175/50R15 vs 165/55R15
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 | 175/50R15 | 165/55R15 | Change |
|---|---|---|---|
| Overall height | 21.9" | 22.1" | +1.2 % |
| Sidewall | 3.44" | 3.57" | +3.7 % |
| Section width | 175 mm | 165 mm | -5.7 % |
| Circumference | 68.8" | 69.6" | +1.2 % |
| Revs per mile | 921 | 911 | -1.2 % |
| Axle height | 10.94" | 11.07" | +3.3 mm |
| Approved rim width | 5–6" | 4.5–6" | 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 175/50R15. Fit 165/55R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.4 mph | +0.4 |
| 50 mph | 50.6 mph | +0.6 |
| 70 mph | 70.8 mph | +0.8 |
| 90 mph | 91.1 mph | +1.1 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,117 on the road, so it under-counts by 117. At a true 70 mph the first turns 1075 times a minute, the second 1062.