Wheel & tyre geometry, made visible
Know what fits.
See how it sits.
Compare your current setup with the wheels you want. Get the position, clearance and speedometer changes in millimetres—not forum guesswork.
- POSWheel position
- DIARolling diameter
- SPDSpeed difference
Wheel fitment calculator
Compare the setup you have with the one you want.
Enter the sizes printed on your current and proposed wheels and tyres. The calculator shows the measured change instantly.
The new setup sits 23 mm further out.
You gain a small amount of inner clearance and keep the rolling diameter close to the current setup.
- Outer position
- +22.7 mm further toward fender
- Inner clearance
- -2.7 mm slightly less space
- Diameter change
- -0.5% close to current diameter
- At indicated 100
- 99.5 estimated actual speed
This calculation cannot see brake-caliper shape, suspension movement, fender modifications, hub bore, load rating or bolt-seat type. Confirm the exact vehicle with a qualified retailer or installer.
Fitment North may be paid for an accepted introduction. Payment never changes the calculation or guarantees fit.
We will reply before sharing anything with a partner.
Useful numbers. Honest boundaries.
Wheel width and offset tell us how the rim moves around the mounting face. Tyre dimensions tell us how rolling diameter changes. Neither calculation can inspect the physical car, so the final installation still needs a vehicle-specific check.
- MeasureRead the stamped wheel and tyre sizes.
- CompareSee movement in millimetres, not jargon.
- VerifyConfirm the vehicle before ordering.
How the manual comparison works
Wheel position
Declared wheel width is converted to millimetres. Half the width is positioned on either side of the mounting face, then adjusted by the offset. The result shows relative movement only; it does not know the car's available space.
Tyre diameter and speed
Overall diameter is the rim diameter plus twice the sidewall height. The speed estimate assumes the current tyre diameter matches the vehicle's calibration and does not account for tread wear or manufacturer variation.
Where to find your wheel and tyre sizes
Tyre size is printed on the sidewall, for example 225/45 R18. Wheel width and offset are normally stamped or cast into the inside of the wheel, for example 8J and ET35. If you cannot confirm them, ask a qualified retailer or installer before ordering.
Comparison guides and calculators
Start with the tool that matches the measurement you are changing. These pages use declared geometry only and never invent vehicle specifications.