255/55R18 dimensions
| Measure | Inches | Millimetres |
|---|---|---|
| Overall height | 29.04 in | 738 mm |
| Section width | 10.04 in | 255 mm |
| Sidewall height | 5.52 in | 140.2 mm |
| Wheel diameter | 18 in | 457 mm |
| Circumference | 91.2 in | 2,318 mm |
| Revolutions per mile | 694.4 |
The math
| Step | Math | Result |
|---|---|---|
| Sidewall | 255 × 55% = 140.2 mm ÷ 25.4 | 5.52 in |
| Overall height | 18 + 2 × 5.52 | 29.04 in |
| Width | 255 mm ÷ 25.4 | 10.04 in |
| Circumference | π × 29.04 | 91.2 in |
| Revs per mile | 63,360 ÷ 91.2 | 694.4 |
With a 5.5 in sidewall this is a tall sidewall with more cushion and flex. Real tires vary by brand and model, and the loaded radius under the vehicle is a bit smaller than this unloaded figure.
One step either way on a 18 in wheel
Each row changes one thing and shows the height change against 255/55R18, plus what 60 mph on the speedometer would really be if you swapped to that size.
| Change | Size | Height | Height change | 60 mph shows as | Verdict |
|---|---|---|---|---|---|
| Wider | 265/55R18 (compare) | 29.5 in | +1.5% | 60.9 mph | Close match |
| Narrower | 245/55R18 (compare) | 28.6 in | -1.5% | 59.1 mph | Close match |
| Taller sidewall | 255/60R18 (compare) | 30.0 in | +3.5% | 62.1 mph | Check clearance |
| Shorter sidewall | 255/50R18 (compare) | 28.0 in | -3.5% | 57.9 mph | Check clearance |
| Wider, shorter sidewall | 265/50R18 (compare) | 28.4 in | -2.1% | 58.7 mph | Close match |
| Narrower, taller sidewall | 245/60R18 (compare) | 29.6 in | +1.8% | 61.1 mph | Close match |
Calculated sizes within ±3% on other wheels
Plus and minus sizes that keep the overall height within about 3% (a rule of thumb from Discount Tire and 1010tires), widths within 30 mm. Calculated, not a list of tires on sale: check that a tire exists in that size.
17 in wheels (one wheel size smaller)
| Size | Height | Height change | Width change |
|---|---|---|---|
| 255/60R17 (compare) | 29.0 in | +0.0% | +0 mm |
| 235/65R17 (compare) | 29.0 in | -0.1% | -20 mm |
| 275/55R17 (compare) | 28.9 in | -0.5% | +20 mm |
| 285/55R17 (compare) | 29.3 in | +1.0% | +30 mm |
19 in wheels (one wheel size larger)
| Size | Height | Height change | Width change |
|---|---|---|---|
| 255/50R19 (compare) | 29.0 in | -0.0% | +0 mm |
| 285/45R19 (compare) | 29.1 in | +0.2% | +30 mm |
| 235/55R19 (compare) | 29.2 in | +0.5% | -20 mm |
| 225/55R19 (compare) | 28.7 in | -1.0% | -30 mm |
20 in wheels (two wheel sizes larger)
| Size | Height | Height change | Width change |
|---|---|---|---|
| 255/45R20 (compare) | 29.0 in | -0.0% | +0 mm |
| 285/40R20 (compare) | 29.0 in | -0.2% | +30 mm |
| 225/50R20 (compare) | 28.9 in | -0.6% | -30 mm |
| 235/50R20 (compare) | 29.3 in | +0.7% | -20 mm |
Try it with your numbers
Compare 255/55R18 with another size · Convert to metric or find a 33 in size · Sizes that fit my wheel
Calculated from the size alone. Real tires vary a little by brand and model, and the loaded radius is a bit smaller. Confirm the wheel width range, clearance, load index and speed rating for your vehicle. See how to read a tire size, the load index chart and the speed rating chart.
Browse: all sizes in inches · 255/50R18 · 255/60R18.