335/50R20 vs 345/45R20
Going from one to the other changes the overall height by -2.9 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 335/50R20 | 345/45R20 | Change |
|---|---|---|---|
| Overall height | 33.2" | 32.2" | -2.9 % |
| Sidewall | 6.59" | 6.11" | -7.3 % |
| Section width | 335 mm | 345 mm | +3.0 % |
| Circumference | 104.3" | 101.2" | -2.9 % |
| Revs per mile | 608 | 626 | +2.9 % |
| Axle height | 16.59" | 16.11" | -12.3 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 335/50R20. Fit 345/45R20 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.1 mph | -0.9 |
| 50 mph | 48.5 mph | -1.5 |
| 70 mph | 68.0 mph | -2.0 |
| 90 mph | 87.4 mph | -2.6 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,709 on the road, so it over-counts by 291. At a true 70 mph the first turns 709 times a minute, the second 730.