175/60R17 vs 155/70R17
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 | 175/60R17 | 155/70R17 | Change |
|---|---|---|---|
| Overall height | 25.3" | 25.5" | +1.1 % |
| Sidewall | 4.13" | 4.27" | +3.3 % |
| Section width | 175 mm | 155 mm | -11.4 % |
| Circumference | 79.4" | 80.2" | +1.1 % |
| Revs per mile | 798 | 790 | -1.1 % |
| Axle height | 12.63" | 12.77" | +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 175/60R17. Fit 155/70R17 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.3 mph | +0.3 |
| 50 mph | 50.5 mph | +0.5 |
| 70 mph | 70.8 mph | +0.8 |
| 90 mph | 91.0 mph | +1.0 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,109 on the road, so it under-counts by 109. At a true 70 mph the first turns 931 times a minute, the second 921.