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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Suspension | Brakes | Chassis > brake wear (front vs. rear)



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      01-08-2009, 11:23 AM   #1
335inTO
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Question brake wear (front vs. rear)

I have been monitoring the service indicator in my E90 and have been noticing that the service countdown for my rear brakes has been decreasing fairly rapidly whereas the front brakes countdown has actually been increasing. When I first picked up the car (new) they both indicated about 45,000 km until the next service. Now, 2 months and 4,200 later, the front brake indicator is showing 47,000 km until next service and the rear indicator is showing 40,000 km.

Any ideas as to why the rears would wear out faster? Also, does the indicator monitor actual brake life or only an estimate based on driving style, conditions, etc?

I use the parking brake every time I put the car in park. I figured that it would be easier on the transmission this way. Should I only do it when the car is on an incline?
Any thoughts, advice would be much appreciated.
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      01-08-2009, 11:26 AM   #2
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i have the same problem, i told the tech and he couldn't explain? i drive city mostly, so doesn't make sense to him nor me?
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      01-08-2009, 11:38 AM   #3
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Quote:
Originally Posted by damadama View Post
your traction control is kicking in and chewing up your rear brakes faster than your front ones.

to me thats the only reasonable explanation as under normal braking conditions the front is going to be providing the majority of the stopping power and thus faster wear.
Interesting! I hadn't thought of that.
The roads have been quite slippery this winter with snow/slush on almost a daily basis. It will be interesting to see if the pattern changes in the summertime.
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      01-08-2009, 12:20 PM   #4
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haven't noticed that, but interesting reason
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      01-08-2009, 12:27 PM   #5
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All rears will go out faster unless you turn off the DTC everytime. Our lame traction control is just rear brake pads going at it. Every time you over accelerate the brakes come on to comensate.
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      01-08-2009, 12:41 PM   #6
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The wear indicator is deterministic, it does not actually check how much pad you have left. So it could be all wrong. As for the variation, it has to do with your average stopping effort. The harder your stop the more front pads wear because of the weight transfer. It's a good thing what you're seeing, it means you're not a brake jammer.
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      01-08-2009, 06:09 PM   #7
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FWIW my previous two Subaru Legacys ran out of rear pads before the fronts.
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      01-08-2009, 08:26 PM   #8
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      01-08-2009, 09:10 PM   #9
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Quote:
Originally Posted by johnnydad View Post
FWIW my previous two Subaru Legacys ran out of rear pads before the fronts.
My Passat and Golf do the same.

Most of the braking is done by the front, but they are also much larger than the rears. In addition there are issues with how the brake bias behaves under light braking.
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      01-09-2009, 02:13 AM   #10
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My 335i had to get the rear brake pads replaced at about 10.5k miles. Now I'm at just under 14k miles and had a service appointment and the brakes all look fine. The CBS still indicate that the rear brakes will have to be replaced in less miles than the still original front brake pads. It's definitely because of the DSC and no LSD trying to control the high amount of torque going to the rear wheels. You can't just shut off the DSC completely though, because it's not pretty when the car loses all control and spins out all over the place on high boost corners.
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      01-09-2009, 04:30 AM   #11
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Quote:
Originally Posted by noro View Post
The wear indicator is deterministic, it does not actually check how much pad you have left. So it could be all wrong. As for the variation, it has to do with your average stopping effort. The harder your stop the more front pads wear because of the weight transfer. It's a good thing what you're seeing, it means you're not a brake jammer.
My rears are toast. I just checked 'em. I'm a hard and soft stopper (mostly harder). My fronts are close, but nowhere near as bad.
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      01-09-2009, 07:23 AM   #12
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Quote:
Originally Posted by matt_335Ci View Post
i have the same problem, i told the tech and he couldn't explain? i drive city mostly, so doesn't make sense to him nor me?
Same here... I have 32000 on my e92 and the IDrive info tells me that there is 28,000 remaining on the front and 15,000 on the rear. I told my CA and he has no explanation.

I drive 65/35 city, mostly spirited driving and am not happy that the fronts are NOT on pace to be replaced under full maintenance...what gives?
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      01-09-2009, 07:51 AM   #13
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For those who don't have Idrive, can we still get that info?


Quote:
Originally Posted by roho3323 View Post
Same here... I have 32000 on my e92 and the IDrive info tells me that there is 28,000 remaining on the front and 15,000 on the rear. I told my CA and he has no explanation.

I drive 65/35 city, mostly spirited driving and am not happy that the fronts are NOT on pace to be replaced under full maintenance...what gives?
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      01-09-2009, 08:21 AM   #14
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Quote:
Originally Posted by discoboy1 View Post
For those who don't have Idrive, can we still get that info?
+1 how do non-Idriver's pull that data up? Anyone know?
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      01-09-2009, 09:41 AM   #15
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The manual explains it best but go to your turn signal stalk, use the little scrolling lever to flip through the various menus until you get to service info. Press the button on the end of the signal stalk to select, then scroll through the sub-menus. You'll see various icons for front brakes, rear brakes, next service, etc. The engine has to be on however. Otherwise you'll get a limited menu.

Regarding the brake wear, would a car with a mechanical LSD (e.g., M3) experience less brake wear because traction/stability control wouldn't need to intervene as much?
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      12-30-2009, 10:12 AM   #16
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I have a 2007 E90 328i w/o ZSP, it has about 28,000 miles on it now. Over the past year, the service indicator has been increasing for the rear pads and gradually decreasing for the front pads. My fronts have gone from 17,000 miles to 12,000 miles over the past 11 months with about 10,000 miles of driving. However, the rears went from 12,000 to 14,000 back in January and stayed that way until this past weekend. I went on a 600 mile road trip and now, the indicator shows 15,000 miles on the rear pads. I brought up this issue at the dealership once and they told me that it is CBS and the pads looked good and the regular BS.

