My hypothesis is that if you use the auto cruise, it uses the rear brakes to slow the car more than the fronts.

 

I also experience this.
And I don't know why.

 

I recall the parts guy at the dealer telling me rears always wear more than fronts. I rarely use cruise but rears are always dirtier. I will choose less dusty pads when it’s time to replace.

 

I've never really noticed which wheels are dustier but having black gloss wheels they all tend to show build up, dirt too. Recently discovered Sonax wheel cleaner and it's changed my life. Spray on, let sit for 5min, agitate a little with rim brush for really dirty wheels (I use Sonax, there are a ton), spray off with pressure washer. No need to even wipe.

 

I have used P21S gel for 30 years, similar results. Gotta love German car care products.

 

Had an after thought. While we know that the front brakes do most of the work, because the calipurs are so much larger than the rears, perhaps there is less pad wear than the rears with smaller pads and calipurs.. Smaller pad surface means they work harder and therefore shed more dirt. Just a hypothesis.

 

As most cars today have electronic brake proportioning systems, the rear brakes get much more use than before these systems appeared, hence the rear brakes wear much faster than before.

Nothing to-do with the cruise control or electronic limited slip systems.

 

Yes it does. Adaptive cruise uses the rear brakes to regulate speed.

 

Need brake cooling. One surprising area of neglect from Alfa on this car; they were rushed in the development. Very surprising that the GTA didn't get it either though

 

I don’t see how brake cooling has much if any effect on dusting. I think it is a relationship of effectiveness, wear and dusting. Pick any two. NV

 

Yes it does. Adaptive cruise uses the rear brakes to regulate speed.

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I'm not about to dig into the technical docs for the answer as ultimately it's moot but I think the rear EPBs handle some of that, at least on QV. My car with service EPB light won't engage ACC due to said light.

I don’t see how brake cooling has much if any effect on dusting. I think it is a relationship of effectiveness, wear and dusting. Pick any two. NV

I was referring more to the uneven pad wear comments. Dusting is mostly a component of pad and rotor combo

 

I also notice brake dust build up more on my rear, I don't use auto cruise often. I think the front gets more air flow than the rear by comparing the structure. I remember I have seen the aero simulation that front well receives a lot more air from the intake. Therefore, the rear builds up more quickly, although I don't have any proof.

 

I rarely if ever use ACC so thats a non factor for me yet I load up on the rear wheel brake dust. What's weird is that with all the bimmers Ive owned, Ive never experienced this before.. Love my QV over all my bimmers, but just curious why the rear brake dust loading when not experienced with the other cars.