weight + bike weight) an extra three pounds isn't going to suddenly smoke your brakes. It all comes down to the amount of friction you can generate, the friction creates the heat in the caliper and rotor (and whatever bleeds into surrounding parts) and getting rid of the heat. The physics basically tell us that all energy has to be accounted for, and used up in the system.

    I guess at lower speeds, the slower turning wheel means the brakes get more grabby, because the rotor is going through the caliper 10% slower at a given speed.
    Last edited by pimpbot; 12-20-2010 at 11:46 AM.

  14. #14
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    Quote Originally Posted by toddre
    Are you bigger guys warping rotors with the larger wheels?...
    Negative - I am 195# and run Avid G2 160's front and rear w/ Juicy 7's and Exlir-CR's on hardtail and FS 29er's. I switched the front from a 185 because that was overkill in the DC/MD/VA area where there are some significant hills (no 20+ minute descents though). I haven't observed my front rotor changing colors even...

  15. #15
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    Quote Originally Posted by Moustache rider
    No. A specific amount of weight moving at a specific speed will have a specific amount of kinetic energy. Brakes turn that kinetic energy into heat energy. It doesn't matter how large or small the wheels are. The exact same amount of heat will be created in the rotors when you bring that weight to a stop.
    So you think that mechanical advantage, disadvantage, leverage has nothing to do with it?

    No matter how big or small the wheel is using the same 6" brake rotor to stop a specific mass will create the same heat at the rotor? And that the only reason people run bigger rotors on bicycles or race cars it because the bigger rotor disperses heart better? They have no better mechanical advantage? You don't have to squeeze the lever any harder to stop your bike with a 6" rotor over an 8" rotor? Or a 29" wheel over a 26" wheel?

    If you squeeze the lever harder you are creating more heat. If something has a better mechanical advantage it will do the same work with less input which will create less heat in this case.

    I'm sure there is a simple equation relating to the fulcrum point and lever lifting force.

    A wheel is basically a lever rotating around a center fulcrum. You make the lever longer and you change the leverage. That's why you need lower gears on a 29er than a 26er to push the same on your pedals.

    I think you need to put at least one more variable into your equation than just stopping the mass. Or I'm missing something really big.
    No it never stops hurting, but if you keep at it you can go faster.

  16. #16
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    In a a german bike mag brake test, back when when the elixirs came out, they found that G3 rotors were prone to warping (permanently) under high temperatures. Go back to G2 and you'll be good. Of course 160mm rotors are tiny up front and bigger rotor size is more about extra thermal capacity than added stopping power.

  17. #17
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    Quote Originally Posted by modifier
    I think you need to put at least one more variable into your equation than just stopping the mass. Or I'm missing something really big.
    Yes - rpm. For a given bike speed, the smaller wheel will be spinning more quickly.
    Yes - I do own Singular Cycles

  18. #18
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    Throw on some 203mm's and be done with it. When the going gets steep, the rotors go BIG.

    Another solution is to buy a brake caliper that uses a huge sintered metallic pad with copper backing, to help with the heat loss. and dissipation.

  19. #19
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    Quote Originally Posted by Singular
    Yes - rpm. For a given bike speed, the smaller wheel will be spinning more quickly.
    No, the friction generated depends only on the coefficient of friction between pad and disc and the force of the brakepad on the disc.

    The coefficient of friction varies with temperature, for organic brakepads it typically deteriorates rapidly at higher disc temperatures above 400C. Thats what you experience as fading.

    Thats also where bigger discs help dissipate energy faster through larger surface area by radiation and convection and initially store more energy because of plain extra mass = extra heat capacity.

  20. #20
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    Quote Originally Posted by RandyBoy
    Throw on some 203mm's and be done with it. When the going gets steep, the rotors go BIG.

    Another solution is to buy a brake caliper that uses a huge sintered metallic pad with copper backing, to help with the heat loss. and dissipation.
    +1 for the big rotors, but sintered pads are a double-edged sword because they also transfer heat into the calliper faster and can cause your brake fluid to boil much quicker than organic pads. That can lead to total failure of the brake when you need them most. The best solution is to use the disc for heat storage -> big rotors.

  21. #21
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    Well as I said, braking power isn't a huge problem for me with 160's. Our downhills aren't all that long either.
    I'm beginning to think it may be poor caliper set up or maybe I just wack rotors and don't realize it....

  22. #22
    Jacob 34:19
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    Not trying to be argumentative, just trying to understand the physics behind this better.

    If you're saying a larger diameter wheel doesn't effect the braking force required to stop (it's only the physical mass that makes a difference), then wouldn't the opposite be true? A larger diameter wheel requires no more effort to get rolling? I was under the impression it was pretty much a given that larger wheels require more effort or mechanical advantage to get rolling. This is pretty easy to calculate with gear inches or gain. Why is it if they're harder to get moving, they're no harder to get stopped when compared to their smaller diameter brethren?

    Again, not arguing the point one way or the other. Just trying to understand what's been presented.

    For what it's worth, I switched from a 180mm front rotor to a 160 on the same bike and noticed an immediate decrease in stopping power. I'm north or 200lbs but don't typically ride any kind of extended downhills so the 160 has been fine. I did also switch from BB7's to XX brakes so it really wasn't a direct comparison. The BB7's with the 180mm rotor had more bite but it could also be they're simply stronger brakes than the XX hydros.

    -Jake

  23. #23
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    Quote Originally Posted by toddre
    Well as I said, braking power isn't a huge problem for me with 160's. Our downhills aren't all that long either.
    I'm beginning to think it may be poor caliper set up or maybe I just wack rotors and don't realize it....
    I see you're in CT...I'm in MA....probably not the heat from downhills here
    The only rotors I've had warp was my own fault from a sloppy wheel change and a crash. I run 160/140

  24. #24
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    Quote Originally Posted by JAKEtheDOG
    Not trying to be argumentative, just trying to understand the physics behind this better.

