Tire Size Calculator
Original tire size
New tire size
Original diameter —
New diameter —
Speedometer difference —
These are theoretical values from nominal tire specs — actual dimensions vary by manufacturer, tread design, and inflation, so treat this as an estimate rather than an exact reading.
Free tire size calculator — compare an original and replacement tire size to see the diameter difference and how much it will throw off your speedometer.
How it works
- Enter your original tire size (width, aspect ratio, rim diameter)
- Enter the new tire size you're considering
- See both diameters and the resulting speedometer error
Frequently asked questions
How much tire size difference is noticeable?
Differences within about 2% of the original diameter are rarely noticeable day to day — the further you move from that, the more it affects speedometer accuracy and ride characteristics.
Is this exact for my specific tires?
No — these are theoretical values from nominal size specs. Actual tire dimensions vary by manufacturer, tread design, and inflation pressure, so treat the result as an estimate.
From the blog
Update history
- 2026-09-02 Launched: tire size comparison calculator with diameter and speedometer-error output. Entirely client-side.