125/80R16 vs 145/65R16
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 | 125/80R16 | 145/65R16 | Change |
|---|---|---|---|
| Overall height | 23.9" | 23.4" | -1.9 % |
| Sidewall | 3.94" | 3.71" | -5.8 % |
| Section width | 125 mm | 145 mm | +16.0 % |
| Circumference | 75.0" | 73.6" | -1.9 % |
| Revs per mile | 845 | 861 | +1.9 % |
| Axle height | 11.94" | 11.71" | -5.8 mm |
| Approved rim width | 3.5–4.5" | 4–5.5" | overlap 4–4.5" |
Both are approved on a rim 4" to 4.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 125/80R16. Fit 145/65R16 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.4 mph | -0.6 |
| 50 mph | 49.1 mph | -0.9 |
| 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 9,810 on the road, so it over-counts by 190. At a true 70 mph the first turns 986 times a minute, the second 1005.