Pedal Ratios and Brake Pressures

[RaID]

What pedal ratio especially for the brake pedal are you guys using? and what force at the pedal are the brakes designed to lock up?
Carroll Smith recommends a ratio of 3, Fred Puhn reckons 5
yet in examples even uses 10
What are other formulas using? (Formula ford, F3000 etc)

What pressure in your hydraulic systems do your systems need to lock up your front and rear wheels? Just wanna see if my figures are in the ball park

from my calculations at the moment
the Front needs = 4430 Kpa ~ 640 Psi
the Rear needs = 6900 Kpa ~ 1000 Psi

cheers

[Mi_Ko]

We had a pedal ratio set to aprox. 3.5:1 with two 0.75 bore master cilinders and 4 ordinary 125cc motorcycle calipers on 250mm discs, but with crap brake lines (much to flexible)

We did the brake test without any problems, but with moderate load on the pedal. For one braking this isn't any problem, but for the enduro I would reccomend you a bigger pedal ratio. It depends on you, how do you like the brake. Some drivers want to put all their weight on the brake, others want to brake with the movement of the pedal.

Willwood recommends to design the pedall assembly with a ratio of 6.

[Hoosier Daddy]

We are running ratio of approx 5:1

With line pressures of ~790 psi...

It just so happens that our CG and calipers work out for this.

[Dr. Bob Woods]

My textbook "Modeling and Simulation of Dynamic Systems" from Prentice Hall has a complete analysis of the brake system of a FSAE car. It includes all of the parameters you have asked about.

[Alejandro]

Raid.

why your rear pressure is higher than the front?

[Denny Trimble]

Single rear brake, perhaps.

Or 10/90 weight distribution http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Alejandro]

Besides the dragster weight distribution that mentioned denny, in a Formula SAE car with 500 lbs, center of gravity 30cms of the ground and 3 calipers, normally requires less or very similar brake pressure to lock the rear wheels and the front. With 400psi more than the front I think that you are using a too small caliper at the rear..or to big at the front.

[RaID]

Thanks for the responses

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Alejandro:
Besides the dragster weight distribution that mentioned denny, in a Formula SAE car with 500 lbs, center of gravity 30cms of the ground and 3 calipers, normally requires less or very similar brake pressure to lock the rear wheels and the front. With 400psi more than the front I think that you are using a too small caliper at the rear..or to big at the front. <HR></BLOCKQUOTE>

There are 4 piston calipers at the front running on a 10" discs and 2 inboard 2 piston floating calipers on 6" discs (cant make these bigger).
The rear calipers are much smaller they have 42% piston area of the front calipers

The car has 45:55 weight distribution
this changes to 68:32 under maximum deceleration

the difference in front and rear pressure is due to the much smaller disc in rear, plus the rear calipers being much smaller
we havent locked in the rear calipers in yet so.

We chose relatively much bigger front calipers this year due to overheatin problems in 03 car.