You have it backwards. Positive offset wheels have more backspacing and less dish. Negative offsets have less backspacing and deeper dish. Negative offset wheels create more stress on chassis components and increase scrub radius.
As a result, the majority of modern cars feature positive offset wheels.

 

I may have it backwards, but we do agree that the further outward (away from center) that the wheel is away from the mounting position at the brake drum/caliper, the more stress it puts on the bearings.....that is just basic physics......

Lon

 

Lots of wheel manufacturers can build you a 4x108mm bolt circle wheel, in a 6" or wider width, that will bolt right on your trike. Trust me, you really don't want to use adapters to cobble up a fit.

 

My Cragars really looked cool though...chrome with anodized gold centres...my Duster was a chick magnet

 

A high-positive offset wheel (+25mm or more), like those on FWD vehicles or late Vettes and Camaros, tend to put less stress on the bearings than a zero or negative offset wheel. Negative offsets will create the most stress. Stock FW or TG 15x5.5 wheels have roughly a -9 offset. Either a 15x6 or 15x7, with -12 offset, will fit both trikes. The difference between a -9 and -12 offset is less than 1/8" backspacing, a negligible amount.