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Disc brake rotor size
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tiger
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Disc brake rotor size - 1998/08/09 09:00 I just noticed that Avid's mechanical disc brakes come with 160, 185 or 203 mm rotors. It's claimed that the 185mm rotor has 15% more
"power", the 203 26% more.

Does a larger rotor really provide more stopping power? Why? I could understand less fade due to heat, since a larger rotor would dissipate heat better. Does that translate into more "power"?

I assume that dimension is the rotor diameter. But wouldn't a change in rotor diameter change where the caliper gets positioned, i.e. would require a change to the caliper mounting eyelets?

I'm spec'ing these brakes for a road bike; should I expect to need more stopping power than a mountain bike for say long mountain downhills?



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Lord Licky
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re:Disc brake rotor size - 1998/08/09 12:38 I would think the opposite. Mtn bikes "need" large brakes in order to stop
NOW. Road bikes usually don't need the instant deceleration of a mtn bike.

Go with the smallest rotor for the road.

The mounts are adjustable in several directions, so mounting whichever diameter you choose shouldn't be a problem.

FWIW, I run the small diameter Avid mechanical discs on my XC mtn bike and don't have a problem stopping.

You're about to unleash a firestorm about road bikes and disc brakes. Get ready for it.



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SideShowBob36
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re:Disc brake rotor size - 1998/08/10 00:48 Well, from a purely mechanical point of view (pardon pun) leverage would be one possible factor. Hold your wheel in your hands and spin it. now try stopping the spin by grabbing the spokes first near the hub, then again further out.

May you have the wind at your back.
And a really low gear for the hills!

Chris'Z Corner
"The Website for the Common Bicyclist":
http://www.geocities.com/czcorner



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Blameitonus
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re:Disc brake rotor size - 2008/11/24 23:31 im a highschooler in physics, and none of you could answer this... wow. its a matter of torque. the diameter of the rotor provides more neutons of torque than a smaller rotor. the formula is t=Rf
t=torque,R=radius,f=force applied. then you can get more complicated with all the angle of atack and lever arm crap, but screw that. lets say your *snicker* bb7's apply aprox 150 neutons of force. torque for a 160mm rotor would = 12,000 neutons. 185mm rotor = 13875 neutons, and a 203mm rotor = 15,225.
whatd u guys fail physics? jeez...
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Braveheart
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re:Disc brake rotor size - 2008/11/25 08:04 Hi Blameitonus, welcome to the forum




Thanks for that explanation. Some of us (like me) just aren't that good in physics



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trek_dirt
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re:Disc brake rotor size - 2009/06/03 07:22 I am a physicist and it is "Newtons" or N not neutons The torque is actually the cross product of the Vectors of radial position and the Force. Which means that the units are N meters not just Newtons or N mm. But the answer is basically correct.

What this means is that the bigger the rotor the less force you
are required to apply to the brake. The smaller the rotor the more
pressure or force you must apply to the brake compared to the
larger rotor to stop.

It is not particularly impressive to be arrogant and condescending
if you can't at least get Newtons correct.

Post edited by: trek_dirt, at: 2009/06/03 07:51
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