I don't know of a rule of thumb for that, my guess is it would vary based on sidewall height, load rating, PSI etc.. No question it would be less on a 9 inch rim because your tire would be spread out over a wider wheel service so less "bulge" on the outsides. The general rule I've heard for tire width on a wider rim is that for every 1/2" change in rim width, the tire's section width will correspondingly change by approximately 2/10". So your tires (In theory, so many variables) would be 4/10 of an inch wider on the 9 inch wheel. If I had to guess my 10pm on a Friday night beer math would tell me you could anticipate about 2/10 of an inch less bulge on each side of the tire... Keep in mind so many variable when you are talking about tires and wheels...Ah, interesting. Thanks for the tip.
If I spread my 285/60s out another inch being mounting them on a 9" rim, how much decrease in tire bulge should I expect. I have right at an inch of tire bulge now. Would it decrease that tire bulge a 1/2 inch? Is there any sort of thumb for that.
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