145/80R14 vs 135/80R14
Going from one to the other changes the overall height by -2.7 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 145/80R14 | 135/80R14 | Change |
|---|---|---|---|
| Overall height | 23.1" | 22.5" | -2.7 % |
| Sidewall | 4.57" | 4.25" | -6.9 % |
| Section width | 145 mm | 135 mm | -6.9 % |
| Circumference | 72.7" | 70.7" | -2.7 % |
| Revs per mile | 872 | 896 | +2.7 % |
| Axle height | 11.57" | 11.25" | -8.0 mm |
| Approved rim width | 4–5.5" | 3.5–5" | overlap 4–5" |
Both are approved on a rim 4" to 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 135/80R14 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.2 mph | -0.8 |
| 50 mph | 48.6 mph | -1.4 |
| 70 mph | 68.1 mph | -1.9 |
| 90 mph | 87.5 mph | -2.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,728 on the road, so it over-counts by 272. At a true 70 mph the first turns 1017 times a minute, the second 1046.