    If you're saying a larger diameter wheel doesn't effect the braking force required to stop (it's only the physical mass that makes a difference), then wouldn't the opposite be true? A larger diameter wheel requires no more effort to get rolling? I was under the impression it was pretty much a given that larger wheels require more effort or mechanical advantage to get rolling. This is pretty easy to calculate with gear inches or gain. Why is it if they're harder to get moving, they're no harder to get stopped when compared to their smaller diameter brethren?

    Again, not arguing the point one way or the other. Just trying to understand what's been presented.

    For what it's worth, I switched from a 180mm front rotor to a 160 on the same bike and noticed an immediate decrease in stopping power. I'm north or 200lbs but don't typically ride any kind of extended downhills so the 160 has been fine. I did also switch from BB7's to XX brakes so it really wasn't a direct comparison. The BB7's with the 180mm rotor had more bite but it could also be they're simply stronger brakes than the XX hydros.

    -Jake
    Ah sorry (if you mean me): I wasn't saying that bigger wheels or rotors have no influence on the force required to stop the bike. I was only talking about what happens on the frictional force level between disc and brake pads.

    Now with a given frictional force at the caliper, overall stopping power is a matter of the levers involved. It's force x lever (equals torque). The two counteracting levers are "wheel center to brakepad" vs "wheel center to ground".

    The first one is your disc radius: The bigger it is, the more stopping torque you get.
    The second one ist the wheel radius: The bigger it gets, the harder it is to stop the bike.
    So with the same finger force you get more deceleration with a larger disc and less deceleration with larger wheels.

    But this game is limited by the traction of your wheels to the ground. If you can lock up your wheels with a 160mm rotor, they will lock up with a 203mm rotor. All you gain is less strain on your fingers and less fading problems on long descents (or more rider weight).

  25. #25
    Jacob 34:19
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    Thanks Raff. This makes sense. If I'm reading this correctly, it's pretty easy to see that a) larger rotors give you a better mechanical advantage than smaller rotors and b) larger wheels are indeed more difficult to stop. Am I reading this correctly?

    Thanks!

  26. #26
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    +1 on the big rotor. I also did not think I needed any more stopping power than a 180mm rotor but the 203mm rotor feels great and in my opinion will disipate heat better and add longevity to the brake system. I also now have true one finger braking. I went from 180/160 to 203/180 and love it.

  27. #27
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    Quote Originally Posted by modifier
    If something has a better mechanical advantage it will do the same work with less input which will create less heat in this case.
    Wrong. Mechanical advantage changes the distribution of force and distance, but does not change the amount of work done.
    Quote Originally Posted by modifier
    Or I'm missing something really big.
    this
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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  28. #28
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    Quote Originally Posted by Singular
    Yes - rpm. For a given bike speed, the smaller wheel will be spinning more quickly.
    and it's weight is closer to the axle... both are proportional to radius and cancel eachother out (i assume you're talking about momentum).
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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  29. #29
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    zactly!

    Quote Originally Posted by meltingfeather
    Wrong. Mechanical advantage changes the distribution of force and distance, but does not change the amount of work done.

    this
    That's the point I was trying to make. Bigger wheels have nothing to do with thermal capacity... which is the limit of how much braking you can do before things start smoking and/or stop working.

    That said to the OP, yes. If you are overheating your brakes, either your braking technique needs to be changed, your rotors are too small, your brake calipers are too small, or your pads are not adequate. I found that I smoke any and all organic pads, so I use Sintered pads.... preferably with copper or alu back plates. If I feel the brakes heating up too much, I start pulsing my brakes to let the air cool off the pad faces.... or ride slower (allowing more time for the brakes to cool).

  30. #30
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    Quote Originally Posted by JAKEtheDOG
    Not trying to be argumentative, just trying to understand the physics behind this better.

    If you're saying a larger diameter wheel doesn't effect the braking force required to stop (it's only the physical mass that makes a difference), then wouldn't the opposite be true?
    A larger wheel does affect the force, it does not affect the total amount of work required, which is what manifests as heat in the rotor.
    Quote Originally Posted by JAKEtheDOG
    A larger diameter wheel requires no more effort to get rolling? I was under the impression it was pretty much a given that larger wheels require more effort or mechanical advantage to get rolling.
    Not a given at all, in fact proven to not be true. Larger wheels do require more energy to spin up to a certain angular speed (rpm), BUT they also do not rotate as fast for a given linear speed (mph). Both of these effects are proportional to the radius of the wheel and cancel eachother out when comparing acceleration of a bike.
    Gearing changes are similar... you can make it hard to spin and do less crank turns or make it easy to spin and do more... it doesn't change the work it takes to get up a hill, and by changing the wheel size all you're doing is changing the "gearing."
    Quote Originally Posted by JAKEtheDOG
    This is pretty easy to calculate with gear inches or gain. Why is it if they're harder to get moving, they're no harder to get stopped when compared to their smaller diameter brethren?
    I think you're confusing force with energy.
    Quote Originally Posted by JAKEtheDOG
    For what it's worth, I switched from a 180mm front rotor to a 160 on the same bike and noticed an immediate decrease in stopping power. I'm north or 200lbs but don't typically ride any kind of extended downhills so the 160 has been fine. I did also switch from BB7's to XX brakes so it really wasn't a direct comparison. The BB7's with the 180mm rotor had more bite but it could also be they're simply stronger brakes than the XX hydros.
    180s will give you more stopping power than 160s on the same wheel, no question about it. I don't think anybody is saying that. What pimpbot was saying is that 29er vs. 26er doesn't change the heat generated (energy). FWIW the rotor size doesn't change that either, but a larger rotor does dissipate heat better due to more surface area.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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  31. #31
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    I think pimpbot pretty much nailed it. Riding style, and size of the rider can and will give said requirement for an upgrade in rotor size.

    For my riding style, I needed larger rotor up front - 180mm - and a smaller rotor in the rear - 160mm. I carry a lot of speed on down hills and flats and with a 160mm rotor up front was just not enough when pushing deep into the turns to be able to scrub enough speed off without any issues.

