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[T3] long distance gas mileage experiment

I'm back from our trip and I have some interesting things to report.

Last year I did some short distance mileage experiments with my '73 
squareback, just to see what the effect of speed was on my gas 
mileage. You may remember that I found that I did 2 trips, each 100-
150 miles long, and measured the gas mileage on each. The first loop 
was done at 65 mi/hr, while the second was done at 60 mi/hr.

The results were in agreement with Dave Hall's suggesting that my 
poor gas mileage was due to my foot, which had become heavier with 
age. I got about 27 mi/gal at 65 mi/hr and nearly 29 mi/gal at 60 

These past 2 weeks I drove a different car from Madison, WI to 
Tucson, AZ. With a side trip to the Grand Canyon, the total trip 
distance was 4364 miles. On all previous trips with this car, a '96 
Taurus wagon, my driving habits had been the same as in squareback 
trips, and the gas mileage was also about the same: 22-24 mi/gal. I 
tended to drive about 7 mi/hr faster than the legal limit.  

On this trip, I decided to see what happened if I made a concerted 
effort to keep my speed down, so I set the cruise control 
consistently for 67-68 mi/hr. Of course there were slower periods as 
well as occasional faster ones. I also made sure that the tires were 
properly inflated.

The end result was that our overall trip mileage was 28.13 mi/gal 
with 3 tanks actually in the 30-32 mi/gal range. The overall average 
includes 5 days of city driving in Tucson which resulted in one tank 
that gave only 23 mi/gal. The whole trip consumed 155 gals of gas.

Both the overall average and the individual tanks (except for the one 
23 mi/gal tank) were the best figures I had ever seen in this car.

The end result was that I saved considerable gasoline by holding my 
speed down. This was done at the expense of longer driving days, but 
we still made it in the same number of days (3 days each way, a bit 
over 600 miles each day.)  

Three days of driving gives one lots of time to think, and on the way 
home it finally occurred to me that changes in altitude should also 
have a considerable effect on air drag, since there is lots less air 
to push aside at 5000 ft. In fact, my best mileage (31.9 mi/gal) 
occurred traveling eastward across the high plains of Arizona and New 
Mexico. However, I also had a good tailwind at that time, too.  

All of this is enough to convince me that it would be worthwhile to 
plan to drive a bit slower on the way to the 2006 Invasion. I saved a 
bit more than 20% on gas doing this. At current gas prices, that's a 
lot of money and it's worth saving the gas, just because the supply 
is declining.

We saw gas prices ranging from $3.15 to $2.73. The highest were in 
the mountains of Arizona and the lowest were in Nebraska/Iowa.

Jim Adney, jadney@vwtype3.org
Madison, Wisconsin, USA

List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org

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