185/45R16 vs 165/50R16
Going from one to the other changes the overall height by -0.3 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 185/45R16 | 165/50R16 | Change |
|---|---|---|---|
| Overall height | 22.6" | 22.5" | -0.3 % |
| Sidewall | 3.28" | 3.25" | -0.9 % |
| Section width | 185 mm | 165 mm | -10.8 % |
| Circumference | 70.9" | 70.7" | -0.3 % |
| Revs per mile | 894 | 897 | +0.3 % |
| Axle height | 11.28" | 11.25" | -0.8 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 185/45R16. Fit 165/50R16 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.9 mph | -0.1 |
| 50 mph | 49.9 mph | -0.1 |
| 70 mph | 69.8 mph | -0.2 |
| 90 mph | 89.8 mph | -0.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,974 on the road, so it over-counts by 26. At a true 70 mph the first turns 1043 times a minute, the second 1046.