165/75R15 vs 145/80R15
Going from one to the other changes the overall height by -2.5 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 165/75R15 | 145/80R15 | Change |
|---|---|---|---|
| Overall height | 24.7" | 24.1" | -2.5 % |
| Sidewall | 4.87" | 4.57" | -6.3 % |
| Section width | 165 mm | 145 mm | -12.1 % |
| Circumference | 77.7" | 75.8" | -2.5 % |
| Revs per mile | 815 | 836 | +2.5 % |
| Axle height | 12.37" | 12.07" | -7.8 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 165/75R15. Fit 145/80R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.3 mph | -0.7 |
| 50 mph | 48.8 mph | -1.2 |
| 70 mph | 68.3 mph | -1.7 |
| 90 mph | 87.8 mph | -2.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,753 on the road, so it over-counts by 247. At a true 70 mph the first turns 951 times a minute, the second 975.