135/80R17 vs 145/70R17
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 | 135/80R17 | 145/70R17 | Change |
|---|---|---|---|
| Overall height | 25.5" | 25.0" | -2.0 % |
| Sidewall | 4.25" | 4.00" | -6.0 % |
| Section width | 135 mm | 145 mm | +7.4 % |
| Circumference | 80.1" | 78.5" | -2.0 % |
| Revs per mile | 791 | 807 | +2.0 % |
| Axle height | 12.75" | 12.50" | -6.5 mm |
| Approved rim width | 3.5–5" | 4–5.5" | 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 135/80R17. Fit 145/70R17 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 | 68.6 mph | -1.4 |
| 90 mph | 88.2 mph | -1.8 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,799 on the road, so it over-counts by 201. At a true 70 mph the first turns 923 times a minute, the second 941.