ElpiAuto285/75R18 vs 305/70R18
305/70R18 is 0.02″ (0 mm) shorter than 285/75R18, a 0.1% difference in overall diameter — comfortably inside the ±3% band most fitment guides use, so it swaps straight across for gearing and the speedometer.
| Measurement | 285/75R18 | 305/70R18 | Difference | % |
|---|---|---|---|---|
| Overall diameter | 34.83″ | 34.81″ | −0.02″ | −0.1% |
| Section width | 11.22″ | 12.01″ | +0.79″ | +7.0% |
| Sidewall height | 8.42″ | 8.41″ | −0.01″ | −0.1% |
| Circumference | 109.42″ | 109.36″ | −0.06″ | −0.1% |
| Revs per mile | 579.0 | 579.4 | +0.3 | +0.1% |
| Revs per km | 359.8 | 360.0 | +0.2 | +0.1% |
No meaningful speedometer change between these two sizes.
Reading this comparison
The overall diameter is what matters here: 285/75R18 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.