Brake Caliper positioning and WHY? What's best?

SO Ive had this thought for a bit and after watching the 'fastest cars' video posted on here it got me thinking (it was actually a segment of video showing the new NASCAR car that made me think of it) - why do car manufacturers put their calipers where they do and what's 'best'?

 So, let me explain the question a bit more. If we look at, say, the SW20 MR2, the calipers are mounted around the (front) 2 oclock position and (rear) 10 oclock position. Both inside the wheels, I'd assume that keeps mass centralized. 

But then on some Porsches (just for example) we see that it's similar, but now the rear caliper is mounted around 7ish and the front around 9

On some Mercedes it's got them, basically, the same location, on the 'back' side (from the front of car) of the wheel

New NASCAR chassis?  Both on the 'front' side of the wheels

Im using some quick, easy examples, all from world class engineers, but Im curious if one is better or why they would choose one position over the other etc?

I can see the benefit of having things 'inward' for weight centralization, but, obviously, these engineers have a reason for monting on the 'outside' or even, using porsche, more 'under-slung'

Im just curious. It's an exam day here at the school, I have none to give today, Im getting things caught up and thinking about, maybe, trivial automotive questions.

Cheers, God bless, and Merry Christmas

I think the priority is clearing suspension and steering parts, whether the tie rods are in front or behind the center of the wheel, couldn't find a pic of the NASCAR's steering setup but I'd guess it's rear steer.

Then there's the Mazda DPi which had it bottom mounted, which I imagine is tricky to bleed.

Bottom is very tricky to bleed!

There are chassis dynamics reasons to have it rear mounted on the front. I forget exactly what, but it makes a difference for steering feel reasons.  Some manufacturers feel strongly enough about it to package it there even on rear steer applications.

In theory: CG location

In practice: packaging 

Pete. (l33t FS) said:

Bottom is very tricky to bleed!

There are chassis dynamics reasons to have it rear mounted on the front. I forget exactly what, but it makes a difference for steering feel reasons.  Some manufacturers feel strongly enough about it to package it there even on rear steer applications.

Yup, my BMW is rear steer and has the front calipers on the rear of the knuckles.  Rear calipers are to the rear as well.  My Jeep has calipers on the rear of the front knuckles, but that's front steer.  Rear calipers on that are also to the rear. 

The first time I did the brakes on my exes 2008 Hyundai Elantra I was very surprised to find that on this FWD rear-steer economy car they had taken the time to engineer rear mounted calipers on the front axle. First time I had ever seen that.

Rear steer?

hybridmomentspass said:

Rear steer?

Steers from the back side of the knuckles.  Compared to front steer that steers from the front side of the knuckles. 

Pete. (l33t FS) said:

Bottom is very tricky to bleed!

There are chassis dynamics reasons to have it rear mounted on the front. I forget exactly what, but it makes a difference for steering feel reasons.  Some manufacturers feel strongly enough about it to package it there even on rear steer applications.

I just assumed they were bench bled with quick-connects (or vacuum bled) like when you see endurance racers change the friction disc and caliper with new pads, because it's easier to change the caliper with new pads than to change the pads in the calipers. 

rslifkin said:

hybridmomentspass said:

Rear steer?

Steers from the back side of the knuckles.  Compared to front steer that steers from the front side of the knuckles. 

Thank you, sir, never heard that before and when it was first mentioned I was thinking the ATESSA system Nissan had on the 300ZX or something ha

Does torquing of the knuckle come in to play at all? Depending on the knuckle/control arm design I could see one position or another being prone to trying to rotate the entire knuckle forward/backward/upward/downward on hard braking?

therieldeal said:

The first time I did the brakes on my exes 2008 Hyundai Elantra I was very surprised to find that on this FWD rear-steer economy car they had taken the time to engineer rear mounted calipers on the front axle. First time I had ever seen that.

First generation RX-7s are like that. The lower bolt is behind the steering arm, so you need to either loosen the bolt with a box wrench, take it out the rest of the way with an open end, and loosen the wheel bearings so you can move the rotor out to get the last couple turns, then shorten that bolt for next time, or unbolt the steering arm from the strut and work with the upright flopping around.

The strut housings are symmetrical, the caliper mounting plate bolts to it, so the only reason to do it this way is for steering feel.

I was amused and appreciative when I saw that Hyundai started rear mounting their calipers. I wonder if this came after they sniped a BMW head engineerin' guy from M.

Isn't there some random cheap car that had just 1 front caliper design so it was leading on one side and trailing on the other? Or was that a rear caliper?

In reply to Javelin (Forum Supporter) :

A bunch of trucks do it that way in the rear. So did some 70s/80s GMs with integrated parking brakes, same caliper on each side.

From a weight distribution perspective, you want them somewhere between all the way at the bottom (lowest center of mass for the car) and at the 90 degree position towards the center of the car (lowest moment of polar inertia).  If you look at pictures of F1 cars, they're all in that 90 degree arc somewhere.

Street cars it's all about tradeoffs between packaging, performance, and cost.

You can do a single caliper design if you put bleed screws at both ends, lots of Wilwood calipers work this way.  Putting one in front and one behind sounds like trying to use a single rear spindle casting for both sides.

In reply to codrus (Forum Supporter) :

Many multipiston calipers have staggered piston sizes, the leading pistons are smaller than the trailing.  This is to counteract the tendency for the pads to nose in on the leading edge.

For sure all 6 piston calipers are. A lot of OEM 4 piston are, too. A lot of the older Japanese ones aren't but I am fairly sure that Brembo only makes staggered calipers.  Wilwood will make them staggered or symmetrical, whatever you want.  But it is important to know what you have because they are technically directional.

That is for fixed calipers. There may be staggered bore sliding calipers out there, but if there are then I am unaware.  The sliding aspect should make the bore stagger unimportant.

Javelin (Forum Supporter) said:

Isn't there some random cheap car that had just 1 front caliper design so it was leading on one side and trailing on the other? Or was that a rear caliper?

I know on 3rdgen fbodies the first design of rear disc brakes did that. One caliper; forward on one side; rearward on the other.

Pete. (l33t FS) said:

Many multipiston calipers have staggered piston sizes, the leading pistons are smaller than the trailing.  This is to counteract the tendency for the pads to nose in on the leading edge.

For sure all 6 piston calipers are. A lot of OEM 4 piston are, too. A lot of the older Japanese ones aren't but I am fairly sure that Brembo only makes staggered calipers.  Wilwood will make them staggered or symmetrical, whatever you want.  But it is important to know what you have because they are technically directional.

FWIW the (aftermarket) 4-piston Brembos on my M3 are non-staggered.

But yes.  The unstated assumption was that anywhere that people were sufficiently concerned with cost to go asymmetric in order to reduce manufacturing costs by eliminating a casting would be using single piston calipers. :)

Symmetrical Brembos? Neat! 

All four calipers on my Volvo are different part numbers.  I had thought of getting the small rear caliper setup for the front of a small car until I saw how tiny the pistons were.  The calipers are about the size of my Wilwoods but the smaller bore of the set has to be about an inch in diameter.

One of the guys I raced against mounted another pair of calipers on the front side of the disc, leaving the stock one mounted on the back side.  I was never sure what he was trying to accomplish with double the pad area........aside from a lower pedal, of course.

I recall someone asking Marlan Davis this question in the Hot Rod tech advice segment and he asked around with a bunch of different chassis engineers and they all had their reasons (those escape me right now) for where they placed them but also all of them admitted that they weren't certain at all that it really even mattered or had any effect.

wspohn said:

One of the guys I raced against mounted another pair of calipers on the front side of the disc, leaving the stock one mounted on the back side.  I was never sure what he was trying to accomplish with double the pad area........aside from a lower pedal, of course.

If it's on the back, sometimes people do this to retain a parking brake.

In reply to wspohn :

Pulled from the Wayback Machine off the old Mazspeed website.

Symmetrical upright, caliper bracket bolts to it, someone did this.

In reply to Pete. (l33t FS) :

Hah! That looks like a classic case of "just because I can."

AngryCorvair (Forum Supporter) said:

In theory: CG location

In practice: packaging 

This.

codrus (Forum Supporter) said:

wspohn said:

One of the guys I raced against mounted another pair of calipers on the front side of the disc, leaving the stock one mounted on the back side.  I was never sure what he was trying to accomplish with double the pad area........aside from a lower pedal, of course.

If it's on the back, sometimes people do this to retain a parking brake.

A lot of new supercars come with a dedicated handbrake caliper like this, often electrically actuated, so the main brake caliper can be a high-powered race unit and you don't have the compromises of a drum-in-disc setup (such as not being able to use 2-piece rotors).

Dual rear calipers are also a common setup on drift cars for a dedicated hydraulic handbrake caliper - you keep the stock caliper with parking brake capability, and add your dedicated drift brake caliper with super-bitey pads.