Moveable 5th Wheel

UK PROFESSIONAL DRIVERS FORUMS THE UK PROFESSIONAL DRIVERS FORUM (INTERACTIVE)
1

I apologise in advance if this question has been covered before, and / or sounds stupid.

I have only ever really driven class 2, and am preparing to take my class 1 lessons and then test.

Now I understand that the majority of units have a moveable 5th wheel, could somebody please shed some light on why a moveable 5th wheel is used and what the benefits / disadvantages of it are.

How do you decided where to have the 5th wheel positioned? - Is there a rule of thumb? Any legal issues?

Does having the wheel further forward / backwards effect the manoverabilty of the unit / trailer?

I appreciate this question may sound very stupid / simple the the majority of drivers, but its something I know nothing about and is something that is worrying me as I look to move upto class 1.

Many thanks in advance or all help and guidance.

2

To close and open the gap between the back of the cab and front of trailer. Not sure on legal issues, it may impact total combination length though. It can be useful on containers where you have plenty of space for a 40 but not for a 45 so you could slide it back to fit a 45 on. I can’t imagine it would be very useful if it’s the same trailer day in day out. I have mine central though since our trailers scuff the mudwings and runup ramps when it’s furthest forward.

3

DJC:
To close and open the gap between the back of the cab and front of trailer. Not sure on legal issues, it may impact total combination length though. It can be useful on containers where you have plenty of space for a 40 but not for a 45 so you could slide it back to fit a 45 on. I can’t imagine it would be very useful if it’s the same trailer day in day out. I have mine central though since our trailers scuff the mudwings and runup ramps when it’s furthest forward.

Yep, we’ve had a few sets of run up ramps wiped out because the 5th wheel was too far forward (I believe it costs around £300 per pair) backing down ramps onto bays with a turn on (that didn’t sound right [emoji4])
I’ve had 2 TGX’s & both have had the 5th wheel set around the middle/about 7 teeth showing on the ‘thingamajig’, not had any run up ramp problems but it probably uses a bit more diesel than if it was close coupled.

4

Some tractor units are fitted with sliding fifth wheels so that when coupled to a trailer they do not exceed the maximum overall permitted length 16.5m. At the same time the ‘combination’ must not exceed the maximum permitted overall weight of the tractor unit nor exceed the maximum permitted weight of the tractor units individual axles. By allowing the position of the coupling to be moved these dimensions and weights can be altered.

While most trailers have the kingpin 1600mm from the front of the trailer some older trailers have it further forward so it may be necessary to adjust the position of the coupling in order to keep within 16.5m overall length. In practice it is not as simple as that since the rear lights of the unit could hit the trailer landing legs or the front of the trailer could hit the back of the cab. Also in practice not many people pay much attention to the overall length requirement.

On a day to day basis being able to move the position of the coupling temporarily while connecting air lines etc is useful, but until you understand many other things do NOT even think about doing this since getting it wrong can prove fatal. Many companies ban the practice because of this.

A bewildering amount of information about coupling and what needs to be considered is below :

til.scania.com/groups/bwd/docum … 002_01.pdf

5

This is one of those things you really don’t need to worry about. Firstly I would say that most 5th wheels are fixed and the minority move. I have never had to move one ever.

6

With regards to how the combination will handle, having the fifth wheel forward will move the trailer weight forward, thus giving you more positive steering but a better chance of a jackknife should things go bad. Moving the fifth wheel backwards will give better traction to the rear wheels of the unit which will get you up icy or slippery gradients better but reduce the grip of the front wheels on the unit giving less positive steering and the possibility of understeering off the road.
To be honest as a driver its probably better to leave the fifth wheel where it is and drive to the way the combo handles, it leaves you less likely to be blamed for anything that goes wrong.
After all you’re only a driver best you don’t try to think :wink: .

7

Also used with fridge trailers as some drops are on a slope or angle that lifts the back of the trailer enough that it can hit the air spoilers on the top of the cab. Tiverton tesco is one example.

8

Good points from Cav as usual…and edit, and Shrodingers Cat re the jack knife possibility.

There’s a lot to learn about tractor axle weights, these can vary a lot depending on the position of the 5 wheel.
I’m going to ignore lengths cos that’s been covered, as have the dangers of hitting lights and sweeping suzies off the cab, and instead give my humble on weights and handling.
Helps a lot if you use an axle weigher regularly at delivery points.

