Tire Size Calculator

225/45R17 = 225 mm wide, sidewall is 45% of width tall (101 mm), fits a 17-inch wheel. 'R' means radial.

A P-metric code is the US passenger-car sizing standard: an optional 'P' prefix, then section width in millimetres, a slash, the aspect ratio (sidewall height as a percentage of width), the construction letter 'R' for radial, and the wheel diameter in inches. So P225/45R17 is 225 mm wide with a 101 mm sidewall on a 17-inch wheel. 'LT' instead of 'P' means light truck, which carries heavier loads at higher pressures.

As a general guideline, keep the overall diameter within about 1% of stock for all-wheel-drive and four-wheel-drive vehicles, and ideally under 3% at most. AWD systems compare wheel speeds constantly; a mismatch makes the centre differential, viscous coupling or transfer case work permanently against itself, generating heat and wear. Many manufacturers also require all four tires to be replaced together for exactly this reason. Tolerances vary by system, so treat the 1% / 3% thresholds here as guidance and confirm in your owner's manual.

Revolutions per mile is how many full turns a tire makes to cover one mile: 63,360 inches per mile divided by the tire's circumference in inches. It matters because your speedometer, odometer, ABS and traction control are all calibrated to the stock figure. Fit a tire with fewer revolutions per mile and the car travels farther than the computer thinks each turn, so the speedo reads low and the odometer under-counts your mileage.

The load index is a coded number for the maximum weight one tire can carry — 94, for example, means 1,477 lb. The speed rating is the letter after it (H = 130 mph, V = 149 mph, W = 168 mph) and is the maximum sustained speed the tire is certified for. They're independent: never fit a tire with a lower load index than the placard on your door jamb, and matching or exceeding the original speed rating keeps handling as designed.

Yes, on both counts. Wider or heavier tires add rolling resistance and rotating mass, which typically costs a few percent in fuel economy and blunts acceleration. A larger overall diameter acts like a taller final-drive gear: slightly lower engine revs at cruise, but slower off the line. Smaller diameters do the opposite — quicker acceleration, higher revs and usually worse highway economy.

The odometer counts wheel revolutions × programmed circumference. Bigger tires travel farther per revolution, so the speedo under-reports.

Stay within ±3% of stock diameter. Bigger changes can trigger ABS/traction warnings and affect ground clearance.

Not necessarily — wear is dominated by rubber compound, alignment, and inflation, not width.

Usually no, but check your manufacturer's list of approved sizes for TPMS and load rating.