175/55R17 vs 185/50R17
Going from one to the other changes the overall height by -1.2 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 175/55R17 | 185/50R17 | Change |
|---|---|---|---|
| Overall height | 24.6" | 24.3" | -1.2 % |
| Sidewall | 3.79" | 3.64" | -3.9 % |
| Section width | 175 mm | 185 mm | +5.7 % |
| Circumference | 77.2" | 76.3" | -1.2 % |
| Revs per mile | 821 | 831 | +1.2 % |
| Axle height | 12.29" | 12.14" | -3.8 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 175/55R17. Fit 185/50R17 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.6 mph | -0.4 |
| 50 mph | 49.4 mph | -0.6 |
| 70 mph | 69.2 mph | -0.8 |
| 90 mph | 88.9 mph | -1.1 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,880 on the road, so it over-counts by 120. At a true 70 mph the first turns 957 times a minute, the second 969.