Afternoon, I passed my class 1 test this morning and although will still be on rigid lorries for the time being my employer has said that my every other Saturday morning shift I do he will start sending me just running trailers up the road 15/20 miles on class 1 before they let me go full time on artics. Now without trying to sound like a total idiot I’m just wanting some advice on fifth wheel heights, I’ve seen a few trailers marked up with the trailer height based on a 1250mm fifth wheel etc and also I’ve seen trailers that say warning 1.6m pin. Now I asked my instructor about this earlier in the week and sort of got the idea about the pin placement on the trailer with regards to where your fifth wheel should be when coupling up, but could do with a bit more clarification on it if anyone can help please? Also then obviously if your pin is higher than 1250mm then you need to take that in to account for overall trailer height yes?
A fifth wheel has two measurements, depth and height, a 4 wheeler won’t generally have a sliding fifth wheel so a deep pin trailer on a short wheelbase unit won’t work.
A sliding fifth wheel could be 2 or 3 inches higher than a non slider. Ignore all measurements and take you own.
That warning about a 1.6m pin is a different measurement to the fifth wheel height - It refers to the “depth” of the pin - i.e. the distance from the front of the trailer to the pin.
Roymondo:
That warning about a 1.6m pin is a different measurement to the fifth wheel height - It refers to the “depth” of the pin - i.e. the distance from the front of the trailer to the pin.
Yeah I sort of understood that after asking my instructor is that when you’d have to use the sliding fifth wheel then? And is there a standard to go by in regards to the gap between the trailer and unit?
Connect up to trailer, have the unit suspension in drive height, then measure from the floor to the bottom of the trailer and thats your 5th wheel height.
As for the gap between the unit and trailer have it as close as possible without it being a problem doing 90 degree turns, enough room for you to attach the airlines etc
liam6226:
Roymondo:
That warning about a 1.6m pin is a different measurement to the fifth wheel height - It refers to the “depth” of the pin - i.e. the distance from the front of the trailer to the pin.Yeah I sort of understood that after asking my instructor is that when you’d have to use the sliding fifth wheel then? And is there a standard to go by in regards to the gap between the trailer and unit?
You would use the sliding 5th wheel to get the optimum distance between unit & trailer, legal (overall combination length), aerodynamic ( close coupled, usually fridge trailers) & handling ( when pulling a trailer with a shorter pin depth). I would be very cautious about changing the 5th wheel position and also be aware that it is possible to pull the position lever in error when uncoupling a trailer, so my err mate tells me 
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Our sliding 5th wheels have a running height of 1290mm as opposed to the more widely stated height of 1250mm, it’s the sliding mechanism which adds the extra. That is an extra 2" to take into account when calculating your running height.
There’s more to the positioning of a sliding fifth wheel than just getting it close enough for aerodynamics, a valid reason enough in itself.
If you run max weight and have small mid lift tyres (often fitted to bulk tipper and tanker pulling tractors for weight saving purposes) then it’s easy to cause an overload on the mid lift, which in some cases can be as low as 4.3 tons gross axle weight.
If you get issued a regular vehicle it is worth using a weighbridge (doesn’t have to be an axle weigher though obviously the ideal solution) to work out what weight is being imposed on that axle, but generally i’ve found if you position the fifth wheel roughly in the middle of it’s adjustment range you won’t be far out.
By the way, it’s not just swing room twixt lorry and trailer to consider, don’t forget to check enough clearance room between the back of the tractor and the landing legs, particularly important now so many air tanks are being stuck there behind the chassis in direct line of fire.
mrginge:
Connect up to trailer, have the unit suspension in drive height, then measure from the floor to the bottom of the trailer and thats your 5th wheel height.As for the gap between the unit and trailer have it as close as possible without it being a problem doing 90 degree turns, enough room for you to attach the airlines etc
Then the ball game of split coupling ( banned in a lot of places) is also in the equation.
Bottom line of not sure ASK someone. Most people will offer advice
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I thought best not to bring up split coupling to someone who passed their test this morning 
mrginge:
I thought best not to bring up split coupling to someone who passed their test this morning
Hahaha I’ve instantly started searching split coupling now!
Life was so much simpler on the buses 
mrginge:
I thought best not to bring up split coupling to someone who passed their test this morning
Law of sod states: anything you don’t know will be presented before anything you do know.
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