285/60R16 vs 305/55R16
Going from one to the other changes the overall height by -0.9 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 285/60R16 | 305/55R16 | Change |
|---|---|---|---|
| Overall height | 29.5" | 29.2" | -0.9 % |
| Sidewall | 6.73" | 6.60" | -1.9 % |
| Section width | 285 mm | 305 mm | +7.0 % |
| Circumference | 92.6" | 91.8" | -0.9 % |
| Revs per mile | 684 | 690 | +0.9 % |
| Axle height | 14.73" | 14.60" | -3.3 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 285/60R16. Fit 305/55R16 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.7 mph | -0.3 |
| 50 mph | 49.6 mph | -0.4 |
| 70 mph | 69.4 mph | -0.6 |
| 90 mph | 89.2 mph | -0.8 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,913 on the road, so it over-counts by 87. At a true 70 mph the first turns 799 times a minute, the second 806.