About
Clear numbers. Visible assumptions.
TireSpan helps you understand a dimension change before you decide what to ask next.
Tire size calculator
Convert a metric tire size into nominal width, sidewall height, overall diameter, circumference and revolutions per kilometer or mile.
Compare tire sizes
Compare two metric tire sizes with a shared-scale drawing, signed differences and theoretical speed rows. Swap the reference, save locally and export.
See what changes inside and outside the wheel.
Compare wheel width and ET using a fixed mounting plane. Calculate nominal inner-space and outward-position changes with visible sign definitions.
Built around one practical task
A tire comparison often starts with two markings and a simple question: what changes? TireSpan puts the width, sidewall, rim, overall diameter and theoretical speed difference in one view. The wheel tool applies the same approach to width and offset.
A method you can follow
The formulas are public, the reference direction is explicit and the diagrams use a common scale. Results come from deterministic calculations in your browser. There is no runtime AI explanation or hidden vehicle-fitment lookup.
A small, documented directory
The size directory uses selected manufacturer-published markings. Curated comparison pages follow specific documented questions, with their source references kept separate from the geometric calculations. The collection is not a catalog of every tire and does not claim current stock or search volume.
Your working comparisons stay local
Named projects are saved in the current browser when storage is available. You can use temporary mode and download files without an account. JSON backups let you move an editable project yourself.
Precision is not permission
A result can be mathematically precise within a model and still be insufficient for a physical decision. TireSpan does not certify fitment, load capacity or vehicle safety. The method and scope notes are part of the result, including in reports.