ElpiAuto245/45R18 vs 255/35R18
255/35R18 is 1.65″ (42 mm) shorter than 245/45R18, a 6.2% difference in overall diameter — outside the ±3% band, so expect the speedometer to drift and check for rubbing before fitting.
| Measurement | 245/45R18 | 255/35R18 | Difference | % |
|---|---|---|---|---|
| Overall diameter | 26.68″ | 25.03″ | −1.65″ | −6.2% |
| Section width | 9.65″ | 10.04″ | +0.39″ | +4.1% |
| Sidewall height | 4.34″ | 3.51″ | −0.83″ | −19.0% |
| Circumference | 83.82″ | 78.63″ | −5.19″ | −6.2% |
| Revs per mile | 755.9 | 805.8 | +49.9 | +6.6% |
| Revs per km | 469.7 | 500.7 | +31.0 | +6.6% |
Speedometer: with 245/45R18 as the original, 255/35R18 makes an indicated 60 mph really about 56.3 mph, and the axle sits ~0.83″ lower.
Reading this comparison
The overall diameter is what matters here: 245/45R18 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.