295/30R24 vs 305/30R24
Going from one to the other changes the overall height by +0.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 295/30R24 | 305/30R24 | Change |
|---|---|---|---|
| Overall height | 31.0" | 31.2" | +0.8 % |
| Sidewall | 3.48" | 3.60" | +3.4 % |
| Section width | 295 mm | 305 mm | +3.4 % |
| Circumference | 97.3" | 98.0" | +0.8 % |
| Revs per mile | 651 | 646 | -0.8 % |
| Axle height | 15.48" | 15.60" | +3.0 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 295/30R24. Fit 305/30R24 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.2 mph | +0.2 |
| 50 mph | 50.4 mph | +0.4 |
| 70 mph | 70.5 mph | +0.5 |
| 90 mph | 90.7 mph | +0.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,076 on the road, so it under-counts by 76. At a true 70 mph the first turns 760 times a minute, the second 754.