305/45R24 vs 325/45R24
Going from one to the other changes the overall height by +2.0 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 305/45R24 | 325/45R24 | Change |
|---|---|---|---|
| Overall height | 34.8" | 35.5" | +2.0 % |
| Sidewall | 5.40" | 5.76" | +6.6 % |
| Section width | 305 mm | 325 mm | +6.6 % |
| Circumference | 109.3" | 111.6" | +2.0 % |
| Revs per mile | 579 | 568 | -2.0 % |
| Axle height | 17.40" | 17.76" | +9.0 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 305/45R24. Fit 325/45R24 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.6 mph | +0.6 |
| 50 mph | 51.0 mph | +1.0 |
| 70 mph | 71.4 mph | +1.4 |
| 90 mph | 91.8 mph | +1.8 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,204 on the road, so it under-counts by 204. At a true 70 mph the first turns 676 times a minute, the second 663.