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I have a new bike with 160mm rotors and Avid BB5 brakes. I wanted to step up to Avid BB7 brakes as they seem easier to adjust. The BB7s come packaged with rotor options -- 160 / 180 / 200 mm.

  1. Can I go up a rotor size?

  2. What would limit this? My fork has a brand but the manufacturer's website has no indication of rotor size limitation.

  3. Is there any advantage to going up?

I should mention that this is for an electric-assist bike with 20" wheels. I do drag a trailer and live in a hilly area, so good/better brake performance going downhills is definitely appreciated.

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    it is also worth mentioning that rotor size will not be the only thing that affects braking power/quality. a higher quality brake such as trp Spyke/spyre will offer more stopping power. people have also reported that the ice tech rotors and similar ones have greatly increased their stopping power with the increased cooling provided. – Paul Jan 12 '17 at 16:57
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    I installed a BB-7 on an electric assist bike and had clearance issues with the larger hubs of the e-bike. The inboard adjustment mechanism on the BB7 was wider than the Tektro model I was replacing and it required a lot work to get the clearance worked out. – Drew Smith Jan 12 '17 at 22:25
  • I currently have a BB5 installed -- and it's going on the front -- so I think I'll be ok with clearance, but thanks for the cautionary note. – RoboKaren Jan 12 '17 at 22:32
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1) You might be able to do so. Caliper, pads, levers and wheels (apart from the discs) ARE compatible. (For non-compatible parts see 2)

2) You need:

  • the frame/fork to be strong enough to resist the increased load. If you give us the specs, we might be able to find out
  • sufficient clearance in the frame/fork (also check for interference with pannier racks, if any)
  • the correct adapter (they are generally available for almost any combination of original size, current size and mounting systems (IS vs PostMount))

3) Larger rotors give the brakes more "leverage" - more stopping power for given pressure. Also, they cool better, preventing pad overheating and liquid boiling on longer descents. They are heavier and slightly more prone to bending.

20" is quite small, which generally improves braking power. If 180mm discs are not enough and you tend to pull a heavy trailer, a braking mechanism for the trailer might be needed.

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Rotor size is determined by the brake mount adapter. So everything else ie. the caliper - stays the same. Only the Adapter changes.

You must check your fork manufacturer for the maximum size of rotor the fork can be safely operated with.

Also check frame clearances (at the rear) for enough clearance for the size of rotor you are selecting.

Going up rotor sizes is specifically for more braking power.

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