245/40R18
Common fitments: Mustang, 4 Series, A4
Overall diameter
25.72″
653 mm
Sidewall height
3.86″
98.0 mm
Tread width
245 mm
9.6″
Circumference
80.79″
6.7 ft
Revs per mile
784
487 per km
Wheel diameter
18″
aspect ratio 40%
Cross-section
- Overall diameter
- 25.72″
- Sidewall (each side)
- 3.86″
- Wheel
- 18″
245/40R18 compared with other sizes
All 29 practical swaps involving 245/40R18 — diameter change, speedometer impact and a fit verdict for each.
245/40R18 → 205/60R16
205/60R16
Diameter +0.1% · Good fit
245/40R18 → 215/50R17
215/50R17
Diameter +1.0% · Good fit
245/40R18 → 225/50R17
225/50R17
Diameter −0.5% · Good fit
245/40R18 → 235/45R17
235/45R17
Diameter +1.5% · Good fit
245/40R18 → 245/45R17
245/45R17
Diameter +0.1% · Good fit
245/40R18 → 225/40R18
225/40R18
Diameter +2.5% · Good fit
245/40R18 → 225/45R18
225/45R18
Diameter −1.0% · Good fit
245/40R18 → 235/40R18
235/40R18
Diameter +1.2% · Good fit
245/40R18 → 235/45R18
235/45R18
Diameter −2.3% · Good fit
225/45R18 → 245/40R18
225/45R18
Diameter +1.0% · Good fit
235/40R18 → 245/40R18
235/40R18
Diameter −1.2% · Good fit
255/40R18 → 245/40R18
255/40R18
Diameter +1.2% · Good fit
235/45R18 → 245/40R18
235/45R18
Diameter +2.4% · Good fit
225/40R18 → 245/40R18
225/40R18
Diameter −2.4% · Good fit
245/45R18 → 245/40R18
245/45R18
Diameter +3.8% · Marginal fit — proceed with care
245/45R17 → 245/40R18
245/45R17
Diameter −0.1% · Good fit
245/35R19 → 245/40R18
245/35R19
Diameter +0.1% · Good fit
205/60R16 → 245/40R18
205/60R16
Diameter −0.1% · Good fit
255/45R18 → 245/40R18
255/45R18
Diameter +5.1% · Not recommended
225/50R17 → 245/40R18
225/50R17
Diameter +0.6% · Good fit
215/50R17 → 245/40R18
215/50R17
Diameter −1.0% · Good fit
255/35R19 → 245/40R18
255/35R19
Diameter +1.2% · Good fit
235/45R17 → 245/40R18
235/45R17
Diameter −1.5% · Good fit
245/40R18 → 245/45R18
245/45R18
Diameter −3.6% · Marginal fit — proceed with care
245/40R18 → 245/35R19
245/35R19
Diameter −0.1% · Good fit
245/40R18 → 255/35R19
255/35R19
Diameter −1.2% · Good fit
245/40R18 → 255/40R18
255/40R18
Diameter −1.2% · Good fit
245/40R18 → 255/45R18
255/45R18
Diameter −4.9% · Marginal fit — proceed with care
245/40R18 → 225/45R17
225/45R17
Diameter +3.0% · Good fit
Common questions
- What is the overall diameter of a 245/40R18 tire?
- A 245/40R18 tire is about 25.72″ (653 mm) in overall diameter, with a sidewall height of 98.0 mm and a circumference of 80.79″.
- How many revolutions per mile does a 245/40R18 tire turn?
- A 245/40R18 turns roughly 784 revolutions per mile (487 per kilometre). This is the number that determines speedometer and odometer accuracy when you change tire size.
- What do the numbers in 245/40R18 mean?
- 245 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 245 × 40% = 98.0 mm tall.