I have 18x11 fronts and 18x12.5 wheels can I run a 315/30/18 square set up or is it better to run 315/30/18 fronts and 333/30/18 rears? Track use only

 

The 345/35/18 Hoosier will fit on the 18x12.5 and Hoosier says it is only 26.8 inches in diameter which is the same as the stock rear tire. Front Hoosier 315/30/18 will be the same diameter as the stock front tire. This tire combo works very well on a C6 or C7 widebody.

The 315 tire is too small for the 18x12.5 rim. Think of it this way the section width is (315/25.4=12.4 inches wide) which is narrower than the rim. Whenever you put the wheel flat on the ground the rim will hit the ground as the rim protector on the tire isn't large enough. You also want to be near the balance that GM designed in the car with a much larger tire in the rear. Now if you could stick 345s all the way around you might have a machine that would corner hard with a little tendency to oversteer. I know when I went to 315/35/17 tires all the way around on my C5Z it became a cornering monster. I could put it hard into a corner and it would stick. I surprised one Porsche/Vette (9244 with a Corvette TPI V8 for power), driver because I passed him in a tight portion of the track.

Update: Here are a couple of pictures showing the car running with 18x11 and 18x13 wheels with Hoosiers mounted. The second picture is the one in my avatar and it clearly shows the outside tread of the inside wheels being pulled off the ground when going around the Oak Tree corner at VIR.


As you can see it puts some meat on the ground.

Bill

 

Some of the SCCA guys will stretch a tire that much. Some claim it improves things. Personally I have not been brave enough to stretch a tire that much.

 

Understood, my plan is Nankang AR'1's
Fr 315/30/18
Rear 335/30/18

Anyone have significant experience with the Nankang's??

 

No personal experience, but if you are willing to run something more aggressive than a 200TW, then any reason you are avoiding using used racing slicks or Hoosier R7?

 

Still wearing through my first set in those sizes and my initial impressions are positive. Definitely better than R888R and Rivals but I've always really liked NT01's. Those are on backorder so AR1's seem to be the best 100TW tire that is actually available at the moment.