Floating Vs Fixed Calipers: Opinions?

First off, I'll say that I understand that there's more to stopping than just calipers. Brake pad material, tires, wheels, rotors, etc all play their part. This is more of a curiosity for me.

So, I've had both floating and fixed calipers on different cars I've owned. On my clapped out beaters, it has always seemed like the fixed calipers offer better stopping. This may be because fixed calipers need less maintenance. I've certainly never had one seize on me. I've had to pry apart, wire wheel, and lube more than one set of floating calipers.

I've been kind of toying with the idea of adapting the Mercedes brakes I have onto my Volvo. I'm wondering how I might compare, side by side, a fixed and floating caliper?

A quick rundown of both:

Volvo Caliper:

• Floating.
• Dual pistons, 40 mm OD.
• 7061.8 mm pad surface area.
• Designed to stop a 3000 lb car with a 375 lb engine.

Mercedes:

• Fixed.
• Dual piston, 60 mm OD.
• 6619.86 mm pad surface area.
• Designed to stop a ~3700 lb car with a ~600-700 lb engine.

Both cars use a vented rotor. The Mercedes uses a 277 mm OD. Volvo uses either a 262 mm or 287 mm rotor, not sure which I have. Both cars appear to use the same master cylinder. They have more or less them same rear calipers/rotors. Both take the same rear pads. The only difference is that the Volvo uses 40 mm pistons in the rear and the Mercedes uses 38 mm.

They use the same master? You sure the piston size inside the master is the same? If so, the Merc caliper is going to have slightly better stopping power (more area), but worse feel (more pedal travel) as more fluid will need to be displaced for a given piston travel.

For calipers with opposing pistons (IE the Mercedes one) you can only use the area of one piston to calculate clamping force. If you have two pistons on the same side then you use the area of both pistons to calculate the clamping force.

If I did my math right the area of one 60mm piston is 12.5% greater than the area of two 40mm pistons. Like Darwin said though it will be 12.5% more clamping force but 12.5% more pedal travel from the pistons. The flip side of the coin is that non-floating calipers tend to be stiffer so you may end up with less flex and compliance compared to the floater.

Total piston area is what effects stopping power(all other variables held equal). If the two pot floater uses the same diameter pistons as the two pot fixed, they will stop the same.

You are correct in the fixed calipers needing less maintenance to perform optimally, they also cost a lot more to make.

also compare rotor widths before going through with this. would suck to get things mocked up and realize the rotor is too wide or narrow for the new calipers. i made that mistake once.

Kenny_McCormic wrote: If the two pot floater uses the same diameter pistons as the two pot fixed, they will stop the same.

As mentioned above... You have to double the area on a floater. If it had the same diameter pistons, it would have double the power.

40mm area = 5026 * 2 pistons * 2 = 20106
60mm area = 11309 * 2 pistons = 22619

60mm fixed = 112% power of the 40mm floater

Kenny_McCormic wrote: If the two pot floater uses the same diameter pistons as the two pot fixed, they will stop the same.

I've seen this posted on a few sites and I don't fully understand the logic.

The floating caliper applies the force through the pistons but the other half of the caliper body reacts this force to prevent the caliper from shooting off into oblivion. This ends up capturing the rotor between the two pads and the forces within the caliper sum to zero (or get close enough).

The fixed caliper does basically the same thing except instead of the opposite side being an immovable part of the caliper body that only reacts the force it is a movable piston. The two pistons create equal but opposite forces just as the floating caliper would since you essentially have a column of fluid/metal. The issue is that you have half the area creating this force so if all else is equal you'd have half the force.

I've always viewed saying "fixed calipers generate twice the force" being like saying "if I push on a wall and generate a 100 lbs force, the wall has to generate an equal but opposite 100 lbs force to keep me from falling, but the force between my palm and the wall is actually 200 lbs".

No?

Sorry, took me a while for that to click. Had to think of it in terms of work and then go back to force.

Assuming you can lock the wheels with both calipers I don't really think it matters other than dialing in your preferred braking effort. Far more important IMO is considering the compliance of each caliper. Fixed will be less compliant and feel better under foot. Swapping between 996 brakes and OEM brakes on my e36 m3 was like night and day in terms of brake feel.

atm92484 wrote:

Kenny_McCormic wrote: If the two pot floater uses the same diameter pistons as the two pot fixed, they will stop the same.

I've seen this posted on a few sites and I don't fully understand the logic.

Distilled down to its simplest without going too simple, it's leverage. Bigger pistons make less pad travel for the same hydraulic fluid travel travel, meaning more leverage.

When you have a sliding caliper, the pistons has to move twice as far because it is moving both pads. In effect, the caliper body itself are the pistons for the other side. The same amount of fluid is moving (twice as much piston travel times half as many pistons) so the leverage is the same.

Make sense now?

...Wait, back up. For the same piston diameter, a 1 pot floater is the same as a 2 pot fixed. A 2 pot floater is the same as a 4 pot fixed.

The one downside of fixed calipers is that if the rotor has any kind of warp or the wheel bearings any kind of slop this small movement can cause the rotor to wobble and push the caliper pistons back into their bores. This can lead to added pedal travel when the brakes are applied after an extended period of no braking. This one of the reasons most OEMs went to floating calipers.

jimbbski wrote: The one downside of fixed calipers is that if the rotor has any kind of warp or the wheel bearings any kind of slop this small movement can cause the rotor to wobble and push the caliper pistons back into their bores. This can lead to added pedal travel when the brakes are applied after an extended period of no braking. This one of the reasons most OEMs went to floating calipers.

Yeah, knock-back is an issue on-track too where cornering loads with slicks cause things to deflect more that typical. If I have to tap the brakes after a long corner to get pedal for the next one it's time to change a wheel bearing ;)

However, I still prefer them to floaties for racing because the slides expand/contract and bind up on those with the extra heat causing twist under braking. Also, most of the floaties require you to unbolt them to swap pads rather than just pulling a pin. It makes a big difference in how you approach a swap when they are 800F.

I've owned a RX-7 TII with 4 piston fixed aluminum calipers and a RX-8 with single piston floating. According to Mazda documentation they both have similar capacity for heat dispersion. My biggest beef with the 4 piston calipers was that the steel bleeders constantly seize and strip. Galvanic corrosion is very annoying. I had the pistons on the RX-7 caliper stick and I had pads would seize on the pins. The RX-8 brakes are great and the car stops the better than any car I've ever driven. In 5.5+ years the RX-8 has had no stripping or seizing to report. Both cars were winter and track driven.

welp i just learned me something today. thanks for the info.

fixed ie opposed-piston calipers require more packaging space outboard of the rotor, which can limit your rim choices -- or at least, it becomes a consideration when selecting rims.