135/80R14 vs 135/75R14
Going from one to the other changes the overall height by -2.4 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 135/80R14 | 135/75R14 | Change |
|---|---|---|---|
| Overall height | 22.5" | 22.0" | -2.4 % |
| Sidewall | 4.25" | 3.99" | -6.3 % |
| Section width | 135 mm | 135 mm | 0.0 % |
| Circumference | 70.7" | 69.0" | -2.4 % |
| Revs per mile | 896 | 918 | +2.4 % |
| Axle height | 11.25" | 10.99" | -6.8 mm |
| Approved rim width | 3.5–5" | 3.5–5" | overlap 3.5–5" |
Both are approved on a rim 3.5" to 5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 135/80R14. Fit 135/75R14 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 | 87.9 mph | -2.1 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,764 on the road, so it over-counts by 236. At a true 70 mph the first turns 1046 times a minute, the second 1071.