-25 is the offset of the rim. Offset if the distance from the hub mounting surface to the middle of the wheel. Negative offset pushes the wheel further to the outside, and positive offset sucks it in. Offset is determined in MM, easy math 25 mm is more or less an inch. To determine bs you need to know rim witdth you then can determine your bs. As for what bs you need it is all dependant on what type of lift. If you are running a full drop (like procomp), you can really get away with just about anything. If your going with a knuckle lift (cognito, rcd) your bs can be 4.5-4.625 or there abouts. Are you 4wd or 2wd. One small word of advice, the wider the rim and the more neg offset, the tougher the fit (you will have to trim more as to not rub while turning).
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