185/75R16 vs 165/85R16
Going from one to the other changes the overall height by +0.4 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 185/75R16 | 165/85R16 | Change |
|---|---|---|---|
| Overall height | 26.9" | 27.0" | +0.4 % |
| Sidewall | 5.46" | 5.52" | +1.1 % |
| Section width | 185 mm | 165 mm | -10.8 % |
| Circumference | 84.6" | 85.0" | +0.4 % |
| Revs per mile | 749 | 746 | -0.4 % |
| Axle height | 13.46" | 13.52" | +1.5 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 185/75R16. Fit 165/85R16 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.1 mph | +0.1 |
| 50 mph | 50.2 mph | +0.2 |
| 70 mph | 70.3 mph | +0.3 |
| 90 mph | 90.4 mph | +0.4 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,044 on the road, so it under-counts by 44. At a true 70 mph the first turns 874 times a minute, the second 870.