185/55R15 vs 205/50R15
205/50R15 is a safe swap for 185/55R15 by the usual ±3% rule: the diameter differs by +0.26%.
Speedometer and odometer
With 205/50R15 on a car calibrated for 185/55R15, the speedometer reads 59.8 mph when you're really doing 60, and the odometer under-counts by 0.3%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.1 mph |
| 45 mph | 45.1 mph |
| 60 mph | 60.2 mph |
| 70 mph | 70.2 mph |
| 80 mph | 80.2 mph |
Other sizes close to 185/55R15
Questions
Can I replace 185/55R15 with 205/50R15?
205/50R15 is a safe swap for 185/55R15 by the usual ±3% rule: the diameter differs by +0.26%.
What's the difference between 185/55R15 and 205/50R15?
205/50R15 is 0.06" taller and 20 mm wider; the sidewall is +0.03". At an indicated 60 mph you'd actually be doing 60.2 mph.
Will 205/50R15 fit on 185/55R15 wheels?
Both use a 15" rim, so the wheel diameter matches; check the wheel's width range for a 205 mm tire and the fender clearance.