Fixed vs floating calipers

[JHZR2]

Hi,

Can anyone walk me through what the actual practical differences are for fixed vs floating brake calipers?

For example, BMW 135i has six piston fixed calipers, the M3 has two piston floating calipers.

What are the practical differences in terms of performance, feel, wear, etc?

Thanks!

 

[XS650]

This will save me a lot of typing

http://en.wikipedia.org/wiki/Disc_brake

Short version, fixed calipers have pistons on both sides of the disk, floating calipers have pistons on one side of the disk and the caliper slides to apply pressure to both sides of the disk.

Floating calipers have more sticking problems resulting in pad pressure being applied unequally to the two side of the disk. Kept in good condition they work OK.

 

[willix]

W/fixed calipers you have mutiple pistons form both sides of the caliper clamping the pads, a huge plus. Maintenance can be a costly nightmare.

Floaters will last the life of the car if maintained and the only issues might be pads.

 

[willix]

W/fixed calipers you have mutiple pistons form both sides of the caliper clamping the pads, a huge plus. Maintenance can be a costly nightmare. With cooling proper a high level of performance exists.

Floaters will last the life of the car if inspected/maintained and the only issues might be pads. Far lower tolerance to disapate heat. A low threshold for repeated max braking.

 

[eljefino]

You could probably make single piston floaters feel pretty darn good with an appropriate premium lining, well adjusted rear drums, and the proper amount of power boost.

I wonder if these fancy brakes in the American near luxury market are the next 19" tire... great on the test drive, then so expensive at maintenance time the cheapest possible solution is chosen.

 

[440Magnum]

Originally Posted By: XS650

Floating calipers have more sticking problems resulting in pad pressure being applied unequally to the two side of the disk.


Correct, although in at least 500k miles of driving cars with simple factory-issue Kelsey-hayes floating calipers, I've had exactly one case of uneven pad wear. One. There's sorta an advertising war going on right now about who makes calipers with the most pistons, and the "tuner" crowd is buying it. More may be better, but if it's only 1% better and costs 60% more... its not really better is it?

 

[sciphi]

Most common cars have floating single-piston calipers. They work for most of the motoring public. Some even stop the car pretty darn short.

 

[JHZR2]

So is it safe to say that in theory at least, a fixed caliper will perform better due to the ability to provide more, more consistent clamping force, at least until the pistons start to get seized in the bores or something similar occurs?

Why is maintenance a costly nightmare, because anything that goes wrong requires a rebuild of the entire unit? I'd think this would be the case regardless with calipers though... is it just the hassle/labor of doing multiple pistons?

 

[mechanicx]

I think fixed calipers can be more picky about rotor imperfections.

 

[XS650]

Originally Posted By: sciphi
Most common cars have floating single-piston calipers. They work for most of the motoring public. Some even stop the car pretty darn short.


Drum brakes were good enough for most people.

 

[expat]

Originally Posted By: XS650
Originally Posted By: sciphi
Most common cars have floating single-piston calipers. They work for most of the motoring public. Some even stop the car pretty darn short.


Drum brakes were good enough for most people.


When? In 1950?

 

[rcy]

Originally Posted By: expat
Originally Posted By: XS650
Originally Posted By: sciphi
Most common cars have floating single-piston calipers. They work for most of the motoring public. Some even stop the car pretty darn short.


Drum brakes were good enough for most people.


When? In 1950?


+1. Is the key word here 'WERE'?

 

[SteveSRT8]

Nothing wrong with drum brakes.

Discs are cheaper to make.

Calipers are another story. Many people with fixed multi piston designs have issues with corrosion damage in the Salt Belt areas.

Sliders also can stick or 'cock and lock' in extreme examples, but it is usually a complete lack of lubrication of the sliding points.

And not all multi piston designs are fixed mount. My newer fleet vans have dual pistons front and rear, but they're still sliders.

 

[bruno]

As far as I'm concerned they were a poor imitation of brakes .

 

[d00df00d]

Originally Posted By: SteveSRT8
Nothing wrong with drum brakes.

They handle heat poorly and are a PITA to maintain.

 

[JHZR2]

Originally Posted By: SteveSRT8

And not all multi piston designs are fixed mount. My newer fleet vans have dual pistons front and rear, but they're still sliders.


Our 94 Previa has dual piston front sliding calipers. One piston seized in the bore and we didn't know it until we did the pads. No abnormal wear, just couldn't get one of the pistons back in...

 

[mechtech2]

A good fixed caliper has the potential to be the best system.

They are way more complicated and expensive. Pad retraction can be a problem either with, as can longer travel for brake inception.

Repairing or replacing? Hah!

 

[MCompact]

I loved the fixed front calipers on my E24 M6- especially when I needed to change pads between track sessions.

 

[440Magnum]

Originally Posted By: XS650
Originally Posted By: sciphi
Most common cars have floating single-piston calipers. They work for most of the motoring public. Some even stop the car pretty darn short.


Drum brakes were good enough for most people.


Yes, but you can actually tell a big difference from behind the wheel between drum and disk brakes. 3 panic stops in a row and even the very best drum brakes would be starting to fade badly, and even mediocre disks would be hanging in there. I don't think any driver could tell whether a car has fixed or floating calipers just by driving it. When everything's working right there's just not a noticeable performance difference. Bigger rotors, or vented vs. non-vented rotors makes a bigger difference than the caliper type.