-4.02%Borderline — noticeable speedometer/odometer error
Speedometer error
With a speedometer calibrated to 205/65R15, fitting 185/65R15 makes it read as follows:
| Speedo shows | True speed | Speedo shows | True speed |
|---|---|---|---|
| 40 km/h | 38.4 km/h | 25 mph | 24 mph |
| 60 km/h | 57.6 km/h | 37 mph | 36 mph |
| 80 km/h | 76.8 km/h | 50 mph | 48 mph |
| 100 km/h | 96.0 km/h | 62 mph | 60 mph |
| 120 km/h | 115.2 km/h | 75 mph | 72 mph |
Full comparison
205/65R15
Overall diameter647.5 mm · 25.49 in
Section width205 mm · 8.07 in
Sidewall height133.3 mm · 5.25 in
Circumference2034.2 mm · 80.1 in
Revolutions per mile791
Revolutions per km492
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
-4.02%Borderline — noticeable speedometer/odometer error
Original
Overall diameter647.5 mm · 25.49 in
Sidewall height133.3 mm
Circumference2,034.2 mm
Revolutions / mile791.2
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 -4.02%. 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 | 38.4 km/h | 25 mph | 24 mph |
| 60 km/h | 57.6 km/h | 37 mph | 36 mph |
| 80 km/h | 76.8 km/h | 50 mph | 48 mph |
| 100 km/h | 96 km/h | 62 mph | 60 mph |
| 120 km/h | 115.2 km/h | 75 mph | 72 mph |
See individual specs: 205/65R15 · 185/65R15. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.