325/55R22 vs 315/60R22
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 | 325/55R22 | 315/60R22 | Change |
|---|---|---|---|
| Overall height | 36.1" | 36.9" | +2.2 % |
| Sidewall | 7.04" | 7.44" | +5.7 % |
| Section width | 325 mm | 315 mm | -3.1 % |
| Circumference | 113.3" | 115.9" | +2.2 % |
| Revs per mile | 559 | 547 | -2.2 % |
| Axle height | 18.04" | 18.44" | +10.3 mm |
| Approved rim width | 9–12" | 8.5–11.5" | 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 325/55R22. Fit 315/60R22 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.7 mph | +0.7 |
| 50 mph | 51.1 mph | +1.1 |
| 70 mph | 71.6 mph | +1.6 |
| 90 mph | 92.0 mph | +2.0 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,224 on the road, so it under-counts by 224. At a true 70 mph the first turns 652 times a minute, the second 638.