Tire & Wheel Calculators
Every tool you need to plan a safe tire or wheel change — diameter math, speedometer error, offset and clearance, pressure adjustment and load index lookup. Built for accuracy, free to use.
Tire Size Comparison
Compare any two tire sizes — diameter, sidewall, speedometer error and ground clearance.
Speedometer Error
See exactly how much your speedometer reads off after a tire size change.
Wheel Offset (ET)
Visualise how a new wheel width and ET change inner clearance, poke and track width.
Tire Pressure Estimator
Estimate adjusted tire pressure when changing tire size — informational only.
Load Index Lookup
Decode any tire load index 70-126 into kg and lbs per tire and per axle.
How to use these calculators
Start with the Tire Size Comparison if you're considering a new size. Then verify speedometer drift, check how a different wheel offset changes inner clearance and poke, and confirm the new tire's load index meets or exceeds your vehicle's placard. Pressure estimates are informational only — always defer to the door placard and tire manufacturer's load tables.