Tire Size Comparison
Compare two tire sizes side-by-side — see diameter difference, speedometer error, and ground clearance change.
Tire Size Comparison Tool
Two codes → side-by-side differences
How It Works
Both tire diameters are calculated from the sidewall codes. Diameter difference directly equals twice the ground clearance change. Speedometer error is the diameter ratio expressed as a percentage.
How to Use This Calculator
- Enter the original (stock) tire code as Tire 1.
- Enter the replacement or comparison tire code as Tire 2.
- Click Compare — see all dimensional differences.
- Check speedometer error — values over 3% may require recalibration.
- Check that ground clearance change doesn’t risk rubbing against arches or guards.
Worked Example
Reference Table
| Stock Tire | Upgrade Tire | Diameter Δ | Speedo Error |
|---|---|---|---|
| 195/65R15 | 205/60R15 | +1.5 mm | +0.24% |
| 205/55R16 | 225/45R17 | +3.0 mm | +0.47% |
| 225/50R17 | 235/45R18 | +0.6 mm | +0.10% |
| 265/70R17 | 275/65R18 | +15.4 mm | +2.17% |
| 235/65R17 | 265/60R18 | +14.8 mm | +2.07% |
Frequently Asked Questions
How much speedometer error is acceptable when changing tire sizes?
Most jurisdictions allow ±4% speedometer error. Staying within ±2% is recommended for road use. Performance vehicles with speed-sensitive steering systems should stay within ±1%.
Will a larger diameter tire affect my gearing and fuel economy?
A larger tyre effectively raises the final drive ratio — engine runs at lower RPM for the same speed. This can marginally improve highway fuel economy (0.5–2%) and slightly reduce low-speed torque response.
Can I fit a wider tire without changing the rim?
As a rough guide, the tyre width should be 1.4–1.8× the rim width in inches. A 225 mm tyre needs a 7–8 inch rim. Excessively wide tyres on narrow rims cause poor handling and void tyre warranties.
Why doesn’t the tyre code tell me if it fits my car?
The code gives dimensions but not load index, speed rating, or rim offset clearance. Always verify the load index (e.g., 91 = 615 kg per tyre) and speed rating (e.g., V = 240 km/h) match or exceed original specs.
