285/65R18 vs 275/65R18
Going from one to the other changes the overall height by -1.6 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 285/65R18 | 275/65R18 | Change |
|---|---|---|---|
| Overall height | 32.6" | 32.1" | -1.6 % |
| Sidewall | 7.29" | 7.04" | -3.5 % |
| Section width | 285 mm | 275 mm | -3.5 % |
| Circumference | 102.4" | 100.8" | -1.6 % |
| Revs per mile | 619 | 629 | +1.6 % |
| Axle height | 16.29" | 16.04" | -6.5 mm |
| Approved rim width | 8–10.5" | 7.5–10" | 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 285/65R18. Fit 275/65R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.5 mph | -0.5 |
| 50 mph | 49.2 mph | -0.8 |
| 70 mph | 68.9 mph | -1.1 |
| 90 mph | 88.6 mph | -1.4 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,843 on the road, so it over-counts by 157. At a true 70 mph the first turns 722 times a minute, the second 734.
What drivers reported
285/65R18 carries 1 complaints and 1 deaths. 275/65R18 carries 30.