185/55R15 vs 225/50R15
225/50R15 is outside the ±3% rule as a replacement for 185/55R15: the diameter differs by +3.68%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
Speedometer and odometer
With 225/50R15 on a car calibrated for 185/55R15, the speedometer reads 57.9 mph when you're really doing 60, and the odometer under-counts by 3.7%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 31.1 mph |
| 45 mph | 46.7 mph |
| 60 mph | 62.2 mph |
| 70 mph | 72.6 mph |
| 80 mph | 82.9 mph |
Other sizes close to 185/55R15
Questions
Can I replace 185/55R15 with 225/50R15?
225/50R15 is outside the ±3% rule as a replacement for 185/55R15: the diameter differs by +3.68%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 185/55R15 and 225/50R15?
225/50R15 is 0.85" taller and 40 mm wider; the sidewall is +0.42". At an indicated 60 mph you'd actually be doing 62.2 mph.
Will 225/50R15 fit on 185/55R15 wheels?
Both use a 15" rim, so the wheel diameter matches; check the wheel's width range for a 225 mm tire and the fender clearance.