    By going to a 180mm front rotor, I eliminated brake fade, but with the 160mm rotor on the rear, that replaced the 180mm that I had on the bike at first, it gave me better moderation on the rear brake and helps minimize rear wheel lockup.

  32. #32
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    Quote Originally Posted by JAKEtheDOG
    A larger diameter wheel requires no more effort to get rolling? I was under the impression it was pretty much a given that larger wheels require more effort or mechanical advantage to get rolling. This is pretty easy to calculate with gear inches or gain. Why is it if they're harder to get moving, they're no harder to get stopped when compared to their smaller diameter brethren?
    If one was to accept bigger wheels are harder to get rolling and also stop...which I don't necessarily believe....you really have to ask by how much. One fellow a while back suggested putting your bike upside down and turning the crank. That is really the only difference you'll have, and it is negligable. Leg power will swamp your arms spinning the crank, and there is so much weight in your body and gear it really should be a non issue.

  33. #33
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    Quote Originally Posted by modifier
    ...

    I think you need to put at least one more variable into your equation than just stopping the mass. Or I'm missing something really big.
    I wish you hadn't said, "Or else I'm missing something really big."

    You're not missing something really big. You're right on.

    Let's simplify this. Imagine any size wheel with a rotor the same size as the wheel. Now put a tire on the wheel for ground clearance. A rotor that comparative size will both stop the vehicle with greater mechanical advantage than a smaller rotor plus it will dissipate heat better.

    When it comes to effective braking and heat dissipation, wheel size is directly related to rotor size. It IS leverage.

    --sParty
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  34. #34
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    P.S. Cool rotors draw heat out of hot brake pads, too.

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    We get old because we quit riding.

  35. #35
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    there was a time that my front rotor always get warped, and then i just learned that i have one lazy piston (im using xt.)

    had the piston cleaned up, changed pads, then havent had the rotor warp ever since.

  36. #36
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    Never had these debates when we all used V brakes!
    Thanks to www.weavercycleworks.com for my awesome bike frames!

  37. #37
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    rotational dynamics

    I hate to be a buzzkill on the radius of the wheel thing, but that's not as relevant as you might think. It's the total mass, not the diameter of the wheel that makes it easier (or more difficult) to accelerate and decelerate.

    However, if you're presuming that being larger in diameter also means more mass, then think again. A 26" diameter wheel (including tires, tubes, sealant, whatever) that has more total mass than a lighter (i.e. less mass) 29er wheel will still be more difficult to accelerate and decelerate.

    But the diameter does come into play as it relates to a rotating masses moment of inertia. If you don't believe me then study up on "moments of inertia" as it applies to torque and angular velocity, angular momentum and angular acceleration/deceleration.

  38. #38
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    Quote Originally Posted by Sparticus
    I wish you hadn't said, "Or else I'm missing something really big."

    You're not missing something really big. You're right on.

    Let's simplify this. Imagine any size wheel with a rotor the same size as the wheel. Now put a tire on the wheel for ground clearance. A rotor that comparative size will both stop the vehicle with greater mechanical advantage than a smaller rotor plus it will dissipate heat better.

    When it comes to effective braking and heat dissipation, wheel size is directly related to rotor size. It IS leverage.

    --sParty
    You guys are confusing force/mechanical advantage (changes with rotor & wheel size) with work/energy (does not change with rotor and wheel size). Stopping power is related to force/mechanical advantage. The total amount of heat generated is a function of the mass that you are stopping, period.
    A bigger rotor dissipates heat better, but does not produce any less heat.
    He was not right on... he said you could use mechanical advantage to do less work... that's dead wrong.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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  39. #39
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    Quote Originally Posted by phillabong
    I hate to be a buzzkill on the radius of the wheel thing, but that's not as relevant as you might think. It's the total mass, not the diameter of the wheel that makes it easier (or more difficult) to accelerate and decelerate.

    However, if you're presuming that being larger in diameter also means more mass, then think again. A 26" diameter wheel (including tires, tubes, sealant, whatever) that has more total mass than a lighter (i.e. less mass) 29er wheel will still be more difficult to accelerate and decelerate.

    But the diameter does come into play as it relates to a rotating masses moment of inertia. If you don't believe me then study up on "moments of inertia" as it applies to torque and angular velocity, angular momentum and angular acceleration/deceleration.
    agreed.
    Last edited by meltingfeather; 12-21-2010 at 09:38 AM.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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  40. #40
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    Quote Originally Posted by Manicmtbr
    Never had these debates when we all used V brakes!
    I guess you're not old enough to remember the canti vs V crap fests in the early days of the interweb.

  41. #41
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    Quote Originally Posted by meltingfeather
    You guys are confusing force/mechanical advantage (changes with rotor & wheel size) with work/energy (does not change with rotor and wheel size). Stopping power is related to force/mechanical advantage. The total amount of heat generated is a function of the mass that you are stopping, period.
    A bigger rotor dissipates heat better, but does not produce any less heat.
    He was not right on... he said you could use mechanical advantage to do less work... that's dead wrong.
    You're splitting feathers. One CAN use mechanical advantage to make the work "easier" (less work? Not really, but whatever). The point is the wheel is a lever... a round lever. The greater the diameter, the more leverage working against the forces trying to stop it. Same is true in reverse for the rotor.

    You're the one missing something. Who cares if the same amount of work is being done if it's done more easily by a employing a more efficient lever. (Rhetorical so no question mark.)

    If the same amount of heat is generated but that heat is spread over a larger component to dissipate more efficiently, this is effectively as functional as generating less heat in the first place.

    --sParty
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  42. #42
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    ignorance is bliss

    Quote Originally Posted by meltingfeather
    Fail.
    I think you need a refresher... or to learn it in the first place.
    This has been done in the 29er "debate" so many times it's not funny. I thought it was a "world is flat" thing at this point.
    My apologies, I didn't get the memo that the Sir Isaac Newton's laws of motion didn't apply to bicycle wheels as discussed in this forum. But to your point, some people thought Newton's second law of motion was a fad several hundred years ago and I'm amused to find that some still feel that way today.

