175/55R15 vs 155/60R15
Going from one to the other changes the overall height by -1.1 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 175/55R15 | 155/60R15 | Change |
|---|---|---|---|
| Overall height | 22.6" | 22.3" | -1.1 % |
| Sidewall | 3.79" | 3.66" | -3.4 % |
| Section width | 175 mm | 155 mm | -11.4 % |
| Circumference | 70.9" | 70.1" | -1.1 % |
| Revs per mile | 893 | 903 | +1.1 % |
| Axle height | 11.29" | 11.16" | -3.3 mm |
| Approved rim width | 5–6" | 4–5.5" | 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 175/55R15. Fit 155/60R15 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 9,887 on the road, so it over-counts by 113. At a true 70 mph the first turns 1042 times a minute, the second 1054.