On a 2 axle tractor its simple enough, within reason the further back the more weight imposed on the drive axle and less on the steer.
If too far forward it can produce some unpleasant driving characteristics, such as you’re going into a bend and the drive axle is light and the trailer is pushing the tractor sideways without enough weight on the drive to control it.
Generally better to be further back within reason, also better wet grip etc.

On a 3 axle with mid lift centre it’s different again and can be quite baffling cos things sometimes work the opposite way.

Its took several loads with my MAN when it was new to find the sweet spot for the 5th wheel (i do this with every vehicle i get issued), when i got it the thing was too far forward, so i shoved it about 3/4 back, used the axle weigher and lo and behold the mid lift was slightly overweight (small tyred mid lift only about 5.2 tons rated IIRC), i naturally assumed that it needed to go further back to put more load on the drive axle, nope, it worked the opposite way.
Moving it forward lessened the load to just about right on the mid lift, which is completely different to what commons sense tells you.
So mine is perfectly sited at more or less the half way mark, all axle weights are fine and complementary, and as a bonus it can pull every one of the company trailers without issue.
My mate took over an identical sister lorry and he mentioned the handling was atrocious, so we compared notes and found the previous driver had shoved the 5th wheel all the way back, hence the mid lift was getting too much air and taking pressure off the drive axle (not good), we moved his wheel to the same position as mine and it too handles fine now.

Can’t help you with rear tag axle 3 axle tractors, no doubt they have their own odd ways.

Danalex, the position of the 5th wheel won’t make a massive difference to manoeuvering IMO, and if you think its wrong for some reason i’d find someone where you work who knows what they are doing and have a word in their shell like.
As said, some companies have set positions that must be used with certain trailers (Argos do or did do this for length reasons) and its a bit of a parlava to shift a 5th wheel till you know what you are doing.
Never apologise for asking such a question mate, its far from stupid its bloody good sense, its those who don’t ask are the stupid ones.

9

Agree completely with the previous posts. Leave well alone.

Edit: As said leave well alone at present. After you have gained substantial experience and understand what effect moving it has then that is the time to think about it again.

10

My MAN TGA has a moveable 5th wheel. First unit i have had with one.

Most people don’t have to worry but i need it for all the different trailers i use.

Move it further back for: Ejector, walking floor, curtain sider, low lowder, flat bed work.

Move it forward for bulk tipper trailers as when the weight is fully on the rear of the unit i find i get lots of under steer. That and im assuming the overall weight wont be evenly distributed on the axles (Anyone on bulk tipper work knows most customers want you at 44T all the time). Also it makes the overall length of the lorry even shorter to make things easier at some of the small scrapyards i go to.

11

m4rky:
This is one of those things you really don’t need to worry about. Firstly I would say that most 5th wheels are fixed and the minority move. I have never had to move one ever.

And moving one thats never been moved for a few years isnt fun either

12

danalex84:
I apologise in advance if this question has been covered before, and / or sounds stupid.

I have only ever really driven class 2, and am preparing to take my class 1 lessons and then test.

Now I understand that the majority of units have a moveable 5th wheel, could somebody please shed some light on why a moveable 5th wheel is used and what the benefits / disadvantages of it are.

How do you decided where to have the 5th wheel positioned? - Is there a rule of thumb? Any legal issues?

Does having the wheel further forward / backwards effect the manoverabilty of the unit / trailer?

I appreciate this question may sound very stupid / simple the the majority of drivers, but its something I know nothing about and is something that is worrying me as I look to move upto class 1.

Many thanks in advance or all help and guidance.

No its not a silly question as a lot of damage can be done if you don`t know its workings or purpose.
Suggest you put it to your Instructor as its highly likely he /she has knowledge on how to use one, better to be taught, than going in “blind” or trying to remember what you read on here

13

Not as much damage as coupling up to trailer with a deep set pin and the 5th wheel mounted too far forward. You’re right to ask and no shame in that. I coupled up to a fridge the other day and had I been a ram it back at speed merchant I would have had frozen croissants on my bunk.

14

I don’t think many drivers, although a poster does on here, bother with checking/moving the fifth wheel judging by the vehicles I have driven, example being a front axle over load on a 3 axle unit at 17000kgs with the mid lift up, which means having to have lift axle down with hardly any weight on the drive axle, resulting in excessive wear on tyres due to wheel spin when turning wet or dry, I never know what truck i am driving, so would never bother moving the 5th wheel, but did set it right when I had the same one permanantly.
Even some truck owners, well mine doesn’t, don’t even bother to make sure their vehicles are set up right, which would save money on tyres and fines.
Its alway a good idea to know how to set your vehicle up, doing it will help balance out the vehicle over the 6 axles making a far comfier ride overall.

