Why do some cars have brake caliper on the rear of the disc?

[dave 911]

I've noticed some cars have rear brake calipers that are on the rear of the disc vs. the front. I have a friend that has an A5, and the front calipers are on the rear of the discs on that car. Why the difference? It's probably a weight/balance thing, but it would seem that the most effective braking would be for the calipers to be on the front of the discs....

[davidbir]

Most cars had the caliper on the rear of the disc-except Porsche. Probably to allow the steering to attach to the front of the upright. Having the caliper in front is more effective though.

[masraum]

How does caliper placement affect braking efficiency or effectiveness?

[John Rogers]

It makes no braking difference. It does occur due to what is attached to the suspension area where the caliper is to be located.

[Mark Henry]

Originally Posted by john rogers

It makes no braking difference. It does occur due to what is attached to the suspension area where the caliper is to be located.

Exactly, it makes no difference at all. It could also be placed top or bottom.
Placement is only dictated by ease of bleeding, clearance of suspension and aesthetics. You probably wouldn't place one on the bottom as it would retain dirt, but that is the only reason.

[tevake]

Funny, I was just thinking about the brake arrangement the other day when I had the front wheels off. I was thinking that the weight would have been better placed nearer the center. Maybe the steering stuff would have been in the way?

Cheers Richard

[Flieger]

Steering stuff is in the way on a 911. Having the calipers towards the center (fronts on rear of front disc, rears on front of rear disc) helps polar moment of inertia but on a 911 with the engine slung out behind the rear axle you are not concerned about polar moment of inertia so much as getting as much weight on the front as possible. So having both calipers on the front of the disc makes sense on a 911 for that reason.

F1 cars usually run them on the bottom of the disc for a lower cg.

Caliper placement circumferentially has no effect on braking performance.

[davidbir]

My understanding is that the placement of the caliper does have an effect on the path of braking loads. Also with the caliper on the front it is easier to provide cooling air.

[wdfifteen]

Some cars (some 80s to 90s GM models that I know of) have one rear caliper at the front of the disc and one at the rear. It's so they can use the same caliper for both sides. Saves a bit in manufacturing costs.

[davidbir]

I cannot find a reference by a noted expert but I did find this on the 'net-this has always been my understanding:

"I agree that from a brake torque stand point it doesnt matter where the caliper is placed. From a force point of view in relation to upright strength it does matter, if only a bit. In the front for instance if the caliper is mounted behind the spindle it will unload the spindle during braking. it will tranfer force/ stress from the spindle (usually the weaker portion) to the upright. the direction will counteract the force/ stress on the spindle due to the weight of the vehicle. if the caliper is mounted forward of the spindle it will transfer force in the opposite direction adding it to the stress on the spidle due to the weight of the vehicle. The same goes for the rear. That being said I think its much more important to protect the caliper than to worry too much about the effect its placement has on the stress experienced by the spindle under braking".

[URY914]

[BReif61]

Placement of the rotors on the front wheels is dictated to some extent by the drive train.

In most FWD cars, the engine and transmission are arranged such that the steering rack sits behind the axle, which puts the brakes in front.

In RWD cars, there's room for the steering rack in front of the axle.

[Bill Verburg]

Mostly it's packaging, ie where they have room, but from a dynamics PoV it does make a difference

You want them as low as possible, between the axles and on the steering wheels(usually the front) w/ positive caster you would want them behind the axle, w/ negative caster in front

[davidbir]

The load transfered to the spindle under braking was a concern for some manufacturers. If you have ever seen a Triumph upright equipped racing car (Elva, Lotus, TVR, etc, etc) lose a front wheel you would know why Triumph were concerned and why replacing the spindles with something of much better quality is Job 1 when race prepping one of these cars. Most of the English manufactures - who were the first to adopt disc brakes- put the calipers behind the upright.

[Flieger]

Well, if you have a marginal design to begin with then it could matter, but unless it breaks the tire won't care where the brake caliper is mounted.

Unless you are using reactive anti-dive.

[Bill Douglas]

You could always have disk brakes like this and it takes away that anoying front or back choice.

[dave 911]

Originally Posted by Bill Douglas

You could always have disk brakes like this and it takes away that anoying front or back choice.

Huh? Whats the deal there?

[Bill Douglas]

Fakes Dave. They are for boy racers who's low spec cars have drum brakes. I think you get a free set of blue neon lights with every fake disk set.

[Flieger]

Or you could go this way, ala McLaren-Porsche F1 car.



Modern F1 cars use 1 caliper, on the bottom usually.

[Zeke]

Max, why is it that F! cars look like a big drum is there when the wheel is off?



My guess it's a cooling chamber.