ElpiAuto225/55R17 vs 235/50R18
235/50R18 is 0.51″ (13 mm) taller than 225/55R17, a 1.9% difference in overall diameter — right at the edge of the ±3% band — fine on most cars, but check clearance at full lock and full suspension compression.
These sit on different wheel sizes — you'd be changing wheels too, not just tires.
| Measurement | 225/55R17 | 235/50R18 | Difference | % |
|---|---|---|---|---|
| Overall diameter | 26.74″ | 27.25″ | +0.51″ | +1.9% |
| Section width | 8.86″ | 9.25″ | +0.39″ | +4.4% |
| Sidewall height | 4.87″ | 4.63″ | −0.25″ | −5.1% |
| Circumference | 84.02″ | 85.61″ | +1.60″ | +1.9% |
| Revs per mile | 754.1 | 740.1 | −14.1 | −1.9% |
| Revs per km | 468.6 | 459.9 | −8.7 | −1.9% |
Speedometer: with 225/55R17 as the original, 235/50R18 makes an indicated 60 mph really about 61.1 mph, and the axle sits ~0.25″ higher.
Reading this comparison
The overall diameter is what matters here: 235/50R18 is the taller tire. It sets ride height, gearing and how far the tire travels per revolution — which is what the speedometer and odometer count. Width and sidewall change fit and feel (a wider tire needs a wider wheel and more clearance; a shorter sidewall sharpens steering) but not the gearing.
Figures are geometric estimates from the size codes; real moulded tires vary by brand by 1–3%. Confirm load rating, wheel width and physical clearance on your vehicle before fitting. To compare any other two sizes, use the tire size comparison tool; to decode one size and see what else fits its wheel, the tire size calculator.