rear wheel venting after fitting skirts, any value in it?

[Tesla]

I am just about happy with the mods on the front end, into version 3.2 now, have partial front skirts fitted and have been looking at what to do with the rear end, at this point considering a small Kammback 6-12 inches on sides and top, diffuser is an issue as the tow bar position restricts this to a max of about 6 degrees, but need to decide exactly how the rear underside and rear wheels will vent before starting on the kammback. I have material ready for the rear skirts, but wondering if I should allow for venting into the rear cavity or just let the air find its own exit.
Being a 4x4 the rear wheel cavities could house a bat colony so there is quite a bit of air tossing around in there, there are also large gaps in the inner guards that let air flow into the rear underbody above fuel tank and around the chassis. I have seen some designs which have special vents to jet out rear wheel air at the back and help with clean seperation.
The easiest solution is to open up the rear underside and let the air flow out under and over fuel tank, towbar etc., but is this the best option?, thinking the answer may be no, but to block all the holes above towbar would drop the air release from the underside at pretty much axle height and this doesn,t seem right either.
So what to do??

[arcosine]

Every time the air is deflected it loses momentum. You want it to flow over a smooth surface, like a dolphin, fish or goose.

[aerohead]

I'd just let the air find its own way out.

[Tesla]

Ok,
So plan is to close off larger gaps on inner guards down to chassis level which is the effective underbody level, then position exterier skirts which are at about same level, maybe lower, rear wheels already have flat covers and let the air go either under or to the outer side whichever the prefference is. I will be looking to streamline a flat underbody from the rear axle to the tow bar down the track as well.

[BamZipPow]

You can kinda see what I did on mine...


My rear wheel skirt thread...
http://ecomodder.com/forum/showthrea...ors-16417.html

[Tesla]

I have been following your progress, and nice work it is.
I assume you have removed mudflaps so the air kicked up by the tyres are channeled to the narrow gaps either side, I remember reading that you dropped in an inner seperator using corroplast sheet to try keep the air from the tyres seperate to the underside until it exits at the rear.
Mine is a wagon, but the lower end is much the same except I do not plan to go as low as I need to maintain some offroad capability but there is already an existing natural channel between the outer line of chassis and the body overhang which I may utilise to do something similar, but the centre section will be closed off in much the same fashion as you have done.
So I am assuming your recent mpg improvements from 23.5 to 25.5+ are primarily due to the rear wheel improvements, yes?
Mine sits around 21 and I'd like to get up to 25, but with the boxy rear, gonna be hard without throwing a major boat tail on it, but that would then kill any offroad capability.
I will do a small Kamm/Boattail and see how that goes, still thinking about and following threads with ideas of easily removable/colapsable/inflatable units.
Keep up the good work.

[BamZipPow]

The rear mud flaps are still in place. I needed something to support the rear wheel strakes on the front end. The inside part of the rear wheel strake is still open...so air will still turbulate between the rear strake and the rear skirts. I'll have to button that up at some point and see what differences it will make down the road. During my 35mpg run (May 2011), I didn't have any rear strakes at that time...but I did have a rear diffuser extension and rear skirts.

I'll have to snap a few piccies when I git the rear end back up on the ramps and it's not raining.

Besides the higher prices fer gas from last year, differences this year were:

pulled the top of the back end of the aero cap in tighter by 12" which added back in the side slopes from my 35mpg run
added rear wheel strakes (last year's drive had none)
added full rear wheel skirts (last year's drive had none)
blocked the lower air dam vents (last year's drive had a air dam mustache fer the first half of the drive)
improved the cab-to-cap gap cover (last year's drive gap cover didn't work out very well and I had to resort to tape.
2 extra passengers along with their luggage/stuff (about 350lbs)
multiple extra stops fer passengers
cleaned the catalytic converter

I might have to experiment with just the upper rear wheel skirt (wheel fairing?) instead of the full skirt setup and see how that turns out.

2011 35mpg run...


2011-12 Tampa drive...


2012-13 Tampa drive...

[BamZipPow]

You can see the gap between the rear wheel strakes and rear skirt here...