Did you see
This Truck Forum Link?This One's Very Helpful...since it's from one of our own members: Capri Racer on RV.net
The bolt pattern and "piloting" are of course important. Wheels are Lug Piloted (the fasteners don't just hold the rim, they center it) or Hub Piloted (the big hole in the center of the wheel mates to a machined hub on the axle, and the lug nuts only hold the wheel to the axle, they don't center it).
Offset is a little trickier. It is NOT the space between the Sidewalls of the Tires, but that's the outcome of the Offset measurement. Picture this with a pair of dual wheels:
1. What is the Rim Width? If they're "Six Inch Rims" then you can measure 6" between the edges of the flanged part of the Rim where the Tire's Bead seats. Measure and mark half of that. That's the center of the Rim.
2. Do this with another Wheel, marking the Center of its Rim
3. Mount them on an Axle, or stack them face to face.
4. Measure between the Marks on each Rim. That is the Offset. Barry's Tire Tech chart calls it Dual Spacing. Say you get 10.2" Those'd work with 225/75R16 tires if you had the right bolt pattern and centering.
In the example I used, you COULD mark one Rim, set it on a flat floor, and measure from Mark to Floor and find 5.1". Twice that is the 10.2" offset.
You do NOT WANT "kissing sidewalls!!!"
If God's Your Co-Pilot Move Over, jd
2003 Jayco Escapade 31A on 2002 Ford E450 V10 4R100 218" WB