Service bodies in both fiber-composite and steel are available for a range of applications from electrical to plumbing to mechanical to construction. - Photo: Canva

Service bodies in both fiber-composite and steel are available for a range of applications from electrical to plumbing to mechanical to construction.

Photo: Canva

Fiberglass or steel: which is the better material for the construction of service bodies?

Both types of service bodies (also known as utility beds) are used in a wide range of applications, including electrical, plumbing, mechanical, heating and air, mobile equipment service, and general construction. Both offer rugged compartments, shelving, and drawers to organize tools and small parts. Both allow for mounting heavy equipment (such as cranes, aerial lifts, welders, and compressors).

Here are eight factors to help fleet managers differentiate and decide:

1. Truck Body Cost

Steel service bodies are typically priced several hundred to a few thousand dollars less than comparably equipped fiberglass (also known as fiber-composite) bodies, depending on truck class and body size. For fleet managers looking for the least expensive option, in terms of initial upfit cost, the steel body has the edge.

2. Body Payload Capacity

The lighter the body, the more weight a truck can carry.

According to BrandFX Company, a Ft. Worth, Texas-based body manufacturer, its standard 8-ft. fiberglass service body, designed for a single rear-wheel, 56-inch cab-to-axle chassis, weighs 590 lbs. The weight range for a similarly equipped steel body is 1,000-1,300 lbs., according to Bob Johnson, director of fleet relations, National Truck Equipment Association (NTEA). That's an additional 410-710 lbs. of payload capacity with the fiberglass body, without having to bump to a larger gross vehicle weight rating (GVWR) truck.

3. Impact on Fuel Economy

According to the U.S. Department of Energy, an extra 100-lbs. in vehicle weight can reduce fuel economy by up to 2 percent. In other words, with payload being equal, a work ruck equipped with the lighter fiberglass body will have the fuel economy advantage over a comparable steel body.

Therefore, the important question to ask is this: Will the vehicle travel sufficient miles per year to recoup the higher price of fiberglass with fuel cost savings? If so, the fiberglass body could be a good fit for that application. With a low-mileage duty cycle, a steel body may make more financial sense if the vehicle won't be driven enough to justify the premium for fiberglass.

4. Chassis Selection Tips

Depending on the application, the fiberglass body may enable the fleet to select a smaller chassis, which not only improves fuel economy but also lowers vehicle acquisition cost by $4,000-$5,000 for light-duty trucks - and substantially more on medium-duties.

Take, for example, a light-duty ¾-ton pickup chassis. This is the most common size work truck for an 8-ft. single rear-wheel service body. Because the payload capacity is 3,500-4,000 lbs., which, assuming the steel body weighs 1,250 lbs., leaves a net payload capacity of 2,000-2,500 lbs., sufficient to serve a broad range of applications.

In comparison, a ½-ton truck, which has a gross payload capacity of 2,000-2,200 lbs., can only carry a maximum of roughly 700 lbs., after factoring the weight of the steel service body.

But, what if the body is fiberglass? In this case, the smaller ½-ton pickup chassis might work, especially if the truck is intended to carry 900-1,200-lbs., as is common in certain telecom, utility, and HVAC/mechanical/electrical applications. Subtract 600-lbs. for the fiberglass body from the truck's 2,000-lbs. payload capacity, and the difference of 1,400 lbs. in net payload is within range for those applications with cargo of 900-1,200 lbs.

Now, consider the impact of moving to a smaller chassis on both acquisition cost and fuel economy - if the application allows for it. A ½-ton two-wheel-drive Chevrolet Silverado 1500 with a 4.8L V-8 engine, for example, is approximately $4,700 less in terms of manufacturer's suggested retail price (MSRP) than a comparably equipped ¾-ton Silverado 2500, with the 6.0L V-8 ($23,990 vs. $28,675). The smaller V-8 also achieves roughly 5 mpg better fuel economy.

Johnson noted that downsizing from a ¾-ton chassis to a ½-ton isn't really a viable option. "I believe the lightest truck available with a box removal option is a 6,400-lb. GVW ¾ ton offered by one OEM only," Johnson commented. "That means you would have to purchase a completed pickup, remove the bed without OEM approval, and install a new body. In many cases, the frame for a pickup is not straight (as with a chassis-cab), so you might also have body compatibility issues in addition to the modified vehicle certification issues involved. Even if you resell the removed box to a body shop, you would not come out ahead in most cases from a cost viewpoint. On the other hand, downsizing from a Class 3 to a Class 2 chassis cab is a viable option."

Another consideration with fiberglass vs. steel in service bodies is chassis weight ratings - particularly work trucks with GVWRs just above certain Department of Transportation (DOT) regulatory thresholds, such as 10,000-lb., 26,000-lb., and 33,000-lb. GVWRs.

Consider vehicles that are on the borderline of the 33,000-lb. GVWR threshold. There is a federal excise tax (FET) applied to all new trucks purchased above that GVWR, which adds several thousand dollars to the total vehicle acquisition cost. In these cases, fleet managers should evaluate whether the lighter weight fiberglass body could allow the fleet to purchase a smaller chassis to avoid FET, without sacrificing payload capacity and performance.

The key is to identify whether the payload requirements fit within those "sweet spots" where lighter-weight materials can make the difference in chassis size and, thus, justify the higher cost for fiberglass.

5. Durability vs. Weight Savings 

One of the selling points for steel is the material's ability to withstand the heavy-duty abuse of a typical work truck.

But, according to Eric Paul, VP sales and marketing, BrandFX Company, the same could be said of fiberglass bodies, despite the material's lighter weight.

