ElpiAuto275/65R18 vs 37X12.50R18
37X12.50R18 is 4.93″ (125 mm) taller than 275/65R18, a 15.4% difference in overall diameter — outside the ±3% band, so expect the speedometer to drift and check for rubbing before fitting.
The sidewall heights are very different — ride and steering feel will change noticeably even though the diameter is close.
| Measurement | 275/65R18 | 37X12.50R18 | Difference | % |
|---|---|---|---|---|
| Overall diameter | 32.07″ | 37.00″ | +4.93″ | +15.4% |
| Section width | 10.83″ | 12.50″ | +1.67″ | +15.5% |
| Sidewall height | 7.04″ | 9.50″ | +2.46″ | +35.0% |
| Circumference | 100.77″ | 116.24″ | +15.47″ | +15.4% |
| Revs per mile | 628.8 | 545.1 | −83.7 | −13.3% |
| Revs per km | 390.7 | 338.7 | −52.0 | −13.3% |
Speedometer: with 275/65R18 as the original, 37X12.50R18 makes an indicated 60 mph really about 69.2 mph, and the axle sits ~2.46″ 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.