Back to the question:
Quote:
Originally Posted by Sentraguy
to see if I can keep my gas mileage the same (38.5~) and still have the rack.
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Short answer: not possible.
A roof rack adds to frontal area
and increases the vehicle's drag coefficient. Even side rails alone will do this. So your fuel economy
will decrease, and the question is: how much?
Answer is: it depends on the vehicle & the rack design.
FYI, I've "tested" (not vigorously; judge the data for yourself) racks on two vehicles:
Edit:
Note the speeds of the tests; the faster you drive, the larger the % change will be.
1998 Pontiac Firefly (Geo Metro - 1.0L 3cyl - 5 spd manual)
@ 88 km/h (54.7 mph)
- 55.2 mpg (US) = no roof racks
- 48.2 mpg (US)(-7.0 mpg / -12.7%) empty roof racks (fixed rectangular cross bars)
- 40.1 mpg (US) (-15.1 mpg / -27.3%) roof racks with mountain bike
Details:
Mini-experiment: the wrath of roof racks - MetroMPG.com
2005 Pontiac Montana (3.x L V6 automatic)
@ 88.5 km/h (55 mph)
33.7 mpg (US) - racks off (including side rails off)
32.8 mpg (US) - racks on (-0.9 mpg)
Details in this thread:
http://ecomodder.com/forum/showthrea...-6-a-6069.html
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I think these may represent extreme examples. If I had to guess, I bet your results would fall somewhere between the two.
So instead of modifying the racks to permanently attach them to the car, I would recommend designing some kind of mounting plate/hardware that you can get the racks on & off fairly easily.