102" (8'6") is the maximum before you are required to look into additional permitting.
Most trailer mfg's stick with 8' width keep with dimensional lumber for floors, the downside to a 102" trailer is that you can not (legally) affix an awning or anything to the side and any side entry doors cannot have hinges, latches etc sticking out, yet another reason that 8' trailers are more common.
More than likely you can measure any 8' trailer from outside fender to outside fender and you'll end up with a measurement close to 102"