305/50R24 vs 325/50R24
Going from one to the other changes the overall height by +2.2 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 305/50R24 | 325/50R24 | Change |
|---|---|---|---|
| Overall height | 36.0" | 36.8" | +2.2 % |
| Sidewall | 6.00" | 6.40" | +6.6 % |
| Section width | 305 mm | 325 mm | +6.6 % |
| Circumference | 113.1" | 115.6" | +2.2 % |
| Revs per mile | 560 | 548 | -2.2 % |
| Axle height | 18.00" | 18.40" | +10.0 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 305/50R24. Fit 325/50R24 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.7 mph | +0.7 |
| 50 mph | 51.1 mph | +1.1 |
| 70 mph | 71.5 mph | +1.5 |
| 90 mph | 92.0 mph | +2.0 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,219 on the road, so it under-counts by 219. At a true 70 mph the first turns 653 times a minute, the second 639.