Anyone read the latest edition of SportsCar? Interesting write up on tire and wheel sizes, lightweight wheels and such? Pretty much throws a wrench in all we've assumed about tire widths vs. weight.

 

Yes, good article. April 08 Vol 66 No.4
http://www.sportscarmag.com/contents.asp

What did they test and find?

1. Plus size tires-
Keeping stock diameter similar they compared Hankook Rs2 in
205/50-15 vs 205/45-16 both on Motegi Traklite 1.0 rims on a Miata.

15"
Quicker launch
Easier to handle
More consistent run times
Corner Exit and braking distance better

16"
More wheelspin
Stiffer sidewall- easier to lock up brakes, more crisp initial turn in, transitional speed better
More difficult to drive at the performance edge
2 mph faster slalom speed

Lateral g-Force was same for both 1.01G
Overall lap times were very close (116.9 dirty vs 117.1 clean for the 15)
Overall 205/45-16 more difficult to control at the limit, more suited to experienced drivers.

2. Street tire vs R compound
Rota P45f 18x8 wheels on a B-stock RX8
Bridgestone Potenza RE-01R 245/40-18 full and 4/32" treads
vs
Kumho V710 245/35-18

V710
Better forward bite
Better corner exit
2 seconds better on a 40 second course
Addition of 24% stiffer front anti-roll bar reduced corner exit oversteer and reduced time gap to 1.7 seconds

3. Full tread or shaved Street tires

Full tread
Squealed much more
0.2 seconds faster
More easily overheated- required more time to cool down between runs

Shaved tread
More quiet except at limit
Handled heat much better

4. Wheel weight
Rota P45f 18" wheels at 21 lbs vs SSR comp in same size at 16 lbs each.
Run on Bridgestone RE-01R and Kumho V710s.

Street tires-
Runs were about the same- no real difference on time
Street tire grip may be a more limiting factor than rim weight.

V710s-
More consistent times and 0.2 seconds faster

A note-
Naturally your actual car and class will make a difference as do the weather conditions, road surface, and time between runs.

Perhaps the biggest challenge is to match your level of driving skill to tires that offer enough performance advantage and still remain within budget.

A stock car with limited camber and power may not be able to fully exploit having V710s vs RE-01Rs. In that case the RE-01Rs would be a better bet, it will cost less, last longer, give adequate feedback to the driver and be usable to drive to events requiring no wheel change.