Well everyone is pretty much missing AGAIN the fact that there isn't and shouldn't be a zero offset wheel. The other fact is no one has asked for the weight of the boat and trailer. Until we know this it's hard to say whether or not or not the OP can go to a 15" or 16" wheel. All conventional13X5,13X5.5,14X6,15X6, 15X7, 16X7wheels are slightly positive offset by 1/8-5/16" to create stability and load to the larger inner bearing. There is NO such thing as a zero offset wheel because of the different diameters of inner and outer bearings. Please remember that this is a straight fixed spindle compressive bearing configuration with no steering capability, torque thrust etc. It is simply load bearing. Offset distributes load across the entire bearing spindle. Negative offset wheels are still used in straight roller bearing configurations, but dont' typically occur in rim widths over 7. I would caution fitting later model 6 lug wheels with a positive offset exceeding 5/8" as these are typically to distribute load into CV or straight bearing configurations, plus probable brake/frame/fender clearance issues.
So, the question really is: what does it weigh? A typical steel wheel in 15X6 or 15X7 will usually be stamped on the inside @ 1500-1750lbs. A 16" wheel will typically be between 2800-3500lbs. A 16.5 wheel which is virtually unheard of anymore is in the same range. Clearly the OP's trailer was designed to utilize the large diameter wheel for a reason. Was it built for his boat? We don't know that. But in all likely hood, he should have little trouble finding a "standard offset (IE; slightly positive) wheel in his load requirements.
Craig Hanson
VP Wheeltec
1985-90
