offset ?

[1NASTYGN]

Ordering wheels. 19 x.9.5 rear and 19 x 8.5 front. Apparently these wheel guys go by offset not back spacing. My rear backspacing is 5.00 and 4.5 or 4.75 for front.What is the correct offset for our GN?

 

[Antbankstwo3]

I believe its right around ZERO to -3mm offset. A lot of older GM's were right around zero offset to my knowledge. Maybe someone can confirm...

 

[buickjeff]

This site i found helpful - of course they dont have a listing for 4.75 backspacing but the math is pretty easy

https://www.rsracing.com/TechWheel.aspx#backspace

 

[1NASTYGN]

Thank you!

 

[1986 Buick GX1]

This site i found helpful - of course they dont have a listing for 4.75 backspacing but the math is pretty easy

https://www.rsracing.com/TechWheel.aspx#backspace

This is a good explanation, however it doesn't take in to account the flange thickness (the distance from the bead to the inside edge of the wheel) which is different between manufacturers. The flange thickness probably doesn't vary more than an 1/8th of an inch, but should still be considered. The wheel width is measured from bead to bead (where the tire contacts the wheel on the outside and the inside).
If you had the overall width of the wheel, that would make it easier.