FRONT AND REAR BRAKE CALIPER POSTION

For you automotive engineers out there. What determines the placement of the front and rear brake calipers? I notice on the F430 that they are postioned in the 3 0'clock position (front) and the 9 o'clock position (rear). And on a earlier model such as the 355 both front and rear calipers are mounted in the 3 o'clock position. Can someone enlighten me...

 

You can't really use the terminology of the "clock" positions (except for 6 and 12) because it depends which side of the chassis that you are viewing (i.e., a design with a caliper at the 3 o'clock position on the LH front has the RH front caliper at the 9 o'clock position).

The moment of inertia of the chassis about a vertical axis is minimized if the front calipers are placed behind the front axle and the rear calipers are placed in front of the rear axle, but on typical road cars, I'd say it's pretty random (i.e. the choice is more driven by "packaging" or hose routing reasons).

There's also an argument that putting the calipers at the 6 o'clock position on all the wheels lowers the overall cg, but they collect a lot of dirt/debris there and are more exposed.

 

You ar absolutely right about the clock position. thats what I get for not thinking out my question. Time to crack open the physics books again. Is this somewhat of a new theory in regards to the moment of Inertia? I only ask because i see older F-cars with calipers in different locations. Or is that example of convienent packaging?

 

No, it's not a "new" thing -- i.e., the lower the moment of inertia about the vertical axis, the more quickly the chassis can yaw (turn), but on a 3000 lb road car, it really doesn't make enough of a performance difference to worry about and the packaging does play a roll. For example, on a 308, putting the rear calipers in front of the rear axle would make the cabling system for the emergency brake system much more difficult/complex.

Like you, I find it an interesting subject, and with today's open wheel designs I often note the caliper locations on neighboring vehicles -- I'm actually surprised at how many road cars have the front calipers mounted in front of the front axle.

 

If you start with a clean slate designing a race car, you can place components to achieve minimal rotational inertia, but yu are still going to compromise because of packaging.

If the rack is in front of the axle, then the caliper will go to the rear, or it will need to be mounted high or low to avoid the steering arm.

With respect to component placement on a serious race car,Carroll Smith once said, "there are no insignificant reductions in CG height". He had been known to rotate the starter 180 degrees so that the starter solenoid was on the bottom of the starter - for a tiny reduction in CG height.

As has been pointed out, changing caliper location on a road car, (if it could be done economically and physically), would have an insignificant change in rotational inertia. It might however make cooling air ducting easier.

chris

 

Thanks to the both of you. I have been trying to increase my ferrari knowledge and paying more attention to the detail that goes into the f-cars. I am sure I'll be back with some questions later.....Thanks again for the lesson