Hi , I ran a '53 plunger ,it was my first bike and did a fair few miles on her both with a chair (double adult ) and often with it removed and just a basic board fitted . thrashed the living daylights out of her .The old guy who set her up for me was insistant that the toe on the chair had to be spot on as well as the position of the front of the chair in relation to the bike frame. from memory I think roughly in line with the fork leg. anyway point of this is he also told me never to change the tyre width on chair as this would create extra drag and effectively screw up the geometry. resulting in it pulling whichever side the chair was fixed. I also think that the improved grip of modern tyres plus the extra width on the sidecar wheel would make the bike "dig in" on right handers (in england ) when the bike's rear would hop up in the air and the outfit spins ( i only did that once and it was enough talk about changing trousers rapidly ) don't think any problem on the rear drive wheel . Ican only say that the handling of my 2 outfits was spot on when this guy set them up slightly tighten steering damper "hands off on the stright" so even though He's long gone and it was over 40 yrs ago I'd still believe what he told me ,hope this is of help.best wishes Bob H
