The job of the brake caliper is to exert force on the pads so they in turn may exert a force on the rotors. There are many iteration of how this is accomplished but we will only concern ourselves with the two most common approaches in the DSM world.
Dual piston floating caliper. This is what we all have in the front of our 95-99 DSM. The caliper has two pistons on one side which push on one pad. To incur a force on the other pad the caliper floats on slider pins attached to the axle hub. The result is the rotor is squeezed between the two pads and your car slows down.
Why two pistons? Because two small pistons are better than a single large piston. The reason being for a given rotor size, which is dictated by wheel size and cost, the only way to get a larger pad surface area is to make it longer. This longer pad, if used with a single piston, would not press evenly on the rotor because the back plate of the pad would flex. Using two smaller pistons allows the designers to press more evenly on the back of the pad exerting a more even force. The next step to this is using three pistons, and the extreme is on a NASCAR caliper I saw at SEMA which used six, yes count them SIX pistons per side. More over they are staggered rather than all in line. Another design usually incorporated with multiple piston calipers is differential piston size. The goal here is to further even out the pressure on the pad. This is done because the leading edge of the pad tends to "bite in" harder than the rear causing differential wear, thus a smaller piston is utilized in the front.
Why upgrade? You need to ask? Seriously though what is wrong with our calipers that we want to upgrade. In many cases not that much. That is why the AEM kit isn’t such a bad idea as it allows us to use a larger rotor with the stock calipers. IMO the biggest benefit to most of the "Big Brake" kits out there is just the larger rotor itself. However there are real world advantages to different calipers so lets talk about them shall we.
First the design of floating calipers. The problem here is that with a floating caliper system you tend to get differential pressure on the inboard pads versus the outboard pads. This is obviously bad for braking ability as well as pad wear. This is caused by the stiction of the caliper riding on the slider pins which is worsened if there is any wear on the pins allowing the caliper to go out of alignment during braking.
Next is the possibility that the slider pins can act as little air pistons causing the caliper to push off to one side forcing the pad to rub against the rotor. This will cause the outer pad to wear faster and even cause some brake drag. Not what we want.
The fix to this is using a non-floating dual sided design. This puts pistons on both sides of the caliper two evenly squeeze the pads into the rotor. The caliper it hard mounted to the axle hub preventing the stiction issues. To ensure both sides of the caliper are moving evenly there is a cross-flow tube to allow fluid to move between sides.
Another reason to update is the ability to run a larger pad. All else being equal a larger pad will heat up slower, wear slower, and for the same pressure (not force) exerted by the pad create a larger braking force. In addition most aftermarket calipers have a larger selection of pad choice in both manufacturer and friction material. Choice is always a good thing don’t you think … email that congressperson and let them know you want the right to choose the brake pad you want not what the guber-mint thinks you should run [putting away my AR-15] … sorry sometimes I digress :)
Another benefit you often (but not always) get is a lighter caliper. Though you might think this would reduce your un-sprung weight, a good thing for handling, you more often than not are barely making up for the larger and thus heavier rotor. But that is still a good thing since it is better than the whole system just being heavier right. In addition they often utilize design and materials in the pistons to reduce heat transfer into the fluid thus helping forestall fluid fade.
Finally many calipers have anti-drag mechanisms which retract the pads away from the rotors to prevent dragging when the brakes aren’t being applied, slowing you down, heating up the pads, and causing excess wear.
So what does all this buy you. Pretty much more of the benefits you get from larger rotors and better pads. Namely consistency, total braking effort, resistance to face and better modulatability … I don’t think that is a real word but I’ll be sure to petition Websters to include it in the next unabridged addition :)
So now you know why you want to upgrade the next question is what are your options.
- AEM Stage 2/3 – uses the same rotors as the Stage 1 but incorporates larger 4-pot calipers as well
- BAER 13" kit – this uses a 13" (or 12" for 16"wheels) rotor with the same calipers as the Corvette ZR1 and Mustang Cobra. This is only a 2-pot floating caliper but it does allow for a larger pad. Over all this kit is heavier than stock but not that much so as some parts are lighter while others heavier.
- Various other custom kits made by some vendors like RRE, DSS (similar to the BAER), and a Club Member who knows a guy who is building upgrade kits using Wilwood calipers and rotors. These kits often cost between $1000 to $3000 but are usually well worth it. When you step on the brakes the car will stop, back up, and make the turn for you :)