TORONTO, Ont. –The mass movement towards air-ride trailer suspensions in Canada has allowed fleets to tackle everything from cargo damage and driver turnover to broken light bulbs.
However, technological advances that address many of the flaws traditionally associated with mechanical suspensions, combined with higher fuel prices may be prompting some fleets to revisit the mechanical versus air-ride debate.
Composite springs and the use of more leafs (as many as seven-or eight-leaf springs) are providing increased durability and a better ride than traditional mechanical suspensions, according to some manufacturers.
“A lot of people just open their mouth and out comes ‘Air-ride logistics, 53-ft.'” says Ray Camball, fleet sales manager with Trailmobile Canada. “It’s a pre-programmed thing. While air-ride has softened the ride for lightly-loaded, high-speed loads and empty return hauls, electronics, potato chips and other sensitive lightweight freight, it has brought with it other complexities.”
When calculating total cost of ownership, there are obvious advantages to the less complex and relatively maintenance-free mechanical suspensions. But concerns about ride quality and durability still ultimately steer many customers towards air-ride suspensions.
ArvinMeritor offers a form of hybrid -a mechanical suspension with a composite spring, called SimilAir. It consists of a main member constructed of fiberglass resin matrix with steel wear pads on each tip. It has a jounce bumper in the middle, which the company says contributes towards an “air-like” ride.
“For many applications, it’s a good alternative to an air-ride suspension and it’s definitely a better product in terms of ride enhancement if you’re moving forward in terms of mechanical suspension technology,” says Mike Lynch, product line manager for the SimilAir composite spring with ArvinMeritor.
A tandem suspension with SimilAir weighs about 250 lbs less than its typical air-ride counterparts and is 100 lbs lighter than traditional steel spring suspensions, the company says. That means extra payload for some fleets -but how about the ride?
Lynch said drivers who have pulled trailers with the SimilAir composite spring have raved about a smooth ride that rivals that of an air-ride suspension. He attributes it to the monoleaf design combined with the jounce bumper.
“Most of the traditional trailer springs are a pack of springs, and you get a lot of friction between the springs which causes a stiffer ride,” explains Lynch. “Our SimilAir is a one-piece, one-leaf unit, so we get rid of the friction between leafs.”
ArvinMeritor claims the SimilAir has also addressed another of the traditional knocks against mechanical trailer suspensions: durability.
“Having a composite spring is very beneficial in terms of corrosion resistance,” says Lynch. “It’s not susceptible to corrosion.”
One customer, propane hauler H. J. Martens out of Junction City, Wis., made the switch from a conventional three-leaf steel spring system in response to suffering about a dozen steel spring failures each spring season. The company’s owner, Steve Martens, said the composite spring (combined with aluminum hubs and wheels) has enabled him to increase payload by 300-400 lbs, increasing revenue by 3% while also reducing downtime.
While ArvinMeritor’s SimilAir spring has its fans (Canadian Springs and Reimer Express are among its Canadian users), some other suspension manufacturers remain skeptical about the potential of composite spring suspensions.
Larry Stevenson, marketing manager, trailer systems with SAF-Holland, notes that in general “market acceptance (of composite springs) has been limited.”
Scott Fulton, director of engineering with Hendrickson agrees.
“I don’t differentiate between a composite spring and a steel spring,” he explains. “From an engineering perspective, what an air-ride does that no mechanical spring can do, is change its spring rate based on the load applied to the trailer. The height control valve maintains the same height and it always inflates the air bags to bring the trailer to the proper height so it has a certain amount of jounce. That’s what gives the air-ride its softness.”
While weight and overall cost of ownership are the two main motivators for spec’ing mechanical suspensions, SAF-Holland’s Stevenson doesn’t foresee a widespread movement back towards mechanical suspensions, even with record fuel prices forcing many fleets to look at new ways to reduce weight.
“More recently, the trend (towards air-ride suspensions) has leveled out and most fluctuations can be traced to specific buying patterns of traditional mechanical fleets versus air-ride fleets,” he says. “A reversal of current trends is unlikely, considering that cost and weight differences between mechanical and air-rides have been substantially narrowed over the past 15 years and that trailers with air-rides warrant a higher resale value.”
Gary Wasney, Canadian sales manager with Ridewell Suspensions, says while composite springs have been used with “a certain degree of success” in the past, he feels shippers will continue to drive demand for air-ride suspensions.
“More shippers are saying that if you’re going to haul their product on a trailer, it’s going to have to have air-ride,”Wasney says.
While composite spring suspensions have their critics, Trailmobile’s Camball is a proponent of exploring all possible solutions. He suggests customers consult with a reputable supplier to determine the best fit for their specific application.
“It can be worth the time up-front to consult with knowledgeable, unbiased suppliers to discuss your loads and docking situations to help decide on the type of system that best suits your needs,” he says.
He suggests not to underestimate the dampening quality that can be achieved by using composite springs, or for that matter, even seven-or eight-leaf spring suspensions. He has satisfied van customers using both solutions, as well as air-ride.
“Spring ride gets a bad wrap,” he says, chalking it up to the fact many customers’ only experience with mechanical suspensions was based on a suspension unfit for the task, perhaps with too few springs, offering little flex and resulting in a stiff ride.
While current economics may not have quelled the mechanical versus air-ride debate, the emergence of composite springs and continuing weight-saving measures taken by manufacturers of both air-ride and mechanical suspensions are providing unprecedented options – and that’s good news for customers.
“The current fuel crisis will serve as a catalyst to drive innovation to the next level,”Stevenson predicts.