Spec’ing the Right Fifth Wheel

June 29, 2016
When it comes to selecting the right fifth wheel for your application, SAF-Holland offers a guide to simplify the process. Together with your application requirements and performance preferences, this easy-to-use Fifth Wheel Selection Guide takes you step-by-step through the process of choosing the fifth wheel that best fits your application.

When it comes to selecting the right fifth wheel for your application, SAF-Holland offers a guide to simplify the process. Together with your application requirements and performance preferences, this easy-to-use Fifth Wheel Selection Guide takes you step-by-step through the process of choosing the fifth wheel that best fits your application. Whether you’re spec’ing a fifth wheel for a standard, moderate or severe duty application, this comprehensive guide includes top plate selection, mounting systems, height selection as well as cost considerations and spec’ing tips.

Here’s a brief look at spec’ing your next fifth wheel:

VEHICLE PROPERTIES

Consider the type(s) of vehicles and trailers in your fleet operation. A single trailer setup and a B-train setup will have vastly different functions and demands to take into account. Same with a rear-tilt vs. a side-tilt dump trailer, a tanker vs. a dry van, or a long-haul tractor-trailer vs a yard spotter. Different loads and forces are at play in every distinct application. Your unique combination of vehicle and load will play a big role in determining whether you can specify a basic, universal fifth wheel or a more specialized model.

VEHICLE CAPACITY

Although there can be some overlap, most all tractor-trailer combinations can be classified as one of three types: standard duty (100% on-road; <95,000 GCW); moderate duty (<10% off-road; <115,000 GCW); and severe duty (>10% off-road; >115,000 GCW). Because each classification calls for unique capabilities in a fifth wheel, there are factors that must be considered. There is one common factor that is of the utmost importance: no matter the vehicle size or application, it always pays to spec a fifth wheel for a somewhat higher capacity than you need. The extra margin can avoid safety issues and maintenance headaches down the road, and ultimately lead to lower cost of operation.

TOP PLATE SELECTION

The top plate is not just the platform on which the trailer rests. It encompasses a variety of components that work together to secure the trailer to its tow vehicle. A variety of available options can add to the efficiency and durability of the top plate, but they can add weight and cost. When you consider that the weight difference between a lightweight top plate and a heavy-duty unit can be over 300 pounds, it’s clear that weight is one of the top factors in selecting the right unit and the right options.

OPTIONS SELECTION

While there is some overlap, fifth wheel options generally fall into four main categories: efficiency; safety; cost; and application suitability.

MOUNTING SYSTEM SELECTION

A fifth wheel is only as good as its mounting system. As simple as it can appear to bolt a mounting assembly onto the frame of a truck, that assembly is crucial to the stability and longevity of the entire system. Mounting systems come in two varieties: stationary, which  cannot be adjusted front-to-back once mounted on the tractor frame; and sliding, which allows for adjustments to the distance between the fifth wheel and the back of the cab, for fleets that run a variety of trailers and a variety of loads. A sliding mount can easily accommodate changes in axle loading, kingpin setting and vehicle combination length, creating maximum versatility and productivity.

HEIGHT SELECTION

Whether you select a stationary or sliding mount, you must take into consideration the height of the fifth wheel unit. The top plate of the fifth wheel, when horizontal and matched to the trailer upper coupler (bolster plate), must be low enough that the total height of the tractor-trailer does not exceed 13’ 6”, but high enough that articulation between tractor and trailer is not compromised or hampered.

COST CONSIDERATIONS

Which cost is more important to your fleet? Acquisition cost? Total cost of ownership (TCO)? Resale value? Chances are, you assign a unique weight to each of these cost considerations, and consider them all when making a spec’ing decision. Here again, having a host of options and selections can make a purchasing decision easier. A wide variety of fifth wheel options can make it easier to balance the acquisition cost against the total cost of ownership, which includes warranty coverage, maintenance costs, wear life, and availability of parts and service, wheels, or the trailer.

SPEC’ING TIPS

Among the keys: the extreme demands of off-highway applications call for high-capacity fifth wheel; a lightweight aluminum top plate is a good option for an on-highway application where fuel economy and load capacity are top considerations; and a heavy-duty on-highway fleet is a good candidate for a low-lube top plate, while a no-lube option is ideally-suited to a standard-duty on-highway application.

To obtain a copy of the Fifth Wheel Selection Guide, email [email protected].