In Board--or Out?

[jack]

just wondering how many teams have/are running outboard rear brakes? why is in board better than out (other than weight) or vice versa. how about front brakes? just want to know what you people think.

JACK
www.etec.wwu.edu

[Sleeque]

Either inboard or outboard brakes work okay, but the arguments in my book for a single inboard brake is as follows.
1. Weight and packaging. It is a fairly simple matter to put a single disk on the opposite end of the differential carrier but you must use a locking or locked differential.
2. Inboard reacts the brake loads directly into the chassis, outboard requires the brake torque to be passed into the chassis structure via radius arms or the A arms.
3. Reduction in spng weight. When the rotor and caliper is moving with the wheel, that weight must be controlled and damped.

I hope this helps
Slan Leat

Sleeque

[Brent Howard]

We run a 4 brake system because it provides even braking and the judges like it. We had a 3 brake inboard system before and they didn't like ti too much so we switched. I'd go with the 4 brake system over teh 2 front/ 1 rear set-up simply because the judges like it.

Brent

www.ucalgary.ca/fsae

[Marshall]

We simply found that 4 brakes was a complete waste for our car. The rear brakes do so little that we found that the diff generated as much heat as the rotor. Putting something on the car because "the judges like it" is not the way to win. The way to win is to prove to the judges that you made the right decision.

Marshall McLean
University of Western Ontario

UWO FSAE Racing Team
Western Ontario Sports Car Association

[Charlie]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Brent Howard:
I'd go with the 4 brake system over teh 2 front/ 1 rear set-up simply because the judges like it.
<HR></BLOCKQUOTE>

Wow. First, I seriously doubt that the judges would prefer outboard to inboard, unless you run an open diff? Were there any cars in the design finals with outboard rear brakes? I'd be suprised. Secondly, the judges sure don't like it if you do something without knowing why. We've resisted judges opinions before, and from my experience they are usually right. But you've got to understand why they are right or else you are just lost.

-Charlie Ping
Auburn University FSAE 1999-present

[Scott Wordley]

Charlie,

Brent never mentioned anything about outboard brakes. Its possible to have dual inborad brakes at the rear.

Regards,

Scott Wordley & Roan Lyddy Meaney
Monash FSAE Wingmen
http://www-personal.monash.edu.au/~fsae

[Charlie]

Good point. You may very well be correct, however I would still infer from his post that he meant outboard.

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR> We had a 3 brake inboard system before and they didn't like ti too much so we switched. <HR></BLOCKQUOTE>

-Charlie Ping
Auburn University FSAE 1999-present

[Superfumi]

Knowbody said anything about inboard rear brakes stressing the driveshafts? Torque from outboard brakes would be reacted at the tire-road interface (ie is not reacted through driveshafts)

[Schumi_Jr]

Aren't your driveshafts designed to be stressed?? If you have enough torque at your engine, you can theoretically produce more torsional stress in you driveshafts in acceleration than breaking (wheel loads). I see no real argument for outboard rear brakes in FSAE...

Aaron Johnston
University of Waterloo FSAE

www.eng.uwaterloo.ca/~fsae

[Mark Ortiz]

I think the usual choice of a Zexel-type diff for FSAE is sound, but just as a point of discussion, a single brake works fine with an open diff. In fact, it works most like well-matched individual brakes when the diff is open. Or at least that's true as long as neither wheel locks. If one wheel locks, we can add more braking force on the other wheel with individual brakes, whereas with a single brake through an open diff, the rolling wheel is limited to the torque of the locked one.

This is largely academic, because if one wheel locks, we probably want to release the brakes anyway, to avoid flat-spotting the tire.

Frictionally connecting the two wheels is good in terms of avoiding flat-spotting. One penalty is that the diff locking force tries to resist attempts to turn the car. This tends to add understeer on turn-in if we are braking, which is probably undesirable for autocross, though it might actually improve trail-braking behavior on an oval or a road course.

In practice, single rear brakes acting through Zexels seem to work just fine.