[DaveN]

I have searched but no real answer that I can find. What is the relationship between rim width and actual tire size? I.E. I have stock 17" C2 rims labeled 7.5 on the stem. That's 190.5 mm but the tire is a 225 as per the Porsche gas cap label. Obviously one does not buy a rim to fit the tire exactly. The Forgestar wheels I was looking at come in these widths:



18×8.5 offsets from +26 to +50

18×9.0 offsets from +20 to +55

18×9.5 offsets from +26 to +60



So is it still safe to put a 225 on a 8.5 and a 255 on a 9.5?

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[bombfactory]

Unfortunately, actual tire widths often differ from what is listed on the side of the tire - and also differ from manufacturer to manufacturer. So a 225 from say Michelin not only might not be exactly 225mm wide (and where is that even measured, tread width, overall width?) but also might be wider or narrower than the same size tire from say Yokohama. Yes, it's a little crazy!



If you go to a tire manufacturers web site, they should have a chart listing specs for every tire they make, which usually includes the recommended wheel widths - sometimes with the particular tire's 'ideal' wheel width hilighted.



-Austin

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[aslet]

You have to do it by tire specs. They will tell you the width range each tire can go on.



On 17x7.5 I run a 245 wide.

On 17x9 I run a 275.



These also give me a larger tire circumference. That can be hood or bad.

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[StephenHallman]

Wow... I didn't know you could go as wide as 275 on a 17x9.

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[DaveN]

I normally wouldn't want rims that wide for my tires, more weight, but the offsets are good at those widths. I don't think I could get away with anything less than 50 and 60.

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[aslet]

I agree with DaveN. I would put a 225 on a 7 or 7.5 wide wheel. On a 8.5 wide wheel I would do the 255 and a 275 on the 9.5 wide.

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[nissanite]

On my street car with 7.5 & 9 x 17 I run the stock 225 & 255.

On the track car we have 8.5 front & 10 rear with the same size stock tires.

The tires are Bridgestone RE-11 on both cars. The rim width range for the tires

is at the max on the track car. The ride is firmer on the track car & the handling is better.

Tire width is measured on a defined rim width. It is from sidewall to sidewall, not the tread.

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[Lim Yong]

Check Tirerack.They have the charts that show widths for each tire based on the width of the wheel mounted...

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[flash]

those tires are on the absolute minimum recommended rim widths



this means there is a very good chance of sidewall flex, which while potentially getting twitchy in a snap-back condition, would provide for a softer ride



the outside diameter is big, which would affect the speedometer, and raise the final gear ratio, slowing the 0-60 times, but giving you better fuel economy



not a horrible thing overall, but not necessarily optimal - it really depends on what you want

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