The calculation engine for tire & wheel decisions
Compare sizes, upsize wheels, calculate offset, and find your car's factory fitment. With verified data for real-world vehicles.
All Tools
Professional tire & wheel calculators — all free.
Tire Size Comparison
Compare two sizes side by side: diameter, sidewall, speedo error.
Tire Size Calculator
See every dimension of a size: diameter, circumference, revs.
Tires by Vehicle
Factory tire & wheel specs by brand and model.
Plus Sizing Calculator
Upsize your wheels while keeping the overall diameter.
Wheel Offset (ET) Calculator
Will the new wheel tuck in or poke out?
Speedometer Error
How far off is your speedo after a size change?
Bolt Pattern Guide
How to measure PCD and which cars use which pattern.
RPM / Speed Calculator
Engine RPM from tire size + gearing.
Inch ↔ Metric Converter
31x10.5R15 ↔ 265/75R16 conversion.
Rim Width Range
Which rim widths fit this tire?
Tire Size Chart
All common sizes by rim diameter.
Find by Vehicle
Brand → model → year: factory tire & wheel sizes, bolt pattern and pressure specs.