445/60R22.5 vs 425/60R22.5
Going from one to the other changes the overall height by -2.2 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 445/60R22.5 | 425/60R22.5 | Change |
|---|---|---|---|
| Overall height | 43.5" | 42.6" | -2.2 % |
| Sidewall | 10.51" | 10.04" | -4.5 % |
| Section width | 445 mm | 425 mm | -4.5 % |
| Circumference | 136.7" | 133.8" | -2.2 % |
| Revs per mile | 463 | 474 | +2.2 % |
| Axle height | 21.76" | 21.29" | -12.0 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 445/60R22.5. Fit 425/60R22.5 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 | 68.5 mph | -1.5 |
| 90 mph | 88.0 mph | -2.0 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,783 on the road, so it over-counts by 217. At a true 70 mph the first turns 541 times a minute, the second 553.