"Our fiber-composite actually lends itself well to off-road use, and heavy-duty applications with mounted aerials, cranes, and diggers, because of [the fiber-composite's] ability to flex 30 degrees either side of center and return back to its normal shape without any cracks or distortions to the laminate," Paul said. "Steel, on the other hand, does not have any flexural properties. If you bend steel, it does not return to its normal shape. It stays bent."

To illustrate the differences in how fiberglass and steel absorb impact, Paul suggested: "Grab a piece of steel. Have someone hit one end of the steel with a hammer. Do you feel the shock waves on the other end? Steel transfers those shock waves throughout the entire length of the metal. Fiber-composites, on the other hand, actually localize that shock. Consequently, damages from collision [to the fiberglass body] do not spread over the entire body. This is important, because it results in less damage that needs to be repaired [compared to steel]."

There are applications, however, where steel tends to hold up better than fiberglass, said Johnson of the NTEA. "If you have an application, such as a mechanic's service body with a service crane that loads heavy engines and transmissions into the bed of the truck, and the engine bangs against the inner walls of the bed, the steel body will dent and ding, but its not going to crack, which fiberglass may do under similar conditions," he said.

6. Ability to Repair

Another "pro" for steel service bodies is that they tend to be easier to repair in the field, and there's no need for specialized technicians to perform the maintenance. In the event of damage, the steel can be bent back into shape or the piece easily replaced. All of this translates into less downtime and lower repair costs, compared to fiberglass.

"If you're in an application where the body will take a beating, it's much easier to repair steel bodies," Johnson said. "All you need to do is weld or rivet a steel panel or bondo over it and shoot a coat of paint on it."

But, changes in the marketplace are making fiberglass bodies more competitive from a maintenance and repair cost perspective, Paul said. "Since many manufacturers such as Ford, Chevrolet, Dodge, PACCAR, Freightliner, International, and others utilize fiber-composite materials in their vehicles for fenders, hoods, and cowlings, most dealerships have qualified fiberglass technicians on hand," he noted.

7. Corrosion Resistance

Corrosion resistance is an important consideration in the Northern U.S. and Canada, where magnesium chloride and other road salts are sprayed during the winter months, and in coastal areas where there is heavy concentration of corrosive salt air. In these conditions, the fiber-composite body is usually the better fit because of the material's inherent resistance to moisture and rust.

What about steel service bodies? If trucks operate in regions at high risk for corrosion, should steel be avoided altogether? Not necessarily.

Most quality steel body manufacturers thoroughly coat their bodies with corrosion-resistant technologies, such as phosphates, e-coats, and powder coats. 

In most cases, even fiberglass bodies use some steel to serve as the substructure for the body. These steel components are treated to protect against corrosion.

8. Truck Body Lifecycle

The clear advantage from a lifecycle perspective goes to fiberglass. Over time, dents and scratches on a steel body create exposed areas in the metal that are vulnerable to moisture and corrosion, eventually diminishing the body's appearance and usefulness, often within a few years. Fiberglass service bodies, on the other hand, are designed for a lifecycle of more than 20 years, according to Paul.

"You can continue to recycle the bodies [moving them from one chassis to the next] over a longer period of time. This reduces the body's total cost of ownership significantly," he said.

While recycling a fiberglass service body is an attractive option, Johnson of the NTEA doesn't see it as a black-and-white issue.

"Transferring bodies from chassis to chassis may or may not be a viable option," he noted. "It's probably not an issue for high-mileage chassis, which are replaced in a short-time cycle, but, with all of the changes coming in the truck industry to address fuel economy and regulatory issues, it is questionable as to your ability to purchase a body now and transfer it to a new chassis in 10 or 12 years without major compatibility and certification issues. Also, the resale value of a 10-year-old chassis with no body on it is just about zero, so you would have to factor that into your lifecycle cost analysis.

The Bottom Line

Which is the better material for service bodies? The answer depends on the truck's operating conditions and the fleet's overall objectives.

"If you have a low-impact application and plan to keep the truck 10 to 12 years, the savings you get in fuel economy and body lifecycle will easily offset the higher upfront cost of the fiberglass body," Johnson said. "If you have a rugged-use application and plan to keep the truck only three to four years - and it's not in an environment where there's a lot of road salt or corrosion issues - I'm not sure I would want to pay the extra money to get the fiberglass body. Like everything else, it's about matching the [material] technology with the application."

Corrosion-Resistant Treatments for Steel Bodies

One of the downsides of steel, particularly in the Northern U.S. and coastal areas, is its susceptibility to corrosion. However, modern steel truck bodies are often treated with corrosion-resistant coatings that make them better able to stand up to the elements. These treatments include:

  • Electrocoat (e-coat): A coating method that uses electrical current to deposit paint onto a part or assembled product.
  • Powder Coating: Type of coating applied as a free-flowing, dry powder. The primary difference between a conventional liquid paint and a powder coating is the latter does not require a solvent to keep the binder and filler parts in a liquid suspension form. The coating is typically applied electrostatically, then cured under heat to allow it to flow and form a "skin." Powder coating generally is used to create a hard finish tougher than conventional paint.
  • Phosphating: A process in which an acid attacks the steel and re-deposits a material that is a combination of the metal substrate (and other metals, such as zinc) with phosphate. This process creates a surface tightly adherent to the base metal with more surface area, provides improved corrosion inhibition, and helps the powder coating stick better. Phosphating provides a good base coating so the finished part has increased usable life.

Originally posted on Work Truck Online