175/60R15 vs 155/70R15
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 | 175/60R15 | 155/70R15 | Change |
|---|---|---|---|
| Overall height | 23.3" | 23.5" | +1.2 % |
| Sidewall | 4.13" | 4.27" | +3.3 % |
| Section width | 175 mm | 155 mm | -11.4 % |
| Circumference | 73.1" | 74.0" | +1.2 % |
| Revs per mile | 867 | 857 | -1.2 % |
| Axle height | 11.63" | 11.77" | +3.5 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 155/70R15 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 10,118 on the road, so it under-counts by 118. At a true 70 mph the first turns 1011 times a minute, the second 999.