Rim vs tires size question

[Costcocombo]

I currently have 19"x 9" rims with 255/40ZR19 Michelin A/S tires for my four tires. I'm thinking of buying new rims but hoping to keep the tire. Will my tire size fit rims that are 19"x 8.5 or 19 x 9.5"? Thanks!

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[WildHorse]

255's are a tad to narrow for a 19 x 9.5 WHEEL.

 

[WildHorse]

255 on a 10" wide wheel? Come on now...

 

[WildHorse]

Not ideal, but it will physically fit.

So will a 235 on a 10" wide wheel. Personally I think a tire tread width that's < a wheels width greatly increases the chance of a bead failure.

 

[Costcocombo]

Scroll down to the chart, very useful.

https://www.tyresizecalculator.com/charts/tire-width-for-a-wheel-rim-size-chart

thank you! this is very helpful!!!

 

[bluebeastsrt]

The nice thing about rubber. It stretches.

 

[Apex Wheels]

255/40-19 will fit just fine on a 9.5" wide wheel. In fact, you'll get better performance out of that tire when it's on a wheel that wide vs something narrower because the contact patch is stretched out more and the sidewall is better supported so the steering response is quicker/better.

We have had a few customers run 255s on 9.5" wide wheels and the tires don't look stretched out either. A lot of that will come down to the individual tire however as every model differs in actual width, "size of curb feeler", etc.

- Cory

 

[WildHorse]

the steering response is quicker/better

Care to share the data on that? Show how a 255 of a 10" wide wheel is better performing than a 275.

 

[Condor1970]

I personally run 265/40 on 19x10, and the stretch is 1/2" over the recommended 9.5". So, the 255 will fit just fine, and have better steering response due to the slight stretch and angle of the sidewall. German cars like BMW and Porsche readily have factory tire sizing that is stretched 1/2" over for that reason alone. A stretch of only 1/2" WILL NOT present a danger of bead separation. If that was the case, I doubt Porsche would have put 265/40 tires on a 19x10" for track use out of the factory. They did it, because the slight stretch actually does provide a slight increase in steering performance over a 275/40 with the same 19x10 rim.

Here's a pic of mine, which is probably very close to what the profile and slight stretch it would look like with a 255 on a 19x9.5 rim.

 

[NightmareMoon]

They did it, because the slight stretch actually does provide a slight increase in steering performance over a 275/40 with the same 19x10 rim.

Or did Porsche do that because they could fit a 10” wheel but the car only needed a 265 to achieve the required slight understeer bias for the average driver who never does anything interesting with the car?

While yeah, its probably marginally better steering response, but how much better really depends on the tire construction. I’ve run 285 tires on 9” 10” and 11” front wheels, and its very difficult to notice the difference with stiff-sidewalled tires. Maybe its a bigger difference with soft-sidewalled commuter tires? Tire wear suffers when mounted on narrow 9” tires for sure.

 

[Condor1970]

Or did Porsche do that because they could fit a 10” wheel but the car only needed a 265 to achieve the required slight understeer bias for the average driver who never does anything interesting with the car?

While yeah, its probably marginally better steering response, but how much better really depends on the tire construction. I’ve run 285 tires on 9” 10” and 11” front wheels, and its very difficult to notice the difference with stiff-sidewalled tires. Maybe its a bigger difference with soft-sidewalled commuter tires? Tire wear suffers when mounted on narrow 9” tires for sure.

Because of the sidewall angle, the 265's actually provide better overall track performance in steering and also on various surfaces, ie slightly wet. However, the wider 275 will provide slightly better grip during acceleration, like drag racing. That however, is not the Cayman's forte. Keep in mind, the 265's on a Cayman are on the rear, but the forces on the rear offers the same idea in better performance while turning. Not as much rotation, for a more laser like track experience with a lighter car, vs the Mustangs rear sliding all over the place when pushed.

 

[Apex Wheels]

Care to share the data on that? Show how a 255 of a 10" wide wheel is better performing than a 275.

I don't have data, I just have personal experiences on the street and track. But it's pretty common sense that a sidewall that is stretched out will have more response because there's more tension.

I never said it would be faster, nor did I say a 255 should belong on a 10" wide. I agree a 10" wide wheel should have at least a 265 on it, preferably 275 or 285. But it's also important to look at the actual specs for whichever tire you're considering since no two are the same across different manufactures.

 

[Grintch]

255's are a tad to narrow for a 19 x 9.5 WHEEL.

Not according to most tire manufactures that say they are good up to a 10" wheel.

PS - don't ask a bunch of internet yahoo's (like me). Every tire manufacture has a spec sheet for all its tires with recommended sizes, etc. Tire Rack at least has them on their website if you are too lazy to go to the Manufacturers site (I am not sure about other tire dealers).

 

[Grintch]

Care to share the data on that? Show how a 255 of a 10" wide wheel is better performing than a 275.

For one thing a 255 on a 10" wide wheel will be slightly wider than a 255 on a 8.5" wheel (the normal recommended range for a 255 is a 8.5 - 10" wheel). Plus it disapates heat better and flexes less.

Any racer will tell you it is usually better to run the widest recommended wheel size for a given tire (for when tire size is limited by rules or selection) and to run the widest tire that will fit (when wheel size is limited).

 

[WildHorse]

All your answers right here.

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