265/65R18 vs 285/60R18
Going from one to the other changes the overall height by -0.3 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 265/65R18 | 285/60R18 | Change |
|---|---|---|---|
| Overall height | 31.6" | 31.5" | -0.3 % |
| Sidewall | 6.78" | 6.73" | -0.7 % |
| Section width | 265 mm | 285 mm | +7.5 % |
| Circumference | 99.2" | 98.8" | -0.3 % |
| Revs per mile | 639 | 641 | +0.3 % |
| Axle height | 15.78" | 15.73" | -1.3 mm |
| Approved rim width | 7.5–9.5" | 8–10.5" | overlap 8–9.5" |
Both are approved on a rim 8" to 9.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 265/65R18. Fit 285/60R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.9 mph | -0.1 |
| 50 mph | 49.8 mph | -0.2 |
| 70 mph | 69.8 mph | -0.2 |
| 90 mph | 89.7 mph | -0.3 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,969 on the road, so it over-counts by 31. At a true 70 mph the first turns 745 times a minute, the second 748.