30.5" tall, 9.6" wide, 6.3" sidewall
A 245/65R18 tire is 30.5 inches (776 mm) tall and 9.6 inches wide. The sidewall is 65% of the width, 6.3 inches, on a 18-inch wheel, and the tire turns about 660 times per mile.
In flotation terms that is about 30.5x9.6R18. People often call it a 31-inch tire.
The size most often compared with it is 245/70R18, which is 1.0" taller (+3.2%). At an indicated 60 mph you would be doing 61.9 mph on it, more than the 3% change many shops use as a limit.
| Current | New | Difference |
|---|
| Shows | Actual speed |
|---|
Same 18" wheel, within 20 mm of width and 10 points of aspect ratio.
| Size | Diameter | Width | Sidewall | vs 245/65R18 | |
|---|---|---|---|---|---|
| 245/70R18 | 31.5" | 9.6" | 6.8" | +3.2% | |
| 265/65R18 | 31.6" | 10.4" | 6.8" | +3.4% | |
| 265/55R18 | 29.5" | 10.4" | 5.7" | −3.5% | |
| 235/75R18 | 31.9" | 9.3" | 6.9" | +4.4% | |
| 255/70R18 | 32.1" | 10.0" | 7.0" | +5.0% | |
| 245/75R18 | 32.5" | 9.6" | 7.2" | +6.3% | |
| 265/70R18 | 32.6" | 10.4" | 7.3" | +6.8% | |
| 255/75R18 | 33.1" | 10.0" | 7.5" | +8.3% | |
| 265/75R18 | 33.6" | 10.4" | 7.8" | +10.2% |
Sizes within 2% of 30.5" on 17" or 16" or 20" wheels.
| Size | Diameter | Width | Sidewall | vs 245/65R18 | |
|---|---|---|---|---|---|
| 265/65R17 | 30.6" | 10.4" | 6.8" | +0.1% | |
| 245/70R17 | 30.5" | 9.6" | 6.8" | −0.1% | |
| 285/65R16 | 30.6" | 11.2" | 7.3" | +0.2% | |
| 265/70R16 | 30.6" | 10.4" | 7.3" | +0.2% | |
| 245/55R20 | 30.6" | 9.6" | 5.3" | +0.2% | |
| 245/75R16 | 30.5" | 9.6" | 7.2" | −0.2% |
Actual speed when the speedometer is calibrated for 245/65R18.
| Speedometer shows | on 245/70R18 | on 265/65R18 | on 265/55R18 |
|---|---|---|---|
| 30 mph | 30.9 mph | 31.0 mph | 29.0 mph |
| 45 mph | 46.4 mph | 46.5 mph | 43.4 mph |
| 60 mph | 61.9 mph | 62.0 mph | 57.9 mph |
| 70 mph | 72.2 mph | 72.3 mph | 67.6 mph |
30.5 inches (776 mm). The sidewall is 6.3 inches.
9.6 inches (245 mm) section width, measured sidewall to sidewall.
About 30.5x9.6R18.
245/70R18 is +3.2% in diameter, more than the common 3% guideline, so expect a speedometer error and check clearance. It is 0.0" wider.