345/55R24 vs 325/60R24
Going from one to the other changes the overall height by +1.1 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 345/55R24 | 325/60R24 | Change |
|---|---|---|---|
| Overall height | 38.9" | 39.4" | +1.1 % |
| Sidewall | 7.47" | 7.68" | +2.8 % |
| Section width | 345 mm | 325 mm | -5.8 % |
| Circumference | 122.3" | 123.6" | +1.1 % |
| Revs per mile | 518 | 512 | -1.1 % |
| Axle height | 19.47" | 19.68" | +5.3 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 345/55R24. Fit 325/60R24 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.3 mph | +0.3 |
| 50 mph | 50.5 mph | +0.5 |
| 70 mph | 70.7 mph | +0.7 |
| 90 mph | 91.0 mph | +1.0 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,106 on the road, so it under-counts by 106. At a true 70 mph the first turns 604 times a minute, the second 598.