Stretched Tire Theory.

[Norm Peterson]

The issue is that while a 10" wheel probably is optimum for a 255 TIRE. A a 285 or 295 tire is optimum for that WHEEL, and that car.

What you're saying is that there's a difference between extracting the maximum performance from a given tire size (by adjusting wheel width) and extracting the most performance from a fixed wheel width by the choice in tire size. I suspect many people think those are two ways of saying the same thing, but they aren't.

What I can add here is that 285/35's on 11" wide wheels is noticeably more composed and easier to drive at a little over 0.9 cornering g's than 265/40's are on 9.5" wheels at a little under 0.85 g. Tread widths as published by the tire mfr (Michelin) are the same for both sizes (both being MPSS) at 10.2", and the same "unofficial test loop" was used, in comparable driving conditions (clear, dry, cool). It's a max-recommended fitment vs a measuring width fitment.


FWIW, if I didn't already have the 9.5" wide wheels, the 265/40's would have gone on 10".


Norm

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[Norm Peterson]

I'm going to say here that stock/street category autocross rules introduce a significant and artificial distortion into the matter of choosing wheel and tire sizes, generally to the extent that choices made for that very specific form of competition should not be applied to street driving or any other form of corner-carving. At autocross, it's on the driver to work with rules-defined limitations because he can't remove the artificial limitations themselves.


Norm

 

[Norm Peterson]

True. Some nitto brands say a 305/30 or 35 is good to go on a 19x10 wheel.

That would be 305/35. 305/30's get 10.5" as the min-recommended. It's a Tire & Rim Association thing the most tire mfrs follow for nearly all of the sizes they produce (there do seem to be a few exceptions, here and there).


Norm

 

[Norm Peterson]

Through my searches of wheel and tire combos, most people suggest a 285/35 for a 10” wide wheel.

Because it's an easy and perfectly acceptable fitment, and the same offset wheels can be used either at the front or rear.

And essentially every 285 I’ve seen fits square, some even with the slightest bulge. I saw a couple pics where a memeber here put a 295/35 mpss on a 19x10 and there’s some sidewall stretch going on. It’s hard to tell he because like stated previously, not every tire is created equal

Edit; found it

https://www.mustang6g.com/forums/threads/mrr-m350s-with-295-35-psss.104930/

With low profile tires, anything much over a quarter inch of bulge out past the wheel is a lot. "Bulge" as used in these discussions is not the slope of the upper sidewall region (starting from the shoulder).

In your link, outside to outside of the wheel is wider than the tire's tread width, but that does not make it "stretched". Actually, 10" is a min-width fitment for 295/35's, so if anything that's a 'squeezed' or 'pinched' fitment, and there is quite a bit of sidewall peeking out past the wheel (not counting the rub strip).

Here's a better illustration of sidewall shape relative to the wheel for a 295/35 on 10's, and the bulge is clear. 19" vs 18" is irrelevant, the 18" file is just what I had handy.

On 10.5" wide wheels. Note that there is still a tiny bit of 'bulge'.

And finally on 11.5" (max-recommended).

Norm

 

[Ron]

It's also possible they just went nuts [w/the PP2] & wanted to see how wide of a tire they could fit on there before it looked too ridiculous to sell. LOL

Ford wanted the PP2 to exceed 1g on the skid pad. The wheel/tire combo allowed them to obtain a 1.06g skid pad reading.

 

[Norm Peterson]

It's also possible they just went nuts and wanted to see how wide of a tire they could fit on there before it looked too ridiculous to sell. LOL

The PP2 basically borrowed the GT350 wheel sizes and put GT350R front tires on all four.

Kind of like what Chevy did going from the 5th gen ZL1 to the 5th gen SS/1LE.


Norm

 

[19S550PP2]

I am leaning heavily toward ordering Michelin Pilot Sport 4S in 285/35 front (19x10.5) and 295/35 (19x11) rear for my PP2 to replace the Cup2s. I have yet to see anyone running these exact sizes but they seem to match the relative size ratio of the GT350 (295/35r19x11 and 305/35r19x11.5).
Alternatively, I may go with the considerably cheaper NT555G2 in 285/35 and 305/35, though my goal for the car is ultimate handling while still streetable (ie rain)
I appreciate the discussion and would like your thoughts.

 

[BmacIL]

I am leaning heavily toward ordering Michelin Pilot Sport 4S in 285/35 front (19x10.5) and 295/35 (19x11) rear for my PP2 to replace the Cup2s. I have yet to see anyone running these exact sizes but they seem to match the relative size ratio of the GT350 (295/35r19x11 and 305/35r19x11.5).
Alternatively, I may go with the considerably cheaper NT555G2 in 285/35 and 305/35, though my goal for the car is ultimate handling while still streetable (ie rain)
I appreciate the discussion and would like your thoughts.

