125/80R15 vs 135/75R15
Going from one to the other changes the overall height by +0.4 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 125/80R15 | 135/75R15 | Change |
|---|---|---|---|
| Overall height | 22.9" | 23.0" | +0.4 % |
| Sidewall | 3.94" | 3.99" | +1.3 % |
| Section width | 125 mm | 135 mm | +8.0 % |
| Circumference | 71.9" | 72.2" | +0.4 % |
| Revs per mile | 882 | 878 | -0.4 % |
| Axle height | 11.44" | 11.49" | +1.3 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 125/80R15. Fit 135/75R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.1 mph | +0.1 |
| 50 mph | 50.2 mph | +0.2 |
| 70 mph | 70.3 mph | +0.3 |
| 90 mph | 90.4 mph | +0.4 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,043 on the road, so it under-counts by 43. At a true 70 mph the first turns 1029 times a minute, the second 1024.
What drivers reported
125/80R15 carries 1 complaints. Nobody has filed one naming 135/75R15.