445/60R22.5 vs 425/65R22.5
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 | 445/60R22.5 | 425/65R22.5 | Change |
|---|---|---|---|
| Overall height | 43.5" | 44.3" | +1.7 % |
| Sidewall | 10.51" | 10.88" | +3.5 % |
| Section width | 445 mm | 425 mm | -4.5 % |
| Circumference | 136.7" | 139.0" | +1.7 % |
| Revs per mile | 463 | 456 | -1.7 % |
| Axle height | 21.76" | 22.13" | +9.3 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 425/65R22.5 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.5 mph | +0.5 |
| 50 mph | 50.8 mph | +0.8 |
| 70 mph | 71.2 mph | +1.2 |
| 90 mph | 91.5 mph | +1.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,167 on the road, so it under-counts by 167. At a true 70 mph the first turns 541 times a minute, the second 532.