Suggestions for My Jetta's Rear End?

[MetroMPG]

Keep in mind that nascar may not be the ideal place to look for aero mods that will improve fuel economy. They're using aero to generate downforce (reduce lift) more than anything else, and that comes at the expense of fuel economy.

E.G. the extreme angle rear deck spoilers are meant to reduce rear lift at high speed, not smooth out airflow. How many solar racers have you seen with big spoilers on the back?

If you were going to modify the deck lid, I'd go more for a horizontal extension, or raising the deck height, rather than a spoiler.

[northboundtrain]

Originally Posted by MetroMPG

If you were going to modify the deck lid, I'd go more for a horizontal extension, or raising the deck height, rather than a spoiler.

Okay, good. This stuff is all new to me. Makes sense that the deck spoilers don't improve air flow sticking straigh up as they do. So I guess those type of spoilers on regular cars are mainly just for looks, huh?

How about the roof extension on top?

[trebuchet03]

Originally Posted by northboundtrain

So I guess those type of spoilers on regular cars are mainly just for looks, huh?

How about the roof extension on top?

1) Ya, for the most part
2) Yes - that should help flow separate cleanly

[Dynamically Aero]

Originally Posted by trebuchet03

2) Yes - that should help flow separate cleanly

This made me think of two treatments AMC used on the Javelins.

In 1969 they had the Big Bad Javelin option which included a roof-mounted hoop-style "wing".

When they changed the cars for 1971, the trailing edge of the roof now had a little lip. Here are a few photos of the 1971's roof lip.

The question is, were they merely cosmetic or was some real science involved?

[trebuchet03]

Originally Posted by Dynamically Aero

This made me think of two treatments AMC used on the Javelins.

In 1969 they had the Big Bad Javelin option which included a roof-mounted hoop-style "wing".

When they changed the cars for 1971, the trailing edge of the roof now had a little lip. Here are a few photos of the 1971's roof lip.

The question is, were they merely cosmetic or was some real science involved?

Hrmmm.... the spoiler on this one looks rather pronounced. But the roof winglet/lip doesn't look like it protrudes too far. The question is -- why would you want to separate flow at that point with that large spoiler?

This seems easy enough to test with cardboard and tufts - perhaps a little oil (thick) on the rear windshield.