225/40R18 dimensions
| Measure | Inches | Millimetres |
|---|---|---|
| Overall height | 25.09 in | 637 mm |
| Section width | 8.86 in | 225 mm |
| Sidewall height | 3.54 in | 90.0 mm |
| Wheel diameter | 18 in | 457 mm |
| Circumference | 78.8 in | 2,002 mm |
| Revolutions per mile | 803.9 |
The math
| Step | Math | Result |
|---|---|---|
| Sidewall | 225 × 40% = 90.0 mm ÷ 25.4 | 3.54 in |
| Overall height | 18 + 2 × 3.54 | 25.09 in |
| Width | 225 mm ÷ 25.4 | 8.86 in |
| Circumference | π × 25.09 | 78.8 in |
| Revs per mile | 63,360 ÷ 78.8 | 803.9 |
With a 3.5 in sidewall this is a low-profile sidewall: sharp steering response, less cushion over bumps, and wheels that are easier to curb. 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 225/40R18, 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 | 235/40R18 (compare) | 25.4 in | +1.3% | 60.8 mph | Close match |
| Narrower | 215/40R18 (compare) | 24.8 in | -1.3% | 59.2 mph | Close match |
| Taller sidewall | 225/45R18 (compare) | 26.0 in | +3.5% | 62.1 mph | Check clearance |
| Shorter sidewall | 225/35R18 (compare) | 24.2 in | -3.5% | 57.9 mph | Check clearance |
| Wider, shorter sidewall | 235/35R18 (compare) | 24.5 in | -2.4% | 58.5 mph | Close match |
| Narrower, taller sidewall | 215/45R18 (compare) | 25.6 in | +2.1% | 61.3 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 |
|---|---|---|---|
| 205/50R17 (compare) | 25.1 in | -0.1% | -20 mm |
| 255/40R17 (compare) | 25.0 in | -0.2% | +30 mm |
| 225/45R17 (compare) | 25.0 in | -0.5% | +0 mm |
| 235/45R17 (compare) | 25.3 in | +1.0% | +10 mm |
19 in wheels (one wheel size larger)
| Size | Height | Height change | Width change |
|---|---|---|---|
| 195/40R19 (compare) | 25.1 in | +0.2% | -30 mm |
| 255/30R19 (compare) | 25.0 in | -0.3% | +30 mm |
| 225/35R19 (compare) | 25.2 in | +0.5% | +0 mm |
| 215/35R19 (compare) | 24.9 in | -0.6% | -10 mm |
20 in wheels (two wheel sizes larger)
| Size | Height | Height change | Width change |
|---|---|---|---|
| 215/30R20 (compare) | 25.1 in | -0.0% | -10 mm |
| 255/25R20 (compare) | 25.0 in | -0.3% | +30 mm |
| 225/30R20 (compare) | 25.3 in | +0.9% | +0 mm |
| 205/30R20 (compare) | 24.8 in | -1.0% | -20 mm |
Try it with your numbers
Compare 225/40R18 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 · 215/55R18 · 225/45R18.