rear disc caliper location

[copo69]

is there a rule of thumb for rear disc brake caliper location./ does it even matter. i always see them in about the 10 oclock postion . is there a resason for it?

[Salt Racer]

Not a bad question!

Theoretically there are some effects, though I think they are minimal on stick axle rear suspension.

On link suspension such as 4-link, 3-link, L/B, etc, I like placing the calipers at 9 o'clock position (viewed from driver side). This places the mass of calipers closer to instant center so springs/shocks have slightly lighter mass to control.

On IRS with compliant bushings (as on many late model factory suspension), centrifugal force during cornering will try to pull the heavier side of the knuckle towards outside, causing roll steer of some sort. Which side to locate the caliper depends on the design of suspension. Similarly, the top of tires would tip out if the calipers are mounted at 12 o'clock position so that's definetely not desirable.

I've heard of mounting the calipers at 6 o'clock position to lower the CG, but I don't think it helps much unless we're talking about inboard brakes.

When brakes are applied during transient (like trail braking), then there'll be some other effects. I read about this a while ago, but I forgot how it worked.

[Poopy]

Don't forget one small detail....which direction the bleed screw is facing, it should be facing up to make sure all the air gets out when bleeding. I've read that people have not been able to get the spongey feeling out of their brakes, they're tried everything, and that was the problem.