ElpiAuto235/45R18 vs 255/35R19
255/35R19 is 0.30″ (8 mm) shorter than 235/45R18, a 1.1% difference in overall diameter — comfortably inside the ±3% band most fitment guides use, so it swaps straight across for gearing and the speedometer.
These sit on different wheel sizes — you'd be changing wheels too, not just tires.
| Measurement | 235/45R18 | 255/35R19 | Difference | % |
|---|---|---|---|---|
| Overall diameter | 26.33″ | 26.03″ | −0.30″ | −1.1% |
| Section width | 9.25″ | 10.04″ | +0.79″ | +8.5% |
| Sidewall height | 4.16″ | 3.51″ | −0.65″ | −15.6% |
| Circumference | 82.71″ | 81.77″ | −0.94″ | −1.1% |
| Revs per mile | 766.1 | 774.9 | +8.8 | +1.1% |
| Revs per km | 476.0 | 481.5 | +5.5 | +1.1% |
Speedometer: with 235/45R18 as the original, 255/35R19 makes an indicated 60 mph really about 59.3 mph, and the axle sits ~0.15″ lower.
Reading this comparison
The overall diameter is what matters here: 235/45R18 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.