285/65R20 vs 275/70R20
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 | 285/65R20 | 275/70R20 | Change |
|---|---|---|---|
| Overall height | 34.6" | 35.2" | +1.7 % |
| Sidewall | 7.29" | 7.58" | +3.9 % |
| Section width | 285 mm | 275 mm | -3.5 % |
| Circumference | 108.7" | 110.5" | +1.7 % |
| Revs per mile | 583 | 574 | -1.7 % |
| Axle height | 17.29" | 17.58" | +7.3 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 285/65R20. Fit 275/70R20 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.5 mph | +0.5 |
| 50 mph | 50.8 mph | +0.8 |
| 70 mph | 71.2 mph | +1.2 |
| 90 mph | 91.5 mph | +1.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,165 on the road, so it under-counts by 165. At a true 70 mph the first turns 680 times a minute, the second 669.
What drivers reported
285/65R20 carries 2 complaints. Nobody has filed one naming 275/70R20.