    Carry on lads, my work here is done.

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    Quote Originally Posted by Sparticus
    You're splitting feathers. One CAN use mechanical advantage to make the work "easier" (less work? Not really, but whatever). The point is the wheel is a lever... a round lever. The greater the diameter, the more leverage working against the forces trying to stop it. Same is true in reverse for the rotor.

    You're the one missing something. Who cares if the same amount of work is being done if it's done more easily by a employing a more efficient lever. (Rhetorical so no question mark.)

    If the same amount of heat is generated but that heat is spread over a larger component to dissipate more efficiently, this is effectively as functional as generating less heat in the first place.

    --sParty
    you're right... if people want to talk "physics" and "energy" and "rotational dynamics," "whatever" is good enough and "who cares" about the work or if what you're saying is correct.
    so you want to talk in technical terms but you don't care whether what you're saying is right? i get it.
    btw, this thread got on to overheating issues, which have everything to do with work and nothing to do with mechanical advantage, but whatever, that doesn't matter, since it's effectively like having ice cubes on your rotors.
    OP was having warping issues, which can happen due to overheating. he said nothing about his fingers getting tired or not being able to lock up.
    he related it to wheel size, which has no effect on the heat generated, but maybe you can offer us something about hydraulics and relative piston sizes/strokes?
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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    Quote Originally Posted by phillabong
    My apologies, I didn't get the memo that the Sir Isaac Newton's laws of motion didn't apply to bicycle wheels as discussed in this forum. But to your point, some people thought Newton's second law of motion was a fad several hundred years ago and I'm amused to find that some still feel that way today.

    Carry on lads, my work here is done.
    You're right, F=ma is for linear motion, for which the leverage between tire and rotor is irrelevant.
    Last edited by meltingfeather; 12-21-2010 at 09:39 AM.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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    the irony

    Quote Originally Posted by meltingfeather
    Your appeal to Newton is silly, since you don't have the basics down.
    It's not nearly as silly as the quote in your sig.

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    Quote Originally Posted by meltingfeather
    you're right... if people want to talk "physics" and "energy" and "rotational dynamics," "whatever" is good enough and "who cares" about the work or if what you're saying is correct.
    so you want to talk in technical terms but you don't care whether what you're saying is right? i get it.
    btw, this thread got on to overheating issues, which have everything to do with work and nothing to do with mechanical advantage, but whatever, that doesn't matter, since it's effectively like having ice cubes on your rotors.
    OP was having warping issues, which can happen due to overheating. he said nothing about his fingers getting tired or not being able to lock up.
    he related it to wheel size, which has no effect on the heat generated, but maybe you can offer us something about hydraulics and relative piston sizes/strokes?
    Okay. I get your avatar now.

    --sParty
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    Quote Originally Posted by phillabong
    It's not nearly as silly as the quote in your sig.
    i think we got wires crossed & i interpreted your statement as if it were addressed to another comment. my apologies, i agree with what you've said here, i thought you were saying something else by it.
    i threw down a few key edits.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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  48. #48
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    Quote Originally Posted by Sparticus
    Okay. I get your avatar now.

    --sParty
    You're slower than I thought.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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    Quote Originally Posted by meltingfeather
    You're slower than I thought.
    Okay... I admit to being outgunned here. I might be slower than *I* thought, too. I still don't understand why my argument is wrong, and I'd like to. Without using any big words, would you gently explain why the the things I've said are incorrrect? Thanks. Uh... I think.

    --sParty

    Late edit: Just read bholwell's post below... hallelujah! Don't understand a word (rather equation) of it but in any case it seems to support my argument so I guess I win after all. Whew! Relief. (Where's the tongue-in-cheek emoticon?)
    Last edited by Sparticus; 12-21-2010 at 10:57 AM.
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    Quote Originally Posted by phillabong
    I hate to be a buzzkill on the radius of the wheel thing, but that's not as relevant as you might think. It's the total mass, not the diameter of the wheel that makes it easier (or more difficult) to accelerate and decelerate.
    Are you sure? I think it's the mass and the radius (*i.e. the moment of inertia)

    Tangiential Velocity, V = (radius, r) / (angular velocity, w)
    So, w = V/r

    Rotational Inertia, I = (mass, m) * (radius^2)

    Momentum, L = I * w
    = (m*r^2) * w
    = (m*r^2) * (V/r)
    = m*r*V

    If the momentum of a 26" wheel equals the momentum of a 29" wheel, and the mass and tengiential velocity are equal, then the radius must be equal, no?

    Momentum of 26" wheel = Momentum of 29" wheel
    L1 = L2
    m1 * r1 * V1 = m2 * r2 * V2

    m1=m2
    V1=V2

    r1 = r2 ????

    Am I missing something?
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    Quote Originally Posted by bholwell
    Are you sure? I think it's the mass and the radius (*i.e. the moment of inertia)

    ...

    Am I missing something?
    Other than omitting the last paragraph of my original statement (But the diameter does come into play as it relates to a rotating masses moment of inertia.) - which addresses the radius issue in much less detail than you provided - you're don't seem to be missing a thing.

    And to your point, I should have more carefully constructed the part of my statement that you quoted. Good eye and my apologies for causing you so much effort to explain my gaffe.

  52. #52
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    Quote Originally Posted by Sparticus
    Okay... I admit to being outgunned here. I might be slower than *I* thought, too.
    I was just poking, since it seems to be fairly common knowledge with the regulars that I'm a "dork," "geek," "pencil neck," "propellerhead" or however you like to describe it. Mike T. made that avatar for me based on reading my posts.
    I'm just well versed in the details and try to keep the accuracy of the technical parts of these discussions up to par.
    Quote Originally Posted by Sparticus
    I still don't understand why my argument is wrong, and I'd like to. Without using any big words, would you gently explain why the the things I've said are incorrrect? Thanks. Uh... I think.

