E90/92 M3 Brake question

[smuler]

Friend is looking at E92 M3s and I've been looking at the service/maintenance histories and I drive screenshots of a couple of possibles, mostly low miles.

Which brake pads/discs need replacing first, the front or the rear?
When the pads need replacing, do the discs always need replacing too?

Thanks

[4130]

As with most cars, front brake pads will typically need replacement first since they do most of the stopping. Rotors usually will last through a couple of pad changes, but should be measured or at least looked at for wear.

[jphughan]

^ Correct

[Richbot]

My stock front set still had 10-15% of its life left at 60000 miles. If the car has only seen street use they will last quite a while as they are overkill for a street car

Front rotors were not going to make it through another set of pads. Only had a couple tenths of a mm before minimum thickness.

[masschaoz]

Aftermarket or factory brakes?

Factory brakes: rear wears out faster. Typically pads and rotors are changed at the same time

[Dougeefresh]

Originally Posted by masschaoz

Aftermarket or factory brakes?

Factory brakes: rear wears out faster. Typically pads and rotors are changed at the same time

Do you work for the brake parts industry?

[scoale]

Originally Posted by masschaoz

Aftermarket or factory brakes?

Factory brakes: rear wears out faster. Typically pads and rotors are changed at the same time

Rear brakes on my 335is wore out waaay faster than fronts.

[BzsBimmer]

Fronts should wear out faster than rears if all were replaced at the same time and same OEM compound. Around 80% give or take some, is front brake bias so that's how it should work.

Always mic your rotors when swapping pads. The MIN rotor thickness is stamped on the edge of the rotor. I've typically experienced two pad swaps for one rotor swap.

[dparm]

Originally Posted by smuler

Friend is looking at E92 M3s and I've been looking at the service/maintenance histories and I drive screenshots of a couple of possibles, mostly low miles.

Which brake pads/discs need replacing first, the front or the rear?
When the pads need replacing, do the discs always need replacing too?

Thanks

Fronts will wear far faster since the bias is typically 70-80% front. Rears aren't even doing anything for a lot of normal/low-speed stops.

No, rotors do not necessarily have to be replaced with pads.

[masschaoz]

Originally Posted by Dougeefresh

Do you work for the brake parts industry?

No I don't.. I own a e92 m3.. 82k km mileage .. Changed my rear pads and rotors around 70k km. Yet to change my fronts. Our ride is very well balanced. Unlikely to have front brake pads wearing out faster. Then again, it could also be because I seldom use my brakes..

[DSilk]

Originally Posted by masschaoz

No I don't.. I own a e92 m3.. 82k km mileage .. Changed my rear pads and rotors around 70k km. Yet to change my fronts. Our ride is very well balanced. Unlikely to have front brake pads wearing out faster. Then again, it could also be because I seldom use my brakes..

Fronts will almost always wear out faster than rears. Even the most balanced of cars will experience a transfer of weight forward when the car is braked, which is why the front rotors are larger than the rears, and why cars that do not have ventilated discs t all 4 corners will have them in front rather than in back. Unless you purchased your car new, I would suspect that your front pads had already been changed and had fewer than 70K km on them when you changed the rears. Either that or there is something wrong with your braking system.

[dnoble37]

My understanding is 335is uses rear brakes + onboard computer as a simulated LSD rather than the m3 which uses an actual mechanical LSD.
Therefore it makes sense the 335 would need rear breaks sooner. Also makes sense why they have such large rear brakes.

[masschaoz]

Originally Posted by DSilk

Fronts will almost always wear out faster than rears. Even the most balanced of cars will experience a transfer of weight forward when the car is braked, which is why the front rotors are larger than the rears, and why cars that do not have ventilated discs t all 4 corners will have them in front rather than in back. Unless you purchased your car new, I would suspect that your front pads had already been changed and had fewer than 70K km on them when you changed the rears. Either that or there is something wrong with your braking system.

Well.. I'm the one and only owner for my M3. And there is nothing wrong with my braking system..lol.. Maybe it's different cos our m3 here in our country cost $290k usd per car..

My rear really wears out faster than the fronts.. Probably my driving style has a big influence..

[meyergru]

Originally Posted by dparm

Fronts will wear far faster since the bias is typically 70-80% front. Rears aren't even doing anything for a lot of normal/low-speed stops.

Originally Posted by BzsBimmer

Fronts should wear out faster than rears if all were replaced at the same time and same OEM compound. Around 80% give or take some, is front brake bias so that's how it should work.

Sorry guys, but that is not the whole truth. Since at least the E36 series. modern BMWs have a brake force distribution that is controlled electronically instead of mechanically. While it is correct that with large brake force applied, at some point the back axle has much less dynamic weight to build up the same force as the front, this does not have to be the case with light braking.

Nowadays, it is up to the car maker how brake force distribution is done - at least up to the point were wheels begin to block and ABS sets in.

Contrary to what you think, BMW has chosen a back axle bias with light braking, which gives less weight shifting and front dip than if the opposite were the case, mainly for comfort reasons. That way, the car does not tilt forward, but lowers itself on all corners during light braking.

So, in effect, rear brakes wear out much faster with "normal" road driving. Forums are full of users of non-M BMW models asking why the rear brakes wear out faster. If really your front brakes wear out faster (mine do), it is only a result of driving style, not of a supposed 80/20 default brake force bias.

