225/40R18
A 225/40R18 tire is 25.09 inches tall and 8.9 inches wide, with a 3.54-inch sidewall, mounted on a 18-inch wheel.
Common fitments: Golf R, A3, 128i
Overall diameter
25.09″
637 mm
Sidewall height
3.54″
90.0 mm
Tread width
225 mm
8.9″
Circumference
78.81″
6.6 ft
Revs per mile
804
500 per km
Wheel diameter
18″
aspect ratio 40%
Cross-section
- Overall diameter
- 25.09″
- Sidewall (each side)
- 3.54″
- Wheel
- 18″
225/40R18 in inches and millimeters
Every dimension of a 225/40R18, converted both ways. Calculated from the size code, accurate to about 1%.
| Measurement | Inches | Millimeters |
|---|---|---|
| Overall diameter (height) | 25.09″ | 637 mm |
| Tread width | 8.9″ | 225 mm |
| Sidewall height | 3.54″ | 90.0 mm |
| Wheel diameter | 18″ | 457 mm |
| Circumference | 78.81″ | 2002 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.
225/40R18 compared with other sizes
All 27 practical swaps involving 225/40R18 — diameter change, speedometer impact and a fit verdict for each.
225/40R18 → 185/55R16
185/55R16
Diameter +4.5% · Borderline. Check clearance first
225/40R18 → 195/55R16
195/55R16
Diameter +2.6% · This fits
225/40R18 → 205/55R16
205/55R16
Diameter +0.8% · This fits
225/40R18 → 215/55R16
215/55R16
Diameter −0.9% · This fits
225/40R18 → 205/50R17
205/50R17
Diameter +0.1% · This fits
225/40R18 → 215/45R17
215/45R17
Diameter +1.9% · This fits
225/40R18 → 225/45R17
225/45R17
Diameter +0.5% · This fits
225/40R18 → 235/45R17
235/45R17
Diameter −0.9% · This fits
235/40R18 → 225/40R18
235/40R18
Diameter +1.3% · This fits
225/45R18 → 225/40R18
225/45R18
Diameter +3.5% · Borderline. Check clearance first
245/40R18 → 225/40R18
245/40R18
Diameter +2.5% · This fits
255/40R18 → 225/40R18
255/40R18
Diameter +3.8% · Borderline. Check clearance first
225/45R17 → 225/40R18
225/45R17
Diameter −0.5% · This fits
235/45R18 → 225/40R18
235/45R18
Diameter +4.9% · Borderline. Check clearance first
205/50R17 → 225/40R18
205/50R17
Diameter −0.1% · This fits
205/55R16 → 225/40R18
205/55R16
Diameter −0.8% · This fits
215/55R16 → 225/40R18
215/55R16
Diameter +0.9% · This fits
235/45R17 → 225/40R18
235/45R17
Diameter +1.0% · This fits
215/50R17 → 225/40R18
215/50R17
Diameter +1.5% · This fits
225/50R17 → 225/40R18
225/50R17
Diameter +3.1% · Borderline. Check clearance first
215/45R17 → 225/40R18
215/45R17
Diameter −1.9% · This fits
245/45R17 → 225/40R18
245/45R17
Diameter +2.4% · This fits
225/40R18 → 225/45R18
225/45R18
Diameter −3.4% · Borderline. Check clearance first
225/40R18 → 235/40R18
235/40R18
Diameter −1.2% · This fits
225/40R18 → 235/45R18
235/45R18
Diameter −4.7% · Borderline. Check clearance first
225/40R18 → 245/40R18
245/40R18
Diameter −2.4% · This fits
225/40R18 → 255/40R18
255/40R18
Diameter −3.6% · Borderline. Check clearance first
Common questions
- What is 225/40R18 in inches?
- A 225/40R18 tire is 25.09 inches tall and 8.9 inches wide, with a 3.54-inch sidewall, mounted on a 18-inch wheel. In metric that is 637 mm tall and 225 mm wide. The circumference is 78.81 inches.
- How tall is a 225/40R18 tire?
- 25.09 inches, or 637 mm. That is the overall diameter, wheel included. It turns about 804 times per mile, which is what your speedometer counts.
- What do the numbers in 225/40R18 mean?
- 225 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 225 × 40% = 90.0 mm tall.