355/65R20 vs 335/65R20
Going from one to the other changes the overall height by -2.7 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 355/65R20 | 335/65R20 | Change |
|---|---|---|---|
| Overall height | 38.2" | 37.1" | -2.7 % |
| Sidewall | 9.08" | 8.57" | -5.6 % |
| Section width | 355 mm | 335 mm | -5.6 % |
| Circumference | 119.9" | 116.7" | -2.7 % |
| Revs per mile | 528 | 543 | +2.7 % |
| Axle height | 19.08" | 18.57" | -13.0 mm |
| Approved rim width | 10–13" | 9.5–12.5" | overlap 10–12.5" |
Both are approved on a rim 10" to 12.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 355/65R20. Fit 335/65R20 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.2 mph | -0.8 |
| 50 mph | 48.7 mph | -1.3 |
| 70 mph | 68.1 mph | -1.9 |
| 90 mph | 87.6 mph | -2.4 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,732 on the road, so it over-counts by 268. At a true 70 mph the first turns 616 times a minute, the second 633.