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E90/E91/E92/E93 (2006 - 2013)
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  #1  
Old 09-27-2013, 09:27 AM
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LarkHouston LarkHouston is offline
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Brake pressure question

I know that the amount of braking force is unequal from front wheels to back wheels. However are brake systems designed so that brake pressure would be unequal from side to side on any one individual wheel? In other words, are current brakes designed such that the inboard pad on a given wheel would wear out faster than the outboard side because the inboard pad is designed to exert more pressure on the rotor than the outboard pad? Or is the pressure equal such that the pads should wear equally? And, of course, I am referring to a system being designed in that fashion, not that wear pattern would more on the inboard pad than the outboard pad because there is some problem. Thanks.
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  #2  
Old 09-27-2013, 11:20 AM
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DSXMachina DSXMachina is offline
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Good questions Lark, I think I can help you.
The short answer to your question is No, brakes are not designed to exert more force on one side of the rotor than the other. This would flex the rotor, cause a weird braking sensation, and not have any benefits at all.

When a caliper has pistons which are on only one side of the rotor the piston(s) are rigidly fixed to a caliper slide which moves in a caliper frame. When pressure inside the cylinder(s) increases, the piston(s) move outwards. This causes the brake pad on that side to contact the rotor first and therefore results in the inner pads wearing faster than the outers. Once those pads hit the rotor the force is transmitted to the slide, which moves within the frame, and this causes the pad on the other side to push against the rotor.
High performance braking systems have pistons on both sides of the rotor and for various reasons this is a better, but more expensive, way to apply force. This system usually results in both the inner and outer pads wearing at an even rate.

Note: It is common for caliper slides to seize up in the frame. This results in a funky pedal, and unusual pad wear. It can be tapered wear, or much greater wear on either the inner or outer pad. If the slide is 'sticky' then the outer pad will be much more worn. Once the slide locks up the inner pad will wear faster because the outer pad will not move against the rotor. You can imagine the problems this can create with braking.

Last edited by DSXMachina; 09-27-2013 at 11:29 AM.
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Old 09-27-2013, 11:47 AM
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LarkHouston LarkHouston is offline
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Makes perfect sense. Thanks much. I had a feeling you would be the guy to answer the question.
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Old 09-27-2013, 06:15 PM
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CALWATERBOY CALWATERBOY is offline
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Quote:
Originally Posted by DSXMachina View Post
No, brakes are not designed to exert more force on one side of the rotor than the other. This would flex the rotor, cause a weird braking sensation, and not have any benefits at all.

TGIF!!!

Truly 'at the end of the day,' Friday après le travail is a dream come true! The week's troubles pile up Fri morn, and one thing pushes out another....it is a day for Desperadoes....

Now, then....let's remember that BMW's e-diff applies brake pressure to the wheel with least traction. That applies torque to the opposite wheel, the poor mans Limited Slip.

Thus, differential brake pressure!

Oh, the wages of overwork....it's Miller Time!



Last edited by CALWATERBOY; 09-27-2013 at 06:19 PM.
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Old 09-28-2013, 12:14 AM
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Last edited by DSXMachina; 09-28-2013 at 07:28 AM. Reason: Double post.
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Old 09-28-2013, 12:15 AM
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DSXMachina DSXMachina is offline
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Originally Posted by CALWATERBOY View Post
TGIF!!!

Truly 'at the end of the day,' Friday après le travail is a dream come true! The week's troubles pile up Fri morn, and one thing pushes out another....it is a day for Desperadoes....

Now, then....let's remember that BMW's e-diff applies brake pressure to the wheel with least traction. That applies torque to the opposite wheel, the poor mans Limited Slip.

Thus, differential brake pressure!

Oh, the wages of overwork....it's Miller Time!
Right about the poor man's (or engineers' with budget contraints) LSD, but I think you just performed a 'workaround' on Lark's question.
Um...Cal...glad you made it sorta OK to the weekend. Just curious. What do you do for a living?
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Old 09-28-2013, 03:17 AM
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CALWATERBOY CALWATERBOY is offline
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Right about the poor man's (or engineers' with budget contraints) LSD, but I think you just performed a 'workaround' on Lark's question.
Um...Cal...glad you made it sorta OK to the weekend. Just curious. What do you do for a living?

You kiddin' me? I'm more than OK....I'm limber! Golly I love Saturdays....

I am best thought of as entrepreneur. Trained in computer science at the dawn of personal computation, I am a dinosaur muckin' through the swamp of new-to-BMW 2nd & 3rd owners.

I miss BJ.
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Old 09-28-2013, 07:30 AM
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DSXMachina DSXMachina is offline
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Originally Posted by CALWATERBOY View Post
You kiddin' me? I'm more than OK....I'm limber! Golly I love Saturdays....

I am best thought of as entrepreneur. Trained in computer science at the dawn of personal computation, I am a dinosaur muckin' through the swamp of new-to-BMW 2nd & 3rd owners.

I miss BJ.
I knew it! That is you in your avatar.
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