285/70R20 vs 295/65R20
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 | 285/70R20 | 295/65R20 | Change |
|---|---|---|---|
| Overall height | 35.7" | 35.1" | -1.7 % |
| Sidewall | 7.85" | 7.55" | -3.9 % |
| Section width | 285 mm | 295 mm | +3.5 % |
| Circumference | 112.2" | 110.3" | -1.7 % |
| Revs per mile | 565 | 575 | +1.7 % |
| Axle height | 17.85" | 17.55" | -7.8 mm |
| Approved rim width | 8–10.5" | 8.5–11" | overlap 8.5–10.5" |
Both are approved on a rim 8.5" to 10.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 285/70R20. Fit 295/65R20 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.5 mph | -0.5 |
| 50 mph | 49.1 mph | -0.9 |
| 70 mph | 68.8 mph | -1.2 |
| 90 mph | 88.5 mph | -1.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,829 on the road, so it over-counts by 171. At a true 70 mph the first turns 659 times a minute, the second 670.