The drive guides a rail vehicle on the track . It supports the vehicle on the track and transfers forces between the track and the vehicle. The running gear consists of the wheel sets , the wheel set bearings and the suspension .
For short and light vehicles, where two or three wheel sets are sufficient to transfer the vehicle mass, these are connected directly to the car body via the bearings and suspension springs . In order to be able to drive on narrow curves even with longer vehicles, steering axles are used , which adapt them to the curve with a larger bearing clearance.
Bogies are preferred for vehicles with more than three axles . Here, two or more axles are stored in a separate frame that is movably connected to the vehicle. The shorter distance between rigidly connected axles improves the ability of longer vehicles to move around curves. Smaller bumps in the track are absorbed by the bogies and only passed on to the car body to a reduced extent . This improves the smoothness.
There are also a number of special designs, such as loose wheel sets , in which individually mounted wheels are used instead of wheel sets with two rigidly connected wheels.