I’m sure I’m like most folks when it comes to the position of the 5th wheel, I just hook the trailer up and go.
I drive a 65 plate Volvo FH and it has a switch in the cab to release the locking pins for the 5th wheel, enabling you to move it forwards or backwards on the rail.
That got me thinking, what is the correct position?
Well behind the unit drive axle.What could possibly go wrong. 
Ideally, the tractor and trailer should be positioned as closely as possible to each other without actually fouling when cornering. However, unless you always travel on completely level surfaces this is easier said than done so it’s normally better to allow a safety margin of three inches or so.
goshow:
I’m sure I’m like most folks when it comes to the position of the 5th wheel, I just hook the trailer up and go.I drive a 65 plate Volvo FH and it has a switch in the cab to release the locking pins for the 5th wheel, enabling you to move it forwards or backwards on the rail.
That got me thinking, what is the correct position?
Depends what trailer you are pulling ,for a tipper trailer nearer to the drive axle than the midlift is norm .
Punchy Dan:
goshow:
I’m sure I’m like most folks when it comes to the position of the 5th wheel, I just hook the trailer up and go.I drive a 65 plate Volvo FH and it has a switch in the cab to release the locking pins for the 5th wheel, enabling you to move it forwards or backwards on the rail.
That got me thinking, what is the correct position?
Depends what trailer you are pulling ,for a tipper trailer nearer to the drive axle than the midlift is norm .
pulling euroliners and boxes 99.99% of the time. Very occasionally a flat bed.
Attached to the tractor unit is your best bet. Its difficult to connect a trailer if your fifth wheel is lying 150 miles away in the dept workshop
As a rough guide, position it somewhere between the mid and drive axle.
Depends how deep the pin is under the trailer.
We used to have air operated 5th wheels that you operated from in the cab. Pain in the ■■■■ so they where. And if you forgot to lock it off the first time you hit the brakes the trailer would slam you forward 
My policy about 5th wheels is don’t ■■■■ about moving them, leave them be. It is a policy that has never caused me any problems.
Must admit I’ve wondered this too. Doing supermarket work I pull a selection of different types and lengths of trailer and the 10m trailers seem to have a massive gap between the headboard and the back of the cab. Probably a good few feet. Should I be moving this? I haven’t in the past but is there a problem in not?
There is a specific distance from the centre of the drive axle to the centre of the fifth wheel on a mid lift three axle unit for maximum weight to be imposed on the unit without overloading any of the axles, Volvo will be the best people to speak to, or google it.
For an employed driver I would suggest only moving it if hooking up a trailer with a deep set back pin that unless you move it the trailer will be too close to the cab.
It’s not just fouling the cab that’s a problem with it being too far forward the rear of the chassis can hit the trailer on humpback bridges etc.
For fuel economy you want it as far forward as you whilst allowing enough room between the trailer and the cab and the legs and the lights, whilst not over loading the front axle.
For traction you’ll want it a bit further back to take the weight off the steer and put it on the midlift and drive axle, whilst not over loading them
If you want to move it, lock the 5th wheel onto the pin, adjust the suspension so you have the slightest gap between the 5th wheel and the trailer rubbing plate, then unlock the slider, move to where you want it, lock it, will probably have to move a bit to get it to drop in, check your clearances, the check you axle weights
The reason for moving it is to alter the weight distribution between the steer and drive axle (s).
In the US vehicle and axle weights are checked all the time by US vosa so with a heavy load you would go to a public scale, ( there’s loads all over the place) weigh it, then redistribute the weight by moving the trailer axle and if necessary the 5th wheel to make it legal. Usually
moving the fifth wheel forward one hole will move about 250kg onto the steers if you have a 3 axle tractor.
In the UK I never moved one, and I can’t remember what the axle weights are over there.
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The closer the trailer is to the back of the cab the more economical the vehicle is, it reduces drag but … You have to make sure you re not overloading the front or drive axles.
The points made re: fuel economy, traction etc. are all valid, particularly if you have a les than maximum length trailer such as a tanker, tipper or ‘urban’ type.
Ultimately though, the overall length of the combination should not exceed 16.5m.
Also depends if tag axle or mid lift.
GCR2ERF:
The points made re: fuel economy, traction etc. are all valid, particularly if you have a les than maximum length trailer such as a tanker, tipper or ‘urban’ type.Ultimately though, the overall length of the combination should not exceed 16.5m.
If you have a 15.5 m trailer like I have today you’ll exceed it .
bald bloke:
GCR2ERF:
The points made re: fuel economy, traction etc. are all valid, particularly if you have a les than maximum length trailer such as a tanker, tipper or ‘urban’ type.Ultimately though, the overall length of the combination should not exceed 16.5m.
If you have a 15.5 m trailer like I have today you’ll exceed it .
Good point well put squire 
(must forgive me as we’re not running any extra-long stuff 
)
