How to improve the aerodynamics of a roof rack

Submitted: Friday, Mar 14, 2003 at 21:52
ThreadID: 3854 Views:5335 Replies:8 FollowUps:7
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I have read that the cost wind resistance of a roof rack results in about 25% worse fuel consumption. That is about as much as a trailer.
Are there any cost effective ways to create an efficient airflow? I have thought about a piece of perspex bolted to the rack protruding forward at an angle of 30 degrees off the horizontal. Any comments or other suggestions would be appreciated.
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Reply By: Truckster - Friday, Mar 14, 2003 at 22:06

Friday, Mar 14, 2003 at 22:06
I find the best way with mine is to leave it at home.

Ive tried 4in round pipe on the front, the white stuff plumbers use, the perspex idea but still its a parachute.....
Im actually going to look for ex army trailer... that would do, should be cheap and solid.
AnswerID: 15221

Follow Up By: Member - Alan- Friday, Mar 14, 2003 at 22:59

Friday, Mar 14, 2003 at 22:59
Unfortunately I cannot leave it at home. I need both the rack and the trailer as I am going for six months with family of 5.
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FollowupID: 9261

Follow Up By: Truckster - Friday, Mar 14, 2003 at 23:15

Friday, Mar 14, 2003 at 23:15
Try the pipe, its the cheapest way to start with then.

if not happy go to a perspex place nad get a chunk and try that.

There isnt much else, or an Air dam ala 1967 Fords on a roofrack bar, or like old farts with Falcodores with a mobile road block (caravan) on the back.
Good luck on the trip anyway!
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FollowupID: 9265

Follow Up By: Graham - Saturday, Mar 15, 2003 at 20:39

Saturday, Mar 15, 2003 at 20:39
Typical Truckster response......bag the crap out of something/someone and give an absolute stupid response........(stepping down off my soapbox now) Alan, not sure if you use one, but I have seen solar cells being used as wind deflectors that are set up on an angle in front of the roofrack. They say that all good camping gear should have 2 uses.
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Follow Up By: Truckster - Sunday, Mar 16, 2003 at 00:25

Sunday, Mar 16, 2003 at 00:25
Hey Graham know what you can do with your soap box? use the soap so it doesnt hurt as much.


I gave him a genuine response that others have done in the past... Hope you dont get too many splinters.
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FollowupID: 9298

Reply By: Voxson - Friday, Mar 14, 2003 at 22:08

Friday, Mar 14, 2003 at 22:08
If you sit on 90kmh... That helps heaps..
I figure if i have my roof rack on that i am in no hurry......

Regards........

PS.. But that doesnt help you much,, it is just my 3½ x 22mm² bits worth._____________________________________________
Countin the days till July 5th. *Cape York Trip*
_____________________________________________
AnswerID: 15222

Reply By: brian - Saturday, Mar 15, 2003 at 06:58

Saturday, Mar 15, 2003 at 06:58
Alan, i have full length alloy rack on gu patrol, i fitted a perspex deflector but larger than the original,mine goes from half an inch from the roof and extends two inches above the rack,this eliminated any wind noise from the rack. by the way my 3.l turbo,manual averages 8.5 k per litre around town with winch bull bar and heaps of other weight.from other postings on this forum this consumption seems about normal,that being the case the roof rack doesnt appear to have that much effect .certainly not 25 %
AnswerID: 15243

Follow Up By: Member - Bob - Saturday, Mar 15, 2003 at 08:23

Saturday, Mar 15, 2003 at 08:23
That sounds like pretty good set-up Brian. I wonder if making it a bit higher so as to deflect air over the load as well would make it even more effective? The alternative would be to place all your load in one or two of those fibre glass boxes from Thule. They look like they'd cut through the air like a hot knife through butter. With regard to fuel consumption, you would't expect much penalty at low speeds around town. You'd expect wind resistance to increase exponentially with speed (maybe 4 times as much at 120 kph as at 60 kph).
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Reply By: brian - Saturday, Mar 15, 2003 at 11:08

Saturday, Mar 15, 2003 at 11:08
Bob,i should have been more clear the consumption i quoted applies around town and on highway at around 100k/h im on east coast and travel through small towns with streches of highway in between eg wollongong to bega.
AnswerID: 15253

Follow Up By: brian - Saturday, Mar 15, 2003 at 11:12

Saturday, Mar 15, 2003 at 11:12
Bob,i forgot to mention i feel it is just as important to bring the deflector as close to the roof as possible as it is to have it reasonably high,just my thoughts.
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Reply By: Bruce from Budget Signs - Saturday, Mar 15, 2003 at 17:51

Saturday, Mar 15, 2003 at 17:51
Gday alan
dont know what state you are in but if you are in perth let me know becauce we through out lots of old perspec so i might have some around you can have if thats the way you decide to go
Regards BruceBudget Signs
AnswerID: 15269

Follow Up By: Member - Alan- Tuesday, Mar 18, 2003 at 21:33

Tuesday, Mar 18, 2003 at 21:33
Bruce thank you for the kind offer. I am in Sydney now and will not get to Perth until Aug/Sep. Thanks again.
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FollowupID: 9423

Reply By: Member - Willem- Saturday, Mar 15, 2003 at 20:39

Saturday, Mar 15, 2003 at 20:39
To improve the wind flow over your roof rack you need to cover the complete underside of the rack with either an aluminium sheet or light timber and adding a perspex or light tin/alloy curved foil at the front of the rack also helps with the drag. Open plan roofracks grab hold of the wind in every nook and cranny. After many years of roofracks I have turfed mine and enjoy a 20% decrease in fuel consumption. Fitting the stuff off the roofrack and into the vehicle was a nightmare.Cheers, Willem
Never a dull moment
AnswerID: 15272

Reply By: Member - Alan- Sunday, Mar 16, 2003 at 10:21

Sunday, Mar 16, 2003 at 10:21
Many thanks everyone.
I will go with the perspex - Poly carbonate - and relpy in a months time when I have tried it out.
Alan
AnswerID: 15303

Reply By: dougie - Monday, Mar 17, 2003 at 19:59

Monday, