Brembo brake caliper or any other made by a respected company is nice to hold in your hands,study it carefully, appreciate the geometric solutions of the engineer, who designed this product.
And that’s the moment when a question arises: why some calipers has pots of same diameter, and others have pots of different diameter?
There is also calipers with pots of the same diameter, but with different distance between them and the contact surface.
Lots of questions – same answer! As always it’s friction force!
To cheer you up, here are some pictures of 4-pot calipers:
Pictures are signed by use on a certain car and pot sizes (in milimeters)
Brembo Audi RS3 Front caliper
Brembo Audi RS3 Front caliper 40 & 44(mm)
Brembo BMW M3 F80 Front caliper
Brembo BMW M3 F80 Front caliper 40 & 40 (mm).
Brembo BMW M3 F80 Rear caliper
Brembo BMW M3 F80 Rear caliper 34&34(mm) offset ~10(mm)
Brembo Porsche 911 Front caliper
Brembo Porsche 911 Front caliper 40&44(mm)
Brembo Porsche Panamera rear caliper
Brembo Porsche Panamera rear caliper 34 & 34 (mm).
The Beauty, 6-pot caliper:
Brembo BMW M5 F10 Front caliper
Brembo BMW M5 F10 Front caliper 30-34-36(mm).
Brembo Nissan GTR Front caliper
Brembo Nissan GTR Front caliper 30-34-36(mm)
Brembo Porsche Cayenne Turbo S 955 Front caliper
Brembo Porsche Cayenne Turbo S 955 Front caliper 32-36-38 (mm)
Brembo Cayenne 958 Turbo Front caliper
Brembo Cayenne 958 Turbo Front caliper 36-36-36(mm)
While looking at those pictures question arises, why on some calipers pins stand out and on some they don’t?
I searched for a long time for an example to give you to help you understand the trick with those “pistons”.
We are all moved around heavy capboards, especially fond of this activity our better halves, though they do it with OUR help!
Imagine we are trying to move a cupboard filled with stuff, that we too lazy to take out, as we don’t need to move this cupboard very far.
Let’s say this cupboard is 2 meters high and we are applying our force about 1 meter from the floor lever.
Normally this cupboard’s cross-section starts to change it’s shape, and becomes PARALLELOGRAM out of rectangle.
Now, imagine that you apply your force not 1 meter from the floor level, but 1 cantimeter (practically at the floor level). This way your cupboard will “slide” on the floor without any deformation.
Basically same process happens with a brake pad, where the force of gravity (weight of the cupboard) is the friction force that appears in a pair brake pad/rotor.
This particular trick is set for specific pressure of brake pad on working surface of brake rotor in every point tends to a constant, so the brake rotor during it’s service period wouldn’t wear off into a “cone”.
More subtle processes (formation of a gas layer) I described earlier in this blog.
Here I schematically showed the brake pad contour, the abutment surface, the forces, the direction of rotation and the pots. In such constructions the “last” pot is always of a larger diameter!
Let’s look at the bering response in a plane parallel to a brake rotor rotation axis.
Brembo BMW M5 F10 Front caliper response_friction force
Caliper thrust marked w/ blue color, the direction of the brake rotor rotation and brake pad contour are marked w/ red.
Forces developed by pots of different diameter marked by color green.
It is obvious that friction force is developed at the point of contact of brake pad and caliper.
If pots are made of the same diameter, then specific pressure of brake pad’s working surface on the brake rotor would be diverse.
Grease is used to lower friction coefficient in the caliper/brake pad pair, in sports caliper iron plates w/ hardness 40+ HRC (incandescent)
To make it easier to understand, if friction force (purple arrow) is subtracted from force F1, as they are multidirectional then the brake pad would press onto the brake rotor w/ equal force at every point of contact.
Friction force developed at the end face of the brake pad is marked w/ purple color.
The same effect can be achieved using pistons of the same diameter, but with the displacement relative to the symmetry plane.
Displacement – delta
It’s even more interesting with the pins. The first version is classical, like, for example, Brembo Porsche Cayenne Turbo S 955 Front caliper, it’s the same as on the picture above, the only difference is that the pad rests on the pin
The 2nd version was invented by a genius, I have no doubt about that. To be more accurate, he was forced to come up with more cost effective brake system.
Calipers gained same size pistons, the pad gained a ear.
If you look closely, you will see why. The pad rests on the first pin in the course of travel.
This way the pad doesn’t lock itself during movement towards the brake rotor surface.
A question arises, what all those tricks are for?! Isn’t there a simpler way?
That’s what BMW company has done with calipers (front ones) on M4 cars
(all the М performance and all (F series)), and on Х5М Е70 (performance for F15)
Brake pad is made very tall and narrow, pistons are of sme size. Those this version has it’s cons. Working part of the brake rotor must be made of much bigger height, specific pressure distribution on the brake rotor working surface from the pad isn’t optimal.