Downspeeding can contribute 2-3% in fuel savings: NACFE report

by Sonia Straface

NEW YORK, N.Y. – A new confidence report released today by the North American Council for Freight Efficiency (NACFE) and Carbon War Room claims that downspeeding can slash truck fuel consumption by 2-3% when optimally applied.

Downspeeding is the practice of speeding up the rear axle on trucks to lower the speed of the engine, allowing the truck to run at the most fuel-efficient RPM under cruise conditions, thus saving fuel and money. Downspeeding can also help in other areas like noise reduction and improved driveability, NACFE said.

According to the report, downspeeding is now a primary focus for OEMs to help improve fuel economy for regional and long-haul applications that operate at highways speed, mainly because of the technologies that complement it to make downspeeding more attractive.

“We see (downspeeding) in two configurations,” said Mike Roeth operation lead, trucking efficiency with NACFE. “The first is downspeeding with a direct drive transmission. And that’s being done by fleets (that) are most aggressive on fuel economy. The other is downspeeding with an overdrive transmission with a slower rear axle ratio. That offers different advantages but loses that direct drive opportunity.”

NACFE said one of its main conclusions from the report is that, after the finding it can improve fuel economy by 2-3%, downspeeding should be adopted by long-haul operations.

“We strongly consider that in long-haul fleets, they be considering downspeeding,” Roeth said.

One of the only concerns with downspeeding NACFE found in its research is that it poses a risk of potential driveline failures. However, NACFE said by talking to the right people, you can avoid this is you think downspeeding is the right move for your business.

“One of the concerns we uncovered is the consequences of potential driveline failure due to higher torque,” Roeth said. “The good news is the component manufactures and truck manufactures, have solutions for that. And that particularly happens in day cab, pick-up and delivery type of operation where there’s the opportunity to deal with that higher torque. But, there are solutions there, and we recommend that anyone considering downspeeding speak about this with your transmission supplier, rear axle supplier, engine suppler…to make sure that the spec’ will work for you and your duty cycle and your business practices as a fleet.”

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  • How is this any different from the “old” technology of GEAR FAST, RUN SLOW?….. this has been around a LONG while, in fact i began hearing this in the late 80s ….not sure I see anything groundbreaking here, unless that’s what we do these days, change the terminology and take credit for ground breaking ideas.

  • Lee,
    Actually, it is different than the old days way back “in the late 80’s”. Its a lot different. Lets start with the engine. Today’s big bore engines make torque and horsepower at very low rpms compared to older engines. Some engine’s torque peak is as low as 1000 rpm and then it stays flat until 1400 to 1500 rpm before dropping off precipitously. This is also known as the sweet spot or most fuel efficient area of the engine power curve so the driveline needs to be geared to operate in that area. And since the peak torque is so low the truck can actually stay in the top gears a higher percentage of the time. Less gear down time at higher rpm. Also, by operating the engine at lower rpms there are further efficiencies to be gained through a large reduction in friction and by having fewer combustion cycles. Cruising at 1200 rpm or less instead of 1800 rpm means the engines fires about 30% less. Is that different enough for ya?

  • NoBS,
    Still sounds like gear fast, run slow to me. Just gear even faster and run even less rpm than with the old engines. And don’t use big rubber to make up the difference.