    --sParty
    Your argument isn't "wrong" per se, I think that modifier split the discussion into two aspects that aren't necessarily related, and incorrectly tied them together.
    The OP started this by talking about warping, which can be a heat-related thing in disc brakes. The leverage differences you described don't affect heat, especially when you're talking about different sized whees with the same rotor. That's what prompted pimpbot's comment, and that's what modifier was incorrect in stating: that the leverage allows you to do more work with the same effort.
    The bottom line is that a 26" bike and a 29" bike of the same total weight will produce the same heat in the rotor for the same stop.
    Quote Originally Posted by Sparticus
    Late edit: Just read bholwell's post below... hallelujah! Don't understand a word (rather equation) of it but in any case it seems to support my argument so I win after all. Whew! Relief.
    mmm... that's something different. Phillabong was correct in stating the irrelevance of the radius, and that's the bottom line.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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  53. #53
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    Quote Originally Posted by bholwell
    Are you sure? I think it's the mass and the radius (*i.e. the moment of inertia)

    Am I missing something?
    Good catch, but I think some confusion is coming from talk about both angular velocity (rpm) and linear velocity (mph), and that may be why I misinterpreted Phillabong's comment at first.
    The part that's missing in what you show is the effect of radius on angular velocity relative to linear velocity, and that was one of the things I was trying to get across.
    A 29er wheel is harder to spin up to a certain rpm than a 26" wheel, but for a given mph at the ground it will have a lower rpm, so when comparing acceleration of whole bikes to a set linear speed (mph), these effects cancel eachother out and the bottom line is mass, which is (I think) what Phillabong is saying.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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  54. #54
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    All this because because I'm warping rotors? My head hurts....

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    A little math fun. I'm not even very good at math (fortunately Google will do it for you).

    Someone at 200 lbs riding weight (rider+bike+gear) traveling at 15mph has a kinetic energy of 2039.58 Joules. Kinetic energy calculator.

    2039.58 Joules is equivalent to 1.933 BTUs. Joules to BTU.

    The specific heat of stainless steel is .12 BTU/lb/deg F. That means .12 BTUs will raise the temperature of 1 pound by 1 deg F.

    If you were to bring that 200 lbs at 15mph to a stop using one brake it would raise the temperature of:
    160 mm rotor that weighs 110 grams by 66 deg F.
    185 mm rotor that weights 150 grams by 48 deg F.

    Please feel free to check my math because it could be wrong entirely.

    This ignores the effect of wind/rolling resistance, pads and caliper absorbing heat and uneven distribution in the rotor because these would be difficult to include in the calculation. The larger rotor will also dissipate heat into the air faster through a larger surface area.

    Wheel size doesn't come into the equation at all. Heat creation/dissipation and wheels size/braking power are two completely different issues that should be considered separately in regards to brake rotor size.

    The OP is only having heat related issues and said he doesn't need more power. There is no reason to bring up wheel size, leverage, moments of inertia, etc at all address his problem.

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    Quote Originally Posted by Moustache rider
    Heat creation/dissipation and wheels size/braking power are two completely different issues that should be considered separately in regards to brake rotor size.

    The OP is only having heat related issues and said he doesn't need more power. There is no reason to bring up wheel size, leverage, moments of inertia, etc at all address his problem.
    Bingo!
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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  57. #57
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    This is frustrating. I usually grasp problems like this easily but the explanations offered to counter what I said still don't make any sense to me.

    If trying to figure this out or word it in a way that everyone agrees upon and understands annoys anyone just click off and read something else. I prefer to try and get to the bottom of it.

    Maybe if you can explain how the following doesn't work then perhaps I can grasp it. I also sent an email with the initial 26 vs 29 problem to my Uncle who is an aeronautical engineer and maybe he can put it into terms more easily understood by everyone.

    Take a 10 foot pole pivoting on a hinge at one end 24" off the ground with a 12' rotor attached at the pivot point along with a fixed caliper brake. You drop the pole from almost vertical and try and stop it from hitting the ground by applying brake pressure.

    In one test you fix a 5 lb weight at 5 feet from the pivot and with the second test you fix the 5lb weight at 10 feet from the pivot.

    Now what my detractors are stating is that there will be no additional heat generated at the the rotor/caliper while stopping the fall of the pole with the weight at the end of the pole vs at mid point. My idea is that it will take considerably more force to stop the fall of the pole with the weight on the end than in the middle so therefore more heat will be generated in the process since the friction of the pad on the rotor is what will stop the pole, and friction creates heat.

    Can you {simply} explain why this is not the case and that it makes no difference where the weight is placed, that it will always generate the same amount of heat at the rotor/caliper no matter how much brake force is required to stop the falling weight?
    No it never stops hurting, but if you keep at it you can go faster.

  58. #58
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    Quote Originally Posted by modifier
    This is frustrating. I usually grasp problems like this easily but the explanations offered to counter what I said still don't make any sense to me.
    Fair enough, maybe someone hasn't put it right... half of communication is the transmission side.
    Quote Originally Posted by modifier
    If trying to figure this out or word it in a way that everyone agrees upon and understands annoys anyone just click off and read something else. I prefer to try and get to the bottom of it.
    We're birds of a feather, so to speak.

    Quote Originally Posted by modifier
    Maybe if you can explain how the following doesn't work then perhaps I can grasp it. I also sent an email with the initial 26 vs 29 problem to my Uncle who is an aeronautical engineer and maybe he can put it into terms more easily understood by everyone.
    Not likely. No offense to your uncle, but I'm an engineer and it mostly just gets crap flung at me because I tend to talk like the dood in my avatar in the interest of precise and accurate communication. It's critical in my line of work, and the fact that my brain works that way is probably what lead me (and your uncle) to engineering in the first place.
    Quote Originally Posted by modifier
    Take a 10 foot pole pivoting on a hinge at one end 24" off the ground with a 12' rotor attached at the pivot point along with a fixed caliper brake. You drop the pole from almost vertical and try and stop it from hitting the ground by applying brake pressure.

