445/65R22.5 vs 425/65R22.5
Going from one to the other changes the overall height by -2.3 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 445/65R22.5 | 425/65R22.5 | Change |
|---|---|---|---|
| Overall height | 45.3" | 44.3" | -2.3 % |
| Sidewall | 11.39" | 10.88" | -4.5 % |
| Section width | 445 mm | 425 mm | -4.5 % |
| Circumference | 142.2" | 139.0" | -2.3 % |
| Revs per mile | 445 | 456 | +2.3 % |
| Axle height | 22.64" | 22.13" | -13.0 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 445/65R22.5. Fit 425/65R22.5 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.3 mph | -0.7 |
| 50 mph | 48.9 mph | -1.1 |
| 70 mph | 68.4 mph | -1.6 |
| 90 mph | 88.0 mph | -2.0 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,774 on the road, so it over-counts by 226. At a true 70 mph the first turns 520 times a minute, the second 532.