billet wheel offset

I am looking at getting some 20x8.5 billets for my deo but am not sure what offset i need. The truck is BD'd 80mm, and at the moment i still have stock control arms. What have you all done on your rides? And do i need to change out the control arms or anythinf else to get them on there? or do i need to get a thinner wheel? Thanks

well from the 80mm, im guessing your not in the US...and Deo, ROdeo? which also if your in Austrailia (and most ofthere countries), the Rodeo is a pickup there, with control arms, not a-arms like the US rodeos. either way, a 8.5" wide rim will need 5.5" of back spacing to tuck. im running 18x8 titan rims on one of my trucks and it has 5" backspacing and JUST tucks inside the inner lip of the fender. so a .5" wider rim will need .5" more backspacing. i would see if you could get a different width, though 20s are hare to find narrower then 8.5 without going total custom like boyds/foose etc...hope this sheds some light on your issues
Ron