285/40R21
Overall diameter
29.98″
761 mm
Sidewall height
4.49″
114.0 mm
Tread width
285 mm
11.2″
Circumference
94.17″
7.8 ft
Revs per mile
673
418 per km
Wheel diameter
21″
aspect ratio 40%
Cross-section
- Overall diameter
- 29.98″
- Sidewall (each side)
- 4.49″
- Wheel
- 21″
285/40R21 compared with other sizes
All 23 practical swaps involving 285/40R21 — diameter change, speedometer impact and a fit verdict for each.
285/40R21 → 275/45R20
275/45R20
Diameter +0.8% · Good fit
285/40R21 → 245/50R20
245/50R20
Diameter +1.1% · Good fit
285/40R21 → 255/50R20
255/50R20
Diameter −0.2% · Good fit
285/40R21 → 265/40R21
265/40R21
Diameter +2.1% · Good fit
285/40R21 → 265/45R21
265/45R21
Diameter −1.4% · Good fit
285/40R21 → 275/45R21
275/45R21
Diameter −2.5% · Good fit
265/45R21 → 285/40R21
265/45R21
Diameter +1.4% · Good fit
265/40R21 → 285/40R21
265/40R21
Diameter −2.1% · Good fit
285/45R21 → 285/40R21
285/45R21
Diameter +3.7% · Marginal fit — proceed with care
275/45R21 → 285/40R21
275/45R21
Diameter +2.6% · Good fit
255/50R20 → 285/40R21
255/50R20
Diameter +0.2% · Good fit
275/45R20 → 285/40R21
275/45R20
Diameter −0.8% · Good fit
245/50R20 → 285/40R21
245/50R20
Diameter −1.1% · Good fit
245/55R19 → 285/40R21
245/55R19
Diameter −1.2% · Good fit
265/50R20 → 285/40R21
265/50R20
Diameter +1.5% · Good fit
265/55R19 → 285/40R21
265/55R19
Diameter +1.7% · Good fit
265/50R19 → 285/40R21
265/50R19
Diameter −1.8% · Good fit
265/45R20 → 285/40R21
265/45R20
Diameter −2.0% · Good fit
285/40R22 → 285/40R21
285/40R22
Diameter +3.3% · Marginal fit — proceed with care
275/40R22 → 285/40R21
275/40R22
Diameter +2.3% · Good fit
285/40R21 → 285/45R21
285/45R21
Diameter −3.6% · Marginal fit — proceed with care
285/40R21 → 275/40R22
275/40R22
Diameter −2.2% · Good fit
285/40R21 → 285/40R22
285/40R22
Diameter −3.2% · Marginal fit — proceed with care
Common questions
- What is the overall diameter of a 285/40R21 tire?
- A 285/40R21 tire is about 29.98″ (761 mm) in overall diameter, with a sidewall height of 114.0 mm and a circumference of 94.17″.
- How many revolutions per mile does a 285/40R21 tire turn?
- A 285/40R21 turns roughly 673 revolutions per mile (418 per kilometre). This is the number that determines speedometer and odometer accuracy when you change tire size.
- What do the numbers in 285/40R21 mean?
- 285 is the tread width in millimetres, 40 is the aspect ratio — the sidewall height as a percentage of the tread width — and 21 is the wheel diameter in inches. So the sidewall is 285 × 40% = 114.0 mm tall.