165/55R15 vs 175/50R15
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 | 165/55R15 | 175/50R15 | Change |
|---|---|---|---|
| Overall height | 22.1" | 21.9" | -1.2 % |
| Sidewall | 3.57" | 3.44" | -3.6 % |
| Section width | 165 mm | 175 mm | +6.1 % |
| Circumference | 69.6" | 68.8" | -1.2 % |
| Revs per mile | 911 | 921 | +1.2 % |
| Axle height | 11.07" | 10.94" | -3.3 mm |
| Approved rim width | 4.5–6" | 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 165/55R15. Fit 175/50R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.7 mph | -0.3 |
| 50 mph | 49.4 mph | -0.6 |
| 70 mph | 69.2 mph | -0.8 |
| 90 mph | 89.0 mph | -1.0 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,884 on the road, so it over-counts by 116. At a true 70 mph the first turns 1062 times a minute, the second 1075.