Brake caliper mounting angle on steering knuckle

[theStruggler]

Hi,

I have looked quite a bit for an answer to this but with little success. I am in the process of designing a custom steering knuckle and would like to know whether there is an optimimum angle from horizontal or vertical at which brake calipers should be mounted. Most of the moutings I have seen are about 5 to 6 degrees from vertical. Is there a specific reason for this? Does mounting angle matter?

Thank you for helping me clarify this

 

[theStruggler]

P.S. The caliper going to be used with this knuckle is very likely going to from the AP Racing CP8250 series

 

[BrianPetersen]

As far as I can tell, packaging is the number one consideration. Wherever the suspension and steering parts aren't, is where the brake caliper can be.

If the vehicle is transverse engine front wheel drive, the engine/trans is in front of the axle which means the steering rack is behind the axle centerline (because it can't share space with the drivetrain) and the brake caliper will probably be in front, although it can and has been done otherwise.

Rear drive vehicles might not have the same constraint on where the steering rack is. My (rear drive) car has the steering rack ahead of the axle centerline and the brake calipers behind.

Theoretically, having front brake calipers behind the axle centerline puts less load on the wheel bearings because the upward force on the caliper while braking means there is a downward force on the wheel bearings which is the opposite direction that the weight of the vehicle is applying. But correctly sizing the wheel bearings means this isn't likely to be meaningful.

Don't forget that the caliper bleed screw has to be at the top.

 

[CoryPad]

In addition to the excellent answer above, racing applications have given consideration to polar moment of inertia and center of gravity. Hence, on a front axle the caliper ideally would be below and behind the centerline.

 

[theStruggler]

Thank you both for your answers. That clears up a lot. Just so as to make sure I am getting this: as long as all the other parts are well defined and set, the caliper can pretty much go anywhere. There are some positions such as "below and behind the centerline" that would be ideal but it can still be placed pretty much anywhere.

 

[BUGGAR]

I’ve been thinking about caliper position and forces on the wheel bearing. My gut tells me that the braking forces all resolve themselves and there are no net forces on the wheel bearing, other than those from vertical and lateral vehicle forces.

I tried to write a proof of this last night, drawing little free body force arrows all over the place until my wife finally leaned over and said, “Why don’t you draw some little bows too, dear”.

The upshot is that I can’t prove it mathematically. But if the brake caliper were positioned to apply a lifting load on the wheel bearing, why wouldn’t the braking forces, if sufficient, also lift the car off the ground.

Maybe this is how Mary Poppins could fly. Her calipers were mounted to apply lift to her bearings and up she went, so long as she had her brakes on. Doesn’t sound right does it?

Anybody got a mathematical proof?

Bob

 

[BrianE22]

Bob -

I looked at the forces and torques on the brake disc. I think you can either add or subtract from both the vertical and longitudinal loads on the bearings depending on where you locate the caliper.

 

[GregLocock]

as hard as the rotor pushes up on the wheel bearing, and hence the knuckle, the calliper pushes down on the knuckle, so it is all internally resolved. The bearings do see the braking force from the rotor.



Cheers

Greg Locock


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