175/75R14 vs 155/85R14
Going from one to the other changes the overall height by +0.2 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 175/75R14 | 155/85R14 | Change |
|---|---|---|---|
| Overall height | 24.3" | 24.4" | +0.2 % |
| Sidewall | 5.17" | 5.19" | +0.4 % |
| Section width | 175 mm | 155 mm | -11.4 % |
| Circumference | 76.4" | 76.6" | +0.2 % |
| Revs per mile | 829 | 827 | -0.2 % |
| Axle height | 12.17" | 12.19" | +0.5 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 175/75R14. Fit 155/85R14 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.0 mph | +0.0 |
| 50 mph | 50.1 mph | +0.1 |
| 70 mph | 70.1 mph | +0.1 |
| 90 mph | 90.1 mph | +0.1 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,016 on the road, so it under-counts by 16. At a true 70 mph the first turns 967 times a minute, the second 965.