185/55R16 vs 175/55R16
Going from one to the other changes the overall height by -1.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 185/55R16 | 175/55R16 | Change |
|---|---|---|---|
| Overall height | 24.0" | 23.6" | -1.8 % |
| Sidewall | 4.01" | 3.79" | -5.4 % |
| Section width | 185 mm | 175 mm | -5.4 % |
| Circumference | 75.4" | 74.1" | -1.8 % |
| Revs per mile | 840 | 855 | +1.8 % |
| Axle height | 12.01" | 11.79" | -5.5 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 185/55R16. Fit 175/55R16 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.5 mph | -0.5 |
| 50 mph | 49.1 mph | -0.9 |
| 70 mph | 68.7 mph | -1.3 |
| 90 mph | 88.4 mph | -1.6 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,820 on the road, so it over-counts by 180. At a true 70 mph the first turns 980 times a minute, the second 998.