ElpiAuto275/70R18 vs 285/65R18
285/65R18 is 0.57″ (14 mm) shorter than 275/70R18, a 1.7% difference in overall diameter — right at the edge of the ±3% band — fine on most cars, but check clearance at full lock and full suspension compression.
| Measurement | 275/70R18 | 285/65R18 | Difference | % |
|---|---|---|---|---|
| Overall diameter | 33.16″ | 32.59″ | −0.57″ | −1.7% |
| Section width | 10.83″ | 11.22″ | +0.39″ | +3.6% |
| Sidewall height | 7.58″ | 7.29″ | −0.29″ | −3.8% |
| Circumference | 104.17″ | 102.37″ | −1.79″ | −1.7% |
| Revs per mile | 608.3 | 618.9 | +10.7 | +1.8% |
| Revs per km | 378.0 | 384.6 | +6.6 | +1.8% |
Speedometer: with 275/70R18 as the original, 285/65R18 makes an indicated 60 mph really about 59.0 mph, and the axle sits ~0.29″ lower.
Reading this comparison
The overall diameter is what matters here: 275/70R18 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.