ElpiAuto285/65R18 vs 305/70R18
305/70R18 is 2.22″ (56 mm) taller than 285/65R18, a 6.8% difference in overall diameter — outside the ±3% band, so expect the speedometer to drift and check for rubbing before fitting.
| Measurement | 285/65R18 | 305/70R18 | Difference | % |
|---|---|---|---|---|
| Overall diameter | 32.59″ | 34.81″ | +2.22″ | +6.8% |
| Section width | 11.22″ | 12.01″ | +0.79″ | +7.0% |
| Sidewall height | 7.29″ | 8.41″ | +1.11″ | +15.2% |
| Circumference | 102.37″ | 109.36″ | +6.99″ | +6.8% |
| Revs per mile | 618.9 | 579.4 | −39.5 | −6.4% |
| Revs per km | 384.6 | 360.0 | −24.6 | −6.4% |
Speedometer: with 285/65R18 as the original, 305/70R18 makes an indicated 60 mph really about 64.1 mph, and the axle sits ~1.11″ higher.
Reading this comparison
The overall diameter is what matters here: 305/70R18 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.