165/75R14 vs 145/85R14
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 | 165/75R14 | 145/85R14 | Change |
|---|---|---|---|
| Overall height | 23.7" | 23.7" | -0.2 % |
| Sidewall | 4.87" | 4.85" | -0.4 % |
| Section width | 165 mm | 145 mm | -12.1 % |
| Circumference | 74.6" | 74.5" | -0.2 % |
| Revs per mile | 849 | 851 | +0.2 % |
| Axle height | 11.87" | 11.85" | -0.5 mm |
| Approved rim width | 4.5–6" | 4–5.5" | overlap 4.5–5.5" |
Both are approved on a rim 4.5" 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 165/75R14. Fit 145/85R14 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.0 mph | -0.0 |
| 50 mph | 49.9 mph | -0.1 |
| 70 mph | 69.9 mph | -0.1 |
| 90 mph | 89.9 mph | -0.1 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,983 on the road, so it over-counts by 17. At a true 70 mph the first turns 991 times a minute, the second 993.