175/85R17 vs 185/85R17
Going from one to the other changes the overall height by +2.3 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 175/85R17 | 185/85R17 | Change |
|---|---|---|---|
| Overall height | 28.7" | 29.4" | +2.3 % |
| Sidewall | 5.86" | 6.19" | +5.7 % |
| Section width | 175 mm | 185 mm | +5.7 % |
| Circumference | 90.2" | 92.3" | +2.3 % |
| Revs per mile | 702 | 686 | -2.3 % |
| Axle height | 14.36" | 14.69" | +8.5 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 185/85R17 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.7 mph | +0.7 |
| 50 mph | 51.2 mph | +1.2 |
| 70 mph | 71.6 mph | +1.6 |
| 90 mph | 92.1 mph | +2.1 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,233 on the road, so it under-counts by 233. At a true 70 mph the first turns 819 times a minute, the second 801.