305/60R24 vs 325/55R24
Going from one to the other changes the overall height by -0.9 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 305/60R24 | 325/55R24 | Change |
|---|---|---|---|
| Overall height | 38.4" | 38.1" | -0.9 % |
| Sidewall | 7.20" | 7.04" | -2.3 % |
| Section width | 305 mm | 325 mm | +6.6 % |
| Circumference | 120.7" | 119.6" | -0.9 % |
| Revs per mile | 525 | 530 | +0.9 % |
| Axle height | 19.20" | 19.04" | -4.3 mm |
| Approved rim width | 8.5–11" | 9–12" | overlap 9–11" |
Both are approved on a rim 9" to 11" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 305/60R24. Fit 325/55R24 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.7 mph | -0.3 |
| 50 mph | 49.6 mph | -0.4 |
| 70 mph | 69.4 mph | -0.6 |
| 90 mph | 89.2 mph | -0.8 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,913 on the road, so it over-counts by 87. At a true 70 mph the first turns 613 times a minute, the second 618.