Adjutable Pedal Ratio

[Funky Town]

I'm designing the pedal assembly for a first time car and I have a question about brake pedal ratios. I designed the brakes system for our car and due to uncertainties in the tire COF and brake pad COF came up with a range of pedal ratios. For our car we are going to need a ratio somewhere between 4 and 8 (I realize 8 is ridiculously high).

My question is this, why havent I seen any teams with adjustable brake pedal ratios? It seems that you would want some adjustability there so that you can tune the feel of the pedal. Do most teams just make the pedal long enough so that you can vary where you put your foot on the pedal and that's how you adjust for a comfortable ratio. Or should I just pick a ratio from the ratio tree and go with that?

Any advice would be appreciated. Thanks.

[Funky Town]

I'm designing the pedal assembly for a first time car and I have a question about brake pedal ratios. I designed the brakes system for our car and due to uncertainties in the tire COF and brake pad COF came up with a range of pedal ratios. For our car we are going to need a ratio somewhere between 4 and 8 (I realize 8 is ridiculously high).

My question is this, why havent I seen any teams with adjustable brake pedal ratios? It seems that you would want some adjustability there so that you can tune the feel of the pedal. Do most teams just make the pedal long enough so that you can vary where you put your foot on the pedal and that's how you adjust for a comfortable ratio. Or should I just pick a ratio from the ratio tree and go with that?

Any advice would be appreciated. Thanks.

[B Hise]

You will very likely not get any good use of testing time changing pedal ratios. I think ours is somewhere around 4 and has decent feel. Its not too hard to lock up the brakes but you can get a good amount of modulation too. Of course since you may not have the same MCs, calipers, pads, rotors and tires as we do, my ratio doesn't mean a whole lot.

Anyway, pick something reasonable, and spend your time testing things that make the car go faster. Changing pedal feel may yield marginal gains in driver comfort however your time is better spent elsewhere on the car. Besides, an adjustable brake pedal is probably heavier than a set one http://fsae.com/groupee_common/emoticons/icon_wink.gif


- Bryan

[Tony K]

Agreed; adjustable pedals is an interesting concept, but implementing a reliable design would take quite a bit of time that could be well spent somewhere else. The pedal box in our '06 car is adjustable (not in motion ratio, but in position) and it's overly complicated and doesn't work very well. We've also never felt the need to adjust it, so we're removing it in favor of a fixed, less complicated design that should work better. Unless you have a ton of free time and have everything on the car working well in the first place I wouldn't bother.

[Brian Evans]

In the real world, you design the pedal for optimum leverage to the MC pushrod, a useful pivot location for your chassis connection point, and a comfortable position to activate the pedal with driver's foot. You pick a leverage ratio such that you are in a range of available MC bore sizes to produce the pressure that you want. Then, you vary system leverage by swapping out the MC if required, since that is usually very simple to do. Then, you produce your production cars based on the testing that you do with the pre-production prototype.

Brian

[Homemade WRX]

if you don't have pad options and are worried about locking up, you can still change out th mastercylinder to increase line pressure.