Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: Fuel efficiency versus speed



The obvious soln. here is (was) to to enforce the 55 (actually, of course 65), and give the truckers a govt. subsidy to make up for their losses to switch transmissions (after first detmng. if this
was cost effective). The rationale is that the total fuel saving (enuff more autos than trucks) "out weighs" the retrofit cost. The alternative; allow higher speed for the trucks (conforms to the
intent of the law) is non starter as wildly varying speeds accident contributes. This reminds the unexpected concomitant 55 speed result, very reduced accident rate. Anyone know how much the rate has
increased as a result of the 75/80 (CA) present speed limit? My impression: that it went up, but not to the previous, because of tech. advance.

bc

Larry Cartwright wrote:

brian whatcott wrote:
There should be a proviso in there that the speed to engage top or
overdrive is likely to provide best mpg.

This was the gripe of the big-rig truckers when the expressway speed
limit was abruptly lowered in the 1970s. Engineering big truck fuel
economy is much more complex than just lowering speed and lowering air
friction. It is not a simple textbook problem.

1970's long-haul powertrains were geared to provide optimum engine rpm's
and torque for economy at 70 mph. Slowing down to 55 mph forced them
into a lower gear ratio, where most of them wound up using as much fuel
as ever even with the lower speed. *Theoretically* the decreased air
friction should have resulted in fuel economy, but that wasn't the
actual outcome for most of the truckers.

They felt they were political victims of a poorly conceived strategy,
forced to choose between spending more time on the road or doing less
business, and they weren't using any less fuel than they ever did and it
cost more. There was an alternative: spend thousands up front to
rebuild your rig with a new "Jimmy Carter powertrain" that would run
efficiently at 55 mph. Big outfits retooled their fleets. A lot of
little guys were forced out of the business.

Best wishes,

Larry
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Larry Cartwright <exit60@ia4u.net>
Physics and Physical Science Teacher
Charlotte HS, Charlotte MI USA
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~