Max tire width for PP wheels

[Norm Peterson]

Sidewall flexing and the resulting heat buildup isn't a problem for a dragstrip pass or even a minute around an autocross course. It is for longer durations on the street in the summer. Tire design for street use is very much concerned with heat and tire carcass deformation (flexing). Even tire load ratings are essentially defined by allowable deflection under the (rated) load.


Norm

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[ETCH]

Norm,

Take a freaking pill and chill bro. if someone wants wider on the rear and it fits, why have such a spaz attack about it. Heck if someone spends 40 plus K on a car and wants a little wider on the rear tires, so be it...

and MikeG, that looks sick bro...
my .02 cents

 

[Norm Peterson]

How about you do a little real learning about tires instead of working only in terms of "wants". Getting a wide tire to physically mount on a too-narrow rim and hold air isn't good enough, and if you want to know the truth makes for a pretty lame, "cheaped-out" look when you do know a little more about tires.

All anybody who can spend $40k on a car and wants to put wider tires on it than it came with stock needs to do is mount those tires on wheels of proper width. If right at this moment a person can't spend the $ to do it right, he shouldn't be doing it until he can. Simple enough.


Insulting me . . .

Take a freaking pill and chill bro. if someone wants wider on the rear and it fits, why have such a spaz attack about it.

is a losing argument that isn't going to change the tech behind the proper fitment of tires to wheels.


Norm

 

[Budwise]

+1 Norm. Just because it can be made to mount doesn't mean it fits right.

 

[Mikeg4572]

I'm not talking 345's, I was thinking 295/35/19's on PP rears

 

[Norm Peterson]

Two issues.

One is that the line between fully acceptable and not has to be drawn somewhere, and no matter where that is there will be people who will feel that "only another 10 mm of tire size isn't going to matter".

Which kind of leads to the second . . . there will be people who will stretch any recommendation for running 295/35's on 9.5's into an OK for 305's . . . . Slippery slope.

I wish it was possible to convey what the difference in car behavior really feels like when a rear tire gets cut down, between tires mounted on a min-recommended width wheel and tires mounted on a wheel out around max-recommended. But the Cliff's Notes version is you don't want to be at min-recommended, let alone below that. Free experience-based advice because I've been there, both scenarios.


Norm

 

[Need4SpeedMotors]

Norm thats true

 

[Grintch]

How about you do a little real learning about tires instead of working only in terms of "wants". Getting a wide tire to physically mount on a too-narrow rim and hold air isn't good enough, and if you want to know the truth makes for a pretty lame, "cheaped-out" look when you do know a little more about tires.

All anybody who can spend $40k on a car and wants to put wider tires on it than it came with stock needs to do is mount those tires on wheels of proper width. If right at this moment a person can't spend the $ to do it right, he shouldn't be doing it until he can. Simple enough.


Insulting me . . .
is a losing argument that isn't going to change the tech behind the proper fitment of tires to wheels.

Norm

So where are your documented cases of tires blowing up because they were 10-20mm outside the recommended range? I wouldn't run wider than that (no 305's), but I see hard driven cars with oversized tires on stock wheels pretty often with no problems. Are they giving up some performance with the narrower wheels, yes, but they still have more than they would with narrow tires.

 

[Norm Peterson]

Mine didn't "blow up because of sizing relative to the rim widths", but the level of control following a sudden deflation due to road debris was worlds apart between min and max recommended. It's this controllability that I'm most familiar with, personally.

Heat build-up due to excessive sidewall flexing is a well known phenomenon, and on too narrow rims the heat can become concentrated in a region of the tire not particularly designed to withstand it as well. This from an actual conversation with a tire engineer.

The min recommended fitment wanted to lurch every which way but straight from even the gentlest steering inputs.

The ~max recommended fitment was hardly any less controllable than the car's OE wheel and tire fitment and more capable than I could explain and expect you to believe (so let's just say it was harder than most people generally drive and leave it at that). But I do have a picture that should give you some idea how much tire damage we're talking about by the time I had even a poor place to pull over and change it (and how much the extra lateral stiffness on the other tire on that axle matters). I did have to cut a few carcass cords to completely separate the outer sidewall from the rest of it, but only a few. Didn't hurt the rim at all.

Norm

 

[Strokerswild]

Slightly related semi-threadjack, but I had a stock size rear on my GT500 have a similar failure mode (car was very controllable despite it).....

 

[BlackPP]

You really shouldn't be putting passenger car 295's on wheels that are only 9.5" wide. 10" minimum.

285/xx is the widest passenger car tire that 9.5" wide wheels should ever have to support, and 9" wide wheels are good for up to 275/xx - per Tire & Rim Association tables.

A 295/xx LT tire would probably be OK'd for 9.5" wide wheels if you can find any, as LT's are designed to somewhat different needs and requirements and allow fitment to narrower rims. But Light Truck tires on a Mustang???

Why people are so ready to throw away any of the performance that their wide tires promise by squeezing them down onto too-narrow rims has never made much sense to me.


Norm

Norm,

I like the information you have given here.

Thanks for the technical input you have on this

So would it be best to put a 305 on an 11" wheel instead of a 10"? I am looking at having my stock rear PP wheels widened to 11" or maybe 12" and run a 305/35/19.

 

[Budwise]

305 would go on a 10.5"-11" perfectly.

 

[rcb020]

Would you guys recommend a 285 or 295 on a 10" wheel? I plan on doing quite a bit of road course events.

 

[fionic]

Just found this

 

[Norm Peterson]

So would it be best to put a 305 on an 11" wheel instead of a 10"?

Yup. Maybe even 11.5". Depending on profile, 10" may not even be wide enough to fall within the recommended rim width range for a 305 tire.

Would you guys recommend a 285 or 295 on a 10" wheel? I plan on doing quite a bit of road course events.

For any road course duty I'd rather see the 285 on 10.5" or even 11" and the 295 on 11". Slightly wider than "measuring width" is going to favor response and linearity, generally at a slight ride quality penalty. For 100% street-only duty, 285's on 10's and 295's on 10.5's are probably better combinations for most folks.


Norm

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