3 replies to this topic

[Nigelr32]

Hi all,

Something I've seen a few times, but never really questioned..............................

Why do some US tractors have their 5th wheel right at the back of the chassis/frame? Doing this leaves a large gap between the trailer and sleeper, which i think looks amazing!!

Thanks for looking

Nige

[WillyChang]

more weight = traction over the drive axles?

[speedy_w_beans]

If the 5th wheel is the sliding type, not the fixed type, then there are several reasons for moving it around:

1) Distributing weight more evenly over the axles to comply with road weight limits.
2) Adjusting the wheelbase of the vehicle to comply with bridge laws.
3) Adjusting the wheelbase to affect turning radius.
4) Closing the gap between the cab and the trailer for better fuel economy (less air resistance).
5) Providing clearance for the landing gear -- not all kingpins are in the same location.
6) There is some debate about trailer position and ride comfort -- is more weight or less weight on the front axle more comfortable for the driver?

I can't see why a trailer would be all the way back unless there is a clearance issue with the landing gear. Usually you'd want to tuck the trailer in closer to the cab for a variety of weight, turning radius, fuel economy, and legal reasons.

-Paul

[gozone]

Another thing about having the fifth wheel way back on the chassis, is that you may encounter loss of traction on your front wheels, when carrying heavy loads..



This is a Scania however, and it is probably done on purpose, but it will also happen if the trailer is putting too much weight behing the tandem-suspension. (I have tried it on a 6x2 Volvo-model i built once) and it was unable to turn with a loaded dump-trailer, simply because the front wheels lifted off the ground.