345/55R20 vs 335/55R20
Going from one to the other changes the overall height by -1.2 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 345/55R20 | 335/55R20 | Change |
|---|---|---|---|
| Overall height | 34.9" | 34.5" | -1.2 % |
| Sidewall | 7.47" | 7.25" | -2.9 % |
| Section width | 345 mm | 335 mm | -2.9 % |
| Circumference | 109.8" | 108.4" | -1.2 % |
| Revs per mile | 577 | 584 | +1.2 % |
| Axle height | 17.47" | 17.25" | -5.5 mm |
| Approved rim width | 9.5–12.5" | 9.5–12.5" | overlap 9.5–12.5" |
Both are approved on a rim 9.5" 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 345/55R20. Fit 335/55R20 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.6 mph | -0.4 |
| 50 mph | 49.4 mph | -0.6 |
| 70 mph | 69.1 mph | -0.9 |
| 90 mph | 88.9 mph | -1.1 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,876 on the road, so it over-counts by 124. At a true 70 mph the first turns 673 times a minute, the second 682.