[SoftShoe]

Test from tirerack.

TLDR: For faster times, amount of stretch on the wheel can matter more than trying to maximize width.

[dradernh]

That's a very useful video. Unsurprisingly, given the quality of service offered by the Rack, it matches two rules of thumb I got from professionals:

1) Ideally, a tire's tread width should fall in the range of -1" to +1" of the wheel's width. (Source: a Hoosier tire engineer) When they're available, I use the Rack's tire tread widths. They measure each tire in their catalog, so the comparison between two tires' tread widths is valid. The Rack's tire tread width measurements can vary from tire manufacturers' published data.

The Hoosier engineer's emphasis was that a narrower tire on a wider wheel was to be favored over a wider tire on a narrower wheel. The context of that conversation was lap times on road courses.

2) In the wet, a narrower tire does a better job of staying in contact with the pavement. Additionally, increasing tire pressure ~2-4# above what you'd run in the dry improve the ability of a tire to do that. Water depth on the surface will influence what you choose to do with tire pressure. Think snow tires; it's the same problem. (Source: a pro driver)

[ggggbmw]

That was a fascinating video. I cringe when so many people are asking "what's the widest thing that will fit". Then again, if you're doing it just for looks I suppose it doesn't matter. But I'm more about real performance than cosmetics.

[harma24]

Originally Posted by ggggbmw

if you're doing it just for looks I suppose it doesn't matter. But I'm more about real performance than cosmetics.

I'm an engineer, and I say this all the time to architects I work with: Functional is beautiful.

Conversely, if it serves no practical function, I think it looks hideous. Nope, you won't find me going to many modern art museums.

[230iZTR]

As someone who definitely advocates for going as wide as possible, I'll point out a few things:

1. The widest 245mm/9" combination is the fastest tire combination that met the tire manufacturer's recommended specs. The 225mm/9" combination that was marginally faster in the dry is recommended as a track-only fitment because its really stretched.
2. Corner exit was significantly better on the 245mm/9" combination, and that's in a GR86 with ~200whp. Our cars can very easily get double that with just an off-the-shelf tune. Maxing the rear tire is hugely important for the F22.
3. The turn in hesitancy and mild-understeer Tire Rack took issue with on the 245mm/9" combo can be tuned out with alignment and/or a bigger rear bar. I'm using both, and turn-in is very crisp and the car is neutral on 255mm/9". I'd go to a square 265mm/9.5" in a heartbeat if it weren't for this car's weird staggered offset requirements.

[SoftShoe]

Fair enough.

For me, it’s all too much work to barely do better than a 225 on an 8” (or whatever the BMW equivalent is) in the dry and worse if it’s wet.

But I do appreciate the idea of knowing what you want and making it happen.