165/70R16 vs 145/80R16
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 | 165/70R16 | 145/80R16 | Change |
|---|---|---|---|
| Overall height | 25.1" | 25.1" | +0.2 % |
| Sidewall | 4.55" | 4.57" | +0.4 % |
| Section width | 165 mm | 145 mm | -12.1 % |
| Circumference | 78.8" | 79.0" | +0.2 % |
| Revs per mile | 804 | 802 | -0.2 % |
| Axle height | 12.55" | 12.57" | +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 165/70R16. Fit 145/80R16 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 938 times a minute, the second 936.