ElpiAuto245/40R18 vs 255/40R19
255/40R19 is 1.31″ (33 mm) taller than 245/40R18, a 5.1% difference in overall diameter — outside the ±3% band, so expect the speedometer to drift and check for rubbing before fitting.
These sit on different wheel sizes — you'd be changing wheels too, not just tires.
| Measurement | 245/40R18 | 255/40R19 | Difference | % |
|---|---|---|---|---|
| Overall diameter | 25.72″ | 27.03″ | +1.31″ | +5.1% |
| Section width | 9.65″ | 10.04″ | +0.39″ | +4.1% |
| Sidewall height | 3.86″ | 4.02″ | +0.16″ | +4.1% |
| Circumference | 80.79″ | 84.92″ | +4.13″ | +5.1% |
| Revs per mile | 784.2 | 746.1 | −38.2 | −4.9% |
| Revs per km | 487.3 | 463.6 | −23.7 | −4.9% |
Speedometer: with 245/40R18 as the original, 255/40R19 makes an indicated 60 mph really about 63.1 mph, and the axle sits ~0.66″ higher.
Reading this comparison
The overall diameter is what matters here: 255/40R19 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.