Tire Ruler245/40R18 dimensions
| Overall diameter (height) | 25.72″ · 653 mm |
| Section width | 9.65″ · 245 mm |
| Sidewall height | 3.86″ · 98 mm |
| Wheel diameter | 18″ |
| Rim width (rule of thumb) | 7–8.5″ |
| Circumference | 80.8″ |
| Revolutions per mile | 784 |
| In inches (flotation style) | 25.7 × 9.6R18 |
How it’s calculated: the sidewall is 40% of the 245 mm width = 98.0 mm (3.86″). Add two sidewalls to the 18″ wheel: 18 + 2 × 3.86 = 25.72″.
Bigger tires than 245/40R18 on 18″ wheels
| Size | Height | Taller by | 60 mph reads |
|---|---|---|---|
| 225/45R18 | 26.0″ | +0.26″ (+1.0%) | 60.6 mph |
| 235/45R18 | 26.3″ | +0.61″ (+2.4%) | 61.4 mph |
| 245/45R18 | 26.7″ | +0.96″ (+3.8%) | 62.3 mph |
| 235/50R18 | 27.3″ | +1.54″ (+6.0%) | 63.6 mph |
| 215/55R18 | 27.3″ | +1.59″ (+6.2%) | 63.7 mph |
“60 mph reads” is your real speed when a speedometer set up for 245/40R18 shows 60. Above about 3% taller, most trucks need a leveling kit or lift, and the speedometer should be recalibrated.
Sizes equivalent to 245/40R18
Within 1.5% of the same height on an 18″ wheel. Usually interchangeable for the speedometer; check width, load index and clearance.
| Size | Height | Width | Difference |
|---|---|---|---|
| 225/45R18 | 26.0″ | 8.9″ | +1.0% |
Same height on a different wheel size
Changing wheel size (plus or minus sizing) while keeping the overall height keeps your speedometer right:
- 205/65R15: 25.5″ tall on a 15″ wheel (−0.9%)
- 205/60R16: 25.7″ tall on a 16″ wheel (−0.1%)
- 225/50R17: 25.9″ tall on a 17″ wheel (+0.6%)
- 215/50R17: 25.5″ tall on a 17″ wheel (−1.0%)
Frequently asked questions
Is 245/40R18 a 26 inch tire?
Not quite. 245/40R18 is 25.72 inches tall, between a 25 and a 26 inch tire.
What size is 245/40R18 in inches?
245/40R18 is 25.7 inches tall (overall diameter), 9.6 inches wide, with a 3.9 inch sidewall, and fits an 18 inch wheel.
What tire size is equivalent to 245/40R18?
Sizes within 1.5% of the same diameter on an 18" wheel: 225/45R18 (26.0"). Check load index and width before swapping.
What rim width fits 245/40R18?
As a rule of thumb, about 7–8.5 inches. The tire maker's spec sheet lists the approved range for each model.
How many revolutions per mile does 245/40R18 make?
About 784 revolutions per mile in theory (circumference 80.8 in). Real tires turn slightly more because they flatten under load.