I rode the converted auto rack on a fall Gettysburg special steam trip to Biglersville behind the CN Mike which is now at Steamtown. I remember the ride as being rough, but I figured that was because it was just a freight car with seats (bus seats, at that). Autos being transported aren't known to complain if the ride is jerky.

As a comparison, the internal combustion - electric streetcars used in Galveston, Tex. before the last hurricane used ordinary "3 piece" freight car trucks (truck bolster and 2 side frames) with electric motors added. They rode hard and rough like a freight car over every rail joint and other bump, not more smoothly like a passenger car.

I think there was a similar car at the Little River RR in Michigan in the 1990s as well - I rode one there behind steam engine 110.

Chris