15

I’ve only ever had to move one on a UK truck once and that was on the German/Swiss border in 2009 on my last trip before moving to Canada. I got sent for a secondary inspection in the Zollhof by Swiss customs and they measured my truck and informed me it was over length. I then had to park next to a tree and attach a ratchet strap to the handle used to slide the 5th wheel and ratchet it out, as it hadn’t ever seen use in the three years of its life until that point so was well and truly stuck and not going to come out by hand alone. Ultimately I managed to slide it forwards enough, after removing my fire extinguisher box on the back of the cab and they let me proceed.

Over here they’re obsessed with axle weights and most trucks have a sliding 5th wheel, though in reality you pick your spot and just keep it there permanently. 12,000lbs is the max steer axle weight in the US unless the steer axle is actually plated higher but you never get questioned over steer axle weights anyway. I always run mine at about 12,600 or 700 when fully freighted and full of fuel and in 6 and a half years of crossing two dozen DOT scales each and every week in every state of the US, it has never been a problem. My current truck actually has a fixed 5th wheel, the first one over here that has being so, and my steer axle weighs off at about 12,400lbs when at full gross weight with full tanks of diesel etc.

16

a tag with the fifth wheel at the legal setting will be forever breaking stuff, so we have a hydraulically movable fifth wheel on all trucks, if the need should arise to move it to the front again. better for traction to have it set back as well

17

martinviking:
Yep, we’ve had a few sets of run up ramps wiped out because the 5th wheel was too far forward

Be very surprised if that was the case.

18

in the olden days trailers used to have the pins set all over the place , and it was quite a regular event for drivers to wipe our back of cab when coupling up a deep pin trailer .

these days with tri axles pin position is much more consistent and cant remember moving many in last 10 years . only times are when hire motor susies foul on front of fridge motor casing .

if you do have to move one , try carefully to connect pin in fifth wheel . even if cab is too tight to turn . then pull the locking mechanism and use truck to move fifth wheel forward or back , with trailer brakes on obvs . when in good position kick handle in and move truck til pin engages .

can remember sitting in yard ■■■■■■■ myself while idiot driver tried to push fifth wheel with his hands and got painted with grease .took him 15 minutes ! i told him how to do it properly , after he had finished , and he was not best pleased !

laughs !!

19

Conor:

martinviking:
Yep, we’ve had a few sets of run up ramps wiped out because the 5th wheel was too far forward

Be very surprised if that was the case.

We do a certain collection on a bay & you have to bend it round & down a ramp, one of ours came limping back to the yard, wounded, last year, with his run up ramps bent, the next time he went there, I met him & watched as it reversed into place & as the trailer rolled down the ramp & the tractor was still on the flat, one side of the run up ramp started to catch the trailer chassis, 5th wheel was in the forward position, so we moved it back to halfway (about 7 teeth back) & did the reverse again without any problems.
I reported it back to my TM to warn him of any future problems with new tractors & in True Transport Manager Style, no one was made aware of the problem & another older tractor did the same thing about 6 months ago, then a new tractor did the very same thing about a month ago.

Every time the run up ramps got bent, it was on the same ramp with the 5th wheel set too far forward, but different tractor units.

If you think about it, with the 5th wheel set forward the trailer pivots at a different point, so if you’re on uneven ground & turning it has the potential to catch the chassis & wipe out run up ramps, mud guards & even lights if it’s too steep.

Our self employed resident fitter loves it, just brought a Brand New 4x4 Audi & is laughing all the way to the bank, the ramps only take about half an hour to replace & every time one comes back in pieces, he stands there Rubbing his hands together thinking about his next Exotic Holiday [emoji1]

20

martinviking:

Conor:

martinviking:
Yep, we’ve had a few sets of run up ramps wiped out because the 5th wheel was too far forward

Be very surprised if that was the case.

& in True Transport Manager Style, no one was made aware of the problem &

[emoji1]

Isn’t that the truth, you get to the point that you don’t bother wasting your breath any more, they don’t want to hear it.
Is it because they didn’t come up with it? too complicated for 'em? something they can’t apply lowest common denominator to?