Tractor Trailer, extendable links, wheels that move, etc

trucks

#1

I’m in the Pacific Northwest, and I often see double trailers linked by a long bar that extends and contracts with a safety light attached. Also, some of the tractors and trailers have wheels that retract up when not in use. What are the purposes of these thingies?


#2

@wondertoad…some of the tractors and trailers have wheels that retract up when not in use. What are the purposes of these thingies?

These are called landing gear and they are lowered to hold the front of the trailer up so the tractor can be detached from the trailer.

A long bar that extends and retracts with a light on it??? Where on the trailer is this part?


#3

Right or wrong, we always called the retractable wheels tag axles. When the truck has a heavy load, they lower the extra axle. Mostly on dump trucks. No expert but I’ve never seen wheels on the front of a detachable trailer, only jack stands with pads. Been seeing more of them with Push it You Own It on them. They prefer truck moves them around…


#4

Many tractors have tandem axles but the rear axle is not connected to the engine and when running unloaded that axle can be pinned up to increase fuel mileage, improve handling and cut tire wear just as Twin Turbo described for trailer axles.


#5

Don’t know about this extendable bar between double trailers; every time I ever saw double trailers out west they were connected with a fifth-wheel coupler-equipped dolly that was hitched behind the first trailer and hooked via fifth wheel under the nose of the second trailer. Also, in some of the midwest states like Michigan, Indiana, and Illinois, as well as in Canada, they use what are called “B-Train” doubles, in which the first trailer will have its Second axle protruding behind its rear cargo box, and will be supporting a platform on which a fifth wheel is mounted; the second trailer will then be hooked to the first trailer’s fifth wheel.


#6

I have seen tractors with the tandem trailer 5th wheel riding upside down on top of the trucks 5th wheel. Could be one of the raised axles?


#7

@TwinTurbo
Right or wrong, we always called the retractable wheels tag axles. When the truck has a heavy load, they lower the extra axle. Mostly on dump trucks. No expert but I’ve never seen wheels on the front of a detachable trailer, only jack stands with pads.

Your explanation makes more sense. First thing I thought of was the landing gear but in the days of old there were metal wheels on them and they always sank in dirt and hot asphalt, pads are better.


#8

Meaneyedcatz, now that you mention it, I do recall the metal rollers on the jacks! They may not be as common now for exactly the reason you mentioned.


#9

I’m not sure the OP isn’t referring to the extra axle that comes down to distribute the weight of heavy loads better rather than the “landing gear”.

These not only cause less damage to roadways, I’ve also seen them dropped to add more floatation on soft sand, as is often in construction sites.