-1.65%Safe swap — speedometer error is minor
Speedometer error
With a speedometer calibrated to 205/55R16, fitting 185/65R15 makes it read as follows:
| Speedo shows | True speed | Speedo shows | True speed |
|---|---|---|---|
| 40 km/h | 39.3 km/h | 25 mph | 24 mph |
| 60 km/h | 59.0 km/h | 37 mph | 37 mph |
| 80 km/h | 78.7 km/h | 50 mph | 49 mph |
| 100 km/h | 98.4 km/h | 62 mph | 61 mph |
| 120 km/h | 118.0 km/h | 75 mph | 73 mph |
Full comparison
205/55R16
Overall diameter631.9 mm · 24.88 in
Section width205 mm · 8.07 in
Sidewall height112.8 mm · 4.44 in
Circumference1985.2 mm · 78.2 in
Revolutions per mile811
Revolutions per km504
185/65R15
Overall diameter621.5 mm · 24.47 in
Section width185 mm · 7.28 in
Sidewall height120.3 mm · 4.73 in
Circumference1952.5 mm · 76.9 in
Revolutions per mile824
Revolutions per km512
-1.65%Safe swap — speedometer error is minor
Original
Overall diameter631.9 mm · 24.88 in
Sidewall height112.8 mm
Circumference1,985.2 mm
Revolutions / mile810.7
New
Overall diameter621.5 mm · 24.47 in
Sidewall height120.3 mm
Circumference1,952.5 mm
Revolutions / mile824.2
Speedometer & odometer error
The new tire changes overall diameter by -1.65%. With a speedometer calibrated to the original tire, that same percentage is how far the speedometer and odometer read off — a taller tire means your true speed is higher than indicated and the odometer under-counts distance.
| Speedo shows | True speed | Speedo shows | True speed |
|---|---|---|---|
| 40 km/h | 39.3 km/h | 25 mph | 24 mph |
| 60 km/h | 59 km/h | 37 mph | 37 mph |
| 80 km/h | 78.7 km/h | 50 mph | 49 mph |
| 100 km/h | 98.4 km/h | 62 mph | 61 mph |
| 120 km/h | 118 km/h | 75 mph | 73 mph |
See individual specs: 205/55R16 · 185/65R15. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.