An 18 Wheeler! Which Is the Fifth Wheel?
Which is the fifth wheel? The answer is “none”, if you thought you had to select among the 18 wheels that is. Our articles are balanced so that we provide good information for both the newbie and the seasoned trucking dispatcher. So, the fifth wheel is the plate above the tractor’s back dual wheels where the trailer’s king pin hooks to the tractor.
The Old Days
The name derives from the horse drawn carriage days where a trailer was attached to the “wheel” like attachment on the rear of the carriage. A carriage had 4 wheels and so this was then called the “fifth wheel”. So we’ve added a whole bunch of other wheels since those days, but the fifth wheel provides the same duty.
The King Pin is King
The king pin and the fifth wheel are the only two components working together to keep the trailer behind and attached to the tractor. Of course this puts a lot of pressure, no pun intended, on keeping up with safety concerns. Because the service plate on the trailer rotates on the fixed position of the fifth wheel, a lot of grease is used to keep this working smoothly. King Pin locks in different shapes and sizes are available that prevent trailer theft. This unfortunately is a big issue in the van trailer industry, so when parking a loaded van trailer you should really have it secured.
Adjusting the Fifth Wheel
A fifth wheel can also be slid forward or backward over the tractor duals in order to adjust weight distribution. The same way you would adjust the trailer tandems to adjust for weight. For example if you needed more weight on your tractor duals you could adjust the fifth wheel forward and that would shift more weight to the tractor duals. A notch forward or backward changes weight distribution about 500 lbs.
Following is a video demonstrating how grease is applied to the fifth wheel.
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My name is Travis Smith and I've been working in the trucking business since 1994 and with Heavy Haul Trucking since 2001. Our office knows about oversize, heavy and specialty loads and how to get your load exactly where you need it, safely and on time. I enjoy writing about Heavy Haul and if you're interested in learning more, please sign up for our free newsletter. If you need a shipping quote, just call (417) 312-2920 or visit our Free Freight Quote page for more details. Google+
