[Kailec]

Originally Posted by MONSTAR

The trick is to replace the pads before the sensor is tripped so that you don't have to pay for a new sensor.


I was doing a lot of hooligan shit; sliding on every turn that I could, and my rear pads had to be replaced at 53k while the fronts (according to idrive) had another 15k left to go. It was my understanding that when you are lighting up the traction control, the rear brakes are activating to help you regain traction. This could be a good reason why the rears go quicker than the fronts, considering that most of your braking is done up front anyways.

Ah okay. Well my rear sensor has already tripped 100km ago according to iDrive. I still need to drive another 500-600km before I will be able to swap them, will that be problematic unless I drive like an idiot?

[MONSTAR]

Originally Posted by Kailec

Ah okay. Well my rear sensor has already tripped 100km ago according to iDrive. I still need to drive another 500-600km before I will be able to swap them, will that be problematic unless I drive like an idiot?

I think I went like 2k miles past when iDrive said to replace them. There's typically some life left in them still

[Billfitz]

When mine tripped it said 1,000 miles until service. It was down to maybe 300 miles when I changed the pads, and it was in no danger of metal on metal at that point. It's a pretty conservative warning system, as opposed to a metal clip that hits the rotor and screams like a banshee. There's a clip, but it makes contact with the caliper to set off the warning, not the rotor.

[MacklinUSOB]

Originally Posted by Kev314

Not sure if that is true. I could easily be wrong, but it was my understanding that braking is biased toward the rear to minimize nose dive.

Braking is progressively biased towards the front wheels. The fronts are responsible for 60% or more braking force in more than a light application. Putting brake bias to the rear is dangerous solution as it might mitigate nose dive, but only at the cost of an extreme increase in stopping distance. Nose dive is a function of the intertia of the mass going one way, and the brakes (front and rear) pulling the other, overcoming the spring rate (weight to which compresses the spring a given distance). The inertia will push weight onto the forwardmost axle regardless of what axle is braking given the same resistence, but as the weight transfers off the rear forward, the rear wheels will have greatly reduced grip and be forced to reduce braking pressure to maintain traction. Since this occurs naturally while braking, all vehicles are biased to the front where they can leverage extra braking force with the increased grip on the front axle. To mitigate nose dive, the correct answer would be to increase the front spring rate.

Originally Posted by desmat

Also, xDrive system is using rear brakes (x times/sec?) when detecting wheel slippage. That's one of the reason dealer told me about when I asked why rear pads were going quicker than fronts.

This also occurs on sDrive models as the "E-LSD".

Edit: to reflect comments following.

[HighlandPete]

Originally Posted by MacklinUSOB

Braking is absolutely biased towards the front wheels. The fronts are responsible for 60% or more braking force in every condition. Putting brake bias to the rear is dangerous solution as it might mitigate nose dive, but only at the cost of an extreme increase in stopping distance. Nose dive is a function of the intertia of the mass going one way, and the brakes (front and rear) pulling the other, overcoming the spring rate (weight to which compresses the spring a given distance). The inertia will push weight onto the forwardmost axle regardless of what axle is braking given the same resistence, but as the weight transfers off the rear forward, the rear wheels will have greatly reduced grip and be forced to reduce braking pressure to maintain traction. Since this occurs naturally while braking, all vehicles are biased to the front where they can leverage extra braking force with the increased grip on the front axle. To mitigate nose dive, the correct answer would be to increase the front spring rate.

My E39 braking was clearly biased to the front brakes and showed up in disc/pad wear. E91 wore the rear brakes much faster than the front, was hard to keep the front brakes clean and shiny in winter, due to little brake effort on the front. Current F11 is the same as the E91, the rear brakes show much more disc wear and the same evidence of front brakes having it easy.

Same driving style and conditions for all 3 vehicles. I know DSC will use the rear brakes under hard driving, but most of my driving it won't be DSC intervention causing the extra rear wear rates.

I think one of the reasons may be light braking, (my normal use), brake harder and the fronts take up the front bias.

If my brakes rust overnight, even after 12 miles driving, the rears will be completely clean and polished, the fronts can still be patchy with rust. Takes some heavy braking to polish up the front discs.

[HighlandPete]

Originally Posted by Kev314

Interesting. As a very mild mannered driver this suggests that to maximize brake life that I need to brake harder at least some of the time. But of course too much hard braking would cause exessive wear - so the optimum must be at some hard to quantify and even harder to execute inbetween level of braking.

I have to brake harder on occasion than I'd choose to do, to work my front brakes, in an attempt to prevent corrosion from building up.

[MacklinUSOB]

Originally Posted by HighlandPete

My E39 braking was clearly biased to the front brakes and showed up in disc/pad wear. E91 wore the rear brakes much faster than the front, was hard to keep the front brakes clean and shiny in winter, due to little brake effort on the front. Current F11 is the same as the E91, the rear brakes show much more disc wear and the same evidence of front brakes having it easy.

Same driving style and conditions for all 3 vehicles. I know DSC will use the rear brakes under hard driving, but most of my driving it won't be DSC intervention causing the extra rear wear rates.

I think one of the reasons may be light braking, (my normal use), brake harder and the fronts take up the front bias.

If my brakes rust overnight, even after 12 miles driving, the rears will be completely clean and polished, the fronts can still be patchy with rust. Takes some heavy braking to polish up the front discs.

I think you're right on the money with your observations, it sounds like the change in wear from your E39 has to do with the switch from hydraulic to electric brake proportioning. This page has a great explaination of it:

http://www.aa1car.com/library/brake_balance.htm

So while braking force is progressively more biased to the front for all the reasons I explained, this seemingly fast rear wear is totally understandable if not expected if it isn't being driven more aggressively.

[Jincredible]

Same occurred to me. Back brakes were ~30k left before I dropped it off for maintenance at dealer. Now they're at 1900 miles remaining. Fronts didn't change though.

[nissanite]

Remember, DSC can squeeze the rear calipers when the wheels start to spin. Saw a 991 Porsche go through rear pads in 1000 miles at a HPDE

[yoon_209]

on my 13' n55 i had the brake service lights go off at 25k miles and took it to the dealer and they proceeded to tell me my software wasnt updated and it was a software issue and reset the CBS.

im at 35k miles and have no issues with pads or rotors on my n55