BWM 525 Brake Rotor - Wear Sensor Ridges

That's not a "feature". It's just the part of the rotor surface the pads don't hit. All new rotors (OEM or aftermarket) will be flat, and full thickness.

If you buy good ones that match the OEM ones (like the various ones that Bavarian Motorsport and other BMW suppliers will sell), but not necessarily if you buy the lowest grade crappy ones from AutoZone.

--scott

As was pointed out, ridges are typical of a rotor that has been in service for a while. They are the result of the metal being worn away by the friction surface of the pads.

Assuming that this is not some sort of new idea in German brake technology, you should get the disks resurfaced to get rid of the ridges or have them replaced before installing new pads. My guess is that a lot of do-it-yourselfers will just load in a fresh set of pads and then go have a brewski. Mostly these guys will own Fords or Chevys, not BMWs. :-)

Those wear "lands" are all I have ever seen.. I am not current with a lot of things, but I dont know of rotors having an intentionally machined "wear sensor ridge". Scott, have you seen this sort of design, or have I misinterpreted your post.

I don't know for sure, but I suspect that BMW's pad wear sensors are similar to those used on other German cars with which I'm familiar, which are basically just a little tiny puck that fits into a slot in the brake pad, and when the pad wears down enough to allow the puck to contact the rotor, the rotor wears away at the puck and eventually opens a circuit, lighting the light on the dashboard. Nothing special about the rotors at all.

As an aside, with a system like this, the sensors can be reused if the pads are replaced before they wear down to the sensor, but once the light is lit, the sensor(s) must be replaced.

nate

Some of the newer BMW rotors have a little lip at the outer ridge. I don't know what it's for, but I know the OEM replacmeent ones have it too.

I don't know how the wear sensors on the new BMWs work; on my E28 it's just a little metal piece that is inserted into a notch in the pad and is ground down when the pad wears; when it grinds down complete and becomes an open circuit, the light comes on. You replace the sensor when you replace the pad.

Either way, if you buy proper OEM ones everything will be fine.

--scott

Here's a wear indicator :

They got their money's worth out of that disk.

They sure did. Probably some noisy stops toward the end.