345/50R24 vs 325/50R24
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 | 345/50R24 | 325/50R24 | Change |
|---|---|---|---|
| Overall height | 37.6" | 36.8" | -2.1 % |
| Sidewall | 6.79" | 6.40" | -5.8 % |
| Section width | 345 mm | 325 mm | -5.8 % |
| Circumference | 118.1" | 115.6" | -2.1 % |
| Revs per mile | 537 | 548 | +2.1 % |
| Axle height | 18.79" | 18.40" | -10.0 mm |
| Approved rim width | 9.5–12.5" | 9–12" | 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 345/50R24. Fit 325/50R24 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 | 68.5 mph | -1.5 |
| 90 mph | 88.1 mph | -1.9 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,790 on the road, so it over-counts by 210. At a true 70 mph the first turns 626 times a minute, the second 639.