Well here's one problem with street tires -- full tread street rubber is likely to chunk and overheat with serious track use.
Also, you have less grip available for braking which can make it easier to lock up the wheels and flat-spot your tires.
I have seen guys pretty much destroy their $150-250 (ea) Dunlops, Michelins etc. in a single track day, by either chunking and/or flat-spotting them.
The Yoko A032R or Toyo Proxes RA1 (or is it R1A?) are both DOT-R tires that are street legal but are designed for track use, and will last much much longer than the more "serious" DOT-R tires such as the Kumho V700 or Hoosier R3S03.
I guess it really depends how much track driving you plan to do, what type of events and how often. If you get really into it you will soon find yourself wanting at least one spare set of wheels with "track tires", even if they are still technically street tires, so your daily driver wheels & tires don't get thrashed.
Cheers,
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Chris C.
73 914 2.0
70 911E Targa
campbell.chris@gte.net