How to properly read wear on a rotor.

[Driver407]

I have a track day coming up at the end of the month. Trying to figure out if I need to replace my front rotors now or if they have more life in them. I just went out and measured with a caliper. 1.175in/29.845mm. Recommended lowest is 28.4?

However the one part of this that im unsure of... There is a little bit of a lip that prevents me from getting a flush reading. Since the lip protrudes out then in. Is my reading done correctly? With the lip. Car has 8 track days and 65k.

I feel like they should be good for another event. However rotor wear is not something i have a lot of experience with. here are a few pics. Tried to show the topography.

[robbo mcs]

I have run into that issue. When there is a big lip, you need some measuring calipers with curved ends, rather than ones with flat profile. I have an old school set, which don't actually record the measurement. I put them on, set them, lift them off and measure the distance with my electronic calipers. You need to measure in a few spots.

However, having said that, the whole rotor started out as thick as the lip at the edge. They were flat when new. So when you have a prominent lip, that usually means they are pretty worn

[///Mvy]

You're probably using a caliper to measure which won't give you an accurate measurement because of the lip. Look up micrometer on Amazon. That's the tool you're looking for.

[jfritz27]

I think you're fine -- it takes longer than you think to wear the rotor thickness 1+mm. More importantly, the surfaces look good -- I can't see any major cracks. What you're really worried about is a catastrophic failure on-track, which would come from part of the rotor just chunking off. Without any visible cracks, there's no clear reason why your rotors would do that.

EDIT: In looking closer at your pics, I do see a few small cracks emanating from the cross holes, but nothing that I would call concerning at this point.

[Driver407]

I went out and bought a micrometer and sure enough I am right at the threshold 1.120in/28.45mm. Thanks for the tip.

Thunderhill is having an east/west in the same day event, so i will be running more sessions than usual in a day. Looks like i am going to buy a new set to be safe! Now i gotta decide between FCP OEM or some fancy girodiscs

[NYG]

Unless I've been running the rotors for over a year, I just look for large cracks propagating to the perimeter of the rotor. Microcracks are ok/normal.

[bimmerboyE92]

That's alot of street use. Haven't met a rotor used on track that develops a lip that noticeable before it cracks.

If you feel safe with them on the street you'll be fine for a track day IMO.