[BXL4]

I just took my 2015 328i in for my first post-warranty oil change. Local shop but one I haven't used before. Oil change goes fine but they say that the rear brakes will need to be changed soon (44,000 mi).

First, this seems a little early for a car that isn't driven very hard. Second, the REAR brakes? Third, when I checked the remaining brake life on the internal diagnostics, I get 80,000 miles for the rears and 70,000 miles left on the fronts.

I don't think that I believe anyone!

In a couple of weeks, I'll be taking off the winter tires/wheels and can see for myself. What thicknesses should I be looking for on the pads? Finally, how does one tell if the rotors will need changing too? Thanks to all for sharing your wisdom.

[Billfitz]

The iDrive assessment is only a guesstimate, and a poor one at that. There is no active pad thickness measurement mechanism. You can go from '40,000 miles remaining' to 'Brake pads require replacing in 1,000 miles' literally in two seconds, the time it takes a tripped sensor to trigger the warning. Mine were improperly lubed at the factory, so I had to replace them at 11,000 miles. Only visual inspection is accurate, of both the inside and outside pads on all four wheels. If the bevel on the front and rear edges of the pads is gone they need replacing. Rotors need to be replaced if they're too thin to resurface. If you've never had them resurfaced before then they probably are thick enough to turn, but it's a PITA to have them turned unless you have a second vehicle you can use to take them to a shop to have it done. If you need rotors rockauto.com has them as cheap as anyone. Consider Raybestos Element 3 rotors, which have a rust retardant coating.

[sspade]

The rears usually wear out first on this platform (from my research). Strange, I agree.

[F30dud]

Its possible, my mk7 would wear out the rears super fast compared to the front.

[MacklinUSOB]

I roasted through a set of OE rear pads with 10k road miles and then one track day. The stability and traction management systems are constantly using them while driving hard even without flashing the DSC light. I also recall the rear pads having less material to start with than the fronts, so it doesn't surprise me they need replacing first.

As for the sensors, Bill is right, the iDrive estimate is not to be trusted and shouldn't even be considered until the sensor trips. Visual inspection is best but when the sensor goes you'll at least know to swap pads before any metal on metal contact. Once that happens you should definitely do a quick visual inspection because remaining pad material can vary pad to pad since it's only measuring one.

[Eschmacher]

In general, most modern cars use the rear brakes more for light braking, because it increases stability. So the rears wearing down earlier is 100% normal. I have seen this on every single one of my friend's and relative's cars.

[Maz99]

I actually had the opposite problem, i-drive was telling me it was time to replace my brakes but my mechanic told me it was not correct, so he reset it.

[328iX]

I got 53k miles on original rears and they still look like they got at least 40-50%, iDrive says 3,800 miles remaining but it's obviously very off. Hope that gives you an idea

[Billfitz]

Originally Posted by Maz99

I actually had the opposite problem, i-drive was telling me it was time to replace my brakes but my mechanic told me it was not correct, so he reset it.

The iDrive shouldn't say you need brakes unless one of the sensors has tripped. It's not an accurate method, because sensors are only attached to two of the eight pads. Once a sensor is tripped it can't be reset unless the sensor is replaced, so whatever warning you got wasn't from a sensor.

[AK415]

Did the shop mention the thickness of the pads? In terms of rotor, I usually run my finger from the center to the edge to get a sense of the smoothness and if there is any "lip" feel on the edge. Please only do that when the car is completely cold. It can burn.

[Billfitz]

A ridge on the rotor edge is normal. The pads don't contact the edge, so it doesn't wear down there, but it does rust, which expands the rotor thickness there. You can't gauge if the rotor is below minimum thickness, or it's above minimum thickness enough to resurface, by the presence of a ridge.

[328iX]

Here is 53k on my original pads. Quite often I get on my brakes hard as well. The rears hardly do any work.

[BXL4]

See photos of my disks and rotors. Rotors seem to be worn about 0.025" on front a bit less on the rear.

I don't know how to interpret what I see and measure. Photos of LR on top and LF below disks attached.

[Billfitz]

The pads consist of the metal part that contacts the caliper and the ceramic composite part that contacts the rotors. You want the distance from the metal part to the rotor to be at least 4mm. That's on both the inner and outer pads on all four wheels. I believe the sensors trip at 3mm. It looks like you're close to 3mm in the top picture. Your rotors look OK, they'd work without resurfacing, though I prefer to resurface mine even if they don't have deep grooves in them. BMW rotors tend not to wear badly, because BMW pads are softer than most. That's also why they dust so badly. The harder the pad the less dust, but the trade off is lessened rotor life.

[johnung]

The minimum spec on brake pads is 3mm. The manual says to measure the thickness of the brake rotor in 8-10 places and use the smallest value that you find. I've attached a table of the rotor size when new and minimum rotor size before they have to be replaced. Harbor Freight makes a nice caliper that makes it easy to measure brake rotors. See the attached photo for part# and price.

[BXL4]

Originally Posted by johnung

The minimum spec on brake pads is 3mm. The manual says to measure the thickness of the brake rotor in 8-10 places and use the smallest value that you find. I've attached a table of the rotor size when new and minimum rotor size before they have to be replaced. Harbor Freight makes a nice caliper that makes it easy to measure brake rotors. See the attached photo for part# and price.

Thanks for this. I was only able to measure the wear on one side. If I double that, I'm at 0.050" to 0.060" of wear. I'm right up to the minimums. Time to shop for pads and rotors.

[Z K]

Originally Posted by MacklinUSOB

I roasted through a set of OE rear pads with 10k road miles and then one track day. The stability and traction management systems are constantly using them while driving hard even without flashing the DSC light. I also recall the rear pads having less material to start with than the fronts, so it doesn't surprise me they need replacing first.

+1

The rear brakes are applied for stability whether it trips the DSC light or not. Only way around it is to disable traction control completely. I imagine you didn't completely disable DSC on track which is why it used the rear brakes a lot.

Brake pads are relatively easy to replace so it's not a big deal.