When you’re looking to acquire new rims for your Buick Grand National (or other model Turbo Regal), most wheel manufacturing companies use the “backspace” method.
A few car rim producers however, utilize the “offset” method.
Neither is really better than the other, but you absolutely must know the right specs to get a rim that’s going to fit on your G-body correctly.
The below chart gives you the conversion from one to the other if the new vehicle rims you’re looking at don’t come in the standard format that you’re use to.
[and as a last resort, you can always add wheel spacers behind your rims to get just the right “look” or to correct uncentered rear end issues]
According to someone in one of the buick regal forums, the below is what was posted that will work for our Turbo Buicks. (generally speaking, for stock unmodified Regals)