Tire Ruler275/40R20 dimensions
| Overall diameter (height) | 28.66″ · 728 mm |
| Section width | 10.83″ · 275 mm |
| Sidewall height | 4.33″ · 110 mm |
| Wheel diameter | 20″ |
| Rim width (rule of thumb) | 7.5–9.5″ |
| Circumference | 90.0″ |
| Revolutions per mile | 704 |
| In inches (flotation style) | 28.7 × 10.8R20 |
How it’s calculated: the sidewall is 40% of the 275 mm width = 110.0 mm (4.33″). Add two sidewalls to the 20″ wheel: 20 + 2 × 4.33 = 28.66″.
Bigger tires than 275/40R20 on 20″ wheels
| Size | Height | Taller by | 60 mph reads |
|---|---|---|---|
| 255/45R20 | 29.0″ | +0.37″ (+1.3%) | 60.8 mph |
| 265/45R20 | 29.4″ | +0.73″ (+2.5%) | 61.5 mph |
| 245/50R20 | 29.6″ | +0.98″ (+3.4%) | 62.1 mph |
| 275/45R20 | 29.7″ | +1.08″ (+3.8%) | 62.3 mph |
| 255/50R20 | 30.0″ | +1.38″ (+4.8%) | 62.9 mph |
“60 mph reads” is your real speed when a speedometer set up for 275/40R20 shows 60. Above about 3% taller, most trucks need a leveling kit or lift, and the speedometer should be recalibrated.
Sizes equivalent to 275/40R20
Within 1.5% of the same height on a 20″ wheel. Usually interchangeable for the speedometer; check width, load index and clearance.
| Size | Height | Width | Difference |
|---|---|---|---|
| 245/45R20 | 28.7″ | 9.6″ | +0.1% |
| 255/45R20 | 29.0″ | 10.0″ | +1.3% |
Same height on a different wheel size
Changing wheel size (plus or minus sizing) while keeping the overall height keeps your speedometer right:
- 235/75R15: 28.9″ tall on a 15″ wheel (+0.8%)
- 225/75R15: 28.3″ tall on a 15″ wheel (−1.3%)
- 235/70R16: 29.0″ tall on a 16″ wheel (+1.0%)
- 225/70R16: 28.4″ tall on a 16″ wheel (−0.9%)
- 235/65R17: 29.0″ tall on a 17″ wheel (+1.3%)
- 225/65R17: 28.5″ tall on a 17″ wheel (−0.5%)
- 225/60R18: 28.6″ tall on an 18″ wheel (−0.1%)
- 255/55R18: 29.0″ tall on an 18″ wheel (+1.3%)
- 255/50R19: 29.0″ tall on a 19″ wheel (+1.3%)
Frequently asked questions
Is 275/40R20 a 29 inch tire?
Not quite. 275/40R20 is 28.66 inches tall, between a 28 and a 29 inch tire.
What size is 275/40R20 in inches?
275/40R20 is 28.7 inches tall (overall diameter), 10.8 inches wide, with a 4.3 inch sidewall, and fits a 20 inch wheel.
What tire size is equivalent to 275/40R20?
Sizes within 1.5% of the same diameter on a 20" wheel: 245/45R20 (28.7"), 255/45R20 (29.0"). Check load index and width before swapping.
What rim width fits 275/40R20?
As a rule of thumb, about 7.5–9.5 inches. The tire maker's spec sheet lists the approved range for each model.
How many revolutions per mile does 275/40R20 make?
About 704 revolutions per mile in theory (circumference 90.0 in). Real tires turn slightly more because they flatten under load.