Free wheel, tyre and tint tools
Measure twice. Buy once.
Work out what changes before you change the wheels. Start with the sizes on your car, compare a new setup and take the numbers to your fitter. No account needed.
Tyre size calculator
Compare diameters, sidewalls and speedometer changes.
Open the toolWheel offset calculator
See the change in inner clearance and outer poke.
Open the toolTyre stretch calculator
Get a starting rim width range for your tyre.
Open the toolBolt pattern finder
Find your pattern, or cars that share it.
Open the toolOffset and backspacing converter
Convert ET in mm to backspacing in inches, or back again.
Open the toolTyre plus-size calculator
Find tyre sizes close to your current diameter on a different rim.
Open the toolHub-centric ring size finder
Compare your car hub and wheel bore to find the ring dimensions.
Open the toolTyre code and DOT date decoder
Read sidewall sizes, load and speed ratings, and tyre age.
Open the toolGear speed and RPM calculator
Calculate road speed or engine RPM with your tyre and gear ratios.
Open the toolWheel and tyre fitment checker
Estimate tyre-shoulder clearance, poke and arch gap together.
Open the toolMetric and inch tyre size converter
Convert metric sizes to inches, or inch dimensions back to metric.
Open the toolWindow tint visualizer
Compare 5% to 70% tint on a real car, with combined VLT on factory glass.
Open the toolSpeedometer calculator
Bigger tyres cover more ground per revolution. See how a size change affects road speed at 30, 60 and 70 mph, plus 50 and 100 km/h, in the tyre size calculator.
Check speedometer changesWindow tint
Not sure how dark to go? See what 5% to 70% tint looks like on a real car, how film adds to factory glass, and what UK law allows on each window.
Read the window tint guideStart with your car
Our fitment guides put factory sizes, bolt patterns and clearance notes in one place, with links straight into these tools.
Find a fitment guideExplained in our guides
- Wheel offset explained: choosing ET without guessingUnderstand positive and negative wheel offset, calculate inner clearance and outer position, and choose an ET using measurements from your own car.
- Plus-sizing wheels: tyre diameter and speedometer changesWork through a 17 to 18 inch wheel change, compare tyre diameters and speedometer effects, and understand why a 3% rule cannot approve fitment.
- How to read a tyre size, load index and sidewall markingsDecode tyre width, aspect ratio, rim diameter, load and speed markings, then calculate sidewall height and diameter using a 225/45 R17 example.