155/60R15 vs 175/50R15
Going from one to the other changes the overall height by -1.9 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 155/60R15 | 175/50R15 | Change |
|---|---|---|---|
| Overall height | 22.3" | 21.9" | -1.9 % |
| Sidewall | 3.66" | 3.44" | -5.9 % |
| Section width | 155 mm | 175 mm | +12.9 % |
| Circumference | 70.1" | 68.8" | -1.9 % |
| Revs per mile | 903 | 921 | +1.9 % |
| Axle height | 11.16" | 10.94" | -5.5 mm |
| Approved rim width | 4–5.5" | 5–6" | overlap 5–5.5" |
Both are approved on a rim 5" to 5.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 155/60R15. Fit 175/50R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.4 mph | -0.6 |
| 50 mph | 49.0 mph | -1.0 |
| 70 mph | 68.6 mph | -1.4 |
| 90 mph | 88.3 mph | -1.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,806 on the road, so it over-counts by 194. At a true 70 mph the first turns 1054 times a minute, the second 1075.