How to Determine Fifth Wheel Position?

[dmlinton]

My question follows from some of the discussion at http://www.bigmacktrucks.com/index.php?/topic/36019-ontario-1955-b-30-fully-restored-seen-on-kijiji-big-bucks/#entry249042. I am not a professional trucker so my question my seem a little basic to some.

How is the fifth wheel positioning normally determined? I know that load distribution and axle weights become more important as the vehicle axle ratings and/or licensed gross weight is approached. Do drivers do a calculation to determine fifth wheel position to ensure proper load distribution over front and rear tractor axles or do they refer to a chart for their rig or do they follow dimensions set out in a regulation or is it more a rule of thumb sort of thing?

[Freightrain]

Fixed or sliding fifth wheel? My guess the sliding would be something you would figure out as you use it. Knowing how much weight each slot equates to on the front axle weight.

A fixed? Not sure how the factory decides where it should be put? I suppose they do some math and put it close to where the front axle would max out with maximum GCVW(gross combined vehicle weight).

My .02 on the subject.

[dmlinton]

Fixed or sliding fifth wheel? My guess the sliding would be something you would figure out as you use it. Knowing how much weight each slot equates to on the front axle weight.

A fixed? Not sure how the factory decides where it should be put? I suppose they do some math and put it close to where the front axle would max out with maximum GCVW(gross combined vehicle weight).

My .02 on the subject.

Well, yes, sliding - a fixed position would not leave a driver many options. I guess maybe what I am trying to get at is, with a sliding fifth wheel, is it any kind of customary to re-position it depending on what is being hauled? And, if so, how the positioning is determined. I presume that any sort of routine fifth wheel repositioning would be largely the domain of heavy haulers.

I doubt if the pros do it the way I do with my RAM 2500, which is to move the load up the trailer until just before the truck sets level, which tells me I have about the max weight of just over a ton on the gooseneck ball or fifth wheel plate, whichever I am using.

Edited June 13, 2014 by dmlinton

[RowdyRebel]

I've worked for companies that used fixed-position 5th wheels to save on weight, and if my axle weights weren't correct I'd take it through their shop & make them move it to where it needed to be. On my truck, I've got an air slide and it pretty much stays in the same spot unless I'm dropping & hooking and need to insert or remove the blocking pin (needed for frameless end dumps, but can't be there for tanks, flats, van, etc...)....which won't clear my 1/2 fenders unless I'm slid all of the way back. Also if I'm hooking to a trailer that was dropped too low I'll slide the 5th wheel all of the way back to make it easier to get under the new trailer. But, once I get situated with the new trailer, I slide it right back to where it was, since that puts me within spitting distance of 12K on my steers when my drives are around 34K. Depending upon what you pull, you MIGHT need to keep the 5th wheel slid farther back for clearance with the rear frame of the tractor (i.e. step decks) or the back of the cab (i.2. A long load that overhangs on the nose of the trailer) or to stretch the wheel base a little for bridge law if your trailer is a shorter one. Having the ABILITY to slide CAN come in handy...but for most drivers, once it is set, you'll pretty much leave it be...which is why they sell fixed 5th wheels.

[RowdyRebel]

...and you aren't really moving the 5th wheel/gooseneck ball on your Dodge. You are repositioning the load on the trailer. Moving the 5th wheel affects the weight distribution between the steer axle and the drive axle(s). The trailer axle weight is unaffected. You shifting the load on the trailer is going to affect ALL of the axle weights. Load forward = heavier steer & drive axle weights, but lower trailer axle weights. Some trailers (i.e. dry vans) you can slide the trailer tandems...which is going to affect weights the same way. Slide the axles forward and the trailer tandems carry more weight taking it off of the tractor. Slide 'em back to stretch it out and the tractor carries more weight, taking it off the trailer. And if you can't get it right you take it back to the dock and make 'em reload it...or dodge the scales.

[slpwlker]

What Rowdy said.Mine pretty much stays forward. Way forward. But I do move it. If I drop my trailer to relocate something else it goes all the way back. Otherwise I'd never come close to the kingpin. Kinda trial and error.If you pull the same thing it should be staionary. But start back and go forward1 notch and see what you get.