What is the overall diameter of a 235/45R18 tire?

A 235/45R18 tire is about 26.33″ (669 mm) in overall diameter, with a sidewall height of 105.8 mm and a circumference of 82.71″.

How many revolutions per mile does a 235/45R18 tire turn?

A 235/45R18 turns roughly 766 revolutions per mile (476 per kilometre). This is the number that determines speedometer and odometer accuracy when you change tire size.

What do the numbers in 235/45R18 mean?

235 is the tread width in millimetres, 45 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 × 45% = 105.8 mm tall.

235/45R18

Most common 18″ size

Common fitments: Camry, Accord, Model 3

Overall diameter

26.33″

669 mm

Sidewall height

4.16″

105.8 mm

Tread width

235 mm

9.3″

Circumference

82.71″

6.9 ft

Revs per mile

766

476 per km

Wheel diameter

18″

aspect ratio 45%

Compare 235/45R18 in the tool Compare with a custom size

Cross-section

Overall diameter: 26.33″
Sidewall (each side): 4.16″
Wheel: 18″

235/45R18 compared with other sizes

All 54 practical swaps involving 235/45R18 — diameter change, speedometer impact and a fit verdict for each.

235/45R18 → 215/60R16

215/60R16

Diameter +0.6% · Good fit

235/45R18 → 225/60R16

225/60R16

Diameter −1.1% · Good fit

235/45R18 → 215/55R17

215/55R17

Diameter +0.1% · Good fit

235/45R18 → 225/40R18

225/40R18

Diameter +4.9% · Marginal fit — proceed with care

235/45R18 → 225/45R18

225/45R18

Diameter +1.4% · Good fit

235/45R18 → 235/40R18

235/40R18

Diameter +3.6% · Marginal fit — proceed with care

255/40R18 → 235/45R18

255/40R18

Diameter −1.1% · Good fit

225/45R18 → 235/45R18

225/45R18

Diameter −1.3% · Good fit

245/45R18 → 235/45R18

245/45R18

Diameter +1.3% · Good fit

235/40R18 → 235/45R18

235/40R18

Diameter −3.5% · Marginal fit — proceed with care

235/50R18 → 235/45R18

235/50R18

Diameter +3.5% · Marginal fit — proceed with care

245/40R18 → 235/45R18

245/40R18

Diameter −2.3% · Good fit

255/45R18 → 235/45R18

255/45R18

Diameter +2.7% · Good fit

235/40R19 → 235/45R18

235/40R19

Diameter +0.3% · Good fit

225/40R18 → 235/45R18

225/40R18

Diameter −4.7% · Marginal fit — proceed with care

215/55R17 → 235/45R18

215/55R17

Diameter −0.1% · Good fit

205/65R16 → 235/45R18

205/65R16

Diameter +0.6% · Good fit

215/60R16 → 235/45R18

215/60R16

Diameter −0.6% · Good fit

255/35R19 → 235/45R18

255/35R19

Diameter −1.1% · Good fit

225/60R16 → 235/45R18

225/60R16

Diameter +1.2% · Good fit

235/45R18 → 235/50R18

235/50R18

Diameter −3.4% · Marginal fit — proceed with care

235/45R18 → 245/40R18

245/40R18

Diameter +2.4% · Good fit

235/45R18 → 245/45R18

245/45R18

Diameter −1.3% · Good fit

235/45R18 → 235/40R19

235/40R19

Diameter −0.3% · Good fit

235/45R18 → 245/35R19

245/35R19

Diameter +2.2% · Good fit

235/45R18 → 245/40R19

245/40R19

Diameter −1.5% · Good fit

235/45R18 → 255/35R19

255/35R19

Diameter +1.1% · Good fit

235/45R18 → 245/35R20

245/35R20

Diameter −1.6% · Good fit

235/45R18 → 205/65R16

205/65R16

Diameter −0.6% · Good fit

235/45R18 → 255/40R18

255/40R18

Diameter +1.1% · Good fit

235/45R18 → 255/45R18

255/45R18

Diameter −2.6% · Good fit

235/60R18 → 235/45R18

235/60R18

Diameter +10.5% · Not recommended

255/55R18 → 235/45R18

255/55R18

Diameter +10.3% · Not recommended

265/60R18 → 235/45R18

265/60R18

Diameter +15.9% · Not recommended

225/60R18 → 235/45R18

225/60R18

Diameter +8.7% · Not recommended

235/55R18 → 235/45R18

235/55R18

Diameter +7.0% · Not recommended

235/65R18 → 235/45R18

235/65R18

Diameter +14.1% · Not recommended

245/60R18 → 235/45R18

245/60R18

Diameter +12.3% · Not recommended

245/65R18 → 235/45R18

245/65R18

Diameter +16.0% · Not recommended

255/60R18 → 235/45R18

255/60R18

Diameter +14.1% · Not recommended

255/65R18 → 235/45R18

255/65R18

Diameter +17.9% · Not recommended

255/70R18 → 235/45R18

255/70R18

Diameter +21.8% · Not recommended

265/65R18 → 235/45R18

265/65R18

Diameter +19.9% · Not recommended

265/70R18 → 235/45R18

265/70R18

Diameter +23.9% · Not recommended

275/60R18 → 235/45R18

275/60R18

Diameter +17.7% · Not recommended

275/65R18 → 235/45R18

275/65R18

Diameter +21.8% · Not recommended

275/70R18 → 235/45R18

275/70R18

Diameter +25.9% · Not recommended

285/60R18 → 235/45R18

285/60R18

Diameter +19.5% · Not recommended

285/65R18 → 235/45R18

285/65R18

Diameter +23.8% · Not recommended

285/70R18 → 235/45R18

285/70R18

Diameter +28.0% · Not recommended

295/70R18 → 235/45R18

295/70R18

Diameter +30.1% · Not recommended

305/60R18 → 235/45R18

305/60R18

Diameter +23.1% · Not recommended

235/45R18 → 225/45R17

225/45R17

Diameter +5.4% · Not recommended

245/40R19 → 235/45R18

245/40R19

Diameter +1.5% · Good fit

Common questions

What is the overall diameter of a 235/45R18 tire?: A 235/45R18 tire is about 26.33″ (669 mm) in overall diameter, with a sidewall height of 105.8 mm and a circumference of 82.71″.
How many revolutions per mile does a 235/45R18 tire turn?: A 235/45R18 turns roughly 766 revolutions per mile (476 per kilometre). This is the number that determines speedometer and odometer accuracy when you change tire size.
What do the numbers in 235/45R18 mean?: 235 is the tread width in millimetres, 45 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 × 45% = 105.8 mm tall.