[M3 Number 86]

Originally Posted by masschaoz

No I don't.. I own a e92 m3.. 82k km mileage .. Changed my rear pads and rotors around 70k km. Yet to change my fronts. Our ride is very well balanced. Unlikely to have front brake pads wearing out faster. Then again, it could also be because I seldom use my brakes..

that's weird. Traction control is kicking in all the time for your usage apparently.

[meyergru]

Originally Posted by M3 Number 86

that's weird. Traction control is kicking in all the time for your usage apparently.

Nope. It's just driving-style related, as I wrote above.

The traction control does kick in at very low speeds, such that it does not account for much wear. I had a 335i with a Quaife LSD before my M3, which changed nothing for the rears wearing out faster. I just drove it differently than my M3.

In Germany, many E9x cars have engines that do not even light up the rears (i.e. DSC does never kick in), and reportedly, those wear out the rears even faster in comparison.

[Richbot]

Just because the light's not on doesn't mean it's not doing anything. See, for an extreme example, many US and Euro MDM users who never get the traction light on the dash but cook their brakes PDQ on track

I have records going back to my E36 328i and all of them wore the fronts out more quickly than the rear, but not by a ton. The rears have lasted about 15-20% longer than the fronts but not double or something like you get on your typical FWD car. The 80/20 bias is about weight distribution and work performed at threshold and not about brake force distribution at light loads, so y'all are talking past eachother to some extent

[meyergru]

Yours did. Some don't - you can read it right here in this thread.

I can give you links to several threads in german forums stating that as well. All I say is that brake balance is not 80/20 on the front by default, but more on the rear unless physical limits are reached, only in which case more braking force is on the front axle - must be because of weight transfer.

And I did not talk about lights. I can certainly discriminate when DSC is kicking in and it did much less with the Quaife LSD.

[dparm]

Originally Posted by meyergru

Sorry guys, but that is not the whole truth. Since at least the E36 series. modern BMWs have a brake force distribution that is controlled electronically instead of mechanically. While it is correct that with large brake force applied, at some point the back axle has much less dynamic weight to build up the same force as the front, this does not have to be the case with light braking.

Nowadays, it is up to the car maker how brake force distribution is done - at least up to the point were wheels begin to block and ABS sets in.

Contrary to what you think, BMW has chosen a back axle bias with light braking, which gives less weight shifting and front dip than if the opposite were the case, mainly for comfort reasons. That way, the car does not tilt forward, but lowers itself on all corners during light braking.

So, in effect, rear brakes wear out much faster with "normal" road driving. Forums are full of users of non-M BMW models asking why the rear brakes wear out faster. If really your front brakes wear out faster (mine do), it is only a result of driving style, not of a supposed 80/20 default brake force bias.

Point taken, it's definitely more complicated with modern ABS, EBD, CBC, and all of the other technologies.

Care to go into some detail on what specific "driving styles" will cause the fronts to wear out faster? I know that when I finally did my brakes at 65k, the rear rotors had WAY more life left than the fronts did. Same goes for the pads.

[meyergru]

Obviously, when you drive fast and thus need to decelerate from higher speed levels and more often - aka hard braking. I like to call it "spirited driving"...

I have experienced both wear patterns on my car.

Matter-of-fact, when I exchanged my 335i for the M3 as a daily driver, I had the impression that I needed the brake less often than before - which was probably the case because the engine braking is way more pronounced with the M3. Also, I did not use that much "digital driving" any more - here in Germany, you can go 150mph on the Autobahn and I often did with the 335i, only to be forced to brake once you reach the next road block on the left lane. Essentially, you always go from 100mph to 150mph and back.

With the M3, you can have the same average speed while only accelerating to ~120mph and decelerating only using engine braking. In my first three years of daily driving it, the remaining brake life was reduced evenly between rear and front.

Now, since I use the M3 only for fun (have a diesel SUV as my DD), the usage pattern has obviously changed - I go to drift events, ride mountain road in the alps and so on. During the last 2 years, the rear brakes showed no reduced mileage, whereas the front are now almost finished (the display of remaining mileage has just reduced from 9000km to 4000km while I did only 1000km through the alps).

BTW, this factor 5 is also about the ratio you can influence the brake life on your cars via driving style: My car is now at ~42000km and the front brakes are almost used up (rears are now at 15000km, just as 2 years before). If I had gone on to use the car as DD and not pushing it, they would have lasted for 50.000km! I know people that use up their front pads all 10.000kms.

P.S.: I avoid Autobahn now mostly with the M3, as I found far better uses for it...

[DanielLee5]

Originally Posted by smuler

Friend is looking at E92 M3s and I've been looking at the service/maintenance histories and I drive screenshots of a couple of possibles, mostly low miles.

Which brake pads/discs need replacing first, the front or the rear?
When the pads need replacing, do the discs always need replacing too?

Thanks

Check this store , seems like these guys have rather wide assortment and can suggest/recommend the most suitable to you brake parts. I ordered some accessories at this company , didn't regret about that.

[DSilk]

In every car I have owned, and that includes 2 M3s and many more BMWs, I have always had to replace front rotors and pads at nearly twice the frequency as those at the rear. I don't think the question is what driving style causes the fronts to wear out more quickly than the rears, but rather what odd things are you doing to generate so much wear at the rears as contrasted with the fronts.