175/60R15 vs 155/65R15
Going from one to the other changes the overall height by -1.4 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 175/60R15 | 155/65R15 | Change |
|---|---|---|---|
| Overall height | 23.3" | 22.9" | -1.4 % |
| Sidewall | 4.13" | 3.97" | -4.0 % |
| Section width | 175 mm | 155 mm | -11.4 % |
| Circumference | 73.1" | 72.0" | -1.4 % |
| Revs per mile | 867 | 879 | +1.4 % |
| Axle height | 11.63" | 11.47" | -4.3 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 175/60R15. Fit 155/65R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.6 mph | -0.4 |
| 50 mph | 49.3 mph | -0.7 |
| 70 mph | 69.0 mph | -1.0 |
| 90 mph | 88.7 mph | -1.3 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,856 on the road, so it over-counts by 144. At a true 70 mph the first turns 1011 times a minute, the second 1026.