I know pretty much any aftermarket braking system is going to be better than the stock one. I will only be using my car for the street. Is 2 pistons more than adequate or will I see more gains by going with more pistons on the caliper to say 3 or 4?

 

What multiple pistons do is distribute the braking pressure more evenly dispersed onto the backing plate of the brake pad.

As for pressure, A single piston caliper can sometimes have more pressure than a 4 piston caliper if the volume of the piston size is bigger than the equivilant of the 4 smaller ones (not usually the case, but can happen based on size of ppistons used ex: 1.38" pistons as oppsed to 1.75" pistons. Some singles can give diameter up to 3".

A better example is my setup for instance. I have 6 piston Wilwood fronts that have a 1.62"/ 1.12"/ 1.12" pistons on each side. For volume, even though I have 6 pistons, I only measure one side of the caliper for volume (or 3 pistons).

Superlite 4 piston 1.75/1.75= 9.60 sq inches
Superlite 6 piston 1.62/1.12/1.12= 8.04 sq inches
FDL 4 pistons 1.38/1.38= 5.98 sq inches

You can see that the 1.75" 4pot calipers have more brake force than the 6pot's do. Here's the catch- the 6pot allow for a smoother distribution of pressure onto the pad allowing for harder push before they lock- you don't want lock, but you want the hardest pressure on them without locking.

Important fact #2- The other main thing that increases brake force is the size (or surface area) of the actual brake pads. More pad surface will give more stopping power.

#3 Rotor size will increase leverage, thus increase brake force.

#4 Caliper rigidity (or lack of flex) during pressure force is very important also. Bridge bolts going over the center of the caliper eliminate pressure flex and loss of force.

 

#2 Ignoring operating temperatures pad size has nothing to do with stopping power. If it did there would be area in the friction force equation but there isn't. It's just friction coefficient times force. Pad size actually decreases your stopping power with most race pads because they take longer to get up to temp. Conversely, the larger pad will be harder to overheat making it more powerful during heavy braking... more resistant to fade but you should look into a different pad compound if that's the case. The only time I'd consider pad size is for a daily driver. A larger pad will last longer if the compound is the same.
#3 is correct if everything else is equal
#4 is confusing me. What do you mean "loss of force."?

 

He's talking about the force that is trying to spread the caliper. If it doesn't have adequate ribbing in the casting or some other method of increasing rigidity, the caliper can flex and spread, causing decreased pad to rotor force.

Not really loss of force, but the force is acting to spread the caliper, not slow the car down.

 

J Prevost,

I would have to agree with you that most readings I have seen tend to yeild towards pad surface area being a non issue, but most studies will admit also that the findings are inconclusive if pad surface area has affect or is it just piston volume.

I still tend to personally believe that you take lets say 1000lbs force and apply that pressure to the back of 1sq inch and to a pad of 4 sq inhces. you will heat the 1 faster than the 4 of course with 1000lbs per sq inch on the 1 and 250lbs per sq inch on the 4. the 4 has the potential to go to 1000lbs per sq inch yeilding a total of 4000lbs pressure to equate the heat and friction risistance of the 1. There is the potential for much greater friction are with more pedal pressure delivered to the larger surface area pad. Line pressure and bias of course play a major part, but more pad surface area can yeild greater stopping power if adjusted to do so.

Pedal pressures being equal, there is no diference. Yet, if you press the pedal harder, the larger pad surface area will in fact yeild more stopping force where the smaller pad will overheat or just loose that sweet spot feel. The smaller surface area seems to render a smaller temp range curve that a brake setup with a larger pad area

Dean

 

For a street machine, no.

 

yes and no.
It depends on the availibitity of very soft pad compounds for the larger racing calipers. If ones were on the market for street use then this would be a potential issue. Tale a car like a GT2 Porcshe that is pretty much designed a a race car for daily street use and you HAVE to go with the factory compound brake pads they make for it to control noise and low temp pressure.

Hence the reason why when I went to a Wilwood 6 piston setup I looked at a caliper that would retain a smaller pad surface area so heating a pad to get softness for low street noise and bite would have hopefully been a non issue. I am really glad I did not go to a GT caliper with larger surface area because even the samller "superlite" size pad is still giving me a little noise trouble and bitetyness at low temp. they smooth out with a little heat but the alum hubs and hats cool them pretty quickly. I still need a very soft pad - the reason why I am going to try the EBC greens.
I'll say again, I wish Stillen made a pad to fit my SL-6 calipers.

I might even be better suited to drop the large 1.25" rotor down to a 1.10 and shim the calipers so that the rotor will not absorb as much heat for lower temp street use.