"Traditionally, cars have had smaller rotors and calipers on the rear than on the front. These days, many production cars, road racers, and autocrossers are using rear brakes that are just as big as the front brakes. While this arrangement isn't necessarily better, in some cases it is more practical. As more efficient caliper designs have become necessary for both safety and performance, calipers with integral parking brakes have begun to lose favor. On a race car, parking brakes aren't necessary, but that's not the case with a street car. A popular alternative to integrating the parking brake mechanism into the caliper is to build a shoe inside the rotor hat, which acts as a drum brake. However, to accommodate the shoe a larger rotor diameter is mandatory. Even though your street machine may not warrant a caliper and pad the same physical size and shape as the front, once the pistons are appropriately sized it's easy to achieve proper brake balance. Other than weight, there is no particular downside to a large diameter rear rotor, and the aesthetics of a brake system is now an important element of design used by hot rod builders and OE manufacturers alike."
Carl Bush: "You should put your priorities in proper order when deciding which rotor may be best for a given application. Sometimes, rotor selection is merely a function of wheel-filling aesthetics, and optimized performance is not the priority. However, for road racing and autocross, we usually prefer to use the biggest front rotors possible within the wheel constraints or rules. Rear rotor size will vary depending on the need for rear cooling capacity and leverage to help maintain optimized front-to-rear bias balance. Another factor to consider is that a lighter rear rotor reduces driveline inertia, which helps with acceleration and deceleration as well."
Todd Gartshore: "Four-piston calipers used to be considered pretty exotic, but now six- and eight-piston calipers are becoming more common. Having lots of pistons looks nice, but there is a point of diminishing returns. It really depends on the job at hand, size limitations, weight, and cost. As the piston count goes up, pedal response time, pedal feel, and ease of modulation are improved. Multiple pistons also afford the opportunity to stagger the bore diameters. On longer pad shapes, staggered bore sizes allow the pressure to be evenly distributed to reduce taper wear across the pad. That said, if you're more concerned with bragging rights than having better control over the pads, you have likely reached the point of diminishing returns in terms of piston count."
"The final determining factor in caliper selection is not necessarily piston count, but overall piston volume. Piston volume determines how much clamping force can be generated based on the amount of hydraulic pressure that is being applied to the pistons, and that volume must be in harmony with the rest of the brake system. Using multiple-piston arrangements is beneficial in terms of how the clamping force load is applied over the length of a pad. As calipers get bigger, and the pads get longer, the benefits of spreading the clamping force out over a longer length of the pad with multiple small pistons become more measurable and justifiable."
Michael Jonas: "The number of pistons inside a caliper doesn't make a lot of difference in performance. What's more important is the size of the pistons. It's like comparing a V-12 Ferrari to a big-block Chevy. The Ferrari motor has more cylinders, but because they're so much smaller than in a big-block Chevy, it won't make as much power. The same thing goes for calipers; you want big pistons. Our Tri-Power three-piston calipers work well because the pistons are very large. The pistons are so large in our Tri-Power calipers that they actually generate more clamping force than many six-piston calipers on the market. While we do offer eight-piston calipers, the reason for this type of arrangement is to maximize the surface area behind the pad for even clamping force distribution. A master cylinder can only handle so much, so there is a limit to the number and size of pistons you can use."
Carl Bush: "Radial mounting is a very secure and accurate way of attaching a caliper. In this type of setup, the mounting bolts run through the top of the caliper instead of the side. The majority of aftermarket radial mount calipers use a bolt-on mounting bracket. The brackets can then be shimmed for perfect lateral alignment over the rotor centerline, and perfect radial height for alignment of the outside radius of the brake pads and the outside radius of the rotor. This is in contrast to only having a lateral plane of adjustment on a conventional lug mount caliper."