Hitch Hints     
 
A Smooth Ride (35-1) by Andy Thomson

For the best ride possible, eliminate chassis flex in your fifth wheel.

Andy Thomson
Although fifth wheels offer very stable towing, it sometimes comes at the price of surging in the ride of the tow vehicle.

When you tow a conventional travel trailer, the tow vehicle chassis and trailer are pretty much in line with the pivot point of the hitch, which means push and pull motions are minimized. The other cause of surging in a fifth hitch is slight movement in the pin box assembly. Again, this is not a problem with a travel trailer, since torsion bars tension everything and remove most movement.

With a fifth wheel, the pivot point is well above the truck frame, resulting in push and pull motions created by the tires catching bumps in the road, and flexing truck chassis rails. As well, the gooseneck on the trailer flexes. When the resonant frequency of the hitch or gooseneck matches the rhythm of road imperfections, it can set up a repetitive surge in the ride. When you get on a road with expansion joints at the right distance, surging can be severe.

There are factors that minimize surging. Triple axles surge less because six soft suspensions donít catch bumps as hard as four stiff suspensions. Plus, you operate a tri axle with lower tire pressures. Air or rubber ride supplements on the trailer suspension also reduce surging. If truck suspension is too stiff for the weight of the trailer, it will make surging worse, as will excessive air pressure in the combinations tires. Usually a short box is a little better than a long box, as the shorter frame has less flex.

For years, our best answer to reduce that surge motion was to use the strongest hitches we could find, with the least amount of movement and flex. We knew that trailers with stronger construction also rode better due to their reduction in chassis flex. When trying to eliminate this in an RV, the wall construction is more important than that of the frame, because most of an RVís strength comes from its body.

Products have been introduced to address surging. One you see regularly is the Air Ride Pin Box, which helps save the trailer from road shocks transmitted by the truck, but doesnít do a lot to prevent a surging motion.

I tried a unit that had springs mounted to the front and rear of the fifth wheel head assembly, but I couldnít feel any real difference with these units.

Recently, I test-drove a truck with a new hitch design called Star Performance. This hitch carries the fifth wheel head in a cradle, not unlike a glider rocking chair. I thought I was likely wasting my time, as I didnít expect it to work any better than the others.

Was I wrong. By the time I had travelled 500 feet, it was obvious this example was different, and virtually all sensation of the fifth being attached was gone. The Star Performance easily drops into the same rails as many other hitches used, so itís easy to try it out on an existing combination. Every one of our customers who has tried it now owns one.

(Page Top)


Copyright © Taylor Publishing Group. All Rights Reserved.