>>1744346Bogies/trucks on locomotives are not, contarary to what many people think, attached to some sort of fixed pivot. Instead they are attached to a system of bars, springs, levers and hydraulic or friction dampeners that allow for the bogie to twist and move to the side. Same system is also built in a manner that makes the bogie want to return to its natural position.
In case of the Tribo ( because it is Bo'Bo'Bo' axle arrangement ) the middle bogie is almost universally hung using flexicoil suspension:
https://en.wikipedia.org/wiki/Flexicoil_suspensionThe telltale sign of this are those long springs on which the weight of the locomotive is transferred to the bogies - which allows it to move to the side. By then arranging the rest of the system to take that into account - all bogies move to the side as the train takes a turn.
Makes for a very flexible and peacefully running, well gripping locomotive, great for mountains ( which is why it found success in Italy, Japan or NZ ) but at a cost if increased maintenance.