There are far, far better tires available for similar price to the Nitto. Pilot 4S, Pilot Super Sport, Conti ExtremeContact sport are all excellent summer tires that have great rain performance and much better dry grip than the nitto. Even the Firestone Indy 500 is a better choice. One that's not been talked about much because it's new is the Bridgestone S007A. That slots in between the Michelins mentioned above and a track tire like the Cup 2 or a RE71R. It still has good rain performance, but more focused on dry grip than comfort.

 

[ModularKid21]

There are far, far better tires available for similar price to the Nitto. Pilot 4S, Pilot Super Sport, Conti ExtremeContact sport are all excellent summer tires that have great rain performance and much better dry grip than the nitto. Even the Firestone Indy 500 is a better choice. One that's not been talked about much because it's new is the Bridgestone S007A. That slots in between the Michelins mentioned above and a track tire like the Cup 2 or a RE71R. It still has good rain performance, but more focused on dry grip than comfort.

Interesting, sounds like they’re worth looking into. Prices are awesome, as Tire Rack has 285/35/19 s007a’s for $247 a tire!

 

[Grintch]

I'm going to say here that stock/street category autocross rules introduce a significant and artificial distortion into the matter of choosing wheel and tire sizes, generally to the extent that choices made for that very specific form of competition should not be applied to street driving or any other form of corner-carving. At autocross, it's on the driver to work with rules-defined limitations because he can't remove the artificial limitations themselves.


Norm

Are they any more artificial than other categories that restrict tire size? Isn't the fixed wheel approach of Stock/Street similar to all the people who say, I have these wheels, what tires should I run?

But the general trend in road racing & autocross is to run bigger wheels and tires. If the wheels sizes are limited, you run big tires for that wheel. If the tire sizes are limited, you run big wheels for that tire. If neither is limited cost, weight, and availability are the main secondary considerations, with the primary always being to fit as much wheel & tire as will fit.

On many production cars, one of the big limitations is clearance to the spring/strut/shock. And fitting max wheel widths for a given tire size tends to make that worse and thus limits how much tire you can run.

 

[NightmareMoon]

Are they any more artificial than other categories that restrict tire size? Isn't the fixed wheel approach of Stock/Street similar to all the people who say, I have these wheels, what tires should I run?

Yes, autox is a bit more extreme in how far outside the box they will go. You dont see too many street cars cramming 285s on 9” wheels. In competition its sometimes worth sacrificing some tire longevity and wear to get a 1/10 second faster, disregarding what it might do to handling feel.

 

[Norm Peterson]

Are they any more artificial than other categories that restrict tire size?

My opinion - yes, because it leads to people running tire and wheel combinations that the tire mfr would never officially sanction.

Isn't the fixed wheel approach of Stock/Street similar to all the people who say, I have these wheels, what tires should I run?

Yes and no.
Yes, in that it is the same question.
No, in that the questioner should not feel entitled to receive advice that falls outside of Tire & Rim Ass'n guidelines.

On many production cars, one of the big limitations is clearance to the spring/strut/shock. And fitting max wheel widths for a given tire size tends to make that worse and thus limits how much tire you can run.

You run into the same situation even faster when it's tire width that is uncontrolled.


Seems to me if wheel width is to be fixed at OE, choices in tire size should probably be limited to what that width wheel is the minimum recommended width for. No more of this 285/xx on 8" wide wheels or 295/xx on 8.5's silliness.


Norm

 

[BmacIL]

My opinion - yes, because it leads to people running tire and wheel combinations that the tire mfr would never officially sanction.



Yes and no.
Yes, in that it is the same question.
No, in that the questioner should not feel entitled to receive advice that falls outside of Tire & Rim Ass'n guidelines.



You run into the same situation even faster when it's tire width that is uncontrolled.


Seems to me if wheel width is to be fixed at OE, choices in tire size should probably be limited to what that width wheel is the minimum recommended width for. No more of this 285/xx on 8" wide wheels or 295/xx on 8.5's silliness.


Norm

Far sillier is this 225/xx on 10"+ wheels trend on the stancebros cars.

 

[Norm Peterson]

Far sillier is this 225/xx on 10"+ wheels trend on the stancebros cars.

True.

FWIW, I've been calling that sort of thing "Euro-stretched" to distinguish it from the milder amounts of stretch that are within T&RA guidelines . . . up to maybe half an inch outside it on the wide end for 60 and taller profiles .


Norm

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