175/70R16 vs 155/75R16
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 | 175/70R16 | 155/75R16 | Change |
|---|---|---|---|
| Overall height | 25.6" | 25.2" | -1.9 % |
| Sidewall | 4.82" | 4.58" | -5.1 % |
| Section width | 175 mm | 155 mm | -11.4 % |
| Circumference | 80.6" | 79.0" | -1.9 % |
| Revs per mile | 786 | 802 | +1.9 % |
| Axle height | 12.82" | 12.58" | -6.3 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 175/70R16. Fit 155/75R16 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 | 68.7 mph | -1.3 |
| 90 mph | 88.3 mph | -1.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,808 on the road, so it over-counts by 192. At a true 70 mph the first turns 917 times a minute, the second 935.