Sliders on truck semitrailers

[321GO]

Why and for what reason are these slider suspension used in the states?

Are these common on trailers or only for special applications?

Here in Europe they are quite rare.

Thanks guys

 

[BrianPetersen]

You're talking about sliding the trailer wheels fore / aft?

Lots of box van trailers have them. They are for changing the weight distribution so that the axle loads are within (as close to as possible, but not over) legal limits, as opposed to (say) having too much weight on the trailer axles while the tractor loads are below the limits.

Likely reason for those not being used in Europe is a different regulatory environment.

 

[321GO]

Thanks Brain,

when do they check / make these adjustments? Going from state to state or only on actual loading?
But then why not simply make sure the trailer is more evenly loaded in the first place?

Does this also has to do with your brdige laws?

 

[NormPeterson]

Different states have different requirements concerning trailer wheelbase.

http://www.cartaste.com/transport-safety/article-4-07862.html

Getting the allowed 80,000 lbs properly distributed can involve moving the 5th wheel as well. With heavy loads, the amount of fuel load matters else the tractor axles could be over, and it occasionally happens that a driver will have to run with less than half a full fuel load or even estimate how much fuel he'll burn before he encounters the next weigh station if he knows he'd be a bit over if weighed right at the time of refueling.

As to "more evenly loaded", I doubt that you can assume uniform density for the load, nor do I know how the weight of a load is estimated when it is assembled for a dedicated run pickup or posted to a load board for anybody available. Sometimes even a single load picked up will be split to two or more destinations. No receiver is going to want to spend his time (money) handling another customer's cargo twice (out of the trailer and back in) just to get at his own supplies, and the driver is constrained by legal limits on allowable drive time and on-duty time, as well as by delivery schedules. The "path of least resistance" then comes down to the driver making vehicle adjustments, and they get pretty good at estimating how far they'll have to move things once they have a weight report telling them what their truck's weight distribution is. Many truck stops have scales where (for a fee) the driver can do this without involving an overweight citation.

My son drives CDL class A, and I've watched him reset the trailer wheelbase and/or 5th wheel and heard that he's had to run with light fuel loads for precisely these reasons.


Norm