Suspension Fork Help Max Rotor Size???
- Thread starter kyle888
- Start date
scottproonly
Retro Guru
Re:
This means that the largest rotor you can use for that fork is 185mm,whether you use an adapter for the calliper or not
This means that the largest rotor you can use for that fork is 185mm,whether you use an adapter for the calliper or not
valve bouncer
Retro Guru
The theory goes that the leverage exerted by the larger diameter rotor could possibly rip the wheel out of the fork drop-outs if using a standard 9mm quick release lever. Most 200mm+ rotors are used with a 20mm bolt on axle.
Modernscrap
Retro Newbie
Stick with what you've got, it will be absolutely fine.
What the manufacturers are trying to do by recommending a maximum disc size is to limit the amout of torque being applied to the fork (i.e. how much the effect of braking is trying to bend the fork backwards), although this is a fairly vague way of doing it.
They'll be working on a worst case scenario and assuming your towards the upper end of the average weight scale, probably up around 95-100kg. The heavier the rider, the more force there is pushing against the brake but also more grip available to the front tyre, hence more torque will be applied to the fork before the wheel locks.
They should also be assuming your using fairly decent hydraulic brakes with plenty of power. I have two bikes with 180mm rotors up front, one has a Saint 4 pot caliper and the other has a 2 pot XTR. The Saint feels much stronger as the caliper is able to generate more braking power (friction) so applies more torque to the fork.
Increasing the disc size increases the amount of leverage the caliper has against the wheel so increases the torque being applied to the fork - hope this all makes sense so far!!
I used to run the exact same setup as you on my commuter bike a few years back, BB7 with 203mm disc and XT lever. I upgraded these with XT M775 and 180mm rotor, there was a small but noticeable increase in power with shorter braking distances despite the smaller disc (much better feel and modulation though). I'm not knocking the BB7's as they are great brakes when setup properly, it's just that the hydraulic brakes were able to generate more braking power at the caliper.
The point I'm trying to get to here is that if the XT setup is giving as much if not more power than yours with a 180mm disc and is considered safe by the manufacturer, then surely yours will be safe too??
Another thing to take into account is that you are used to the amount of power you already have, do you really want to reduce that power considering you are just about to increase the amount of available grip, especially when braking into bumpy corners??
What the manufacturers are trying to do by recommending a maximum disc size is to limit the amout of torque being applied to the fork (i.e. how much the effect of braking is trying to bend the fork backwards), although this is a fairly vague way of doing it.
They'll be working on a worst case scenario and assuming your towards the upper end of the average weight scale, probably up around 95-100kg. The heavier the rider, the more force there is pushing against the brake but also more grip available to the front tyre, hence more torque will be applied to the fork before the wheel locks.
They should also be assuming your using fairly decent hydraulic brakes with plenty of power. I have two bikes with 180mm rotors up front, one has a Saint 4 pot caliper and the other has a 2 pot XTR. The Saint feels much stronger as the caliper is able to generate more braking power (friction) so applies more torque to the fork.
Increasing the disc size increases the amount of leverage the caliper has against the wheel so increases the torque being applied to the fork - hope this all makes sense so far!!
I used to run the exact same setup as you on my commuter bike a few years back, BB7 with 203mm disc and XT lever. I upgraded these with XT M775 and 180mm rotor, there was a small but noticeable increase in power with shorter braking distances despite the smaller disc (much better feel and modulation though). I'm not knocking the BB7's as they are great brakes when setup properly, it's just that the hydraulic brakes were able to generate more braking power at the caliper.
The point I'm trying to get to here is that if the XT setup is giving as much if not more power than yours with a 180mm disc and is considered safe by the manufacturer, then surely yours will be safe too??
Another thing to take into account is that you are used to the amount of power you already have, do you really want to reduce that power considering you are just about to increase the amount of available grip, especially when braking into bumpy corners??
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