255/40R18
A 255/40R18 tire is 26.03 inches tall and 10.0 inches wide, with a 4.02-inch sidewall, mounted on a 18-inch wheel.
Overall diameter
26.03″
661 mm
Sidewall height
4.02″
102.0 mm
Tread width
255 mm
10.0″
Circumference
81.78″
6.8 ft
Revs per mile
775
481 per km
Wheel diameter
18″
aspect ratio 40%
Cross-section
- Overall diameter
- 26.03″
- Sidewall (each side)
- 4.02″
- Wheel
- 18″
255/40R18 in inches and millimeters
Every dimension of a 255/40R18, converted both ways. Calculated from the size code, accurate to about 1%.
| Measurement | Inches | Millimeters |
|---|---|---|
| Overall diameter (height) | 26.03″ | 661 mm |
| Tread width | 10.0″ | 255 mm |
| Sidewall height | 4.02″ | 102.0 mm |
| Wheel diameter | 18″ | 457 mm |
| Circumference | 81.78″ | 2077 mm |
Nominal dimensions from the size code. A real tire varies by a few millimeters between manufacturers, and a loaded tire sits slightly shorter than its free diameter.
255/40R18 compared with other sizes
All 26 practical swaps involving 255/40R18 — diameter change, speedometer impact and a fit verdict for each.
255/40R18 → 215/60R16
215/60R16
Diameter −0.5% · Fitment not determined
255/40R18 → 225/40R18
225/40R18
Diameter +3.8% · Fitment not determined
255/40R18 → 225/45R18
225/45R18
Diameter +0.2% · Fitment not determined
255/40R18 → 235/40R18
235/40R18
Diameter +2.5% · Fitment not determined
255/40R18 → 235/45R18
235/45R18
Diameter −1.1% · Fitment not determined
255/40R18 → 235/50R18
235/50R18
Diameter −4.5% · Fitment not determined
255/40R18 → 245/40R18
245/40R18
Diameter +1.2% · Fitment not determined
255/40R18 → 245/45R18
245/45R18
Diameter −2.4% · Fitment not determined
255/40R18 → 235/40R19
235/40R19
Diameter −1.4% · Fitment not determined
255/40R18 → 245/35R19
245/35R19
Diameter +1.1% · Fitment not determined
255/40R18 → 255/35R19
255/35R19
Diameter +0.0% · Fitment not determined
225/45R18 → 255/40R18
225/45R18
Diameter −0.2% · Fitment not determined
235/45R18 → 255/40R18
235/45R18
Diameter +1.1% · Fitment not determined
245/40R18 → 255/40R18
245/40R18
Diameter −1.2% · Fitment not determined
235/40R18 → 255/40R18
235/40R18
Diameter −2.4% · Fitment not determined
245/45R18 → 255/40R18
245/45R18
Diameter +2.5% · Fitment not determined
255/45R18 → 255/40R18
255/45R18
Diameter +3.9% · Fitment not determined
225/40R18 → 255/40R18
225/40R18
Diameter −3.6% · Fitment not determined
255/35R19 → 255/40R18
255/35R19
Diameter −0.0% · Fitment not determined
235/50R18 → 255/40R18
235/50R18
Diameter +4.7% · Fitment not determined
215/60R16 → 255/40R18
215/60R16
Diameter +0.5% · Fitment not determined
225/50R17 → 255/40R18
225/50R17
Diameter −0.7% · Fitment not determined
215/55R17 → 255/40R18
215/55R17
Diameter +1.1% · Fitment not determined
245/35R19 → 255/40R18
245/35R19
Diameter −1.1% · Fitment not determined
245/45R17 → 255/40R18
245/45R17
Diameter −1.3% · Fitment not determined
255/40R18 → 255/45R18
255/45R18
Diameter −3.7% · Fitment not determined
Common questions
- What is 255/40R18 in inches?
- A 255/40R18 tire is 26.03 inches tall and 10.0 inches wide, with a 4.02-inch sidewall, mounted on a 18-inch wheel. In metric that is 661 mm tall and 255 mm wide. The circumference is 81.78 inches.
- How tall is a 255/40R18 tire?
- 26.03 inches, or 661 mm. That is the overall diameter, wheel included. It turns about 775 times per mile, which is what your speedometer counts.
- What do the numbers in 255/40R18 mean?
- 255 is the tread width in millimeters, 40 is the aspect ratio — the sidewall height as a percentage of the tread width — and 18 is the wheel diameter in inches. So the sidewall is 255 × 40% = 102.0 mm tall.