235/40R18
A 235/40R18 tire is 25.40 inches tall and 9.3 inches wide, with a 3.70-inch sidewall, mounted on a 18-inch wheel.
Common fitments: Model 3, Mustang, BRZ
Overall diameter
25.40″
645 mm
Sidewall height
3.70″
94.0 mm
Tread width
235 mm
9.3″
Circumference
79.80″
6.7 ft
Revs per mile
794
493 per km
Wheel diameter
18″
aspect ratio 40%
Cross-section
- Overall diameter
- 25.40″
- Sidewall (each side)
- 3.70″
- Wheel
- 18″
235/40R18 in inches and millimeters
Every dimension of a 235/40R18, converted both ways. Calculated from the size code, accurate to about 1%.
| Measurement | Inches | Millimeters |
|---|---|---|
| Overall diameter (height) | 25.40″ | 645 mm |
| Tread width | 9.3″ | 235 mm |
| Sidewall height | 3.70″ | 94.0 mm |
| Wheel diameter | 18″ | 457 mm |
| Circumference | 79.80″ | 2027 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.
235/40R18 compared with other sizes
All 29 practical swaps involving 235/40R18 — diameter change, speedometer impact and a fit verdict for each.
235/40R18 → 205/60R16
205/60R16
Diameter −1.1% · This fits
235/40R18 → 215/55R16
215/55R16
Diameter +0.4% · This fits
235/40R18 → 205/50R17
205/50R17
Diameter +1.3% · This fits
235/40R18 → 215/50R17
215/50R17
Diameter −0.2% · This fits
235/40R18 → 225/45R17
225/45R17
Diameter +1.7% · This fits
235/40R18 → 235/45R17
235/45R17
Diameter +0.3% · This fits
235/40R18 → 245/45R17
245/45R17
Diameter −1.1% · This fits
235/40R18 → 225/40R18
225/40R18
Diameter +1.3% · This fits
235/40R18 → 225/45R18
225/45R18
Diameter −2.2% · This fits
225/40R18 → 235/40R18
225/40R18
Diameter −1.2% · This fits
245/40R18 → 235/40R18
245/40R18
Diameter +1.2% · This fits
225/45R18 → 235/40R18
225/45R18
Diameter +2.2% · This fits
235/45R18 → 235/40R18
235/45R18
Diameter +3.6% · Borderline. Check clearance first
255/40R18 → 235/40R18
255/40R18
Diameter +2.5% · This fits
235/45R17 → 235/40R18
235/45R17
Diameter −0.3% · This fits
245/45R18 → 235/40R18
245/45R18
Diameter +5.0% · Too big a jump
215/50R17 → 235/40R18
215/50R17
Diameter +0.2% · This fits
215/55R16 → 235/40R18
215/55R16
Diameter −0.4% · This fits
245/45R17 → 235/40R18
245/45R17
Diameter +1.1% · This fits
205/60R16 → 235/40R18
205/60R16
Diameter +1.1% · This fits
205/50R17 → 235/40R18
205/50R17
Diameter −1.3% · This fits
245/35R19 → 235/40R18
245/35R19
Diameter +1.4% · This fits
225/45R17 → 235/40R18
225/45R17
Diameter −1.7% · This fits
235/40R18 → 235/45R18
235/45R18
Diameter −3.5% · Borderline. Check clearance first
235/40R18 → 245/40R18
245/40R18
Diameter −1.2% · This fits
235/40R18 → 245/45R18
245/45R18
Diameter −4.8% · Borderline. Check clearance first
235/40R18 → 245/35R19
245/35R19
Diameter −1.4% · This fits
235/40R18 → 255/35R19
255/35R19
Diameter −2.4% · This fits
235/40R18 → 255/40R18
255/40R18
Diameter −2.4% · This fits
Common questions
- What is 235/40R18 in inches?
- A 235/40R18 tire is 25.40 inches tall and 9.3 inches wide, with a 3.70-inch sidewall, mounted on a 18-inch wheel. In metric that is 645 mm tall and 235 mm wide. The circumference is 79.80 inches.
- How tall is a 235/40R18 tire?
- 25.40 inches, or 645 mm. That is the overall diameter, wheel included. It turns about 794 times per mile, which is what your speedometer counts.
- What do the numbers in 235/40R18 mean?
- 235 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 235 × 40% = 94.0 mm tall.