345/50R20 vs 335/55R20
Going from one to the other changes the overall height by +2.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 345/50R20 | 335/55R20 | Change |
|---|---|---|---|
| Overall height | 33.6" | 34.5" | +2.8 % |
| Sidewall | 6.79" | 7.25" | +6.8 % |
| Section width | 345 mm | 335 mm | -2.9 % |
| Circumference | 105.5" | 108.4" | +2.8 % |
| Revs per mile | 601 | 584 | -2.8 % |
| Axle height | 16.79" | 17.25" | +11.8 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 345/50R20. Fit 335/55R20 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.8 mph | +0.8 |
| 50 mph | 51.4 mph | +1.4 |
| 70 mph | 71.9 mph | +1.9 |
| 90 mph | 92.5 mph | +2.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,275 on the road, so it under-counts by 275. At a true 70 mph the first turns 701 times a minute, the second 682.