325/60R22 vs 315/65R22
Going from one to the other changes the overall height by +2.1 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 325/60R22 | 315/65R22 | Change |
|---|---|---|---|
| Overall height | 37.4" | 38.1" | +2.1 % |
| Sidewall | 7.68" | 8.06" | +5.0 % |
| Section width | 325 mm | 315 mm | -3.1 % |
| Circumference | 117.4" | 119.8" | +2.1 % |
| Revs per mile | 540 | 529 | -2.1 % |
| Axle height | 18.68" | 19.06" | +9.8 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 325/60R22. Fit 315/65R22 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.6 mph | +0.6 |
| 50 mph | 51.0 mph | +1.0 |
| 70 mph | 71.4 mph | +1.4 |
| 90 mph | 91.8 mph | +1.8 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,206 on the road, so it under-counts by 206. At a true 70 mph the first turns 630 times a minute, the second 617.