30.1" tall, 10.0" wide, 7.5" sidewall
A 255/75R15 tire is 30.1 inches (764 mm) tall and 10.0 inches wide. The sidewall is 75% of the width, 7.5 inches, on a 15-inch wheel, and the tire turns about 671 times per mile.
In flotation terms that is about 30.1x10.0R15, closest to the common 30x9.50R15 (30.0"). People often call it a 30-inch tire.
The size most often compared with it is 235/75R15, which is 1.2" shorter (−3.9%). At an indicated 60 mph you would be doing 57.6 mph on it, more than the 3% change many shops use as a limit.
| Current | New | Difference |
|---|
| Shows | Actual speed |
|---|
Same 15" wheel, within 20 mm of width and 10 points of aspect ratio.
| Size | Diameter | Width | Sidewall | vs 255/75R15 | |
|---|---|---|---|---|---|
| 30x9.50R15 | 30.0" | 9.5" | 7.5" | −0.2% | |
| 275/70R15 | 30.2" | 10.8" | 7.6" | +0.3% | |
| 265/70R15 | 29.6" | 10.4" | 7.3" | −1.5% | |
| 245/75R15 | 29.5" | 9.6" | 7.2" | −2.0% | |
| 265/75R15 | 30.6" | 10.4" | 7.8" | +2.0% | |
| 235/85R15 | 30.7" | 9.3" | 7.9" | +2.2% | |
| 31x10.50R15 | 31.0" | 10.5" | 8.0" | +3.1% | |
| 255/70R15 | 29.1" | 10.0" | 7.0" | −3.3% | |
| 235/75R15 | 28.9" | 9.3" | 6.9" | −3.9% | compare |
| 275/75R15 | 31.2" | 10.8" | 8.1" | +3.9% |
Sizes within 2% of 30.1" on 14" or 16" or 17" wheels.
| Size | Diameter | Width | Sidewall | vs 255/75R15 | |
|---|---|---|---|---|---|
| 255/80R14 | 30.1" | 10.0" | 8.0" | +0.0% | |
| 255/70R16 | 30.1" | 10.0" | 7.0" | −0.0% | |
| 255/65R17 | 30.1" | 10.0" | 6.5" | −0.0% | |
| 275/65R16 | 30.1" | 10.8" | 7.0" | +0.1% | |
| 275/60R17 | 30.0" | 10.8" | 6.5" | −0.2% | |
| 235/70R17 | 30.0" | 9.3" | 6.5" | −0.4% |
Actual speed when the speedometer is calibrated for 255/75R15.
| Speedometer shows | on 235/75R15 | on 30x9.50R15 | on 275/70R15 |
|---|---|---|---|
| 30 mph | 28.8 mph | 29.9 mph | 30.1 mph |
| 45 mph | 43.2 mph | 44.9 mph | 45.1 mph |
| 60 mph | 57.6 mph | 59.9 mph | 60.2 mph |
| 70 mph | 67.2 mph | 69.9 mph | 70.2 mph |
30.1 inches (764 mm). The sidewall is 7.5 inches.
10.0 inches (255 mm) section width, measured sidewall to sidewall.
About 30.1x10.0R15; the closest common flotation size is 30x9.50R15 at 30.0".
235/75R15 is −3.9% in diameter, more than the common 3% guideline, so expect a speedometer error and check clearance. It is 0.8" narrower.