Tire Size Comparison Visualizer
A free, browser-based calculator. Runs entirely in your browser — no sign up, nothing stored.
Difference
| Measure | A | B | Δ |
|---|---|---|---|
| Diameter (mm) | 802.8 | 830.8 | +28.0 mm |
| Width (mm) | 265.0 | 285.0 | +20.0 mm |
| Sidewall (mm) | 185.5 | 199.5 | +14.0 mm |
| Circumference (m) | 2.522 | 2.610 | +0.088 m |
| Revs / km | 396 | 383 | -13 |
Ground clearance changes by about +14.0 mm (half the diameter change). At an indicated 100.0 km/h your true speed is about 103.5 km/h (+3.5%).
Overlay & speedo
| Speedo (km/h) | Actual |
|---|---|
| 40 | 41.4 |
| 60 | 62.1 |
| 80 | 82.8 |
| 100 | 103.5 |
| 110 | 113.8 |
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.
How to use this calculator
- Enter your OEM tyre (A) and the new tyre (B) in any format (265/70R17, 33x12.50R15…).
- Read the measurement differences, the ground-clearance change, the speedometer table and the fitment-risk badge.
- Use the overlay to see the two tyres to scale. Add an indicated speed to check the speedo effect.
How it works
Each size is decoded into diameter, width, sidewall, circumference and revolutions per km, then the tool shows the A→B difference for each.
Ground-clearance change is half the diameter change (the axle sits at the centre). Speed is proportional to rolling circumference, so actual speed = indicated × (new circumference ÷ old). The risk badge bands the diameter difference: under 1% low, 1–3% check, over 3% high.
Worked example
265/70R17 → 285/70R17. About +28 mm overall diameter (+3.5%), ~+14 mm ground clearance, and the speedo reads roughly 3.5% low — a 'High' fitment-risk flag worth checking against guards and gearing.
Frequently asked questions
How much bigger can I go safely?
There's no single answer — it depends on the vehicle, guards, suspension and local rules. The diameter % and risk badge are a starting point, not approval. Always check clearance and your local regulations.
Why does a bigger tyre change my speedo?
The speedo counts wheel revolutions. A taller tyre travels further per turn, so you're actually going faster than indicated. The speedo table shows the effect.
What is the ground-clearance change?
Roughly half the overall-diameter change, because the wheel centre (axle) rises by that much. It's an estimate — real clearance also depends on suspension and load.
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.