tire sizing

just purchased a hannigan bandito sidecar for my vtx1800c.
the lower support bracket bolts on to the "Y"muffler bracket
i presently have a 200 metzler on the rear.it is too big for the bracket to fit properly so i have to go to the stock 180
my question is this-is the car tire size that everyone uses for the vtx 1800 wider than a 180?
i would like to be able to use a car tire but i need a size the same as or slightly narrower than a stock 180.
any help is greatly appreciated-Thanks :

the 205's are close to the same width as a 200, most 195's I would assume are going to be slightly wider to about the same width and I'm not sure what would be available in a 185 width for C rim... might have to do some searching. That or look at the couple 195's that guys are already running and check the manufacturers specs for tire width against what your 200 and 180 measures out to....

Welcome! Good luck with the search! Let us know what you find.