125/75R14 vs 135/65R14
Going from one to the other changes the overall height by -2.2 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 125/75R14 | 135/65R14 | Change |
|---|---|---|---|
| Overall height | 21.4" | 20.9" | -2.2 % |
| Sidewall | 3.69" | 3.45" | -6.4 % |
| Section width | 125 mm | 135 mm | +8.0 % |
| Circumference | 67.2" | 65.7" | -2.2 % |
| Revs per mile | 943 | 965 | +2.2 % |
| Axle height | 10.69" | 10.45" | -6.0 mm |
| Approved rim width | 3.5–4.5" | 3.5–5" | overlap 3.5–4.5" |
Both are approved on a rim 3.5" 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 125/75R14. Fit 135/65R14 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.3 mph | -0.7 |
| 50 mph | 48.9 mph | -1.1 |
| 70 mph | 68.5 mph | -1.5 |
| 90 mph | 88.0 mph | -2.0 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,779 on the road, so it over-counts by 221. At a true 70 mph the first turns 1100 times a minute, the second 1125.