A while ago I asked about the differences between the earlier models of running gears. I have a little more info and thought I'd post it. Maybe someday when I forget it, I can search the archives and answer my own questions.
VW: all-steel gear on steel wheels, plain bearings, horse and tractor speeds
VWT: all-steel gear with rubber tires, bronze bearings, speeds up to 20 mph
VT: highway trailer with rubber tires, tapered roller bearings, speeds up to 40 mph
VWTA: rubber tires, tapered roller bearings
I don't see any difference between the VT and VWTA other than that the VT offered brakes and spring suspension. The VWTA may have had a little more ground clearance as well. One brochure (1940) had the VW, VWT, and VT; and a different brochure (1947) had the VW and VWTA. I'm guessing the VWTA replaced both the VWT and VT.
VW: all-steel gear on steel wheels, plain bearings, horse and tractor speeds
VWT: all-steel gear with rubber tires, bronze bearings, speeds up to 20 mph
VT: highway trailer with rubber tires, tapered roller bearings, speeds up to 40 mph
VWTA: rubber tires, tapered roller bearings
I don't see any difference between the VT and VWTA other than that the VT offered brakes and spring suspension. The VWTA may have had a little more ground clearance as well. One brochure (1940) had the VW, VWT, and VT; and a different brochure (1947) had the VW and VWTA. I'm guessing the VWTA replaced both the VWT and VT.