Some cars have them in front of the strut and some have them behind the strut. Does it make any difference in braking ability? Other considerations?

no difference, 'cept make sure the bleed screw is at the top so you can bleed the air out.

The front or back on the horizontal is prefered in order to minimize the effect of any slight play in the wheel bearing being transfered to the brake caliper/pads. There is also the flexing component to deal with. The other issue is the space on the vertical usually being occupied by suspension members and pick up points. AFAIK.

Andys

Ive seen brake calipers mounted at the bottom of the upright to lower the cg of unsprung mass. Its not all too common, but Ive seen it done.

QUOTE (MattR @ Sep 14 2005, 10:10 PM)

Ive seen brake calipers mounted at the bottom of the upright to lower the cg of unsprung mass. Its not all too common, but Ive seen it done.

i've also seen rollbar padding swiss cheesed.

I've also seen cars with two calipers per wheel...

I'm no engineer, but I've always suspected that the only consieration other than not fouling suspension components is that the caliper at the back of the front wheels would be nearer the car's cg and would lower the turning inertia. Pretty minor, I know.

they tend to be on the side where the steering parts aren't.

there are some advantages to "front steer" or "rear steer" setups dealing with toe change in bump, but i don't recall them all.

I have discussed this with our brake development group here at Ford.

It does not matter where the caliper is mounted.

Cooling and packaging are the considerations when deciding where it is located.

Way back in 74 I bought a new Suzuki 750 with dual discs. The calipers were in front of the struts. There was some discussion as to the best location, and it was determined that behind the strut was better for stability. As I assembled the bike I rotated the struts to place the calipers behind. Never had a reason to change that.

On a Porsche, I would always look to see what the factory cars are running. If there was any advantage to a location I'm certain the factory racing department would use it.

Back in the earliest days of disc brakes on bikes, calipers mounted to the front of the sliders was the common setup. Mounting them to the rear of the sliders, as is common today, happened in the early to mid-80s. One reason for this is the cast slider bosses are slightly stronger in compression than in tension, and the rear mounting fed the braking loads in compressing the mounts.

There's also some benefit on a bike due to distribution of the mass closer to the steering axis, rather than farther away, as a front mount will do, esp. with deep offset triple clamps (which are no longer in vogue, as they were in the early 70s). With the mass closer to the steering axis, the mass has a reduced lever arm to do things like set up a wobble that can easily turn into a tank-slapper.

In a car, the choices are, as stated, usually made more for packaging concerns than anything else. There are theoretial effects to positioning them, but these effects are pretty small, and generally can't really be felt by the driver unless all of the rubber bushings in the suspension and steering systems are replaced by solid bits.

QUOTE (MattR @ Sep 14 2005, 09:10 PM)

Ive seen brake calipers mounted at the bottom of the upright to lower the cg of unsprung mass. Its not all too common, but Ive seen it done.

Ferrari's F1 car has calipers on the bottom for this purpose.

Spoke

James, that sounds like the arguments used when I did the switch back in 1974. Having a physics background, they sound perfectly reasonable.

I like to think in terms of fail-safe ability. If the caliper is on the front of the strut, and the bolts fail, it has to make a complete (or damn close) revolution before it hits something. If it's on the rear of the stut and fails it will hit the strut almost imediatly, and hopefully still let you stop the car...

Lets hope no one ever has to test this thought