Calcvers
Tire Size Calculator
Vehicle Costs & Sizing
Generated
September 24, 2026
Size A diameter
25.97 in (660 mm)
26.4 in (671 mm)
Your inputs
- Width (A)
- 225 mm
- Aspect ratio (A)
- 45 %
- Rim diameter (A)
- 18 in
- Width (B)
- 235 mm
- Aspect ratio (B)
- 40 %
- Rim diameter (B)
- 19 in
Breakdown
- Size B diameter
- 26.4 in (671 mm)
- Difference
- -0.43 in
- Speed at 60 mph
- 59 mph
Overall diameter
| Item | Value |
|---|---|
| Size A | 25.97 in (660 mm) |
| Size B | 26.4 in (671 mm) |
What this means
A tire's overall diameter is the rim diameter plus two sidewalls, where the sidewall is the width times the aspect ratio. Comparing two sizes shows how a change alters the distance the wheel rolls per revolution. A larger diameter rolls farther each turn, so at any given speedometer reading you're actually going faster — and the car sits higher. Keeping the diameter within about 3% of the original is the usual safe guideline.
Recommendations
- Keep the diameter change within ±3% of the original to avoid speedometer and gearing issues.
- Check wheel well and suspension clearance (and offset) for wider or larger tires before buying.
- With a larger overall diameter, your speedometer reads low — note the new 'speed at 60' figure for awareness.
Watch out
- Wider tires also change the offset fitment and can rub at full steering lock or under load.
- Changing diameter beyond the safe margin may require a speedometer recalibration fitted by the shop.