135/80R17 vs 135/75R17
Going from one to the other changes the overall height by -2.1 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 135/80R17 | 135/75R17 | Change |
|---|---|---|---|
| Overall height | 25.5" | 25.0" | -2.1 % |
| Sidewall | 4.25" | 3.99" | -6.3 % |
| Section width | 135 mm | 135 mm | 0.0 % |
| Circumference | 80.1" | 78.5" | -2.1 % |
| Revs per mile | 791 | 808 | +2.1 % |
| Axle height | 12.75" | 12.49" | -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 135/80R17. Fit 135/75R17 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.4 mph | -0.6 |
| 50 mph | 49.0 mph | -1.0 |
| 70 mph | 68.5 mph | -1.5 |
| 90 mph | 88.1 mph | -1.9 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,792 on the road, so it over-counts by 208. At a true 70 mph the first turns 923 times a minute, the second 942.