345/40R18
345 mm across the tread, a sidewall 40% of that — 138 mm — on a 18-inch rim. That puts the whole wheel at 28.9 inches tall.
- Sidewall
- 5.43"
- 138 mm
- Overall
- 28.9"
- 733.2 mm
- Circumference
- 90.7"
- 2.303 m
- Revs per mile
- 699
- per minute at 60 mph
What it needs to sit on
It mounts on a rim between 9.5" and 12.5" wide, and the tread follows the rim: roughly 5 mm of section width for every half-inch, so about 330 mm across at the narrow end and 360 mm at the wide one. Written the way lift kits and wheel wells are, it is a 28.9×13.6R18 — tall by wide, in inches.
What fits instead
Same 18-inch rim, height within 3%. Past that the speedometer starts lying and things begin to rub.
| Size | Height | Ride height | Speedo reads 60, you do | Compare |
|---|---|---|---|---|
| 335/40R18 | 28.6" -1.1 % | -4.0 mm | 59.3 mph | side by side |
| 355/40R18 | 29.2" +1.1 % | +4.0 mm | 60.7 mph | side by side |
| 325/40R18 | 28.2" -2.2 % | -8.0 mm | 58.7 mph | side by side |
| 325/45R18 | 29.5" +2.3 % | +8.3 mm | 61.4 mph | side by side |
Same height, different rim
Bigger rim, same overall height. Sharper steering, harsher ride, and far less rubber between your wheel and the next pothole.
If you fit something taller
A taller tire covers more ground per turn, so the needle reads low and the odometer counts short. Over ten thousand miles on the dial, the last column is what you really drove.
| Fitted instead | Reads 30 | Reads 50 | Reads 70 | Real miles per 10,000 shown |
|---|---|---|---|---|
| 335/40R18 | 29.7 mph | 49.5 mph | 69.2 mph | 9,891 |
| 355/40R18 | 30.3 mph | 50.5 mph | 70.8 mph | 10,109 |
| 325/40R18 | 29.3 mph | 48.9 mph | 68.5 mph | 9,782 |
| 325/45R18 | 30.7 mph | 51.1 mph | 71.6 mph | 10,225 |