335/45R20 vs 345/45R20
Going from one to the other changes the overall height by +1.1 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 335/45R20 | 345/45R20 | Change |
|---|---|---|---|
| Overall height | 31.9" | 32.2" | +1.1 % |
| Sidewall | 5.94" | 6.11" | +3.0 % |
| Section width | 335 mm | 345 mm | +3.0 % |
| Circumference | 100.1" | 101.2" | +1.1 % |
| Revs per mile | 633 | 626 | -1.1 % |
| Axle height | 15.94" | 16.11" | +4.5 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 335/45R20. Fit 345/45R20 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.3 mph | +0.3 |
| 50 mph | 50.6 mph | +0.6 |
| 70 mph | 70.8 mph | +0.8 |
| 90 mph | 91.0 mph | +1.0 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,111 on the road, so it under-counts by 111. At a true 70 mph the first turns 738 times a minute, the second 730.