ElpiAuto275/65R18 vs 305/70R18
305/70R18 is 2.74″ (70 mm) taller than 275/65R18, a 8.5% difference in overall diameter — outside the ±3% band, so expect the speedometer to drift and check for rubbing before fitting.
| Measurement | 275/65R18 | 305/70R18 | Difference | % |
|---|---|---|---|---|
| Overall diameter | 32.07″ | 34.81″ | +2.74″ | +8.5% |
| Section width | 10.83″ | 12.01″ | +1.18″ | +10.9% |
| Sidewall height | 7.04″ | 8.41″ | +1.37″ | +19.4% |
| Circumference | 100.77″ | 109.36″ | +8.60″ | +8.5% |
| Revs per mile | 628.8 | 579.4 | −49.4 | −7.9% |
| Revs per km | 390.7 | 360.0 | −30.7 | −7.9% |
Speedometer: with 275/65R18 as the original, 305/70R18 makes an indicated 60 mph really about 65.1 mph, and the axle sits ~1.37″ 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.