185/80R16 vs 165/85R16
Going from one to the other changes the overall height by -2.2 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 185/80R16 | 165/85R16 | Change |
|---|---|---|---|
| Overall height | 27.7" | 27.0" | -2.2 % |
| Sidewall | 5.83" | 5.52" | -5.2 % |
| Section width | 185 mm | 165 mm | -10.8 % |
| Circumference | 86.9" | 85.0" | -2.2 % |
| Revs per mile | 729 | 746 | +2.2 % |
| Axle height | 13.83" | 13.52" | -7.8 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 185/80R16. Fit 165/85R16 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.3 mph | -0.7 |
| 50 mph | 48.9 mph | -1.1 |
| 70 mph | 68.5 mph | -1.5 |
| 90 mph | 88.0 mph | -2.0 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,779 on the road, so it over-counts by 221. At a true 70 mph the first turns 851 times a minute, the second 870.