What would be the correct backspacing for 15x7 wheels on a ‘66 LeSabre coupe? Is 4” good? That seems to be the most common.
4-3/8" backspace is typical for the later 15x7 small bolt pattern Buick Rally wheel. Or are you asking about the standard steel wheels? I'm thinking the '66 LeSabre used the 4-3/4" bolt pattern and not the 5" ? I do know the LeSabre center section was the same as the A-body Skylark, and IIRC the wheel bearings are same as Skylark GS.
If the wheels are correct for your car, take one off and measure it. Then go from there. https://www.teambuick.com/reference/library/66_chassis/files/100-a.php 1966 LeSabre is 45000 series. Standard wheel is 15 X 5.5" Optional wheel is 15 X 6" (Chrome??), 5 X 5 bolt pattern. If the optional wheel is the Chrome Rally wheel, it is 15 X 6" with 3 3/8" back spacing. So, a 15 X 7" wheel would need an additional 1/2" of back spacing, 3 7/8", so 4" back space would work just fine.
