Tire Size Calculator
Compare tire sizes, see diameter differences, and speedometer correction.
Original Tire
mm
%
in
New / Compare Tire
mm
%
in
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Comparison
Diameter Difference
+10.9 mm
(+1.7%)
Speedometer at 60 mph
61.0 mph actual
Visual Comparison
Original225/45R17
New235/40R18
Detailed Specs
| Metric | Original | New | Diff |
|---|---|---|---|
| Overall Diameter | 24.97" | 25.40" | 0.43" |
| Sidewall Height | 101.3 mm | 94.0 mm | -7.3 mm |
| Circumference | 78.5" | 79.8" | 1.3" |
| Revs/Mile | 808 | 794 | -14 |
| Revs/Km | 502 | 493 | -8 |
Documentation
How It Works
Reading Tire Size: 225/45R17
- 225 — Tread width in millimeters.
- 45 — Aspect ratio (sidewall height = 45% of width).
- R17 — Radial tire with a 17-inch rim diameter.
When switching tire sizes, keep within 3% of the original diameter to maintain accuracy of your speedometer, odometer, and vehicle safety systems.
Tire Formulas
Frequently Asked Questions