I think I read somewhere, sometime that the awd system can handle 1/4'' of tire circumference. So 1/4'' = 6.35mm divide that by 3.14 and you get about 2mm. so 1mm of tread depth difference is no big deal. But thats just what I read somewhere around here. but now that I think about it....1 mm tread depth really isnt alot.
~Josh~