175/85R17 vs 185/75R17
Going from one to the other changes the overall height by -2.7 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 175/85R17 | 185/75R17 | Change |
|---|---|---|---|
| Overall height | 28.7" | 27.9" | -2.7 % |
| Sidewall | 5.86" | 5.46" | -6.7 % |
| Section width | 175 mm | 185 mm | +5.7 % |
| Circumference | 90.2" | 87.7" | -2.7 % |
| Revs per mile | 702 | 722 | +2.7 % |
| Axle height | 14.36" | 13.96" | -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 175/85R17. Fit 185/75R17 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.2 mph | -0.8 |
| 50 mph | 48.6 mph | -1.4 |
| 70 mph | 68.1 mph | -1.9 |
| 90 mph | 87.5 mph | -2.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,726 on the road, so it over-counts by 274. At a true 70 mph the first turns 819 times a minute, the second 843.