Roof Rack -Reducing Drag

[bc4r]

Hi There

I Have a 99 Toyota 4runner which I will later this year be taking on a fairly extensive overland trip, Now due to the amount of equipment I'm taking I will be using a roof rack which will have a spare wheel on it and some low profile lightweight boxes.

I have been looking around on the web for any information about lowering the drag with out any success and was wonder if anybody has any tips or links they could share, the only thing I've done so far is replace the rack support towers to get it as low to the roof as possible.

The Rack is a Surco chosen because it aluminum.

Thanks in advance

G

[Frank Lee]

Someone, either here or I think at gassavers, went on at length about building an "aero cap" for hauling stuff- I think it was on the roof of a k-car?- and they claimed vast improvements over hauling the same junk uncovered.

[MetroMPG]

I seem to remember a thread like that. But weren't they saying something like it got improved fuel economy with the covered junk up top? I didn't put much stock in what they were saying.

Lowering the rack is a good first step. If you HAVE to carry stuff on the roof (do you? What about a rear hitch style box?) take the same steps as designing anything else for good aero:

- minimize frontal area
- round the leading edge
- enclose with a shape that approximates a tear drop
- taper in plan and profile at the rear if possible

Sorta like this:

[MetroMPG]

test - ignore

[bc4r]

Thanks for the info I'll have a dig around for that old thread, i was thinking just maybe putting an inclined wind deflector in front of the rack might help anyone have any experiences in doing that.

On the subject of rear hitch mounts they are fairly small so not so versatile and also as we are going to live in the 4runner during the trip they have to be removed every time we need to get to the rear hatch, which as that area doubles up as our kitchen/bathroom/living room would be a major pain on a 6/7 month trip although i do agree the lower drag option, also from time to time we are going to be carrying gas which i don't want hanging off the rear bumper.

Thanks

G

[winkosmosis]

Ask in this thread on expedition aerodynamics Expedition Aerodynamics, MPG and Sleeping in Your truck - Pirate4x4.Com Bulletin Board

[winkosmosis]

BTW, you see those crossbars? Thule makes a deflector that attaches to theirs. I don't know if it would work. I got a set of crossbars and deflector with my Jeep when I bought it, but I think I have it in storage so I can't examine it.

Found them for sale:
2009 Thule 872XT Fairing - 44 inch. Large Roof Rack Wind Deflector

[bikin' Ed]

I'd haul a trailer. It could improve your overall aerodynamics while only adding slightly to rolling resistance.

When I used to haul bicycles on the roof, the fairing made by the rack manufacturer (Thule) did seem to help. I do not have any hard numbers.

[lunarhighway]

the most practical approach, and keeping everything that has been said before in mind would be to arrange all the cargo in a semi aerodynamic shape, and than enclose everything with a fabric cover... perhaps with a rig like solid airdeflector at the front... if you could hinge this at the front you could even adjust the angle for
the load. perhaps a foldable convertable like cover would be handy...but it would require some skill to put together... a little attention could pay off though over a long trip.

[MetroMPG]

Lots of ideas, anyway!

And, yes, a deflector would help a small amount if the stuff it's ahead of is aerodynamically dirty.