I understand that the rear spoiler on the G3 coupe lowers body lift coefficient. Does anyone know if it may improve milage performance?

 

Highly unlikely. And considering the speeds you need to travel at in order for it to make a noticeable contribution, gas mileage would not be the priority for a winger-G. At conservative speeds, one would think it'd add drag and a little bit of weight, decreasing gas mileage.

The underbody diffusers, on the other hand, are supposed to lower drag coefficient. Assuming the effect is substantial enough to counter the added weight, that would improve gas mileage (and just about everything else).

It'd be nice if they didn't package these things together. If the underbody stuff is that effective, it ought to come with it stock. The winger is mostly for show, unless you take your car to the track (not a dragstrip or autocross, those don't get to high enough speeds long enough).

-Jack
Obsidian '03 G35 Sports Coupe
Titanium '03 MX-5 Shinsen #532

 

I agree it probably won't do much to improve fuel efficiency - but I would not say that it adds drag. The whole purpose of the spoiler and the diffusers is to reduce drag by .01 !!

G35 6MT/DG/Fully Loaded

 

The diffusers reduce drag. A rear spoiler's purpose is to use downforce to push the rear tires against the road. It must necessarily *create* drag by causing the air to push down on it as it rushes past. Anything you tack on to the top of the smooth surface of your hood or trunk is going to create drag simply by existing. A hood ornament creates drag. Bolt half a lunch tray to the trunk (not much different from the spoiler), that'll drag. The (simplified) reason adding things to the underside of the car reduces drag is because it's not a smooth surface underneath there.

Until you reach speeds where the rear of your car is being pulled off the ground, the rear spoiler is (very slightly) hindering your performance. That's why you see big huge wings on formula 1 cars, but not much of a spoiler on slower, heavier race cars. The huge wings you sometimes see on Civics are the height of hilarity, because they're adding all that drag and weight just to provide downforce to wheels that don't provide any power (or even help steer). Besides, they usually have 300 pounds of stereo equipment back there, so it ought to stay planted.

-Jack
Obsidian '03 G35 Sports Coupe
Titanium '03 MX-5 Shinsen #532

 

Civics can at least get up to reasonable speed.. Now Chevy Cavaliers, etc. with stock spoilers, THAT"S the height of hilarity!

<font color=green>GG</font color=green>

 

Not to take anything away from this post, but yesterday I saw an STI with about 1.5 feet high spoiler. It was a rectangular spoiler, which something like this:

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I was going to laugh my aS$ off, because that think looked hillarious.

 

True that smcallis.