445/55R22.5 vs 425/55R22.5
Going from one to the other changes the overall height by -2.1 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 445/55R22.5 | 425/55R22.5 | Change |
|---|---|---|---|
| Overall height | 41.8" | 40.9" | -2.1 % |
| Sidewall | 9.64" | 9.20" | -4.5 % |
| Section width | 445 mm | 425 mm | -4.5 % |
| Circumference | 131.2" | 128.5" | -2.1 % |
| Revs per mile | 483 | 493 | +2.1 % |
| Axle height | 20.89" | 20.45" | -11.0 mm |
| Approved rim width | 13–16" | 12–15" | overlap 13–15" |
Both are approved on a rim 13" to 15" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 445/55R22.5. Fit 425/55R22.5 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.4 mph | -0.6 |
| 50 mph | 49.0 mph | -1.0 |
| 70 mph | 68.5 mph | -1.5 |
| 90 mph | 88.1 mph | -1.9 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,793 on the road, so it over-counts by 207. At a true 70 mph the first turns 563 times a minute, the second 575.