Tire Ruler225/40R18 dimensions
| Overall diameter (height) | 25.09″ · 637 mm |
| Section width | 8.86″ · 225 mm |
| Sidewall height | 3.54″ · 90 mm |
| Wheel diameter | 18″ |
| Rim width (rule of thumb) | 6–8″ |
| Circumference | 78.8″ |
| Revolutions per mile | 804 |
| In inches (flotation style) | 25.1 × 8.9R18 |
How it’s calculated: the sidewall is 40% of the 225 mm width = 90.0 mm (3.54″). Add two sidewalls to the 18″ wheel: 18 + 2 × 3.54 = 25.09″.
Bigger tires than 225/40R18 on 18″ wheels
| Size | Height | Taller by | 60 mph reads |
|---|---|---|---|
| 245/40R18 | 25.7″ | +0.63″ (+2.5%) | 61.5 mph |
| 225/45R18 | 26.0″ | +0.89″ (+3.5%) | 62.1 mph |
| 235/45R18 | 26.3″ | +1.24″ (+4.9%) | 63.0 mph |
| 245/45R18 | 26.7″ | +1.59″ (+6.4%) | 63.8 mph |
“60 mph reads” is your real speed when a speedometer set up for 225/40R18 shows 60. Above about 3% taller, most trucks need a leveling kit or lift, and the speedometer should be recalibrated.
Same height on a different wheel size
Changing wheel size (plus or minus sizing) while keeping the overall height keeps your speedometer right:
- 195/65R15: 25.0″ tall on a 15″ wheel (−0.4%)
- 205/55R16: 24.9″ tall on a 16″ wheel (−0.8%)
- 225/45R17: 25.0″ tall on a 17″ wheel (−0.5%)
- 235/45R17: 25.3″ tall on a 17″ wheel (+1.0%)
- 205/50R17: 25.1″ tall on a 17″ wheel (−0.1%)
Frequently asked questions
Is 225/40R18 a 25 inch tire?
Yes. 225/40R18 is 25.09 inches tall, so it's sold and talked about as a 25-inch tire.
What size is 225/40R18 in inches?
225/40R18 is 25.1 inches tall (overall diameter), 8.9 inches wide, with a 3.5 inch sidewall, and fits an 18 inch wheel.
What tire size is equivalent to 225/40R18?
No common size on an 18" wheel is within 1.5% of 225/40R18's diameter. Use the calculator above to compare any size.
What rim width fits 225/40R18?
As a rule of thumb, about 6–8 inches. The tire maker's spec sheet lists the approved range for each model.
How many revolutions per mile does 225/40R18 make?
About 804 revolutions per mile in theory (circumference 78.8 in). Real tires turn slightly more because they flatten under load.