This may be a bit off topic, but I just got through reading a few brake related threads on the front page which lead me to ask a question to those of you out there more knowledgable than I:

What is the advantage in going to a brake system with:

- More pistons?

- Larger diameter rotors?

To the best that I can imagine, I can see a few benefits, but I am looking for someone to check my thinking.

In particular, someone mentioned single piston 11 inch rotors versus dual piston 12 inch rotors, which made me think. I suppose, by my thinking one of the advantages of dual piston brakes is force distribution. Clamping force is distributed more evenly across the face of the pad as it contacts the rotor. Another advantage, as with differentially sized pistons, is more mechanical advantage provided by the difference in piston diameters in the hydraulic system, as well as an even better brake force distribution.

I have already expressed my thoughts on larger diameter rotors, and my belief that at least from what I have read (Wilwood's site, for example) the diameter of a rotor is a factor because of the mechanical advantage clamping farther from the axis provides. Can anyone verify this to be true or false?

Also, if more pistons allow you to, by way of force multiplication, apply more clamping force to the rotor, would this not decrease braking distance? I fully realize that a braking system is dependent on cooling, mainly, to minimize stopping distance, but from high school physics class we all know one thing about friction: the force of friction acting between to surfaces is determined by the coefficient of friction and the Normal force applied. To put it simply: the harder you clamp, the more friction you are generating, given the same brake pads, etc.

Am I incorrect in any of my thinking?

 

I don't think anything's wrong with your thinking. A couple other things to toss into the mix...

Tires. You probably factored this in already, but I usually get a twitch when someone mentions "braking distance" in one of these threads. Your tires are going to limit your braking distance, for the same frictional reasons you attribute to brakes. The issue with bigger brakes is the ability to create the same ability to transfer the energy of your car flying down toward that turn into heat dissipation, over and over again, not just a one-shot braking distance measure. How late you brake *should* be dependent on the weight of the car, how fast you're going, and the tires you use, and not on how much brake fade you're expecting to have.

The other item is rotor size as a heat sink, in addition to the leverage gained by having the caliper further away from the center. Back to the same energy transfer discussion, I just didn't see it in your notes above.

Dave

 

Yes, thank you. Those are excellent additions I neglected to mention.

 

when i was at university i worked on the fsae project (formula car) and part of my responsiblities on the car was the front suspension and braking for the whole car

the pad size has alot to do with the braking systems "strength" which depends the inner and outer radiuses, but also the start and finish angle of the pad. ie: the arc length of the pad is small, it would have a smaller surface area to contact the brake disk when compared to one with a larger arc length

the way that the dual piston vs. a single piston deals with the surface area of the pistions so that more force could be applied to the brakes by the hydraulic system.

i made an excel sheet that has a small picture of what i'm talking about and used to when it came to sizing the disks, master cylinders and so on


http://www.geocities.com/uofwfsae_2002/index2.html (website for car)