I am considering buying a Lexus ISF and I was just wondering if the rear brakes are fixed or floating. The website says that it features 2 piston rear aluminum calipers but it doesn’t specify if this is a fixed or floating configuration. Does somebody happen to know? Also, for future reference, do calipers with 2 pistons usually use the fixed or floating design? Are there cars with 2 pistons using the fixed design? Thanks.
I’d be surprised if they were using fixed calipers, which are more complex and costly than floating calipers. I’ve never seen a fixed caliper on a passenger car. Maybe there are some, but I’ve never seen one.
The number of pistons has nothing to do with whether a caliper is fixed or floating. You could, in theory, build either type with single or multiple pistons.
Why does this matter?
Full Moon ?
CSA
For the 2007-up model they are fixed calipers according to Road & Tack
Why care?
FoDaddy, It shows fixed calipers, both front and rear. I’m Only Familiar With Floating Calipers. Please Explain The Advantages And Disadvatages Of Fixed Over Floating Calipers.
When the salt and lack of use has turned my wife’s floating calipers to “fixed” calipers (on former car - our GM cars with stainless steel slides don’t seize), the brake pedal pressure becomes greater, stopping distance increases, all because the inboard pad is completely functional (controlled by the moving piston).
What gives ? Am I confused about the term “floating” ? Do fixed calipers still “slide” as do floating calipers ?
Pistons for both inboard and outboard pads with fixed calipers ?
Thanks,
CSA
Front and rear!
I learn something every day.
The short version is that fixed calipers don’t move relative to the rotor and are less likely to stick. Fixed calipers are also less likely to be affected by dirt or rust. The pads will make contact with the rotor flush, whereas with floating rotor there’s fair chance the pad will make contact at a slight angle sometimes.
Longer version:
Fixed calipers are solidly mounted to the suspension components (typically the steering knuckle). The only moving parts with a fixed caliper are the pistons. Because of this, fixed calipers have pistons on opposing sides of the brake rotor.
When the brake pedal is pressed, fluid enters the caliper, and then is distributed evenly to both sides of the caliper, and an equal amount of force is exerted on each brake pad, which makes brake pad wear nice and even (unless you have a seized piston), and gives very consistent braking feel and performance.
Typically, these calipers have a provision in the top of them that allows you to change the brake pads very quick and easily, normally not requiring removal of the caliper from the mounting bracket. You remove a single retaining clip, punch out the pin that holds the pads in place, squeeze the pistons back into the caliper body, and remove the worn pads. Slide in the new pads, put the retaining pin back in place, and reinstall the retaining clip.
A floating caliper is one that has pistons on one side of the caliper (typically the inside on cars). As the brake pedal is pressed, the active pad is pressed against the rotor, which then pushes the caliper away from the brake rotor. This causes the pad on the other side of the caliper to squeeze against the rotor, in effect, causing both pads to squeeze the rotor. The caliper is able to slide because of sliding pins built into the caliper body and/or the mounting bracket.
Sports cars, or cars with sporting intentions, typically have fixed calipers, and multiple piston setups. Some Toyota trucks, like the Tundra, are being marketed with these brakes up front, in a 4 piston caliper body.
My Porsche Boxster has 4 piston, radially mounted calipers at each tire.
I won’t go into the whole radial mounting of brake components, other than saying that it allows the braking forces to only go into the rotor, as there is not outward flex on a mounting bracket, leading to even more precise braking control.
If you want pictures, let me know.
I can post up pictures of the brakes on my motorcycles, Boxster, and my gf’s Chrysler Crossfire for examples of each type.
Hope this clears things up a bit more.
BC.
Because when you’re spending 70 grand for an insane sports sedan that does 0-60 faster than some Porsches, you care about performance-enhancing goodies like that.
Thanks.
CSA
Thanks.
Good information. For many years I have put brakes on all of our vehicles and have become quite familiar with floating caliper set-ups. Regarding the fixed calipers, I already figured they’d have pistons on both sides. I guess the disadvantages would be more moving parts, more expensive to produce, and more complicated to rebuild.
CSA
Couldn’t have put it better! Well stated!
Great explanation. If it’s not too much trouble pictures would be nice! Thanks
That’s a helluva car you’re looking at. Enjoy it, and get it out on a track at least once for a fun run so you can see what it can really do.
As far as I know, most all recent BMWs use single piston sliding caliper brakes, so the performance advantages of fixed/multi piston brakes is not apparently overwhelming. Some of it comes down to looks/trends.
Like this is going to make a difference?
In what?
Commute times? No.
Lap times? Measured in microseconds. If at all.
Repair costs? Oh, yeah!
Is this a make-or-break decision as far as purchasing the car?
Besides, if the car’s that great, they should tell you whether the brake calipers are fixed or floating.
They don’t because it doesn’t matter.
Thanks for info, BC. First time I’ve seen ‘radial mounted’ applied to car calipers. I see it all the time in motorcycle reviews, alway in connection with ‘upside down’ forks. I don’t understand the ‘radial’ part. While I understand that ‘radial’ mounts could be the stiffest mount for the weight, it would seem that other shapes could be just as stiff, if heavier.
If the pistons are on the same side, the caliper floats. If the pistons are on opposite sides, the caliper may be fixed. Fixed ones (I believe) should have four pistons.
Yes they do. It’s on the IS-F website.
As for lap times, assuming they’re paired with a good set of tires and good pads, they’ll reduce them by more than microseconds because you’ll be able to brake later into the corners. Besides, microseconds per lap often mean the difference between winning and losing. It’s not like in the video games where you get out front and the pack is 2 miles behind by lap 3. If performance brakes don’t matter, then I suppose race cars have them on there just for show.
Does it matter as far as commute times? No. But then you don’t buy an IS-F because you plan to only commute in it.
Regarding repair costs, if you’re dropping 70 grand on a car, you can generally afford to maintain it.