I do DE events about 4-5 times a year. Been running a 265/40 summer tire on 18x9.5 RPF1 wheels. Square. These tires are shot and I'm planning on stepping up to some Hankook RS-3s to use on track only.

The 265/40 is close in terms of speedometer reading of OEM 245/45s and they do not rub. Traction control is wacky with this size, probably due to square set up but I don't use TC on track anyway.

However, the 265/35s are $20+ less per tire. The speedo will be off a good bit, which makes no difference. Side wall would be narrower and might improve handling.

Any reason not to go with the 265/35s over the 265/40s?

 

Your gearing will also be better with the 265/35 , depending on your tracks.

265/35 front
265/40 rear

ABC/TCS will like you. I really hate the ABS problems at the track that i get with a square setup.