315/60R22 vs 325/60R22
Going from one to the other changes the overall height by +1.3 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 315/60R22 | 325/60R22 | Change |
|---|---|---|---|
| Overall height | 36.9" | 37.4" | +1.3 % |
| Sidewall | 7.44" | 7.68" | +3.2 % |
| Section width | 315 mm | 325 mm | +3.2 % |
| Circumference | 115.9" | 117.4" | +1.3 % |
| Revs per mile | 547 | 540 | -1.3 % |
| Axle height | 18.44" | 18.68" | +6.0 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 315/60R22. Fit 325/60R22 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.4 mph | +0.4 |
| 50 mph | 50.6 mph | +0.6 |
| 70 mph | 70.9 mph | +0.9 |
| 90 mph | 91.2 mph | +1.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,128 on the road, so it under-counts by 128. At a true 70 mph the first turns 638 times a minute, the second 630.