OK, since the ET Streets basically don't have any tread to begin with how do I tell when it's time for new ones?

 

not sure if your still looking for an answer, but ET Streets do have tread. those tiny narrow grooves are what make it street legal (although useless). i use them on a 16x8 rim when i drag my car. when the rubber gets worn to the point where those grooves dont show anymore, id think about new tires. OR atleast not use them on the road cause they will no longer be street legal.

 

There should be a thread dot on the tires if that isnt there anymore you need new tires et streets last bout 3000 miles. I would suggest using mickey thompsons new dr's. There are people running better times on the the drs than the et streets some are running simular times as they do when running slicks.