MPG from long trip

From: mrdancer (mrdancer@camalott.com)
Date: Sat Jul 17 1999 - 18:33:42 EDT


Well, I was recently on vacation and drove the Dak from Abilene, TX up to
south-central South Dakota (to the farm), then came back to TX via Colorado
Springs :)

Following is some mileage figures I came up with. Average speed was
calculated as distance between stops divided by time between stops. The A/C
was on almost constantly.

17.43mpg @ 72.94mph
19.50mpg @ 64.14mph
17.74mpg @ 63.86mph
16.70mpg @ 67.69mph

I took a lot of backroads, with lots of slow driving thru small towns, and
there is road construction EVERYWHERE!!! I swear, every county had a major
road construction project on the road I was taking. Most 4-lane roads were
necked down to 2 lanes about every 50 miles for 5 miles (and I always got
stuck behind a slow RV :( ). A coupla 2-lane roads were just 1 lane with a
flagman and lead car where you have to sit and wait for 5 minutes or so....
:( Anyway, my point is, my average speeds were probably much higher than
indicated in the above numbers. Most of the time I was cruising between 75
and 80mph, occasionally up to 90 (they were some desolate backroads :-)
radar detector saved me a coupla times.

I thought the MPG was pretty decent considering I had just installed wider
tires that were 2" smaller diameter than OE-spec. I also calculated MPG
figures based on the factory odometer (I used the bike computer for above
mileage calculations) and in each case the figures were a little over 1 MPG
higher, indicating that if I were running OE-spec tires, I would have
averaged at least 1 MPG better. Granted, there is some torque loss with
larger diameter tires, but this is probably offset by the wider profile
(more wind resistance) and greater rolling resistance of the wider tire
(speaking in terms of MPG, of course). OTOH, the smaller tires dropped the
truck about an inch, and they may have helped MPG a little (less wind
resistance under the truck).

All in all, I would consider it pretty hard driving (with lots of "punching
the throttle" to get around RV's and combine convoys). With decent traffic
and no road construction, I could have probably averaged 1 MPG better. A
year and a half ago, I made the same trip with OE-spec tires and decent
traffic, and averaged 21mpg with an average speed of 73mph; however, that
was during December when I wasn't using the A/C. The Dak now has 142k miles
on it, the engine may be getting a little tired, but it only uses a quart of
oil every 5-6000 miles.

As an interesting aside, I was coming down from CO into NM through the Raton
Pass. I was cruising up the Pass about 70mph and easing by the weezing
4-cyl. cars, when the Dak started lugging a little (steep grade + thin air).
So, I reached over and hit the OD button, and MAN! did that Dak open up :)
Zoomed right up the hill, whizzing past everybody else, and I was running
close to 4k rpm - got some surprised looks from fellow motorists chugging
away up the Pass :)

'92 Dak CC 2wd 318 3.55 A-518 142k
'84 GoldWing Interstate



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