255/40R18
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 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% · Good fit
255/40R18 → 225/40R18
225/40R18
Diameter +3.8% · Marginal fit — proceed with care
255/40R18 → 225/45R18
225/45R18
Diameter +0.2% · Good fit
255/40R18 → 235/40R18
235/40R18
Diameter +2.5% · Good fit
255/40R18 → 235/45R18
235/45R18
Diameter −1.1% · Good fit
255/40R18 → 235/50R18
235/50R18
Diameter −4.5% · Marginal fit — proceed with care
255/40R18 → 245/40R18
245/40R18
Diameter +1.2% · Good fit
255/40R18 → 245/45R18
245/45R18
Diameter −2.4% · Good fit
255/40R18 → 235/40R19
235/40R19
Diameter −1.4% · Good fit
255/40R18 → 245/35R19
245/35R19
Diameter +1.1% · Good fit
255/40R18 → 255/35R19
255/35R19
Diameter +0.0% · Good fit
225/45R18 → 255/40R18
225/45R18
Diameter −0.2% · Good fit
235/45R18 → 255/40R18
235/45R18
Diameter +1.1% · Good fit
245/40R18 → 255/40R18
245/40R18
Diameter −1.2% · Good fit
235/40R18 → 255/40R18
235/40R18
Diameter −2.4% · Good fit
245/45R18 → 255/40R18
245/45R18
Diameter +2.5% · Good fit
255/45R18 → 255/40R18
255/45R18
Diameter +3.9% · Marginal fit — proceed with care
225/40R18 → 255/40R18
225/40R18
Diameter −3.6% · Marginal fit — proceed with care
255/35R19 → 255/40R18
255/35R19
Diameter −0.0% · Good fit
235/50R18 → 255/40R18
235/50R18
Diameter +4.7% · Marginal fit — proceed with care
215/60R16 → 255/40R18
215/60R16
Diameter +0.5% · Good fit
225/50R17 → 255/40R18
225/50R17
Diameter −0.7% · Good fit
215/55R17 → 255/40R18
215/55R17
Diameter +1.1% · Good fit
245/35R19 → 255/40R18
245/35R19
Diameter −1.1% · Good fit
245/45R17 → 255/40R18
245/45R17
Diameter −1.3% · Good fit
255/40R18 → 255/45R18
255/45R18
Diameter −3.7% · Marginal fit — proceed with care
Common questions
- What is the overall diameter of a 255/40R18 tire?
- A 255/40R18 tire is about 26.03″ (661 mm) in overall diameter, with a sidewall height of 102.0 mm and a circumference of 81.78″.
- How many revolutions per mile does a 255/40R18 tire turn?
- A 255/40R18 turns roughly 775 revolutions per mile (481 per kilometre). This is the number that determines speedometer and odometer accuracy when you change tire size.
- What do the numbers in 255/40R18 mean?
- 255 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 255 × 40% = 102.0 mm tall.