On visual inspection, I notice that the pads still have some meat left on them but the front seem to be in better shape than the rears. After reading this thread I find my issue to be abnormal since everybody else has faster rear pad wear but my CBS indicator shows otherwise.

Has anyone else had the same issue as me?
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      12-30-2009, 09:38 PM   #17
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Quote:
Originally Posted by rambalu80 View Post
I have a 2007 E90 328i w/o ZSP, it has about 28,000 miles on it now. Over the past year, the service indicator has been increasing for the rear pads and gradually decreasing for the front pads. My fronts have gone from 17,000 miles to 12,000 miles over the past 11 months with about 10,000 miles of driving. However, the rears went from 12,000 to 14,000 back in January and stayed that way until this past weekend. I went on a 600 mile road trip and now, the indicator shows 15,000 miles on the rear pads. I brought up this issue at the dealership once and they told me that it is CBS and the pads looked good and the regular BS.

On visual inspection, I notice that the pads still have some meat left on them but the front seem to be in better shape than the rears. After reading this thread I find my issue to be abnormal since everybody else has faster rear pad wear but my CBS indicator shows otherwise.

Has anyone else had the same issue as me?
I'm by no means expert in braking but just want to jump in and say I dont really think there's anything wrong with that. rear pads wearing out faster than fronts doesn't have to be a "must be" process. My idea is that things will wear down differently depending on brake force distribution, as someone mentioned in this thread earlier this year. one of the Infiniti's I've owned few years ago did have that, my E46 330 didn't, and my last car, an E46 M3, did that again. The M also had 15" front and 13.5" rear brembos, still the rears wore faster than the fronts did, not by much, but still faster.

Both my Infiniti tech and a friend's (B7 owner) Audi tech attributed this to the same logic: brake force bias. They said braking systems on those cars mentioned above are designed to distribute breaking power evenly front and back to reduce that "nose dive" kind of movement, to make the car stable even as one slows down. So under "normal" breaking situations the rear brakes either engage a hair sooner than the fronts or would bite slightly harder than the fronts to help achieve this goal. They said this is evidenced as we will see cars on the road with dirtier rear wheels than fronts, which I do confirm seeing all the time here in LA, with the B6/B7 A4s, certain Infiniti models, and even the current gen C-class.

Again, I'm not saying this is the def the answer, dont know if all or most car manufacturers program braking systems this way these days, but the logic certainly seems credible. I'm just saying I dont think your 3er "must" have faster wearing rear pads than the front, most of the times it probably really boils down each driver's style...
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      12-30-2009, 11:06 PM   #18
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Quote:
Originally Posted by Icecreamfoo View Post
Both my Infiniti tech and a friend's (B7 owner) Audi tech attributed this to the same logic: brake force bias.
It seems to me if that were the case, the brake hardware would be designed account for this and provide more front/rear wear equality. That said, I had a Firebird that would munch rear pads/rotors like they were going out of style. I was finally able to correct this problem by putting slightly larger aftermarket brakes on the front.
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      01-04-2012, 09:38 AM   #19
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There is a sensor in the brake pad, that is how it primarily determines the brake life left. What I was told at the dealership that there is actually two wires in the brake pad, one about halfway and the other close to the end. When the first wire cuts, it gets an estimate by multiplying the miles you had driven since the brakes were put in by two (assuming the wire is indeed exactly in the middle, it way not be). I am guessing that prior to the first wire breaking it just guesses based on driving conditions. It is still not perfect and that is why there is a second wire close to the end of the brake. Currently my rear brakes says 7K left on the computer, I also just had it in for service and the guy said there is 3mm left on the pad and I should replace soon.

What would explain the life of the front increasing and the rear decreasing, is if the wire on the rear cut already, but on the front it had not cut yet. The computer could of been expecting the front to cut soon and it did not yet, so it increases the miles left on the front.

BTW my rear brakes wear slightly faster than my front. I have a 06 325xi, not sure if the AWD makes a difference.
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      01-04-2012, 10:40 AM   #20
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Quote:
Originally Posted by 335inTO View Post
Any ideas as to why the rears would wear out faster? Also, does the indicator monitor actual brake life or only an estimate based on driving style, conditions, etc?
Those blaming DTC are correct - BMW's e-diff applies one rear brake to move torque to the opposite wheel. 17k mi not unusual life for rears. Monitor's a calculation.

Some don't know that the rears also brake to maintain speed downhill w/cruise control on.

Hey, e-diff is an inferior solution....get a Wavetrac or Quaife LSD....you'll be SO glad you did! All aspects of driving are enhanced, most felt when applying accel in curves. Remarkably, the improved performance can be felt going down a driveway!

Rear brake life should be greatly improved. Be warned: w/LSD and/or chip, other suspension deficiencies become more noticable - all can be fixed.
.

Last edited by CALWATERBOY; 01-04-2012 at 10:49 AM.
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      01-12-2012, 12:52 PM   #21
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My experience...

2007 335i E90 ZSP original owner. I bought the car off lease (because I loved it) at 48k miles w/ CPO which requires over 50% pads. My rear pads were replaced under warranty at this time based on the CPO.

I monitor my CBS with a Bavarian Technique diagnostic tool. My front brake warning went at about 76k miles. I checked and all 4 rotors needed replacement. The front pads were toast but the rears had a little left.

I replace all rotors and pads at 78k. The front and rear rotors were a little under spec at that time.

So with my car and driving style all for rotors are good for about 75k miles but the rear pads need to be changed at least once before that time.

BTW I went all OEM except with the upgraded 2-piece Z4 rotors courtesy of Tischer and I am super happy with the result!
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