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Old 12-30-2007, 03:53 PM   #1 (permalink)
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Glides like a Brick Wall (Jeep Cherokee, GMC Pick-up)

How large of a factor is vehicle aerodynamics as compared to engine size, driving style, gear ratio and all other factors that influence fuel economy?

I am thinking that Aerodynamics is indeed THE largest factor; ESPECIALLY when the vehicle is grossly underpowered as most 'fuel efficient' vehicles seem to be these days.

Between my wife and I, we have two vehicles:

1) a 1999 Jeep Cherokee Sport 4x4 w/ 4.0L inline 6 cylinder engine - 70k miles

2) a 1992 GMC Pickup, 4x4, 5.7L engine - 160k miles

The Jeep gets around 17mpg, whereas the old truck gets about 10.

It's tough out here in the sticks, because the nearest plowed road is about 3 miles away, creating some serious snow between us and town. I had to get rid of my precious Monte Carlo, that I had up to 32mpg (sticker only said 29 when it was new, AND even with 278,000 miles, I got 32mpg!).

Anyway, aside from those three miles, these vehicles suffer from "pushing a wall of wind" syndrome. The truck plows through it better I think, as it's engine is more appropriately scaled for the weight / size of the vehicle. The Jeep, though it has a lot of torque and power, has a tough time pushing the air efficiently when you get near freeway speeds (70-80mph in Michigan), and their fuel economy suffers. I think the last time I checked, the GMC pickup gets about 7mpg at those speeds.

Okay, I look forward to your responses!


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