325/65R24 vs 345/60R24
Going from one to the other changes the overall height by -0.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 325/65R24 | 345/60R24 | Change |
|---|---|---|---|
| Overall height | 40.6" | 40.3" | -0.8 % |
| Sidewall | 8.32" | 8.15" | -2.0 % |
| Section width | 325 mm | 345 mm | +6.2 % |
| Circumference | 127.7" | 126.6" | -0.8 % |
| Revs per mile | 496 | 500 | +0.8 % |
| Axle height | 20.32" | 20.15" | -4.3 mm |
| Approved rim width | 9–12" | 9.5–12.5" | overlap 9.5–12" |
Both are approved on a rim 9.5" to 12" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 325/65R24. Fit 345/60R24 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.8 mph | -0.2 |
| 50 mph | 49.6 mph | -0.4 |
| 70 mph | 69.4 mph | -0.6 |
| 90 mph | 89.3 mph | -0.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,918 on the road, so it over-counts by 82. At a true 70 mph the first turns 579 times a minute, the second 584.