Jeep Aero mods testing - with results

[aerohead]

Originally Posted by AdrianD

Not much work done in the past two years, a newborn kid and building a house from the ground up took away my free time...


But now I have time to attempt a bit of rear aero cleanup...

This is after a 12 mile drive on a muddy road, with speeds under 30mph:


Jeep made a spoiler to help keep the rear hatch clean and people report it's helping:




Am I right thinking that if the hatch is cleaner, the rear wake is reduced, also reducing drag?

The price tag is around $150, so with 0.2L/100km gain (~2% improvement) it would pay for itself in 2-3 years at the current fuel price.

* The wing is forcing air over the roof to blow over the backlight, hopefully keeping some of the road spray from reaching the glass.
* In the past, measurements showed only drag 'increase' with such devices.
* The wing itself adds frontal area.
* And the wing has its own drag.
* To reduce drag, you'd blend a roof extension out as far as you dared, which included side extensions to box in that area, all the while providing a slight cross-sectional reduction along a streamlined path, generating pressure recovery. The only thing aerodynamics is about.
* You might take a look at the 1987 Renault Vesta-II concept, or Mercedes-Benz' Bionic Boxfish concept. The back of these two 'squarebacks' would be the gold-standard for streamlining.

[AdrianD]

Originally Posted by jimhs

I would remove the roof rack rails if I don’t use them rather than spending $

Do you mean the cross bars in the 2nd and 3rd pictures? Or the longitudinal rails? I've been driving without crossbars for as long as I had this Jeep, the cross bars only go on when I need to carry things.

Originally Posted by aerohead

* The wing is forcing air over the roof to blow over the backlight, hopefully keeping some of the road spray from reaching the glass.
* In the past, measurements showed only drag 'increase' with such devices.
* The wing itself adds frontal area.
* And the wing has its own drag.
* To reduce drag, you'd blend a roof extension out as far as you dared, which included side extensions to box in that area, all the while providing a slight cross-sectional reduction along a streamlined path, generating pressure recovery. The only thing aerodynamics is about.
* You might take a look at the 1987 Renault Vesta-II concept, or Mercedes-Benz' Bionic Boxfish concept. The back of these two 'squarebacks' would be the gold-standard for streamlining.

Understood, thank you very much for the details. I've got a spoiler off a first generation Cayenne which is fairly long, time to see how I can fit it, since I stashed it away hoping the jeep factory deflector would help.