Tire & wheel fitment
Know the numbers before you buy.
Free calculators for tire sizes and wheel offset, and plain-English guides built on manufacturer specifications. No fake tests, just the math and the sources.
Compare two tire sizes
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Figures are nominal geometry calculated from the size code. A tire’s real measured diameter varies by brand, model and tread depth; check the manufacturer’s spec sheet before you buy, and confirm clearance, load index and speed rating for your vehicle.
Popular comparisons: 265/70R17 vs 285/70R17 225/65R17 vs 235/65R17 245/75R16 vs 265/75R16 275/60R20 vs 275/65R20 265/70R17 vs 35x12.50R17 215/55R17 vs 225/55R17 275/55R20 vs 285/55R20 33x12.50R17 vs 35x12.50R17
265/70R17 → 285/70R17
Tire Size Calculator
See the change in diameter, width, sidewall, revolutions per mile and ground clearance, and how far your speedometer will be off.
7.5x17 +44 → 9x17 0
Wheel Offset Calculator
Compare two wheels and see the backspacing, how far the outer lip pokes out and how close the inner barrel gets to the suspension.
113T → 2,535 lbs · 118 mph
Load Index & Speed Rating
Type the code from your sidewall and see the load each tire carries and its maximum speed, with the full charts.
How to read a tire size
Latest guides
The first size guides and tire comparisons are being written now and will appear here.
How we work
Sourced specifications
Sizes, load and speed ratings, UTQG grades and warranties come from the manufacturer or the official tables, and we link to them.
Honest about testing
We do not run our own tire tests. When we cite a braking or treadwear result, we credit the published test it came from.
Math you can check
Every calculator shows its formula and its limits, so you can verify the numbers before you spend money.