305/35R24 vs 285/35R24
Going from one to the other changes the overall height by -1.7 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 305/35R24 | 285/35R24 | Change |
|---|---|---|---|
| Overall height | 32.4" | 31.9" | -1.7 % |
| Sidewall | 4.20" | 3.93" | -6.6 % |
| Section width | 305 mm | 285 mm | -6.6 % |
| Circumference | 101.8" | 100.1" | -1.7 % |
| Revs per mile | 622 | 633 | +1.7 % |
| Axle height | 16.20" | 15.93" | -7.0 mm |
| Approved rim width | 8.5–11" | 8–10.5" | 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 305/35R24. Fit 285/35R24 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.5 mph | -0.5 |
| 50 mph | 49.1 mph | -0.9 |
| 70 mph | 68.8 mph | -1.2 |
| 90 mph | 88.5 mph | -1.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,830 on the road, so it over-counts by 170. At a true 70 mph the first turns 726 times a minute, the second 739.
What drivers reported
305/35R24 carries 1 complaints. Nobody has filed one naming 285/35R24.