Here's the situation:

1. The Z is my daily driver and will also be used in about 6 track days and a few time attacks.
2. I want to run 245/40 and 275/40 in 18's to keep my speedo accurate.
3. I want the tire to last from March till the end of the year... say November.
4. Must be 140 treadwear or higher to conform to time attack class rules.

I really wish the RT615 or RE-01R's were available.

So. What would you do? I'll need to order by mid March as my track season starts March 31st at VIR.

 

Yokohama ADVAN Noeva AD07
BFG gForce KD
Kumho Ecsta MX
Sumitomo HTR-Z2

 

There are threads floating around with the conversion charts on them and the variance from the originals to keep a VDC functioning. I get the impression you've already done some calculating. You might get more help/opinions if you 1)list the original OE tire size,2) the year and model of your car(does it have VDC and whether you care), AND 3) how many miles you expect to drive in this period, and 4)what weather conditions you will regularly encounter.

 

beta- The Neova AD07 isn't available in the sizes I want otherwise it'd be a great choice. The BFG KD isn't bad and the Kuhmo MX has a great price as well.

I1DER- It's an 03 Track edition, 225/45 and 245/45 were the OE sizes in 18". I'm now running the Nismo LMGT4's. I put about 60 miles per day on my car, about 20k miles a year. Normally weather will be dry, sunny and 80 to 100. I don't care about wet traction honestly.

The most important thing to me is overall track performance at Summit Point's Shenandoah Circuit. I have to run a 140+ treadwear tire for Redline's street class time attack.

 

The BF Goodrich g-force TA KD is one of the best street tires available. I just do not know if the bugger is available in the sizes you want for an 18 inch wheel, but if it is, GO FOR IT. However, in the rain..............take the bus.