355/30R20 vs 335/30R20
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 | 355/30R20 | 335/30R20 | Change |
|---|---|---|---|
| Overall height | 28.4" | 27.9" | -1.7 % |
| Sidewall | 4.19" | 3.96" | -5.6 % |
| Section width | 355 mm | 335 mm | -5.6 % |
| Circumference | 89.2" | 87.7" | -1.7 % |
| Revs per mile | 710 | 723 | +1.7 % |
| Axle height | 14.19" | 13.96" | -6.0 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 355/30R20. Fit 335/30R20 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 | 68.8 mph | -1.2 |
| 90 mph | 88.5 mph | -1.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,834 on the road, so it over-counts by 166. At a true 70 mph the first turns 829 times a minute, the second 843.