What is the reason for having such small wheels(trucks) on the autocarriers? Is it because of height restrictions. Not all of them have small wheels either.
Thanks for any answers…
The smaller 28" wheels on Autoracks is due to hight restrictions , usually 28" wheels go on tri levels and 33" wheels on bi- levels .
Larger wheels are preferred to reduce wear. Obviously, smaller wheels wear faster. The only reason for using smaller wheels is restricting the height of the car.
Larger wheels allow a higher axel loading. auto racks have a low GWT as opposed to other cars ie coal
All of this was covered in a recent thread (started by Moookie) about the different sizes of wheels. Both the 28-inch and 33-inch wheels have the same bearing size, for use under cars with a gross rail load of 220,000 pounds (nominally a 70-ton car).
Having wheels with a five-inch reduction in diameter gives a car a 2.5-inch clearance advantage. It may not seem like much, but especially on eastern railroads it could be the difference between going through the tunnel and a lengthy reroute.
You’ll only see the smaller wheels underneath some 89-foot flat cars. The key to which ones (be they intermodal or auto rack) can be found by looking at the ends of the cars. If the coupler of the car appears in a housing above the car’s deck, it’s a low-level car and will have the smaller wheels. In most cases, the entire deck is above the coupler, and there’s room for standard-sized wheels. Auto racks with low-deck flat cars are most likely to be trilevels (I suspect that all of the 20’2" TTQX racks are of this type), but not all trilevels (and no bilevels) are on low-deck flats.