255/45R22 vs 245/45R22
Going from one to the other changes the overall height by -1.1 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 255/45R22 | 245/45R22 | Change |
|---|---|---|---|
| Overall height | 31.0" | 30.7" | -1.1 % |
| Sidewall | 4.52" | 4.34" | -3.9 % |
| Section width | 255 mm | 245 mm | -3.9 % |
| Circumference | 97.5" | 96.4" | -1.1 % |
| Revs per mile | 650 | 657 | +1.1 % |
| Axle height | 15.52" | 15.34" | -4.5 mm |
| Approved rim width | 7–9.5" | 7–9" | overlap 7–9" |
Both are approved on a rim 7" to 9" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 255/45R22. Fit 245/45R22 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.7 mph | -0.3 |
| 50 mph | 49.4 mph | -0.6 |
| 70 mph | 69.2 mph | -0.8 |
| 90 mph | 89.0 mph | -1.0 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,886 on the road, so it over-counts by 114. At a true 70 mph the first turns 758 times a minute, the second 767.