Tire Size Comparison Calculator
See the exact difference in diameter, width, and speedometer reading between two tire sizes.
Quick Answer
When comparing a 225/50R17 to a 235/45R17, the new 235 tire is 0.3 inches (1.2%) smaller in overall diameter and 0.4 inches wider. Because the new tire is smaller, your speedometer will read 60 mph when your actual speed is 59.3 mph.
Enter Tire Specifications
① Original Tire
→ 265/70R17
② Compare Tire
→ 285/70R17
Enter tire specs above and click Calculate to compare
Supports P-metric (225/65R17) and Imperial/flotation (31x10.5R15) formats
Common Tire Size Swaps (17-inch Wheels)
| Original Size | New Size | Diameter Diff | Width Diff | True Speed at 60 mph |
|---|---|---|---|---|
| 225/65R17 | 235/65R17 | +0.5" (+1.8%) | +0.4" | 61.1 mph |
| 225/50R17 | 235/45R17 | -0.3" (-1.2%) | +0.4" | 59.3 mph |
| 265/70R17 | 285/70R17 | +1.1" (+3.5%) | +0.8" | 62.1 mph |
| 245/65R17 | 265/65R17 | +1.0" (+3.4%) | +0.8" | 62.0 mph |
| 205/50R17 | 225/45R17 | -0.1" (-0.4%) | +0.8" | 59.8 mph |
| 275/60R20 | 305/55R20 | +0.0" (+0.1%) | +1.2" | 60.1 mph |
Formula
Difference % = ((New Diameter − Old Diameter) / Old Diameter) × 100
- New Diameter = overall height of second tire in inches
- Old Diameter = overall height of first tire in inches
- Example: ((29.0 − 28.5) / 28.5) × 100 = 1.75% difference