Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - Rear Wheel arch ducting to rear to minimise base drag??

Tesla · 04-01-2012, 08:51 AM

I've been looking at what to do with the rear end, being a solid axle 4x4 makes it hard to do the rear undertray/diffuser because of axle movement & towbar position & it is also hard to close off wheel arches to underside. I have read that the wheel arches develop pressure at the top and need to be ducted, and even more when I do the covers. Looking at all the mechanical mayhem in the area, there are large cavities going to rear of vehicle so I removed rear step today which has opened two slots about 1.5" high and about 3' long one between body and chassis crossmember and a lower one between chassis and tow bar. Before that the air from underneath was only exiting below towbar, the higher exit now is about 8" higher.
Will this help fill the vacuum at the back and reduce drag?
I went for a drive and it feels better, but you know how placebo works.
I am looking at designing a new rear bar & step, so want to begin the basis of a Kamm back style with it. The current bumper sticks out about 3" either side so if I taper the new one in from the wheel arch to skimm the body corner, it comes in at about 15 degrees and taking that line back about 6" should take about 8" out of the width at that point.
If I duct into the lower portion of the rear end, what effect will there be on the rear drag?

04-01-2012, 08:51 AM	#1 (permalink)
Tesla Master EcoModder Join Date: Feb 2012 Location: Australia Posts: 355 The Truck - '02 Nissan GU Patrol ST Thanks: 5 Thanked 76 Times in 50 Posts	Rear Wheel arch ducting to rear to minimise base drag?? I've been looking at what to do with the rear end, being a solid axle 4x4 makes it hard to do the rear undertray/diffuser because of axle movement & towbar position & it is also hard to close off wheel arches to underside. I have read that the wheel arches develop pressure at the top and need to be ducted, and even more when I do the covers. Looking at all the mechanical mayhem in the area, there are large cavities going to rear of vehicle so I removed rear step today which has opened two slots about 1.5" high and about 3' long one between body and chassis crossmember and a lower one between chassis and tow bar. Before that the air from underneath was only exiting below towbar, the higher exit now is about 8" higher. Will this help fill the vacuum at the back and reduce drag? I went for a drive and it feels better, but you know how placebo works. I am looking at designing a new rear bar & step, so want to begin the basis of a Kamm back style with it. The current bumper sticks out about 3" either side so if I taper the new one in from the wheel arch to skimm the body corner, it comes in at about 15 degrees and taking that line back about 6" should take about 8" out of the width at that point. If I duct into the lower portion of the rear end, what effect will there be on the rear drag?