I have an 09 that I am running in BS trim, in an indexed Street Tire class in our local region. My current setup is 245/40-18 on 18x8.
The 2009 8's have a lower final drive, so top speed in each gear is lower than on the 04-08 models, but technically, I guess it is possible to accelerate faster in those gears? Maybe, maybe not.
Anyway, I had a thought that it might be beneficial to try a 245/45-18, in order to gain some of that gearing back. Yes, technically it would accelerate slower, but that never really seems to be a problem with my car, while running out of speed in 2nd gear does happen. I figure worse case scenario, the acceleration may even out with an 04-08, or maybe a bit slower.
Any thoughts and input on this? There are 3 pretty good street tire options in that size: Star Specs, AD08's, RE-11's.

 

I would opt for the acceleration advantage and slightly lower CG of the shorter tire (.5" radius change in this case). These benefits will help on a lot higher percentage of the course than the 2 mph increase in top end speed.

Chris H

 

I also doubt the shorter gearing will be as much of an issue for you on street tires VS the guys on R compounds. Your corner exit speed and top speed will be lower, so you are less likely to run out of gear.

I thought I read one report from an 09' BS driver that the 18" cars on short Rs are not even able to hit 60mph in 2nd.

 

GPS speeds top out at 59+ to maybe 60 on 285's in my 09.