185/50R17 vs 175/50R17
Going from one to the other changes the overall height by -1.6 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 185/50R17 | 175/50R17 | Change |
|---|---|---|---|
| Overall height | 24.3" | 23.9" | -1.6 % |
| Sidewall | 3.64" | 3.44" | -5.4 % |
| Section width | 185 mm | 175 mm | -5.4 % |
| Circumference | 76.3" | 75.1" | -1.6 % |
| Revs per mile | 831 | 844 | +1.6 % |
| Axle height | 12.14" | 11.94" | -5.0 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 185/50R17. Fit 175/50R17 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.5 mph | -0.5 |
| 50 mph | 49.2 mph | -0.8 |
| 70 mph | 68.9 mph | -1.1 |
| 90 mph | 88.5 mph | -1.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,838 on the road, so it over-counts by 162. At a true 70 mph the first turns 969 times a minute, the second 985.