    In one test you fix a 5 lb weight at 5 feet from the pivot and with the second test you fix the 5lb weight at 10 feet from the pivot.

    Now what my detractors are stating is that there will be no additional heat generated at the the rotor/caliper while stopping the fall of the pole with the weight at the end of the pole vs at mid point. My idea is that it will take considerably more force to stop the fall of the pole with the weight on the end than in the middle so therefore more heat will be generated in the process since the friction of the pad on the rotor is what will stop the pole, and friction creates heat.

    Can you {simply} explain why this is not the case and that it makes no difference where the weight is placed, that it will always generate the same amount of heat at the rotor/caliper no matter how much brake force is required to stop the falling weight?
    Work = force * distance
    With the 5' example, the rotor turns twice as far and requires half the force (making some simplifying assumptions about your example). The leverage changes the distribution of force and distance, but does not change the energy required (the total amount of work done). The heat generated is a function of the total work done, not how you got there.
    It's exactly like gearing. Lower gear = less pedal force but more spin (greater distance travelled by your feet).
    Hope that helps.
    Last edited by meltingfeather; 12-21-2010 at 12:07 PM.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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    Quote Originally Posted by modifier
    This is frustrating. I usually grasp problems like this easily but the explanations offered to counter what I said still don't make any sense to me.

    If trying to figure this out or word it in a way that everyone agrees upon and understands annoys anyone just click off and read something else. I prefer to try and get to the bottom of it.

    Maybe if you can explain how the following doesn't work then perhaps I can grasp it. I also sent an email with the initial 26 vs 29 problem to my Uncle who is an aeronautical engineer and maybe he can put it into terms more easily understood by everyone.

    Take a 10 foot pole pivoting on a hinge at one end 24" off the ground with a 12' rotor attached at the pivot point along with a fixed caliper brake. You drop the pole from almost vertical and try and stop it from hitting the ground by applying brake pressure.

    In one test you fix a 5 lb weight at 5 feet from the pivot and with the second test you fix the 5lb weight at 10 feet from the pivot.

    Now what my detractors are stating is that there will be no additional heat generated at the the rotor/caliper while stopping the fall of the pole with the weight at the end of the pole vs at mid point. My idea is that it will take considerably more force to stop the fall of the pole with the weight on the end than in the middle so therefore more heat will be generated in the process since the friction of the pad on the rotor is what will stop the pole, and friction creates heat.

    Can you {simply} explain why this is not the case and that it makes no difference where the weight is placed, that it will always generate the same amount of heat at the rotor/caliper no matter how much brake force is required to stop the falling weight?
    I'm not sure the pivoting pole example really makes a good stand in for a bicycle wheel.

    If you have a 26" wheel and a 29" wheel both with 6" rotors installed you will have to squeeze the brake harder to stop in the same distance with the 29" wheel. That means more heat generated per rotation. However, the larger wheel will make fewer (and slower) rotations to stop in the same distance as the smaller wheel.

    Larger wheel = more heat per rotation but fewer rotations.
    Smaller wheel = less heat per rotation but more rotations.
    It evens out.

  60. #60
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    Quote Originally Posted by Moustache rider
    I'm not sure the pivoting pole example really makes a good stand in for a bicycle wheel.

    If you have a 26" wheel and a 29" wheel both with 6" rotors installed you will have to squeeze the brake harder to stop in the same distance with the 29" wheel. That means more heat generated per rotation. However, the larger wheel will make fewer (and slower) rotations to stop in the same distance as the smaller wheel.

    Larger wheel = more heat per rotation but fewer rotations.
    Smaller wheel = less heat per rotation but more rotations.
    It evens out.
    A wheel is basically a rotating lever with the fulcrum at the center so the pole problems is a direct extrapolation but more extreme so people can easily visualize the forces involved.

    I hear what you are saying so let's see what others say.
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  61. #61
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    I'm sorry for nitpicking. This thread became terribly off-topic!

    Quote Originally Posted by modifier
    This is frustrating. I usually grasp problems like this easily but the explanations offered to counter what I said still don't make any sense to me.

    Can you {simply} explain why this is not the case and that it makes no difference where the weight is placed, that it will always generate the same amount of heat at the rotor/caliper no matter how much brake force is required to stop the falling weight?
    Consider a weight placed at the end of a teetertoter. You lift the weight by pressing down at the other end. You then lift the weight by pressing halfway from the other end to the fulcrum point. In both instances you have done the same amount of work (the work required to lift the weight), yet in the first instance it required half as much force. Although it required less force, the distance you had to push down was greater.

    When looking at the bicycle wheel & rotor, a smaller amount of force will be applied to a rotor with a larger diameter to decelerate equally. But that larger rotor will also have a faster tangiential velocity. Results in equal heat generation. No matter how you cut it, the 100% of the kinetic energy of the bicycle and rider will be converted to heat, and rotor diameter plays no role in this. (Although as mentioned, the larger surface area does dissipate heat more rapidly.)
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  62. #62
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    Quote Originally Posted by bholwell
    Am I missing something?
    The mass of the rim and tire rotates, but the biker's mass doesn't.
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    Quote Originally Posted by asphaltdude
    The mass of the rim and tire rotates, but the biker's mass doesn't.
    I was responding to the statement that wheels of the same mass but different diameter take the same amount of energy to get up to speed. I was not addressing the heat generated by the deceleration of a bicycle & rider.
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    Srry, my fault
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    Quote Originally Posted by asphaltdude
    The mass of the rim and tire rotates, but the biker's mass doesn't.
    That's irrelevant for braking heat generation, which is, um, kind of the point.
    Quote Originally Posted by pvd
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    If you want to stick with the rotating pole example. The weight fixed halfway down the pole will only travel 12" before the end of the pole hits the ground. The weight fixed at the end of the pole will travel 24" before it hits the ground. The end of the pole will have traveled the same distance. This accounts for the different amounts of brake force required to suspend the two in the air.

