min. thread depth for track days

[ChrisZang]

my next 2 track days are coming up early August (Thunderhill).

I track on my street tires (Yokohama AVS 100) and I currently have about 2.5 millimeters left on the rears and 3.5 on the fronts. I'd guess that the track days will cost me about 1 ~ 1.5 millimeters. That means that after the track days these tires will be finished.
So now I am wondering if I should put on new tires before going to the track (and partially ruin them) or "finish the old ones" on the track and then get new ones.
What's the general consensus here:
Is it better to track on old (broken in) tires or on new ones?

By the way: As I live in CA I will not encounter any rain for at least another four months, so hydroplaning is not a factor in my decision.

[racer_d]

You may get your answer at a Pre event Tech Inspection. They check things like tires, brake pads, wheel bearings etc. If they tell you your tires are a no-go, you will have your answer, won't you

You would be happier on your existing (used) tires. The most "wear" you will likely see is not tread wear but "shoulder" wear as the front tires take the abuses of cornering. The smaller the tread block, the less "chunking" your tires will show. That said, since you know they are wearing thin, if you can still see the tread wear indicators, you should be ok.

In order to pass Tech. Inspection for PCA events in the Chicago area, as an example, they require 3/32's in the contact patch area, race tires or shaved tires must have 1/16 tread ware marker depth and no cord showing.

You might want to check with your event sponsor & rules, so you can pass Tech Inspect.