What size R compound on 17x7.5?

Hi guys,

I can't find a straight answer anywhere. What is the best size to use on a solosprint/HPDE car with 17x7.5" rims? I'm thinking RA1/R888 or V710. Toyo says the R888 235/40 is designed for 8"+, but my Falken 235/40s fit perfectly. In one of the GRM issues testing the A6/V710/R888/R1, they were stuffing 285s on an 8" rim (except the Kumho which buckled).

I really really like my rims (Kosei K1 if that makes a difference) and I want to keep them and just stuff the most meat on them that I can. Some people say overfat tires are not a good idea, others (apparently GRM as well) say that you fit the biggest that will fit.

I figure this is the best gathering of people who have actually dunnit. If you think I can just get a 265 or something I will. I'm looking at either a 235-245/40 RA1/R888 or the 245/40 V710.

If it makes a difference, the car is an 87 E30 with an S52 swap, -2.5 camber front, I think around -2 rear.

Thanks! D

BigD wrote: Some people say overfat tires are not a good idea, others (apparently GRM as well) say that you fit the biggest that will fit.

Not necessarily. We conducted tests, and based on the results from that testing we'll decide what to stick with in the future. In the August issue of GRM, Woody Rogers found that a set of skinnier 255/35R18 tires worked better than a set of 285/30R18 tires.

Unfortunately, there isn't an easy answer without testing. Not everybody has access to multiple sets of tires and identical wheels, so sometimes you're forced to make an educated guess as to what will work best. (we do too, in some instances.)

My experience says when in doubt, go bigger unless they simply don't fit.

BigD wrote: I figure this is the best gathering of people who have actually dunnit. If you think I can just get a 265 or something I will. I'm looking at either a 235-245/40 RA1/R888 or the 245/40 V710.

That depends on what you're doing with the car. HPDE? I'd go with whatever's cheapest, since it's not a directly competitive event. I'd rather have more laps than marginally faster laps for my money.

If you're battling for trophies or money, it's probably worth the investment to compare them back-to-back.

My .02, YMMV.

On an E30 I would be surprised if ANY 17" works better than a 225/50r15.

Thanks Tom! So what would you say is the biggest tire that would reasonably fit a 17x7.5, in R888 and V710 form? I think I'd like to get 245s, but if the R888 is not recommended for 7.5" in 235...

In reply to The Brown Stig:

Yep, that or 335 Hoosier A6s, those seem to work well too.

All the tire sizes you mentioned are way too tall for an E30

235/40/17 would be best of the sizes you mentioned, but still too tall. I bet a 225/40/17 would be faster.

That said, The perfect tire setup for E30's without flares is 225/45/15 hoosiers on 15x8s.