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I just noticed that VW sells rear spoilers (http://www.cmgestore.com/vw08/SKUDetailsVW08F1KM071641U.ASP) for the Jetta. Is it worthwhile to get this for aerodynamic purposes? For the record, I'm averaging about 40 mpg at 55 mph on flat highway.

Another thing I noticed is that my fiance's 2000 Passat 1.8T has a lower drag coefficient than my car, not to mention that it has a smaller, more fuel efficient engine (which is good for her since she's the opposite of a hypermiler).

I just noticed that VW sells rear spoilers (http://www.cmgestore.com/vw08/SKUDetailsVW08F1KM071641U.ASP) for the Jetta. Is it worthwhile to get this for aerodynamic purposes? For the record, I'm averaging about 40 mpg at 55 mph on flat highway.

Another thing I noticed is that my fiance's 2000 Passat 1.8T has a lower drag coefficient than my car, not to mention that it has a smaller, more fuel efficient engine (which is good for her since she's the opposite of a hypermiler).
The aero penalty at 55 is minimal. A rear spoiler, whether or not you have one, won't make any difference at that speed.:flag:

Hi Jhu:

___Most of the rear lip spoilers that help reduce a cars Cd are very flat and kind of hang off the edge of the trunk lid vs. rising like the OWM VW one appears to do from your link. Let me try and find a pic of the AH’s (Accord Hybrid) or the HCH-I/II’s (Honda Civic Hybrid’s – Generation I and II) which were put into place and did actually reduce the CD by .01. On the AH it did anyway.

___Good Luck

___Wayne

Hi Jhu:

___I did not find any previous uploads so here are three new ones for you to look at. I do not know if the HCH-I or -II’s lip spoilers actually reduced Cd or not but I do remember reading a tech document from Honda that the AH’s was specifically placed on the back of it to drop the Cd by .01.

http://www.cleanmpg.com/photos/data/2/05_AH_-_05_HCH-I_-_09_HCH-II_Rear_Spolier.jpg
Top to bottom - 05 AH, 05 HCH-I, 09 HCH-II

___Good Luck

___Wayne

So I suppose it's not worth the $130 then.

As long as we're talkinga bout Hondas, what else did Honda do to get the Civic Hybrid a lower drag? The things I can see just looking at the parking lot where I work is the wheel covering and the rear trunk spoiler. They must have done something else too.

I wonder if that civic spoiler would fit on my del sol in place of the stock spoiler.

Hi Jhu:

___The HCH-II has more aerodynamic wheels and underbody panels to help smooth the flow underneath as well.

___Koreberg, I have no idea. Sorry about that :(

___Good Luck

___Wayne

I just noticed that VW sells rear spoilers (http://www.cmgestore.com/vw08/SKUDetailsVW08F1KM071641U.ASP) for the Jetta. Is it worthwhile to get this for aerodynamic purposes? For the record, I'm averaging about 40 mpg at 55 mph on flat highway.

Another thing I noticed is that my fiance's 2000 Passat 1.8T has a lower drag coefficient than my car, not to mention that it has a smaller, more fuel efficient engine (which is good for her since she's the opposite of a hypermiler).

As Wayne said above, the VW spoiler appears to be more of an aesthetic improvement, with minimal (if any) air drag reduction. Modern cars are designed on supercomputers using advanced CFD (computational fluid dynamics) algorithms. Generally speaking, the final shape of the car is "as good as it gets" for the design parameters (overall length, height, slope of front/rear windows, etc). Any manufacturer add-ons are typically for a better "look", or for sports cars, for more downforce. And most passenger cars today are designed for a coefficient of lift as close to zero as possible. Remember that lift or downforce both are forms of drag.

The reason the Passat has less drag than the Jetta is because it is longer yet about the same height. Very low drag numbers are tough to achieve on smaller cars. Consider that drag is, in essence, the resistance of the air to change direction. The shorter car will necessarily have to have a more upright greenhouse, nose and tail than a longer car with the same packaging requirements. The more upright surfaces mean the air that the car strikes must "move out of the way" faster. Technically speaking, the acceleration of the air is much faster, as it needs is pushed aside more abruptly by the upright surface moving through it. A more rounded roof and more slanted rear window will allow the air to remain "attached" to the upper body and flow more smoothly to the trailing edge of the trunk surface, where a sharp lip encourages the air to break away from the trunk surface with minimal turbulence. The spoiler lips shown above for the Hondas make that breakaway more abrupt, reducing the turbulence in the wake of the car, thereby bringing about an improvement in drag coefficient.

The ducktail trunk spoilers have the same basic principle, but are not as effective as the simple slat that the Honda uses. It appears to be a compromise between the flat-slat and the more upright angled spoiler that (in theory) creates downforce on the rear axle. With the low pressure / high velocity air on the surface of the trunk, any spoiler back there will not generate much downforce until well over double the limit posted on the interstate.

i would say not really at all, most are for look unless your driving a 911 gt2 on the nurumberg ring i wouldnt worry about it..