145/70R17 vs 135/80R17
Going from one to the other changes the overall height by +2.0 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 145/70R17 | 135/80R17 | Change |
|---|---|---|---|
| Overall height | 25.0" | 25.5" | +2.0 % |
| Sidewall | 4.00" | 4.25" | +6.4 % |
| Section width | 145 mm | 135 mm | -6.9 % |
| Circumference | 78.5" | 80.1" | +2.0 % |
| Revs per mile | 807 | 791 | -2.0 % |
| Axle height | 12.50" | 12.75" | +6.5 mm |
| Approved rim width | 4–5.5" | 3.5–5" | overlap 4–5" |
Both are approved on a rim 4" to 5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 145/70R17. Fit 135/80R17 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.6 mph | +0.6 |
| 50 mph | 51.0 mph | +1.0 |
| 70 mph | 71.4 mph | +1.4 |
| 90 mph | 91.8 mph | +1.8 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,205 on the road, so it under-counts by 205. At a true 70 mph the first turns 941 times a minute, the second 923.