315/65R20 vs 325/60R20
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 | 315/65R20 | 325/60R20 | Change |
|---|---|---|---|
| Overall height | 36.1" | 35.4" | -2.1 % |
| Sidewall | 8.06" | 7.68" | -4.8 % |
| Section width | 315 mm | 325 mm | +3.2 % |
| Circumference | 113.5" | 111.1" | -2.1 % |
| Revs per mile | 558 | 570 | +2.1 % |
| Axle height | 18.06" | 17.68" | -9.8 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 315/65R20. Fit 325/60R20 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 9,787 on the road, so it over-counts by 213. At a true 70 mph the first turns 651 times a minute, the second 666.
What drivers reported
Nobody has filed a complaint naming 315/65R20. 325/60R20 carries 2.