My '99 has a new motor, a recently rebuilt transmission, and healthy suspension, but it's also got what I have to assume are the original rotors with 90k miles on them.

They're well worn, with a big lip around the outside, peaks and valleys throughout the radius matching the cross-drilled holes, etc. But there's no sign of warping or squeaks, the pads are fine and the car stops like a champ. I do the occasional autocross, but here in Florida I don't have to worry about overheating the brakes while coming down a mountain.

So how long can brake rotors last, anyway?!?
Thinner the rotors, the less unsprung weight and the faster the car, eh?

-Dave
Melbourne Beach, Florida

 

I suspect you're about done.

 

If you have to ask.......

 

Take the wheel off and look at the disc, rotate it and you will find a wear indicator on the outer edge.
If the disc is worn down to the indicator it must be changed.

The wear indicator looks this:

 

I believe that there are minimum rotor thickness specs posted on www.renntech.org. You can get the specs and then measure your rotors at various places with calipers to see if you're within spec. FWIW - Porsche recommends changing the rotors each time the pads are changed. It's unlikely that these are your original pads (although not impossible).

 

Minimum thickness is actually stamped on the rotors. The service manual also shows "new" and minimum thickness as follows:

Front: 28 mm new, 26 mm minimum
Rear: 24 mm new, 22 mm minimum

Measure the thickness where the pads actually contact the rotor (i.e. not the "lip").

For what it's worth, I did a 4-wheel pad change on my '02 996 at about 48,000 miles. The front rotors had worn about 1 mm (and the pads were about "done"), the rear rotors had worn only about 2/3 mm (and the pads were perhaps half "done"). I'm figuring I'll get about 90-100K out of the front rotors so will change them next pad change; the rears will go longer. This is on a car that sees primarily highway/road trip miles, not a daily driver or tracked. Your mileage may vary.

 

Thanks for the responses (even the smart *** ones)
I didn't realize there was a wear indicator on the rotors. I'll check it out, thanks!

 

I can't see this being entirely accurate as the pad swept area does not go out all the way to the edge. Therefore the edge never wears down. You can eyeball it and get a decent idea I suppose but not down to fractions of a mm.

 

For the 5 years I've been checking mine it has been relatively easy to see their still OK. Unless it makes a small hole when the limit is reached, I guess I'll just have to use the micrometre measurement tool when its getting close to the limit.

 

I wish the stock rotors came with a more easier indicator like Balo rotors or other aftermarket rotors with the dimples in them to indicate if they are still good or not. That way you don't even have to take off the wheels.

I do like that kind of dummy indicator on my Continental DW and DWS tires though.

 

That's a tough question to answer because it really depends on how you drive the car and what performance level you really need. I suspect that for most daily driving uses, you can let the rotors go down below the minimum by a bit. However, if you want to keep the car at the factory performance levels (or better), then you're probably done when the rotors hit the factory specs for the minimum.

I had the same questions about brake pads and changing the brake fluid when I talked to a Porsche Tech recently. What he told me is that factory specs are pretty strict -- for example, it's not just about stopping power for the brakes. They are tested to handle a certain number of hard braking maneuvers with a minimal amount of brake fade. At some point, if the pads and/or rotors are low, or the fluid hasn't been changed, the brakes won't meet these performance levels. However, these specs are more relevant to something you'd see in a track or high performance driving environment, but typically not on the street.

In the end, since I enjoy track events too, I keep the car at factory specs or better.

 

Most dealers will tell you that they don't change just pads anymore. Rotors are always done at the same time.

Safest way is to measure the thickness with a caliper in several places. You shouldn't even need to take the wheel off.