billet 20s on mazda?

i know its probably been ask alot but what offset do i need to run a a 18-20 combo?im clueless on back spacing and i will be bdroppin it to rockers.any help be great.i was looking at centerline rims any othere rim companys u guys suggest that makes alot 6 lug billets ill check them out.

centerlines prolly wont give you the backspacing you need... most go with a yota rear end cuz its a lil narrower.. but a 20x8.5 will need 6-6.5 inhces of backspacing at least.... with a 225\35\20 tire.... in the front it gets real close if you run drop spindles and 20s with the 2wd sheetmetal... but again at least 6.5 inches of backspacing will be needed on a 8.5 inch wheel... I dont know that youll be able to run the stock rear end and lay rocker with a 20 and not flair the bed side.. could be wrong i guess... if you wanna keep it six lug find a courier rear end or a isuzu pup rear end... courier is about inch narrower on both sides then the pup and the pup is about in inch narrower then the mazda.... on the front with an 18x7 with 5.25 inches of backspacing just flip you ball joints and run a 215\35\18.. thats what im running... the mazda drop spindle pushes the wheel out like 3\4 of an inch.... Hope that helps... if not go to mazdabscene.com... its got aalot of good info..

My Bros got an 89 b2200 with a set of 20x8.5" BAD's with 7" back spacing. Its not bagged or BD'ed yet but he did his homework before ordering them with plans on laying it on the rocker. like mentioned above go to mazdabscene.com for more information.