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    Quote Originally Posted by raff
    +1 for the big rotors, but sintered pads are a double-edged sword because they also transfer heat into the calliper faster and can cause your brake fluid to boil much quicker than organic pads. That can lead to total failure of the brake when you need them most. The best solution is to use the disc for heat storage -> big rotors.
    This was part of my reasoning for putting mechanicals on our tandem - although I'm told that modern brake fluid, stainless braided hose, and large rotors would prevent this when using hydraulics (plus I already spent too much on my bike - the tandem gets 2nds).

    btw - the tandem is the perfect example of a smaller wheel using a big brake that has to dissipate HUGE heat due to the mass of the system (bike + riders + baggage). If you want to do the KE calculation on what turns into heat you'll see it's a lot.

    +1 on Aztec rotors. Not light, but def. strong. And at 185# I have no qualms about speeds in the high 40's on pavement, or low 30's on dirt using 160mm rotors. There's more brakes than traction in both cases.

    -F

    PS - something about this:
    Quote Originally Posted by modifier
    This is frustrating. I usually grasp problems like this easily but the explanations offered to counter what I said still don't make any sense to me.

    If trying to figure this out or word it in a way that everyone agrees upon and understands annoys anyone just click off and read something else. I prefer to try and get to the bottom of it.

    Maybe if you can explain how the following doesn't work then perhaps I can grasp it. I also sent an email with the initial 26 vs 29 problem to my Uncle who is an aeronautical engineer and maybe he can put it into terms more easily understood by everyone.

    Take a 10 foot pole pivoting on a hinge at one end 24" off the ground with a 12' rotor attached at the pivot point along with a fixed caliper brake. You drop the pole from almost vertical and try and stop it from hitting the ground by applying brake pressure.

    In one test you fix a 5 lb weight at 5 feet from the pivot and with the second test you fix the 5lb weight at 10 feet from the pivot.

    Now what my detractors are stating is that there will be no additional heat generated at the the rotor/caliper while stopping the fall of the pole with the weight at the end of the pole vs at mid point. My idea is that it will take considerably more force to stop the fall of the pole with the weight on the end than in the middle so therefore more heat will be generated in the process since the friction of the pad on the rotor is what will stop the pole, and friction creates heat.

    Can you {simply} explain why this is not the case and that it makes no difference where the weight is placed, that it will always generate the same amount of heat at the rotor/caliper no matter how much brake force is required to stop the falling weight?
    has me thinking that one of those weights was higher and had more energy (potential) to start with. Maybe I read it wrong?

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    i think a distinction that could probably help the discussion....

    there are two separate issues being discussed.

    i think some of the reason that wheel diameter is screwing up people's heads is that it effects brake power, it does not have any effect on the heat generated when you brake from high speeds.

    one is an energy equation (kinetic energy turned into heat energy) the other is a torque equation (T=rFsin(Theta)).

    rotor size plays a role in both of these, but for different reasons. wheel size (r) is only a factor in the torque equation.
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    Quote Originally Posted by whybotherme
    i think a distinction that could probably help the discussion....

    there are two separate issues being discussed.

    i think some of the reason that wheel diameter is screwing up people's heads is that it effects brake power, it does not have any effect on the heat generated when you brake from high speeds.

    one is an energy equation (kinetic energy turned into heat energy) the other is a torque equation (T=rFsin(Theta)).

    rotor size plays a role in both of these, but for different reasons. wheel size (r) is only a factor in the torque equation.
    Got it now. Thanks for delineating the issue so succinctly.

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    I stopped faster and quit warping rotors when I went to a 203mm rotor, and I'm a.Clyde with a degree in Finance /Accounting. I hope this assists the OP. It's a lot less expensive to stop in time with larger rotors and avoid trips to the Emergency Room. You can thank me later for that in depth Financial Analysis of why large diameter rotors are superior to small, overheated warped rotors in keeping your deductible paid down.

  71. #71
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    Quote Originally Posted by whybotherme
    i think a distinction that could probably help the discussion....

    there are two separate issues being discussed.

    i think some of the reason that wheel diameter is screwing up people's heads is that it effects brake power, it does not have any effect on the heat generated when you brake from high speeds.

    one is an energy equation (kinetic energy turned into heat energy) the other is a torque equation (T=rFsin(Theta)).

    rotor size plays a role in both of these, but for different reasons. wheel size (r) is only a factor in the torque equation.
    Yes, I assumed that there was a direct relationship between the 2.

    I acquiesce that was incorrect. The distance/duration of pad contact with the rotor in relation to wheel size helped too.

    Btw I just installed a 203 rotor with a BB7 caliper last week on a xc bike that I would usually run a 160 on because only the 203 set was on sale for $49 and after riding it for a week I think I'll eat the 65gram penalty and keep the rotor because it makes stopping so easy. And cooler
    No it never stops hurting, but if you keep at it you can go faster.

  72. #72
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    Quote Originally Posted by modifier
    Yes, I assumed that there was a direct relationship between the 2.

    I acquiesce that was incorrect. The distance/duration of pad contact with the rotor in relation to wheel size helped too.

    Btw I just installed a 203 rotor with a BB7 caliper last week on a xc bike that I would usually run a 160 on because only the 203 set was on sale for $49 and after riding it for a week I think I'll eat the 65gram penalty and keep the rotor because it makes stopping so easy. And cooler
    Hear hear. I moved to a 203mm rotor on the front wheel primarily to eliminte fade on local multi-mile descents, but the added stopping power is nice, too. Not going back.

    --sParty

    P.S. Cooler... literally.
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  73. #73
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    Quote Originally Posted by Sparticus
    Got it now. Thanks for delineating the issue so succinctly.

    --sParty
    meltingfeather already explained it using pretty much the same words, so I'm not sure why this other poster helped you get it finally, but better late than never.

    After reading page 1, i thought i was going to have to drag out my Ph.D. credentials and gently explain to y'all that meltingfeather is right and some of you are plain wrong. But by page 2 it seems that most everyone has figured this out.

    Originally posted by bucksaw87
    I still fail to see how mustaches, fixies, and PBR are ironic.

