225/40R18
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 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% · Marginal fit — proceed with care
225/40R18 → 195/55R16
195/55R16
Diameter +2.6% · Good fit
225/40R18 → 205/55R16
205/55R16
Diameter +0.8% · Good fit
225/40R18 → 215/55R16
215/55R16
Diameter −0.9% · Good fit
225/40R18 → 205/50R17
205/50R17
Diameter +0.1% · Good fit
225/40R18 → 215/45R17
215/45R17
Diameter +1.9% · Good fit
225/40R18 → 225/45R17
225/45R17
Diameter +0.5% · Good fit
225/40R18 → 235/45R17
235/45R17
Diameter −0.9% · Good fit
235/40R18 → 225/40R18
235/40R18
Diameter +1.3% · Good fit
225/45R18 → 225/40R18
225/45R18
Diameter +3.5% · Marginal fit — proceed with care
245/40R18 → 225/40R18
245/40R18
Diameter +2.5% · Good fit
255/40R18 → 225/40R18
255/40R18
Diameter +3.8% · Marginal fit — proceed with care
225/45R17 → 225/40R18
225/45R17
Diameter −0.5% · Good fit
235/45R18 → 225/40R18
235/45R18
Diameter +4.9% · Marginal fit — proceed with care
205/50R17 → 225/40R18
205/50R17
Diameter −0.1% · Good fit
205/55R16 → 225/40R18
205/55R16
Diameter −0.8% · Good fit
215/55R16 → 225/40R18
215/55R16
Diameter +0.9% · Good fit
235/45R17 → 225/40R18
235/45R17
Diameter +1.0% · Good fit
215/50R17 → 225/40R18
215/50R17
Diameter +1.5% · Good fit
225/50R17 → 225/40R18
225/50R17
Diameter +3.1% · Marginal fit — proceed with care
215/45R17 → 225/40R18
215/45R17
Diameter −1.9% · Good fit
245/45R17 → 225/40R18
245/45R17
Diameter +2.4% · Good fit
225/40R18 → 225/45R18
225/45R18
Diameter −3.4% · Marginal fit — proceed with care
225/40R18 → 235/40R18
235/40R18
Diameter −1.2% · Good fit
225/40R18 → 235/45R18
235/45R18
Diameter −4.7% · Marginal fit — proceed with care
225/40R18 → 245/40R18
245/40R18
Diameter −2.4% · Good fit
225/40R18 → 255/40R18
255/40R18
Diameter −3.6% · Marginal fit — proceed with care
Common questions
- What is the overall diameter of a 225/40R18 tire?
- A 225/40R18 tire is about 25.09″ (637 mm) in overall diameter, with a sidewall height of 90.0 mm and a circumference of 78.81″.
- How many revolutions per mile does a 225/40R18 tire turn?
- A 225/40R18 turns roughly 804 revolutions per mile (500 per kilometre). This is the number that determines speedometer and odometer accuracy when you change tire size.
- What do the numbers in 225/40R18 mean?
- 225 is the tread width in millimetres, 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.