37x13.50R20 vs 38x15.50R20
38x15.50R20 is a safe swap for 37x13.50R20 by the usual ±3% rule: the diameter differs by +2.70%.
Side by side
| 37x13.50R20 | 38x15.50R20 | Difference | |
|---|---|---|---|
| Overall diameter | 37.00" | 38.00" | +1.00" (+2.70%) |
| Section width | 343 mm | 394 mm | +51 mm |
| Sidewall | 8.50" | 9.00" | +0.50" |
| Rim | 20" | 20" | same |
| Circumference | 116.2" | 119.4" | +3.1" |
| Revs per mile | 545 | 531 | -14 |
| Ride height | — | — | +0.50" |
| Speedometer reads 60 mph | 60.0 | 61.6 | +1.6 mph |
Speedometer and odometer
With 38x15.50R20 on a car calibrated for 37x13.50R20, the speedometer reads 58.4 mph when you're really doing 60, and the odometer under-counts by 2.7%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.8 mph |
| 45 mph | 46.2 mph |
| 60 mph | 61.6 mph |
| 70 mph | 71.9 mph |
| 80 mph | 82.2 mph |
Other sizes close to 37x13.50R20
Questions
Can I replace 37x13.50R20 with 38x15.50R20?
38x15.50R20 is a safe swap for 37x13.50R20 by the usual ±3% rule: the diameter differs by +2.70%.
What's the difference between 37x13.50R20 and 38x15.50R20?
38x15.50R20 is 1.00" taller and 51 mm wider; the sidewall is +0.50". At an indicated 60 mph you'd actually be doing 61.6 mph.
Will 38x15.50R20 fit on 37x13.50R20 wheels?
Both use a 20" rim, so the wheel diameter matches; check the wheel's width range for a 394 mm tire and the fender clearance.