[swamp2]

^OK you have me on precision/consistency and actual measurements. I've been far less precise and more careless than I am typically. However, you don't have me on the concept.

Perhaps some prior numbers were guesses from a quick visual or perhaps some measurements were from the wear bars vs. from the channel bottoms. Fronts are now at 5/32" total depth (i.e. from the channel bottom) as measured with a caliper. Of course there is a 32nd or so variation L to R and around the tires and in different positions L to R across one tire. So extrapolating from there I very likely did have 7/32" front and 2/32" rear a short time ago, precisely what you said I must not have had. This comes from the obvious; more fun accelerating in a straight line and on the freeway driving as opposed to time in the canyons or on the track (oh woe is me...). As you know before the wear bars the bulk appearance of the tread is fairly constant with wear. However at some point the tire really begins to change drastically in appearance (near, at and into the wear bars). I was in this spot on the rears only before hitting the track and was not at all in this regime on the fronts.

Again, not sure how many times I am going to have to repeat it, all of my experience on the street to date, over many cars and many tires, along with this recent track experience, tells me the exact same thing. And until confronted with some very strong scientific evidence to the contrary, I will hold my opinion. Traction falls off strongly at the end of a UHP street tires life. This could very well be some combination of effects, bulk tread pattern change, heat cycling effects, the much lower overall rubber thickness (mass), compound variation with depth. My best guess is that these factors are listed in order of decreasing effect size and decreasing probability.