Spring Loaded

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We’ll forgive you if you haven’t noticed steer axle loads creeping upward over the past few years. While we weren’t watching, those zealous sorts over at the EPA heaped nearly 1,000 lb of gear onto our trucks, leaving our steer axles close to being overloaded before we’ve even hooked up to a trailer.

Back in the carefree pre-EPA-2004 days, static steer axle loads hovered around the 10,500-lb mark — bobtail and full of fuel, but with no driver and with none of the gear they usually cart around. When the EPA-2010 trucks hit the road later this year, static steer axle loads will be close to 11,500 lb, generally speaking. Some will be lighter, many even heavier.

Keith Herrington, product marketing manager for highway trucks at Daimler Trucks North America, says steer-axle loads are indeed on the rise, and while EPA-related emissions hardware is partly to blame, the revised hours-of-service rules and even high fuel prices have also had an impact.

"The latest version of the hours-of-service rules changed the duty cycle of a typical over-the-road truck to where it has become more of a commercial RV," Herrington told us. "Drivers are spending more time sitting in their trucks [reset time, and 10 hours off], so they are packing more entertainment devices and appliances to support the downtime. That has increased the demand for storage space and larger sleepers, which all adds weight to a vehicle. And much of that extra weight sits on the steer axle."

Even the tire people were caught a little off guard. Michelin‘s product marketing manager, Don Baldwin, says back in early 2008, his company began getting calls from customers looking to go from load range G to load range H with their steer tires.

"As fuel prices were spiraling upward, customers started paying more attention to the gap between the tractor and trailer in trying to reduce fuel consumption," Baldwin says. "They were looking for the heavier rating on the tires to accommodate the extra loads on the front axle resulting from shifting the load toward the front."

If you missed all the excitement, don’t feel bad, even the fleet council that sits with the engineers at Hendrickson weren’t really aware of the impact that EPA, HOS, high fuel prices, and everything else had on steer axle loads.

"At the meeting we had in the fall, we asked our fleet participants if they were aware of what was happening on the front axles of the vehicles and the weight changes," explained Hendrickson’s director of sales and marketing, Sean Coleman. "None of them were really aware of what was going on." 

While the temptation is there to push a lighter suspension
into heavier service, beware the possible consequences.

While there are many variations across the different OE brands, models, configurations, engine sizes, etc., many trucks spec’d today for delivery after Jan.1, 2010 will need steer axle weight ratings ranging from 12,350 up to 13,200 lb.

Stopping Distance & Steer Axle Weight:

NHTSA’s recent rule requiring brake makers to reduce truck stopping distance by 30 percent will too, will have an impact on steer axle weight as many suspensions and axles will need to be upgraded to handle the additional brake torque. 

"It’s not just an issue of whether disc or drum brakes will do the job," explains Coleman. "Industry will choose the option that works best for them, but either way, the requirement will add more pounds to that suspension."

Coleman advises truck owners to pay close attention to axle load ratings in relation to the position of the fifth-wheel. They should be looking at the base weight of existing vehicles and comparing that to post-2010 vehicle weights, and then determining what might need to be done to take weight off the vehicle.

At several dollars per pound cut from the tare weight, trimming can get expensive. Coleman says Hendrickson is working with various alloys and other materials to find an efficient balance between cost and weight, but it’s never a slam dunk.

"You can go from a three-leaf to a two-leaf front spring, and then to a leaf-and-a-half, but the jump to a mono-leaf spring is quite a leap in terms of technology and cost," he says. "At some point, you approach the point of diminishing returns."

Trailer Axles:

While trailer suspensions won’t directly help take weight off the steer axle or the front suspension, some weight savings can be had in trailer suspensions — and some of that can be seen on the drive axles — but beware of under-spec’ing axles used in Canada-only service.

Higher Canadian weight allowances and our relatively crummy roads may push U.S.-spec’d suspensions to their limit.

Bill Hicks, director of product planning and market development for the trailer business unit at SAFHolland, cautions that while there are similarities in trucks intended for international service, spec’ing for our northern needs might demand a different airbag, different shock locations, or maybe a different beam or a more robust axle.

"That might add weight and cost that the typical U.S. over-the-road carrier wouldn’t need and wouldn’t pay for," he says. "That’s the challenge we have as suppliers: trying to mainstream the products and standardize components, yet serve two slightly different markets."

So, while the temptation might be there to push a lighter suspension into heavier service, beware the possible consequences.

While new regulations are forcing more weight onto our trucks, an old adage gains increasing relevance today: you can’t put 10 lb of potatoes into a five-lb sack. But that’s what everyone is trying to do.

Maybe it’s time lawmakers took a serious look at some meaningful weight tolerances to accommodate all the gear they’re forcing us to use? 

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Jim Park was a CDL driver and owner-operator from 1978 until 1998, when he began his second career as a trucking journalist. During that career transition, he hosted an overnight radio show on a Hamilton, Ontario radio station and later went on to anchor the trucking news in SiriusXM's Road Dog Trucking channel. Jim is a regular contributor to Today's Trucking and Trucknews.com, and produces Focus On and On the Spot test drive videos.

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