Date:         Thu, 18 Aug 2005 07:57:58 -0700
Reply-To:     John Bange <jbange@GMAIL.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         John Bange <jbange@GMAIL.COM>
Subject:      Re: How much fuel efficiency gained by shedding 300 lbs?
In-Reply-To:  <01c001c5a3ba$088cfff0$455e9904@DB7KQF61>
Content-Type: text/plain; charset=ISO-8859-1

> > Vanagon body is 0.75, and the rolling coefficient is 0.014. See
> > http://www.goshen.edu/physics/horsepower/1998_LabReport-87Vanagon.gif )
> 
> 0.75??!  i kinda don't think so. perhaps for the entire bus ... 

Looking at the methodology used to arrive at that .75 number leaves me
with serious doubts. It was a physics project where the students had
to collect data on their own vehicles following a specific protocol of
acceleration, coasting, downshifting, and braking. Too much room for
"pilot error", both in driving and measuring the constants.

> but
> that calculator
> > http://www.bgsoflex.com/aero.html
> only wants the FRONTAL drag coefficient. which vw was giving out to
> the magazines
> as 0.44 when the vanagon first appeared in 1979.

That's about right. I poked around the archives and found a post from
Frank Grunthaner wherein he passes on the actual VW wind tunnel test
numbers:

> Some numbers! The drag coefficient (Cd) and frontal area (A) for the regular
> Vanagon are 0.45 and 3.06 m2;
>
> for the later Vanagon with front spoiler lip,the values are: 0.44 and 3.08
> m2;
>
> for the Westfalia, the numbers are 0.52 and 3.17 m2;
>
> the later Westfalia with spoiler drops the drag coefficient to 0.51.
>
> The European hightop camper (Dehler profile) takes the drag coefficient to
> 0.40 with a frontal area of 3.61 m2.
>
> So highest drag for the Westfalia and the Euro hightop has essentially the
> same drag as the regular passenger version.
>
> BTW, I have info somewhere that the drag coefficient for the syncros is
> higher by about 0.03 but I can't place my hands on those notes just now.
>
>
> Frank (Grunthaner)
>
> This data comes from VW factory wind tunnel tests, conducted as they worked
> out the optimal gearing for the various powerplant combinations.