325/50R20 vs 345/45R20
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 | 325/50R20 | 345/45R20 | Change |
|---|---|---|---|
| Overall height | 32.8" | 32.2" | -1.7 % |
| Sidewall | 6.40" | 6.11" | -4.5 % |
| Section width | 325 mm | 345 mm | +6.2 % |
| Circumference | 103.0" | 101.2" | -1.7 % |
| Revs per mile | 615 | 626 | +1.7 % |
| Axle height | 16.40" | 16.11" | -7.3 mm |
| Approved rim width | 9–12" | 9.5–12.5" | overlap 9.5–12" |
Both are approved on a rim 9.5" to 12" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 325/50R20. Fit 345/45R20 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.5 mph | -0.5 |
| 50 mph | 49.1 mph | -0.9 |
| 70 mph | 68.8 mph | -1.2 |
| 90 mph | 88.4 mph | -1.6 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,826 on the road, so it over-counts by 174. At a true 70 mph the first turns 717 times a minute, the second 730.
What drivers reported
325/50R20 carries 1 complaints. Nobody has filed one naming 345/45R20.