155/70R17 vs 145/70R17
Going from one to the other changes the overall height by -2.2 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 155/70R17 | 145/70R17 | Change |
|---|---|---|---|
| Overall height | 25.5" | 25.0" | -2.2 % |
| Sidewall | 4.27" | 4.00" | -6.5 % |
| Section width | 155 mm | 145 mm | -6.5 % |
| Circumference | 80.2" | 78.5" | -2.2 % |
| Revs per mile | 790 | 807 | +2.2 % |
| Axle height | 12.77" | 12.50" | -7.0 mm |
| Approved rim width | 4–5.5" | 4–5.5" | overlap 4–5.5" |
Both are approved on a rim 4" to 5.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 155/70R17. 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 | 48.9 mph | -1.1 |
| 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 9,784 on the road, so it over-counts by 216. At a true 70 mph the first turns 921 times a minute, the second 941.
What drivers reported
155/70R17 carries 2 complaints. Nobody has filed one naming 145/70R17.