275/70R17 vs 285/70R17
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 | 275/70R17 | 285/70R17 | Change |
|---|---|---|---|
| Overall height | 32.2" | 32.7" | +1.7 % |
| Sidewall | 7.58" | 7.85" | +3.6 % |
| Section width | 275 mm | 285 mm | +3.6 % |
| Circumference | 101.0" | 102.8" | +1.7 % |
| Revs per mile | 627 | 617 | -1.7 % |
| Axle height | 16.08" | 16.35" | +7.0 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 275/70R17. Fit 285/70R17 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.5 mph | +0.5 |
| 50 mph | 50.9 mph | +0.9 |
| 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 10,171 on the road, so it under-counts by 171. At a true 70 mph the first turns 732 times a minute, the second 719.