185/50R16 vs 165/55R16
Going from one to the other changes the overall height by -0.6 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 185/50R16 | 165/55R16 | Change |
|---|---|---|---|
| Overall height | 23.3" | 23.1" | -0.6 % |
| Sidewall | 3.64" | 3.57" | -1.9 % |
| Section width | 185 mm | 165 mm | -10.8 % |
| Circumference | 73.1" | 72.7" | -0.6 % |
| Revs per mile | 866 | 871 | +0.6 % |
| Axle height | 11.64" | 11.57" | -1.8 mm |
| Approved rim width | 5–6.5" | 4.5–6" | overlap 5–6" |
Both are approved on a rim 5" to 6" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 185/50R16. Fit 165/55R16 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.8 mph | -0.2 |
| 50 mph | 49.7 mph | -0.3 |
| 70 mph | 69.6 mph | -0.4 |
| 90 mph | 89.5 mph | -0.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,941 on the road, so it over-counts by 59. At a true 70 mph the first turns 1011 times a minute, the second 1017.