125/80R17 vs 135/80R17
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 | 125/80R17 | 135/80R17 | Change |
|---|---|---|---|
| Overall height | 24.9" | 25.5" | +2.5 % |
| Sidewall | 3.94" | 4.25" | +8.0 % |
| Section width | 125 mm | 135 mm | +8.0 % |
| Circumference | 78.1" | 80.1" | +2.5 % |
| Revs per mile | 811 | 791 | -2.5 % |
| Axle height | 12.44" | 12.75" | +8.0 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 125/80R17. Fit 135/80R17 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.8 mph | +0.8 |
| 50 mph | 51.3 mph | +1.3 |
| 70 mph | 71.8 mph | +1.8 |
| 90 mph | 92.3 mph | +2.3 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,253 on the road, so it under-counts by 253. At a true 70 mph the first turns 946 times a minute, the second 923.