Tire Information Thread

[aw614]

FIY, if anyone wants to see how a 15x8 vs 15x7 205/50/15 RE71 compare with each other

[g3teg97]

I'm confused because the specs say RE71R in 205/50 has a max wheel width of 7.5".

[aw614]

There has been a lot of test and data from grassroots motorsports and a few others that show the 15x8 on a 205/50 being faster even with the slight stretch look it has.

I can't really explain it well. I think the articles from GRM talk about it

[g3teg97]

Damn, didn't know about that.

[coolhandluke]

There has been a lot of test and data from grassroots motorsports and a few others that show the 15x8 on a 205/50 being faster even with the slight stretch look it has.

I can't really explain it well. I think the articles from GRM talk about it

Hrm... I will have to research this.

[aw614]

Here is the most recent test from GRM
https://grassrootsmotorsports.com/artic ... -re-71r-v/

There might be more articles from previous tests, but doing some searches it seems a lot on a lot of forums, the writer of the article, Andy Hollis has mentioned it a few times

[g3teg97]

The tread width on 205/50R15 tires measures about 7.2 inches, which was a nice fit for the 15×8-inch wheels we used in the first round of testing.

That just sounds weird to me.

Bridgestone says 205 width tires are approved for 5.5 - 7.5", seems like the sidewall would be stretched and create problems. Just my $0.02 cents.

[Xian]

Manufacturer recommendations are exactly that... their recommendations for most folks/most applications. Anything motorsports related, where performance is key, is going to be tailored to the best setup regardless of what the manufacturer specs out. In this case, it’s common for street tires (with their softer sidewalls) to be faster when slightly stretched and better supported.

Having said all this, the 71R tends to be on the stiffer end of things for street tires so a half inch isn’t likely to be a huge advantage. Any of the others will benefit even more from being stretched... I ran a 225 Rival on a 15x9. IIRC, Andy’s GRM testing showed substantial gains running the 225 on a 9” wheel vs 8” wheel. Pretty sure the 245 ended up being best on a 15x10.

PS
I highly suggest folks try it for themselves. There are absolutely some cases where the tire may not be faster on the clock but nah be quite a bit easier to drive or more consistent/predictable.

[g3teg97]

Thanks for the insight on that. Guess I was thinking it's more of a hard rule or whatever. Appreciate the feedback and it made sense.

I wanna pick your brain about suspension, but I'll post over in the suspension thread.

[aklackner]

I’ve spent 0 time in on the track but isn’t geometry a concern? Stretching means the tread is smaller than the rim cross section (think trapezoid)? If so the anytime there’s force where the tread is pulling against the cross-section you’re only pulling on a single bead vs where the tread section is at least the width of the cross section you’ll always be pulling against the bead on both sides right?