.
All the tyre manufacturers and road safety bodies tell us that the less tread, the less grip, and especially in wet conditions.
Down here on the south coast it's certainly not cold enough yet to be a factor. We haven't even had an overnight frost yet.
I've never ran any tyres down below 2 mm but definitely have noticed a slight increase in wheelspin tendencies on GY Asymm 1's as tread depth reduces and I try to adjust my driving accordingly although the ESP system and Quaife seem to kill wheelspin very quickly.