185/80R16 vs 175/85R16
Going from one to the other changes the overall height by +0.2 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 185/80R16 | 175/85R16 | Change |
|---|---|---|---|
| Overall height | 27.7" | 27.7" | +0.2 % |
| Sidewall | 5.83" | 5.86" | +0.5 % |
| Section width | 185 mm | 175 mm | -5.4 % |
| Circumference | 86.9" | 87.1" | +0.2 % |
| Revs per mile | 729 | 728 | -0.2 % |
| Axle height | 13.83" | 13.86" | +0.8 mm |
| Approved rim width | 5–6.5" | 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 175/85R16 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.1 mph | +0.1 |
| 50 mph | 50.1 mph | +0.1 |
| 70 mph | 70.1 mph | +0.1 |
| 90 mph | 90.2 mph | +0.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,021 on the road, so it under-counts by 21. At a true 70 mph the first turns 851 times a minute, the second 849.