315/65R23 vs 325/60R23
Going from one to the other changes the overall height by -2.0 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 315/65R23 | 325/60R23 | Change |
|---|---|---|---|
| Overall height | 39.1" | 38.4" | -2.0 % |
| Sidewall | 8.06" | 7.68" | -4.8 % |
| Section width | 315 mm | 325 mm | +3.2 % |
| Circumference | 122.9" | 120.5" | -2.0 % |
| Revs per mile | 516 | 526 | +2.0 % |
| Axle height | 19.56" | 19.18" | -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 315/65R23. Fit 325/60R23 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.4 mph | -0.6 |
| 50 mph | 49.0 mph | -1.0 |
| 70 mph | 68.6 mph | -1.4 |
| 90 mph | 88.2 mph | -1.8 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,804 on the road, so it over-counts by 196. At a true 70 mph the first turns 601 times a minute, the second 613.