  74. #74
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    Quote Originally Posted by RandyBoy
    I stopped faster and quit warping rotors when I went to a 203mm rotor, and I'm a.Clyde with a degree in Finance /Accounting. I hope this assists the OP. It's a lot less expensive to stop in time with larger rotors and avoid trips to the Emergency Room. You can thank me later for that in depth Financial Analysis of why large diameter rotors are superior to small, overheated warped rotors in keeping your deductible paid down.

    ^^^^Thanks, now that something I can understand^^^^

    I too a qualify as a Clyde 220#, and I run 203 fronts and 180 rear discs.

  75. #75
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    Quote Originally Posted by frorider
    meltingfeather already explained it using pretty much the same words, so I'm not sure why this other poster helped you get it finally, but better late than never.

    After reading page 1, i thought i was going to have to drag out my Ph.D. credentials and gently explain to y'all that meltingfeather is right and some of you are plain wrong. But by page 2 it seems that most everyone has figured this out.

    Yes, MF certainly tried to help me, though in a bit of a backhanded way. Guess I had that coming since I was wrong and claimed others were, including him. Apologies.

    See you on the trail.

    --sParty
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  76. #76
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    Larger rotors stop quicker because of their larger radius and surface area - they are able to apply more torque. That is why you see huge brake rotors on the front of high performance sports cars.

    The greater surface area dissipates heat, but not that much faster than a smaller rotor. That is why the brakes on those same sports cars are slotted or drilled, to allow the heat and hot gasses to escape from between the pad and rotor. Also a larger rotor will generate less heat to do the same work.

  77. #77
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    Quote Originally Posted by meltingfeather
    A larger wheel does affect the force, it does not affect the total amount of work required, which is what manifests as heat in the rotor.

    Not a given at all, in fact proven to not be true. Larger wheels do require more energy to spin up to a certain angular speed (rpm), BUT they also do not rotate as fast for a given linear speed (mph). Both of these effects are proportional to the radius of the wheel and cancel eachother out when comparing acceleration of a bike.
    Sorry but I have to challenge this part of the discussion.

    I agree with everything else stated about heat dissipation and rotor size and mechanical advantage being immaterial if wheel traction is the limiting factor in braking.

    As shown in other posts angular momentum of the wheel is proportional to r squared while velocity is only proportional to r.

    This means that a 29'er wheel does take more energy to spin up (acknowledged above) and therefore by definition it takes more energy to slow down.

    The total energy to be dissipated when braking a bike is the linear momentum of the rider (E = mv2) plus the rotational momentum of the wheels (I = mr2).

    Given that a typical 29er wheel has a greater m and r than an equivalent 26'er wheel of the same construction and materials, the I will be greater despite the rpm being lower. This is a well established fact and is the basis for most arguments against 29'ers as being less responsive and slower to accelerate (and turn).

    However with the power of modern disc brakes I have never noticed this effect to be significant. We have something like 90kg/200lb of bike and rider with linear momentum and only about 3-4kg/7-9lbs of wheel and tyre with rotational momentum.

    If we throw grade into the equation, a 10% grade will also have more significance than wheel size in determining the amount of energy to be dissipated. The base equation here is F=ma where a = g/10 (g being the force of gravity). Its 20 years since high school physics so not sure how to turn that into work right now.

  78. #78
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    Quote Originally Posted by PoisonDartFrog
    Also a larger rotor will generate less heat to do the same work.
    Nope.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
    29er Tire Weight Database

  79. #79
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    Quote Originally Posted by toddre
    Are you bigger guys warping rotors with the larger wheels?
    I'm running 160 Elixers and I always seem to be warping them, the front particularly...
    Think a bump up to 180 would help (I don't really need the added stopping power)
    Or is there a better rotor I can try?
    thanks
    Yes.
    Yes.
    Any 180 or 185mm rotor will either warp less or not at all, if you are a Clyde. If you warp a 185 due to heat, go to a 203mm. If you warp a 203mm, lose more weight.

  80. #80
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    Quote Originally Posted by meltingfeather
    Quote Originally Posted by PoisonDartFrog
    ...a larger rotor will generate less heat to do the same work.
    Nope.
    It will generate the same heat.

    It just will not reach as high of a temperature because the heat goes elsewhere.

    -F

  81. #81
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    Quote Originally Posted by Fleas
    It will generate the same heat.

    It just will not reach as high of a temperature because the heat goes elsewhere.

    -F
    I like this. The slide rule crowd don't seem to live on the trail so much as in the lab.

    --sParty
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  82. #82
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    I dunno...

    Quote Originally Posted by Sparticus
    I like this. The slide rule crowd don't seem to live on the trail so much as in the lab.

    --sParty
    It adds up to me in the real world, too. I regularly do this one part of my workout loop where it descends about 300 feet in 0.4 miles. I've done this same loop for a decade. I've been running the same set of Hope Mono Minis on various bikes over the years. I had them on my old stumpy FSR-XC for about 4 of them. I know exactly how fast I can go and how much brake force I can apply before smoking the brakes. These same brakes went to my Monocog29er, and then to my Singular Swift. Except for failed experimenting with different pads, I've stuck to the Hope factory sintered pads.

    How fast I can go with how much brake pressure has remained pretty constant (subjectively, naturally) between my little wheel and big wheel bikes.

    So IMO and IME, real world its samey same between kiddie wheels and wagon wheels.

  83. #83
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    Quote Originally Posted by ozynigma
    However with the power of modern disc brakes I have never noticed this effect to be significant. We have something like 90kg/200lb of bike and rider with linear momentum and only about 3-4kg/7-9lbs of wheel and tyre with rotational momentum.

    .
    yes, and when comparing 26 to 29 don't forget there is only about 200g max between each wheel including tyres, sometimes nothing. My feeling is that the slower to accelerate and slow argument is way over blown.

  84. #84
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    Quote Originally Posted by finch2
    My feeling is that the slower to accelerate and slow argument is way over blown.
    If you run the numbers you get the same answer.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
    29er Tire Weight Database

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