4WD Tyre Clearance Change Calculator
A free, browser-based calculator. Runs entirely in your browser — no sign up, nothing stored.
Tyres & fitment
Result
Also check
Spare wheel well / carrier fit, mudflaps, suspension and CV/steering travel at full lock and full droop, and your local rules on tyre/lift limits. A bigger tyre also affects gearing, braking and the speedo.
Estimates only — check before you fit
These results are calculated from tyre-size geometry and the values you enter. Real tyre dimensions vary by brand, model, load, pressure and wear. Always check the vehicle placard, tyre manufacturer data, local road rules, and guard / brake / suspension clearance, and get professional fitment advice before changing tyre or wheel sizes. This never states that a tyre change is legal or safe — confirm with a 4WD fitter and your local regulations.
How to use this calculator
- Enter your current and new tyre sizes.
- Optionally add a lift height and your current guard clearance.
- Read the ground-clearance gain, diameter/width increase, speedo effect and (if you gave a guard clearance) how much room is left, with a wheel-arch diagram.
How it works
Ground clearance rises by half the overall-diameter increase (the axle is fixed, so the diff/chassis lifts by that much) plus any suspension lift. The tyre's top also rises by half the diameter increase, which is what eats into guard clearance.
Guard clearance left = current clearance + lift − half the diameter increase. A negative result means the tyre likely rubs. A bigger tyre also changes the speedo, gearing and braking.
Worked example
265/70R17 → 285/70R17. About +28 mm overall diameter, so roughly +14 mm ground clearance (before any lift). With 40 mm of guard clearance and no lift, that leaves about 26 mm.
Common mistakes
- Assuming the whole diameter increase becomes ground clearance — only half does (the axle stays put).
- Forgetting the tyre also grows upward into the guard and outward toward the suspension.
- Ignoring the spare, mudflaps and full-lock/full-droop clearance.
Frequently asked questions
How much clearance do bigger tyres add?
About half the overall-diameter increase, plus any lift. A 30 mm taller tyre adds roughly 15 mm of ground clearance.
Will my new tyres rub?
If you enter your current guard clearance, the tool estimates the room left after the tyre grows. It's a guide only — full-lock, full-droop and load all matter, so have a 4WD fitter check.
Is a bigger tyre legal?
This tool never says a change is legal or safe. Tyre and lift limits vary by region and vehicle — confirm with your local regulations and a professional.
Are these results safe to fit?
They're geometry estimates only. Real tyres vary by brand, load, pressure and wear. Always check the vehicle placard, manufacturer data, local road rules and guard/brake/suspension clearance, and get professional fitment advice before changing tyre or wheel sizes.
Related tools
Tip: Enter any known values to calculate the remaining results.
All calculations run in your browser. Your inputs are never saved or transmitted.