185/80R17 vs 175/80R17
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 | 185/80R17 | 175/80R17 | Change |
|---|---|---|---|
| Overall height | 28.7" | 28.0" | -2.2 % |
| Sidewall | 5.83" | 5.51" | -5.4 % |
| Section width | 185 mm | 175 mm | -5.4 % |
| Circumference | 90.0" | 88.0" | -2.2 % |
| Revs per mile | 704 | 720 | +2.2 % |
| Axle height | 14.33" | 14.01" | -8.0 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 185/80R17. Fit 175/80R17 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 9,780 on the road, so it over-counts by 220. At a true 70 mph the first turns 821 times a minute, the second 840.