Brake calipers in front of or behind the axle effects?

This is a rather odd question but what I'd like to know is if putting the brake caliper in front of the axle vs. behind the axle would have any effect on either pushing the axle towards the ground or trying to lift it up off the ground when the brakes are applied.

If it's in front the rotor will be traveling downward and would tend to pull the caliper down when the pads make contact (and vice versa if the caliper was behind the axle). BUT.... does this have any affect at the end of the day on whether the axle gets pushed either up or down when the brakes are applied?

I've noticed that front brake calipers are almost always behind the axle (or spindle centerline) while the location of the rear calipers varies from car to car.

i dont know the answer to your main question (i'm going to guess no it doesn't. I see it in my head but cant describe it so its just a guess)

BUT

I do know that they are positioned wher they are for packaging reasons. Packaging the hub/knuckle (extender on dualies) and such can be trickey, especailly with IFS, routing brake lines and providing maximum cooling. Even though wind tunnel testing for that area is crappy and unreliable at best, some conculsions can be drawn.

Offhand, I can’t think of any real effect, and I can tell you that some cars have them changing front to rear depending on the side of the car

Not really sure about the rear's but RaceCar Engineering had a write up earlier this year about the effects of placing them either in front of or behind the axle center line on the front and what it does to steering inputs.

I'll have to go back and see if I can find it, I don't want to quote something with out having it infront of me. I know they never really got into what if anything it does as far as braking goes.

my boss is back in the office-
i'll ask him by the end of the day if i get finished with the stuff i'm doin right now:rolleyes:

Originally posted by Damon
This is a rather odd question but what I'd like to know is if putting the brake caliper in front of the axle vs. behind the axle would have any effect on either pushing the axle towards the ground or trying to lift it up off the ground when the brakes are applied.

If it's in front the rotor will be traveling downward and would tend to pull the caliper down when the pads make contact (and vice versa if the caliper was behind the axle). BUT.... does this have any affect at the end of the day on whether the axle gets pushed either up or down when the brakes are applied?

I've noticed that front brake calipers are almost always behind the axle (or spindle centerline) while the location of the rear calipers varies from car to car.

No effect, IMO. The caliper's reaction into the knuckle (or rear axle housing) is a torque which tries to rotate the knuckle in the direction the vehicle is going. It doesn't matter where the caliper is located.

Front caliper placement is most generally opposite the steering arm: front steer has rear caliper and rear steer has front caliper...usually. IMO, steering geometry gets precidence over caliper placement.

Recently some F1 cars have used bottom (6 o'clock) placement to lower the CG a tiny bit more. That probably complicates the brake line routing.

Winston Cup cars are generally front-steer cars (steering linkage ahead of center) with rear placed calipers, but you might notice some front calipers on road courses. I'm not sure why, except rear steer may allow larger brake ducts directing air to the center of the rotor for cooling.

Rear caliper placement on a torque arm or link suspension is generally rear, again for packaging.

1LEThumper: I couldn't find the RaceCar Engineering article. If you find it, please tell us.

My $.02

I vote for no differerence. I can't see why it would make a difference and there seems to be both setups on all different types of cars.

Rich Krause

also take into concideration brake fluid, and how it enters/exits in the caliper...

I agree that it probably doesn't matter whether the caliper is in front or back of the axle centerline, but given a choice, since the front caliper is also usually relatively heavy, putting it behind the axle centerline moves that weight towards the center of the car.

Most modern performance cars also locate the front calipers behind the axle centerline because the steering knuckle is located in front, as was mentioned. Here's a web page showing some of the larger brake ducts available for the 3rd gen. RX-7, which has a rear-mounted front caliper and front steering links.

http://reganrotaryracing.tripod.com/cwcbrak.htm

In the rear, it depends on the design of the rear suspension, as OldSStroker stated. The 3rd gen. RX-7 has a rear-mounted rear caliper, because there is a toe-link mounted in front of the rear knuckle. The C5/Z06 Corvette, on the other hand, has a front mounted rear caliper. Neither has any problem with handling or braking performance. :)

http://www.cmeglow.com/daydave/sidevent1.jpg

Originally posted by jimlab
I agree that it probably doesn't matter whether the caliper is in front or back of the axle centerline, but given a choice, since the front caliper is also usually relatively heavy, putting it behind the axle centerline moves that weight towards the center of the car.

The C5/Z06 Corvette, on the other hand, has a front mounted rear caliper. Neither has any problem with handling or braking performance. :)




The knuckles on C5 are the same front and rear, but swapped side to side (RF = LR). Therefore the toe links (like tie rods) on the rear are behind the axle centerline.

I also agree with OldSStroker. It's a torque effect, so it makes no difference to the vehicle dynamics. Some endurance racer have both front and rear cals. on the front disc.

From the May 2003 edition

"This month we move on to wheel intertial forces, because the distribution of the wheel assembly's mass, relative to the steer-axis, has significant influence on the steering.

During cornering there are centrifugal forces acting on both front wheels and on the steering linkage.
If the wheel and steering linkages centre-of-gravity's are in front of the steer-axis , due to say, heavy front mounted brake calipers and front mounted steer-arms and rack and pinion, then the centrifugal forces act to turn the steering towards straight ahead-there is an increased self centring effect. With the CG's behind the steer axis there is a de-centring effect. Brake calipers are often mounted behind the wheel axle to minimise the load on the wheel bearings during braking. The de-centring effect of rear mounted calipers can be counted by the self-centring effect of a front mounted steering linkage. We Can estimate the size of these torque:
Tcg=Fcg*Lcg(Nm)
Where
Tcg=torque about the steer axis due to the inertial force of the wheels assembly
Fcg=inertial force at the CG
Lcg=length of the CG lever-arm"



It goes on for a few more pages about control arm placement, wheel offset...so on and so forth. There is also a lead up article in the issue before this one.

Originally posted by 1LEThumper
From the May 2003 edition

"This month we move on to wheel intertial forces, because the distribution of the wheel assembly's mass, relative to the steer-axis, has significant influence on the steering.

During cornering there are centrifugal forces acting on both front wheels and on the steering linkage.
If the wheel and steering linkages centre-of-gravity's are in front of the steer-axis , due to say, heavy front mounted brake calipers and front mounted steer-arms and rack and pinion, then the centrifugal forces act to turn the steering towards straight ahead-there is an increased self centring effect. With the CG's behind the steer axis there is a de-centring effect. Brake calipers are often mounted behind the wheel axle to minimise the load on the wheel bearings during braking. The de-centring effect of rear mounted calipers can be counted by the self-centring effect of a front mounted steering linkage. We Can estimate the size of these torque:
Tcg=Fcg*Lcg(Nm)
Where
Tcg=torque about the steer axis due to the inertial force of the wheels assembly
Fcg=inertial force at the CG
Lcg=length of the CG lever-arm"



It goes on for a few more pages about control arm placement, wheel offset...so on and so forth. There is also a lead up article in the issue before this one.

Thanks Thumper. It looks like these are lateral forces only, not vertical.

With steering arms and rack attached within a few inches vertically of the axle centerline, calipers and steering bits try to occupy the same spaces. On high-mounted steering arms and racks (open wheel cars, eg. F1 and some FWD) this is more practical than on double wishbone suspensions like C5.

New RaceCar Engrg. has neat article about tyre temp effects not usually looked at. Their cover car, Bentley LM is timely.

Thanks guys, I always wondered about that.