X-AWDriver

That's a generalization of vehicles but not every car is designed the same ( a Vette or Porsche is not being affected by aerodynamic drag the same as a Cavalier is at 60) so spoilers in particular work differently on all cars. Now a spoiler on say your average grocery getter with 200hp isn't going to benefit from a small spoiler across the back but an EVO or Subi STi sans spoiler will see differences around 130mph on long straights of a road course and I've driven two types of last gen Integras,once GSR and the rare Type R with it's taller spoiler and at 130mph the difference is more than you'd expect.

I also don't think you can guess how many MPGs you lose from adding things to your SUV like lights and such (unless you have an arsenal of stuff on your roof) if you drive mostly around town and only highway driving would really be affected. MY mpgs have not changed since I added my bug guard and when I use my Yakima Load Warrior rack I might have documented maybe 1mpg loss. I always average 16-17mpg but it is affected more by heavy acceleration and whether I use the AC or 4wd and that does make a diff.

jposey66

X,
I think the 130 MPH line is true for spoilers that are being used for downforce, but a wind deflector, that is diverting air into the negative pressure area works at much slower speed.

Flamedx4

Sure, anytime you make statements like that it's a generalization. But I wasn't "guessing" about the generalized mpg losses for add-ons. It's been tested and tested and well documented. And yes, a Cavalier and a Vetter are affected exactly the same as the same speed - body shapes just deal with it with different effeciency... But in simple to remember rule-of-thumb terms, most any add-on on a car will cost you 2mpg. Can be more if it disrupts the overall airflow over the whole vehicle (like a Yakima ski rack on a Vette might do) and can be less if the vehicle is not aerodymic anyway (like a Yakima rack on an H1) Even your side mirrors will net 1 to 2 mpg if you took them off.

Years ago the standard firebird body was considerably faster (top speed) and stable (controllable at top speed) than the transam, those bad-boy looking spoilers did not aid anything and simply caused drag, but they looked nice. Race cars looked substantially different, and of course get horrible mileage too! Now days of course we design things better, but the basic rule still applies. Look at modern cars like the Vette Z06, see how very tiny the rear spoiler is and the front air dam is not a flat wall but has a lip (spitter) and the bottom. But then, it's capable of 200 mph-ish. 130 mph isn't fast enough to 'need' extra downforce - hell I used to drive my 4Runner at 100 and I've driven my F150 at 120 and it's rock stable, a WRX better be stable at speeds above those!... A spoiler may help the car feel more planted - but it still comes at the expense of drag - drag that starts to add up at lower speeds (around 60) and must be overcome with extra fuel at any speed above that. You don't get the benefit for nothing.

And certainly, if all your driving is in town aerodynamics don't much matter.

makakio

I haven't done it, buit I'd bet the deck plate mod would help. It just seems right - truck breathes easier (rather than wheezing along) - it's got to increase MPG some...

bob200587

yea, I have no muffler, mud terrains, the beloved W-series gear whine, very slight driveline vibration, no carpet or padding anywhere in the truck, so going fast just doesnt make sense, Not to mention I gotta keep the pedal most of the way depressed to keep up 80mph. Def. Not worth it. If I wanna drive fast, I'll buy a sports car.

sandcrawler

like most, i find it best to stay on top of routine maintenance, and stay light and easy on the gas pedal. tire pressure, wind drag item removal (roof rack), that kind of thing. keep your fuel system clean with techron or the like...

paddlenbike

iTrader: (1)

After putting 155,000 miles on my 3.0 V6/5 speed I found the mileage was best by keeping the RPMs up with a light foot on the throttle. In other words, 3500 RPMs in 4th gear on a hilll versus a heavy foot in 5th gear. I managed to get considerably higher mileage when driving it this way.

My 3.4 5-speed is nearly the opposite. The engine makes more torque down low than the 3.0 (top end is weaker though) and it doesn't seem to mind climbing hills in 5th gear at 2500 RPMs. I get better mileage by NOT using cruise control--I tend to let my speed increase on a downhill and use less throttle on the next hill--I might loose a few MPH by the top but I'm usually slightly over the speedlimit anyways. Cruise control would simply bury the throttle on the hill to maintain speed.