ElpiAuto305/70R18 vs 325/60R18
325/60R18 is 1.46″ (37 mm) shorter than 305/70R18, a 4.2% difference in overall diameter — outside the ±3% band, so expect the speedometer to drift and check for rubbing before fitting.
| Measurement | 305/70R18 | 325/60R18 | Difference | % |
|---|---|---|---|---|
| Overall diameter | 34.81″ | 33.35″ | −1.46″ | −4.2% |
| Section width | 12.01″ | 12.80″ | +0.79″ | +6.6% |
| Sidewall height | 8.41″ | 7.68″ | −0.73″ | −8.7% |
| Circumference | 109.36″ | 104.79″ | −4.58″ | −4.2% |
| Revs per mile | 579.4 | 604.7 | +25.3 | +4.4% |
| Revs per km | 360.0 | 375.7 | +15.7 | +4.4% |
Speedometer: with 305/70R18 as the original, 325/60R18 makes an indicated 60 mph really about 57.5 mph, and the axle sits ~0.73″ lower.
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.