175/85R16 vs 185/75R16
Going from one to the other changes the overall height by -2.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 175/85R16 | 185/75R16 | Change |
|---|---|---|---|
| Overall height | 27.7" | 26.9" | -2.8 % |
| Sidewall | 5.86" | 5.46" | -6.7 % |
| Section width | 175 mm | 185 mm | +5.7 % |
| Circumference | 87.1" | 84.6" | -2.8 % |
| Revs per mile | 728 | 749 | +2.8 % |
| Axle height | 13.86" | 13.46" | -10.0 mm |
| Approved rim width | 5–6" | 5–6.5" | 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 175/85R16. Fit 185/75R16 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.1 mph | -0.9 |
| 50 mph | 48.6 mph | -1.4 |
| 70 mph | 68.0 mph | -2.0 |
| 90 mph | 87.4 mph | -2.6 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,716 on the road, so it over-counts by 284. At a true 70 mph the first turns 849 times a minute, the second 874.