I have noticed that when the bigger trucks used by maintenance crews are on the rails the front rubber tires do not ride on the rail like the smaller pickup trucks do. The rear tires are on the rail obviously doing all the work. Are these trucks equipped with special brakes where only the rear brakes can be applied when the vehicle is used in this fashion?
With the front wheels off the rail…the brakes are only effective on the rear wheels. When the brakes are applied, the fronts ‘lock’ as there is nothing trying to rotate the wheels. The rears perform all the braking.
I have wondered why these larger trucks have their front wheels off the rails.
I suspect it’s because their front wheels are too far apart to ride on the rails.
That and the mass and weight/ lenght of the bigger trucks don’t allow them to track well, no pun intended.
The larger front wheels and heavy front suspension can bounce the front rail wheels off the rail, and the tires can grab a switch point, not a good idea.
The smaller, two ton pickups will track well, don ‘t bounce and are light enough that switch point don’t pose a problem.
Mudchicken will have a better and more detailed explanation.
I would suspect you are correct;
This video linked here really shows what you indicated.