Current Practice
How have these oh-so-important ratings been determined in the past? "First is market considerations," says GM trailering engineer Robert Krouse, who chairs the group putting together the SAE standards. "We hear from our customers--what they want to haul, what they want to trailer--and see what our competitors are doing."
"The starting point is defining the customer's intended usage or purpose for the vehicle," echoes Eric Kuehn, chief engineer for Ford's full-size trucks. "With specifics around our previous model and competitive sets, we define what those capabilities need to be. That sets up overall design metrics around the GCWRs, GAWRs [gross axle weight ratings], tongue weight, and payload, which set up design criteria for the architecture and specific components."
"It all starts when we're developing a platform," adds Richard Miller, regional product manager for Nissan trucks. "We research the market and the customers, see what our competitors are doing, and decide where we want to position our vehicle. If we want to be the leader, we'll check competitors' ratings, project where we expect them to be by the time we launch our new platform, and set that as a target. That target is then cascaded to the different engineering and component groups, who test and develop their parts to meet it."
Karl Forster, a member of the SAE trailer towing group who was vehicle dynamics project leader on Honda's unibody Ridgeline pickup and Pilot SUV, says Honda's ratings come from actual customer usage. "We spent a fair amount of time observing and talking to light-truck customers to understand how they use and load their vehicles and how they tow trailers," he says. "For the Ridgeline, our survey found out that 84 percent of truck buyers tow 5000 pounds or less." Toyota says simply that it uses several measures to determine a vehicle's tow rating, including vehicle dynamics and powertrain effectiveness.
The Ratings
Among key truck specifications, GVWR (gross vehicle weight rating) is the maximum a vehicle can weigh fully loaded, including occupants, cargo, and trailer tongue weight. Payload (GVWR minus curb weight) is the maximum it can carry, including occupants, in addition to its own weight. GCWR is the maximum a fully loaded tow vehicle and trailer combined can weigh.
For obvious reasons, truck makers have often aimed to leap-frog each others' ratings when designing new market entries. "In the 1998 time frame," GM's Krouse points out, "half-ton tow ratings were maybe 7500 pounds, and a duallie's was 10,000. Now, half-tons are about 11,000 and duallies 15,000. Certainly improvements have been made to our vehicles and their capabilities--but 50 percent increases? The marketing people want higher numbers, but the industry has realized that we need to get a handle on it. We all realize something needs to be done to get something in place and stop this escalation."
Both Ford and Chrysler launched new light-duty pickups for 2009, and while the F-150 boasts industry-leading tow ratings, Chrysler took the unusual step of holding its new Dodge Ram's capabilities where the outgoing models' were. "We did a lot of customer research," explains Ram chief engineer Mike Cairns. "That data showed that well over 90 percent of light-duty truck customers were happy and satisfied with their current tow ratings, well over 80 percent tow less than a 6000-pound trailer, and an overwhelming majority were looking for improved fuel economy. We took that to heart. To improve tow ratings, you're going to add weight and cooling drag, both of which reduce fuel economy, so we didn't think that made sense.
"Based on all this research data and customer feedback, we set targets for tow and payload ratings to match our 2008 models. The customers were not asking for more, so that's where 2009 targets were set. Also, our new light-duty Ram has an all-new coil-sprung rear suspension, and we achieved those targets with that rear suspension."
Mike Raymond, Chrysler's senior manager for light-duty truck synthesis and vehicle development, points out that GVWRs, unlike tow ratings, are influenced by federal restrictions within each weight class: "Cargo without a trailer goes into the GVWR calculation, where you have to meet federal stopping requirements, for example. You have to pay attention to payload with a non-trailer vehicle and comply with brake and other standards." He also suggests that customers who really need to tow large, heavy trailers should opt for the heavy-duty Ram.