285/50R24 vs 305/50R24
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 | 285/50R24 | 305/50R24 | Change |
|---|---|---|---|
| Overall height | 35.2" | 36.0" | +2.2 % |
| Sidewall | 5.61" | 6.00" | +7.0 % |
| Section width | 285 mm | 305 mm | +7.0 % |
| Circumference | 110.6" | 113.1" | +2.2 % |
| Revs per mile | 573 | 560 | -2.2 % |
| Axle height | 17.61" | 18.00" | +10.0 mm |
| Approved rim width | 8–10.5" | 8.5–11" | overlap 8.5–10.5" |
Both are approved on a rim 8.5" to 10.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 285/50R24. Fit 305/50R24 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 | 71.6 mph | +1.6 |
| 90 mph | 92.0 mph | +2.0 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,224 on the road, so it under-counts by 224. At a true 70 mph the first turns 668 times a minute, the second 653.