Date:         Mon, 3 Apr 2006 12:55:51 -0700
Reply-To:     Doug F <vanagon@ASTOUND.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Doug F <vanagon@ASTOUND.NET>
Subject:      Re: mpg
Comments: To: Wesley Pegden <wes@CS.UCHICAGO.EDU>
Content-Type: text/plain; charset="iso-8859-1"

An interesting observation and great physics teaser. 
It may indeed be that when an engine is working against gravity it can work more efficiently towards distance. 

Once a "vanagon" reaches a steady speed of say 60-70 mph the majority of the fuel being spent is overcoming the wind drag. 

By allowing the engine to climb a hill at a slower speed it can bank potential energy perhaps at a lower cost. Then when spent coasting down the other side the energy is dissipated at a rate that there is a gain vs. flat land. 

It certainly is more fun to drive in changing elevations than on the flats. Perhaps the little VW is just having more fun. 

We all seem to eat less when we are happy. (grin)

Doug
  


---- Original Message ----- 
  From: Wesley Pegden 
  To: vanagon@GERRY.VANAGON.COM 
  Sent: Sunday, April 02, 2006 9:04 PM
  Subject: Re: mpg


  I've observed the same behavior that Maggie and others have reported,
  and have harbored what I'm sure will be an unpopular theory to explain
  it: rolling hills can be good for gas mileage.  Although it may first be
  counterintuitive, I think it's quite possible that at some speeds, and
  for some grades of hills (depending on the engine and gear ratios) going
  up and then down hills can consume less gas than driving on a flat
  portion of equal length.

  Before someone says that this is obviously impossible, consider this:
  If my goal was to maximize gas mileage over a 100 mile stretch (i.e.,
  minimize gas usage to cover the 100 miles), I would not be at all
  surprised if my best bet was to climb a very steep hill for the first
  10-20 miles, then shut off the engine (or let it idle) and coast down a
  shallower 80 mile hill, leaving me at my original altitude, probably at
  well over the normal 20 mpg.

  It seems like something similar could be going on when we drive over
  more normal hills: the van sometimes gets better gas mileage by
  concentrating its work on the climb, then taking a break on the coast.

  -Wes
  '89 1.9l.  missing the hills.

  Maggie Dew wrote:
  > Well, it's not just that the "grass is greener" - I have recorded every tank
  > of gas and every mile i've driven since I got the bus.  I spent all summer
  > above 7,000 ft. for 2 years, and all winter in the Oklahoma flatlands for 2
  > years, and the mpg is consistently higher in the mountains, although she
  > seems to be at lower power climbing the hills
  >
  > "From:    Paul Connelly <vanagonhummingbird@GMAIL.COM>
  > Subject: Re: MPG
  >
  > I think its just a "grass is greener on the other side thing"! I live at
  > 9,100" and most of my driving is done at over that, and there is always lot=
  > s
  > of climbing, so when I get down to the plains, even over 5,000', my van
  > seems to have wings with all that "extra power".
  >
  >