315/60R17 vs 325/55R17
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 | 315/60R17 | 325/55R17 | Change |
|---|---|---|---|
| Overall height | 31.9" | 31.1" | -2.5 % |
| Sidewall | 7.44" | 7.04" | -5.4 % |
| Section width | 315 mm | 325 mm | +3.2 % |
| Circumference | 100.2" | 97.6" | -2.5 % |
| Revs per mile | 633 | 649 | +2.5 % |
| Axle height | 15.94" | 15.54" | -10.3 mm |
| Approved rim width | 8.5–11.5" | 9–12" | overlap 9–11.5" |
Both are approved on a rim 9" to 11.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 315/60R17. Fit 325/55R17 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.2 mph | -0.8 |
| 50 mph | 48.7 mph | -1.3 |
| 70 mph | 68.2 mph | -1.8 |
| 90 mph | 87.7 mph | -2.3 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,747 on the road, so it over-counts by 253. At a true 70 mph the first turns 738 times a minute, the second 757.