Tire Size for 17x7.5 Rims on Track

[WJBenGTI]

Hi All,

I know that one of the typical GS autocross setups is 245-40-R17 (being stuck with a 7.5" rim), but how does that work on track? I know Tirerack recommends I not exceed 235 on my 17x7.5" rims, but people do it for autocross. I've been told that although this works at an autocross, the pinched tire may actually cause some strange handling characteristics on track. Is this a bunch of BS, or is there any truth to it? I'm looking at the Hankook RS-4's in either 245-40-R17 or 235-45-R17 for use as a daily with a few HPDE's and autocrosses on free weekends. My last tires were 235-45-R17 RE71R's and they seemed to handle fine but it was really the first grippy tire I had on my car and they wore very quickly on track.

Thanks!

 

[glitronic]

245/40-17 on 17x7.5 works fine for track.

Here's a lap at High Plains Raceway in Colorado on that setup (Nexen SUR4G):

 

[jay745]

Pinched tires will cause a floaty feeling during turn in on the track. 235 is about the widest you'd want on a 7.5 wheel. I use 235/45/17 rs4's on an 8" wide wheel

 

[R Golf]

Pinched tires will cause a floaty feeling during turn in on the track. 235 is about the widest you'd want on a 7.5 wheel. I use 235/45/17 rs4's on an 8" wide wheel

Same here. I also suggest 235 max. I run 235 max on 7.5 (18's) and normally run 225's with zero delta in lap times. I like the feedback and price of the 225's more than 235's so I stay with that. I tried 245 RE71's and did not like them.

 

[Dog Dad Wagon]

Yeah 245 is too wide for a 7.5 barrel of performance is a goal. Sure you can run it on a daily for lip protection and comfort but you want square sidewalls, which 225 is ideal for a 7.5 barrel. Perhaps the 235 is better for that width. I’d do what the track guys said above

 

[1970something]

I’ve seen this article on here before and I found it really helpful:

https://motoiq.com/how-to-properly-select-and-size-tires-for-performance/

Main takeaway for me was that you should go to TireRack, look at the specs for a given tire, and look at the “tread width” value rather than using the millimeter width value. Different manufacturers will have different effective widths for a given mm width.

 

[SouthFL_Mk7.5]

I use 225 on a 17x7.5 wheel for track days. Not the widest but feels just right.