I would like to know when pulling the trailer why do some trucks have what i think is called the second axle. The wheel is stuck up in the air. I once got told off for leaving a depot with the wheel up so i always ensure it is down.
Is there a rule to follow on when to lower it. Is there any benefits to it being up or down
It’s called a Lift axle.
Basically you have to have x amount of axles for x amount of weight, so you can have up to 18 tonnes on two axles, 26t on 3 axles and 32t on 4 and so on.
The idea is you have it lower (on the road) when loaded so you’re legal and spread the load and then lift it up when empty, to reduce the tyre wear and fuel consumption.
I think they’re supposed to lower automatically on most modern trucks when the predetermined weight it reached.
You also get them on Rigids, not just artics.
I think they’re supposed to lower automatically on most modern trucks when the predetermined weight it reached.
I must admit I don’t think I have driven one that didn’t drop automatically when loaded.
Since it takes load off the drive axle it can cause the drive axle to lose grip in wet/icy conditions. So empty I would always run with it up - some will go up automatically when not needed - some won’t (or was that just my imagination).
G
mine operates on a switch which is bang handy round here in the winter, a lot of hill starts.
I generally stick to my own rule that if the trailer’s empty, or I’m running solo - axle up, if the trailer’s (even partially) loaded - axle down. Also, if you’re running with very little weight on a 6x2, (where the centre axle’s not driven), I’ve found that the grip is terrible - raising the lift axle gives better traction. None of the ones I’m running with at the moment have automatic raising - I think I’d be lookng for the switch all the time!!
if it drops fine if it stays up all the better 
If you can lift the axle do so because you will have the twin benefits of better diesel figures and better traction. Its quite a marked diference in fuel consumption with the axle up but then if you are paying for the diesel you have a better motive for doing so
Link to an authoritative opinion in the FAQ’s HERE.
(Not that any of you lot ever bother to read them. 
)
I have a switch in the cab to operate the lift axle on the trailer.It comes in handy to drop the wheels and make a tighter turn at an intersection.The axle also has a set of brakes on it so I usually run down even if I’m under on the axle weights.Lastly having the switch in the cab allows picking it up at the toll plazas;toll costs are based on number of axles running over the pressure pad imbedded in the roadway.
Longwayround:
The axle also has a set of brakes on it so I usually run down even if I’m under on the axle weights.
Err… What does it having brakes affect to the need of keeping it down? I don’t know if rules are that much different there that one axle doesn’t have to have enough brake power to stop the load that axle is allowed to carry, but I wouldn’t suppose so.
under eu rues the lift axles on modern trucks must lower whent they reach a certain wieght . if you collect a load it will drop it if is 20+ tonnes but at 15 tonnes it woill stay up
Kyrbo:
Longwayround:
The axle also has a set of brakes on it so I usually run down even if I’m under on the axle weights.Err… What does it having brakes affect to the need of keeping it down? I don’t know if rules are that much different there that one axle doesn’t have to have enough brake power to stop the load that axle is allowed to carry, but I wouldn’t suppose so.
I would assume he means it gives him an extra set of brakes and more rubber on the road, which all helps if you want to stop in a hurry.
Kyrbo:
Longwayround:
The axle also has a set of brakes on it so I usually run down even if I’m under on the axle weights.Err… What does it having brakes affect to the need of keeping it down? I don’t know if rules are that much different there that one axle doesn’t have to have enough brake power to stop the load that axle is allowed to carry, but I wouldn’t suppose so.
You don’t know North American brakes though. They can be a little surprising. We don’t have any vehicles with lift axles on this firm.
When I had my Renault the midlift was a pain sometimes. The movement of the liquid would confuse it. I had a manual lifter on the trailer so I could do radical weight transfers in slippery conditions. Saved me more than once.