ElpiAuto33X12.50R18 in metric
A 33X12.50R18 is 33.0″ (838 mm) tall and 12.50″ (318 mm) wide on a 18″ wheel. Converted directly it reads 320/60R18; the nearest standard metric size is 315/60R18.
Your tire size
e.g. 235/75R15, 33X12.50R15, or 225/45R17 91V
Metric equivalents of 33X12.50R18
315/60R18 is a near-exact match: −0.4% in height and −3 mm in width. The others trade a little height for width, or the reverse — all on the same 18″ wheel, within the ±3% most makers accept.
| Size | Diameter | Height vs 33X12.50R18 | Width vs 33X12.50R18 |
|---|---|---|---|
| 315/60R18 | 32.9″ · 835 mm | −0.4% | −3 mm |
| 325/60R18 | 33.4″ · 847 mm | +1.1% | +8 mm |
| 295/65R18 | 33.1″ · 841 mm | +0.3% | −23 mm |
| 345/55R18 | 32.9″ · 837 mm | −0.2% | +28 mm |
| 305/60R18 | 32.4″ · 823 mm | −1.8% | −13 mm |
33X12.50R18 dimensions
Computed from the size code; moulded tires vary by brand by roughly 1–3%.
| Dimension | Inches | Millimetres |
|---|---|---|
| Overall diameter | 33.0″ | 838 |
| Section width | 12.50″ | 318 |
| Sidewall height | 7.50″ | 191 |
| Circumference | 103.7″ | 2633 |
| Revolutions per mile | 611 | — |
| Revolutions per km | — | 380 |
The same height on other wheels
If you are changing wheel diameter but want to keep a 33.0″ overall height, these metric sizes come closest (within 2%).
| Wheel | Size | Diameter | Difference |
|---|---|---|---|
| 15″ | 305/75R15 | 33.0″ | +0.0% |
| 16″ | 335/65R16 | 33.1″ | +0.4% |
| 17″ | 315/65R17 | 33.1″ | +0.4% |
| 20″ | 335/50R20 | 33.2″ | +0.6% |
| 22″ | 295/50R22 | 33.6″ | +1.9% |
Wheel width and neighbouring sizes
A 318 mm-wide tire mounts on 9.5–12.0″ wide wheels (the usual approved range; the middle is ideal).
One step down is 275/65R18: −2.8% in diameter. With a speedometer calibrated for 33X12.50R18, an indicated 60 mph would be 58.3 mph on 275/65R18.
One step up is 35X12.50R18: +6.1% in diameter. With a speedometer calibrated for 33X12.50R18, an indicated 60 mph would be 63.6 mph on 35X12.50R18.
Figures are geometric: overall diameter = wheel + 2 × sidewall, 25.4 mm per inch. Check the tire maker's data sheet for the exact moulded size before buying.