the axles being so inclined. Since the axles were fixed, the bearings would have been in the wheel hubs. Also, each truck had a pair of horizontal gripper wheels, located in between the two pairs of load-bearing wheels which were about 4 feet (1.2 metres) apart. These gripper wheels were 42 inches (107 cm) in diameter and 3.5 inches (9 cm) thick, and the two wheels rotated independently of each other, not being coupled. They were also flanged, on their lower edges, and these flanges fitted into the slots in the sides of the central traction rail. The vertical wheel axles slotted into box slides fixed to the frame, containing springs which pushed the wheels against the rail. The functions of the wheels were, firstly, to stabilise the vehicle against any rolling motion and, secondly, to be part of the hydraulic braking system. Meigs considered that the braking power of the wheels was adequate, but allowed that the load-bearing wheels could be provided with brakes too. The flanges of the gripper wheels were to hold the vehicle onto the track, so that it was unable to fall off. However, the truck frame was also provided with lugs in the event of wheel assembly breakage: In case any or all of the wheels should break, provision is made to prevent the cars from overturning or leaving the track, by means of a strong shoe, which would slide upon but could not leave the way. The horizontal gripper wheel design was also followed by the separate pair of traction wheels on the locomotive. The vehicle undercarriage consisted of two chassis frames, connected by side trusses on which the vehicle body sat and to which was fixed the floor assembly. Each chassis frame had four vertical tubes containing heavy spiral springs, and these fitted into spring sockets bolted to the underneath of the floor assembly. The chassis frame was attached to its truck frame by a centre turn pin stayed by rods attached to sliders, so as to allow free rotation of the chassis on the truck. When running through curves, the trucks turned on the gripper wheels and it was claimed that the design allowed for very tight turning: <blockquote>It has been found that, by reason of the independent motion of all the truck wheels, curves were followed so closely that the increase of friction of the car wheels passing through curves