The point was probably to reduce, but not necessarily to optimize. There
are vehicles out there that might reach maximum efficiency at 45. All
vehicles may do better at 45 than 55, or they may not. I think they just
picked a number that would save fuel and people could more or less live
with.

Jim

On Sat, Feb 4, 2012 at 6:21 PM, Joy Hecht <jhecht@alum.mit.edu> wrote:

> I thought pretty much all motor vehicles got maximum fuel efficiency at
> 50-55 mph.  Wasn't that the point of Jimmy Carter reducing speed limits to
> 55 in the 70s, to reduce fuel use?
>
>
>
> Joy
>
>
> On Sat, Feb 4, 2012 at 2:48 PM, Loren Busch <starwagen@gmail.com> wrote:
>
> > I returned earlier this week from a long trip, odometer says 3,800+
> miles.
> > Driving a '90 Westy with stock engine, automatic tranny, 167,000 on the
> > original engine, only major work ever done was reseal heads at 88,000.
> And
> > a new (yeah, NEW) AFM installed just before the start of the trip. For
> the
> > first 2/3 of those miles I was either pushing it to meet a schedule,
> > freeway and highway speeds 60-70.  And getting as low as 15.5 mpg on one
> > tank, most segments 16-17 mpg.  Then on the way home no rush and no
> > schedule, I set the cruise control to 55 mph and cruised in the right
> lane
> > no matter what the speed limit was.  I did the last 450 or so miles that
> > way.  And the mileage for that part of the trip was just a little over 20
> > mpg!!
> > This confirms, at least for me, the statement that comes up from time to
> > time that our Vanagons were engineered during the time that the highway
> > speed limits were 55.  And that is where the WBX engines like to run.
> > And seriously YMMV.
> >
>