Trucks at Work

Downspeeding: Divining the benefit for trucking

A report issued yesterday by the North American Council for Freight Efficiency (NACFE) that downspeeding – which means spec’ing faster gear ratios to lower the speed of the engine – can cut commercial truck fuel consumption by 2% to 3%.

OK, great: but what does that means in terms of dollars and cents for fleets? And are there any drawbacks to downspeeding fleets need to be aware of?

Mike Roeth, NACFE’s executive director (at right), discussed some of those issues in a conference call with reporters, noting that the near-record lows for diesel prices may affect the return on investment (ROI) downspeeding offers.

“For a ‘classic’ over-the-road Class 8 tractor accruing 120,000 miles a year, a 1% savings in fuel equates to roughly $700 annually,” he explained. “So a 2% to 3% fuel economy improvement returns anywhere from $1,400 to $2,100 per year.”

However, that’s calculated with diesel prices at $3.75 to $3.85 per gallon, Roeth stressed. Thus with diesel now below $2.50 a gallon, that “return” needs to be cut by about a third, he said, meaning the fuel economy improvements save around $1,000 to $1,500 per year.

Roeth added that those fuel saving “percentages” are generated by lowering the engine RPMs (revolutions per minute) required to keep a truck at highway speed – that’s why this tactic is called “downspeeding,” after all – with a 1% fuel savings accrued for every 100 RPM reduction.

Now, Roeth emphasized that downspeeding is not a new endeavor in trucking circles; indeed, it’s been in use for some two decades.

The reason it’s back in vogue now centers on the rapid rise of fully-automatic gearboxes and automated mechanical transmissions (AMT) that are far more precisely computer controlled than ever before.

“That’s the key enabler; electronically-controlled transmissions,” he said. “More precise shifting can be done by computer.”

That’s also critical because, within a powertrain “optimized” for downspeeding, faster rear axle ratios are in use and much more engine torque is being delivered down the driveshaft.

While that heavier torque load is easily managed in steady-state (read as “highway speed”) operation, it becomes a big problem in start-and-stop applications.

“Torque is up significantly in downspeeding-configured powertrains and so there is the potential for driveline issues – particularly in daycabs operating part of the time in pickup and delivery applications,” Roeth noted.

In those situations, “more robust” components are available, he pointed out, but that can hike the cost of downspeeding-configured powertrains by $500 to $1,000.

NACFE interviewed a number of fleets as part of its research and discerned some other concerns regarding downspeeding:

  • Lower engine horsepower. A fleet used to 425 to 450 hp engines would typically find a downspeeding-configured variant at 400 hp;
  • Resale value impact. Would a lower hp engine affect the resale value of their downspeeding-configured trucks?
  • Driver acceptance. Would drivers accept a truck with lower overall horsepower?

Roeth said fleets testing downspeeding-configured powertrains by and large, though, found those fears to be unfounded.

“They were definitely scared the most about turning off their drivers with less hp, but the faster rear axle ratios made the downsped trucks much more responsive; one fleet said they were surprised how ‘snappy’ the trucks were,” he explained. “Another benefit is that the downsped trucks were far quieter than they expected – and that is great for driver retention.”

In the end, though, the key to downspeeding – indeed, any new technology – is payback, Roeth stressed. “Any new trucking technology needs to pay for itself; that’s been one of our consistent findings in all of our reports,” he said. “Fleets will not buy it if they cannot achieve payback with it.”

That being said, NACFE’s view is that the payback opportunity is there with downspeeding. There isn’t an extra charge per se with downspeeding, Roeth noted; it’s really a matter of spec’ing components on the front end – that’s where the extra work is, he said, unless more robust components are needed to handle specific applications.

Indeed, according to NACFE’s research, about 25% of the truck “build” going on today encompasses downpseeding-configured powertrains; a level the group thinks could reach between 50% and 70% over the next three to five years just due to the fuel savings.

“OEMs are getting in this [downspeeding] because of the fuel economy benefits,” Roeth said. And though diesel fuel is cheap at the moment, he stressed that won’t last forever.

“You just can’t afford to buy a truck with the ‘same old, same old’ technology anymore,” Roeth added. “These [downspeeding] powertrains are simply being fine-tuned for the best possible fuel economy.”

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