7thing3 - I am ecstatic to see someone else is bashing SS cars and trucks with die cast bodies, too.
Those vehicles shown in the picture below are some of the converted SS vehicles I've fitted with 1/43 die cast bodies. Someone asked about a taxi: Solido offers the 1950 Chevy (second row left) as a very nicely outfitted yellow cab - this particular die cast body is quite roomy and it is an easy conversion.
Key points I've learned.
1) Plastic bodies will not work: SS vehicles need the weight of die-cast bodies both to push their center contact springs down on the road and to assure their wheels stay within the rails to get good traction.
2) Most of these had the chassis shortened for a shorter wheelbase. Shortening the wheelbase even a small amount makes an SS vehcile run MUCH smoother around curves. SS vehciles have fixed axles so they don't pivot their wheels with curves but just power through against friction of wheel on rail. Shortening Wheelbase even a bit greatly reduces that friction.
All of these run well on standard SS roads except the bus (only vehcile where I have lengthened the wheelbase). It does not run on 16 inch curves at all (too much wheel friction) and doesn't like 21 inch curves very much - it runs best on custom country roads I've made with 27" dia. curves. The tractor-trailers (one shown without trailer) actually run the smoothest of all, partly because they have very short wheelbases (the rearmost axle on the 18-wheeler pivots to follow curves) and because they have pickup and a center roller on the trailer's axles, too.