295/45R24 vs 305/40R24
Going from one to the other changes the overall height by -2.5 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 295/45R24 | 305/40R24 | Change |
|---|---|---|---|
| Overall height | 34.5" | 33.6" | -2.5 % |
| Sidewall | 5.23" | 4.80" | -8.1 % |
| Section width | 295 mm | 305 mm | +3.4 % |
| Circumference | 108.2" | 105.6" | -2.5 % |
| Revs per mile | 585 | 600 | +2.5 % |
| Axle height | 17.23" | 16.80" | -10.8 mm |
| Approved rim width | 8.5–11" | 8.5–11" | overlap 8.5–11" |
Both are approved on a rim 8.5" to 11" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 295/45R24. Fit 305/40R24 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.3 mph | -0.7 |
| 50 mph | 48.8 mph | -1.2 |
| 70 mph | 68.3 mph | -1.7 |
| 90 mph | 87.8 mph | -2.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,754 on the road, so it over-counts by 246. At a true 70 mph the first turns 683 times a minute, the second 700.