Assuming you have Michelin 235/80R22.5 XRV tires, the minimum spacing for duals is 10.3" as shown on page 23 of the Michelin Tire Guide available
HERE.
Spacing for other Michelin tires is also shown in the guide. Spacing is for properly inflated tires. The 10.3" is centerline distance and takes into account tire width and flex.