Straight answers for tire, VIN and ownership maths

No sign-up, no upload, nothing stored. Every figure is derived from the size you type, with the formula shown so you can check it.

Tire size calculator

Compare any two sizes: diameter change, speedometer error, clearance and revolutions per mile.

Manufacturer, country, model year and check-digit validation, plus the full NHTSA specification for US-market vehicles.

Worked answers for the swaps people actually make, one page per pairing.

Petrol versus electric running costs, handling US and imperial gallons and the public-charging share most comparisons ignore.

Payment, total interest and the full amortisation schedule, with trade-in equity, tax and fees.

Works backwards from income to a price, counting insurance, fuel and upkeep.

Money factor, residual value, and the resale value that buying leaves you with.

What the first three characters mean, for every major marque.