Topic: should I decrease my brake rotor diameter or not??

[CPHjimm]

Im like other doing a dual brake config. on my cb750. But after several E-bay purchases ended up with 2 different front calipers and brackets. compared to the one that was sitting on my CB.

The difference compared to the original F1 ( without the fins) is the dimension between the caliper bolts and the angle og the bracket. The "original" one is approx. 50mm (2") between the caliper bolts and the two purchased ones are slightly smaller ( maybe they are from a cb500/550???)

My plan was then to use the matching set but as the angle is slightly different I will need to mill down the diameter on the rotor to make them fit.

I've been looking for quite some time to get another F1 caliper but they seems to be gone at the moment on Ebay. and the once I've been bitting on I lost due to time difference and lack of funds.

So should I continue looking or just decrease the diameter on the rotors???

[Bodi]

Brake torque is generated in the rotor, and torque is force x distance from centre. So reducing the diameter will reduce braking.
But you're doubling the number of rotors so I think it would be a non-issue for braking performance if all else is equal.
With the reduced rotor diameter, will the disk surface width be smaller than the brake pad? That would be a bad idea. Machining the stainless rotors is difficult. You want to have a finish that doesn't have a lot of stress concentration points like tool chatter marks or , catastrophic failure of the rotor is possible and it would happen at high temperature and high stress.. like in a panic stop when you least want your brakes to go away.

[CPHjimm]

I thought about the torque aswell, but as I only will need to decrease by approx. 6-10 mm and with the double brake pads I should be good to go.
The width will not decrease as the surfaces are smooth.
But I will need to check if all the brakepad surface will cover the disc, but Im quite sure they will.

But Im really wondering what kind of calipers I got a hold on??? anyone have a clue?

[mrrch]

I ran into the same thing. The caliper with the bolts closer together are from a 350/400/500/550. The 750's have a wider bolt spacing on the caliper. Also the earlier 750 calipers are finned.

[CPHjimm]

thats what I thought.... should never have rated those F¤%&/#¤S who sold it as CB750 parts. or maybe I should have asked for the dimension between the caliper bolt

Well, guess I should start the search again, or maybe someone will trade two cb500/550 to one 750F1!?! Or I'll stop by wrenchmonkees, i know they just got a big batch of really nice CB750 parts.