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Old 09-29-2012, 10:00 AM
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DSXMachina DSXMachina is offline
Non compos Mentos
Location: New Hampshire
 
Join Date: Dec 2007
Posts: 10,510
Mein Auto: 335i E92 TiAg 6MT ED
Quote:
Originally Posted by DSXMachina View Post
It is odd, rear pads generally last at least two sets of front pads. (In a hard stop, more than 90% of the braking is being done by the front brakes. In fact there is a device called a proportioning valve which reduces the pressure to the rear brakes to reduce the chance of lockup which would activate the ABS.)
What was the reason you needed rear pads? Excess wear? Was it warranteed?
Quote:
Originally Posted by Bemo View Post
My rear ones are on track to wear out about 15K sooner than the front ones...I also thought it was "normal" until I read DSX' response above. Hmm....
Quote:
Originally Posted by laser View Post
It's widely reported that the BMW 3 and 5 series wear the rear brakes out faster than the fronts. This has been my experience on three 3's and two 5's.

Some have speculated that the DSC is often applying the rear brakes on hard acceleration. I don't drive that hard regularly but have always replaced the rears first on these cars.
Quote:
Originally Posted by Bemo View Post
I wonder if the rear brakes are being applied a tad more to prevent body roll during hard braking but this line of thinking runs contrary to DSX's comments...
Quote:
Originally Posted by Snipe656 View Post
I have read that the rears go out quicker because the cars apply them automatically for some scenarios. The two I remember being cruise control and traction control.
Very interesting comments. From a brake size standpoint(pad surface area and rotor swept area) there is nothing unusual about the E9x rear brakes. They seem to compare favorably to the E46 brakes and the brakes on similar sports sedans and coupes, too. So from a mechanical standpoint I can't see a reason that rears would wear before the fronts.
Because the E9x's are just coming off warranty my shop has not seen many for brakes, and the ones we have seen (including mine) have shown front pads to wear the same as, or more than, the rear pads.
It is very possible you are on to something with the point about DSC activation, and traction control with the 'phony' LSD effect. That certainly would increase the activation of the rear brakes while not activating the fronts. Maybe we'll learn more as time goes by and our sample increases.

Edit: The next time I have a chance I'll compare rotor temperatures, front vs. rear, after some spirited driving. That'll give a real indication of what is going on with the brakes. Then I'll shut off DSC and do it again. If DSC is responsible for increased rear brake application I should see a significant drop in rear rotor temperature when it is shut off.

Last edited by DSXMachina; 09-29-2012 at 10:06 AM.
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