275/65R18 vs 285/60R18
Going from one to the other changes the overall height by -1.9 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 275/65R18 | 285/60R18 | Change |
|---|---|---|---|
| Overall height | 32.1" | 31.5" | -1.9 % |
| Sidewall | 7.04" | 6.73" | -4.3 % |
| Section width | 275 mm | 285 mm | +3.6 % |
| Circumference | 100.8" | 98.8" | -1.9 % |
| Revs per mile | 629 | 641 | +1.9 % |
| Axle height | 16.04" | 15.73" | -7.8 mm |
| Approved rim width | 7.5–10" | 8–10.5" | overlap 8–10" |
Both are approved on a rim 8" to 10" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 275/65R18. Fit 285/60R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.4 mph | -0.6 |
| 50 mph | 49.0 mph | -1.0 |
| 70 mph | 68.7 mph | -1.3 |
| 90 mph | 88.3 mph | -1.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,810 on the road, so it over-counts by 190. At a true 70 mph the first turns 734 times a minute, the second 748.