ElpiAuto325/60R18 vs 37X12.50R18
37X12.50R18 is 3.65″ (93 mm) taller than 325/60R18, a 10.9% difference in overall diameter — outside the ±3% band, so expect the speedometer to drift and check for rubbing before fitting.
| Measurement | 325/60R18 | 37X12.50R18 | Difference | % |
|---|---|---|---|---|
| Overall diameter | 33.35″ | 37.00″ | +3.65″ | +10.9% |
| Section width | 12.80″ | 12.50″ | −0.30″ | −2.3% |
| Sidewall height | 7.68″ | 9.50″ | +1.82″ | +23.7% |
| Circumference | 104.79″ | 116.24″ | +11.45″ | +10.9% |
| Revs per mile | 604.7 | 545.1 | −59.6 | −9.9% |
| Revs per km | 375.7 | 338.7 | −37.0 | −9.9% |
Speedometer: with 325/60R18 as the original, 37X12.50R18 makes an indicated 60 mph really about 66.6 mph, and the axle sits ~1.82″ higher.
Reading this comparison
The overall diameter is what matters here: 37X12.50R18 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.