145/80R14 vs 165/70R14
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 | 145/80R14 | 165/70R14 | Change |
|---|---|---|---|
| Overall height | 23.1" | 23.1" | -0.2 % |
| Sidewall | 4.57" | 4.55" | -0.4 % |
| Section width | 145 mm | 165 mm | +13.8 % |
| Circumference | 72.7" | 72.6" | -0.2 % |
| Revs per mile | 872 | 873 | +0.2 % |
| Axle height | 11.57" | 11.55" | -0.5 mm |
| Approved rim width | 4–5.5" | 4.5–6" | 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 145/80R14. Fit 165/70R14 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.9 mph | -0.1 |
| 50 mph | 49.9 mph | -0.1 |
| 70 mph | 69.9 mph | -0.1 |
| 90 mph | 89.8 mph | -0.2 |
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 1017 times a minute, the second 1019.