Plus-size tire calculator
Moving to bigger wheels? This lists the tire sizes that keep your overall diameter close to the original, so your speedometer and gearing stay right.
Original diameter
| Tire size | Diameter | Difference |
|---|
How plus-sizing works
A bigger wheel needs a shorter sidewall to keep the same overall diameter. The calculator tries every common width and aspect ratio on your new wheel size and keeps the ones within your allowed difference, closest first.
Not every size listed is actually made, and widths need to suit the wheel's width. Confirm availability with a tire retailer, and use the wheel offset & backspacing calculator to check the new wheel's fitment.
Frequently asked questions
Why does keeping overall diameter close to stock matter?
A significantly different overall tire diameter throws off your speedometer accuracy and effectively changes your gearing, since the wheel is covering more or less distance per revolution than the drivetrain was set up for — staying close to stock avoids both of those side effects.
How much diameter difference is considered acceptable?
Many wheel and tire shops treat roughly plus or minus 3% overall diameter as a safe zone that keeps speedometer error and gearing changes small enough to not really notice — bigger differences start to compound into a real speedometer error and a real gearing change.
Does going up a wheel size always mean a shorter-sidewall tire?
Typically yes, if you want to hold overall diameter steady — a bigger wheel diameter has to be offset by a lower-profile (shorter sidewall) tire to keep the total rolling diameter close to what it was before, which is exactly the tradeoff this calculator works out.
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