Adoption of Downspeeding 'at a Tipping Point,' Report Says
Commercial vehicle powertrains that combine lower engine speed and faster rear-axle gear ratios — known as downspeeding — are proved to save fuel, especially in longhaul applications, and likely will be a key to helping equipment manufacturers meet new federally mandated fuel-efficiency standards, according to a report issued Oct. 28 by the North American Council for Freight Efficiency.
“Downspeeding longhaul trucks is a key strategy for fleets and builds upon the use of electronically controlled transmissions and optimizing engine parameters,” NACFE Executive Director Mike Roeth said.
The use of automated manual transmissions along with rear axles with lower gear ratios can produce fuel savings of 3-6% compared with savings of 2-3% for downspeeding alone, according to an analysis by NACFE from interviews with fleets and equipment manufacturers.
With current manufacturers offering powertrains with rear-axle ratios of 2.47:1 and engine rpm of 1,100 to 1,300, Roeth said that downspeeding “is at a tipping point” and that manufacturers are “poised to offer rear-axle ratios of around 2.08:1 and even lower engine cruise rpms of just 900 to 1,000.”
About 25% of trucks are spec’d with downsped powertrains and, according to Roeth, that number easily could increase to more than half of all trucks in three to five years.
Downspeeding faces two major challenges to adoption, Roeth said. One is a greater potential for driveline failure because of improper spec’ing. The second is higher upfront costs because of the need for sturdier components to handle higher torque pressures on axles with lower gear ratios.
Engines running at slower speeds also limit horsepower, which can be a turnoff for some drivers and can have an impact on resale value, Roeth said.
Those issues, however, are not expected to impede adoption of the technology which, according to Roeth, is popular with drivers because the truck is easier to drive and noticeably quieter than previous models.
Trucking Efficiency: Downspeeding from Carbon War Room on Vimeo.
