Some multiple-piston calipers (for example, a caliper that features two pistons per side) may feature all four pistons of the same diameter, or two different-size pistons. When piston diameter varies in a caliper, this is referred to as a staggered-piston design. The smaller piston is located at the entry of the disc, while the larger piston is positioned at the exit. As a result, a staggered-piston caliper is directional; it must be mounted so that the disc is grabbed by the smaller piston on its entry through the caliper body, while the larger piston handles the exit point of the disc. Some caliper bodies will feature a stamped or etched indicator of rotor direction (an arrow, the word rotation, etc.) to indicate how the caliper must be mounted. Always position the caliper so the smaller pistons are located toward the rear and the larger pistons are located toward the front. Where the caliper is mounted in a vertical position, remember that as the rotor turns, it should rotate past the smaller piston first, then pass the larger piston. The larger piston always indicates the exit point in terms of rotor rotation.

The reason a multipiston caliper may feature a staggered-piston format is primarily to reduce the chance of taper-wear on the pads, and to maximize braking efficiency in certain applications. As the brakes are applied, the disc enters the caliper body and is acted upon by the pads, which push against the disc under hydraulic pressure. As the pads push against the disc, the point of caliper entry (where the disc first experiences clamping force) starts performing most of the work.

As the disc continues to rotate and leave the pressure point of the first pair of pistons, the exit pistons try to play catch-up. They may experience added demands, since the pads are being pushed by exit heat (the friction between pad and rotor) and possible evacuation of gases created by pad heat. As a result, in some cases where the pads are relatively long and pedal application is heavy, a taper-wear may start to occur at the entry side of the pads (if the entry pistons are more efficient at pushing the pad than the exit pistons). To balance the clamping force, and to keep pad-to-disc pressures constant throughout the travel length, a larger diameter piston may be used at the exit point.

The exit portion of longer pads does sometimes tend to provide less clamping force as compared to the entry portion. The added clamping force pressure afforded by larger diameter pistons addresses this issue. So why do some four-piston calipers feature same-size pistons on both entry and exit areas? Because the caliper maker, through its own research and development, has concluded that this particular caliper (given its size and the length of its pads) does not create a taper-wear problem for its pads, and therefore doesn't need a staggered-piston setup.