TireSpan help: inputs, projects and exports

Your tire sizes

Get width, sidewall height, diameter and circumference from a tire size.

Enter a tire size

Enter metric tire notation, check parsed fields, use manual dimensions and recover from invalid or incomplete inputs.

Units and precision

Understand metric and imperial displays, exact conversion constants, rounding and machine-readable numeric exports.

What changed?

See two sizes side by side, then check the theoretical speed change.

Compare two tire sizes

Set the reference size, read signed changes, swap inputs and choose common-center or common-ground diagrams.

Use the theoretical speed table

Choose indicated-speed examples and read circumference-ratio estimates without treating them as measured road speeds.

Compare wheel width and offset

Enter original and new wheel widths and ET values, then interpret inner-space and outward-position changes.

Save comparison

Saved only in this browser. Export JSON before clearing site data or moving to another device.

Save and restore a comparison

Save a named project in your browser, reopen it, undo deletion or restore a JSON backup. Understand temporary mode and storage failures.

Import and export

Choose JSON, CSV, SVG or PDF; review an imported project and recover from damaged or unsupported files without replacing valid work.

Download your comparison

PDF is for reading or printing. Choose JSON to restore an editable calculation.

Download a print report

Generate a real PDF download in A4 or US Letter, check the included values and use the private print view.

What the calculations can tell you

Understand what TireSpan calculates, what it leaves out and why a small geometric difference is not a fitment or safety approval.

Docs

Estimate the distance change after a tire size change

Calculate theoretical distance from an odometer reading, understand the inverse percentage, and keep nominal tire geometry separate from measured rolling data.

Before changing tire or wheel size

Gather vehicle-approved sizes, complete tire specifications and wheel-clearance information before treating a size comparison as a replacement decision.

Get a comparison onto the page

Enter an original and a new metric size, then calculate. Check the parsed values before reading the difference. Change the display units without changing the underlying dimensions.

Keep your own copy

Saving in this browser is useful for returning to a comparison. A downloaded JSON file is the portable backup. CSV, SVG and PDF are presentation or calculation outputs; they are not substitutes for the editable project file.

Recover without losing valid work

A rejected input, damaged import or failed export should leave your current comparison available. The guides explain what each message means and how to try again.

How can we help?