Floating vs. Fixed Brake Calipers Explained

What is the difference in how they clamp?

A fixed caliper is bolted rigidly to the steering knuckle and has pistons on both sides of the rotor. When you press the pedal, pistons on each side push their pad toward the rotor at the same time.

A floating (or sliding) caliper has a piston on one side only, usually the inner side. The caliper body rides on slide pins. When the piston pushes the inner pad against the rotor, the reaction pulls the whole caliper the other way and draws the outer pad into the rotor. The result is clamping from both sides, but only one side has a piston.

Why do sliding calipers seize?

The design depends on the caliper being able to slide freely. The slide pins sit in rubber boots with a thin layer of high-temperature grease. If a boot tears, or the grease dries out, moisture and road salt can corrode the pin until it sticks.

• Uneven pad wear: one pad wears faster than the other, often the inner one, or one end of a pad wears more than the other.
• Pulling: a caliper that sticks on one wheel means the two sides no longer brake equally, which can make the car pull to one side under braking.
• Heat and smell: a caliper that does not release fully keeps the pads touching the rotor, which makes heat, sometimes a burning smell, and a wheel that is hotter than the others after a drive.

Do more pistons mean better brakes?

Not automatically. Fixed calipers often have two, four or more pistons, which can spread pressure more evenly across a larger pad and make the caliper stiffer. That can help on heavy or high-performance cars that brake hard repeatedly.

But braking power depends on the whole system: piston size, hydraulic pressure from the master cylinder, pad material, rotor size, and above all the tires. A well-built single-piston floating caliper is entirely adequate for the weight and speed of the car it was designed for. A piston count on a spec sheet describes the caliper, not the stopping ability of the car.

What does your car most likely have?

Most everyday passenger cars use floating calipers on the front, and many use them on the rear as well. Fixed calipers are more common on performance models and some heavier vehicles, although designs vary widely, so the surest way to know is to ask a technician or check the service information for your vehicle.

During a brake inspection, a technician checks pad thickness, rotors, fluid and calipers, including whether a sliding caliper moves freely. If your car pulls, runs hot at one wheel or shows uneven pad wear, that check is the place to start.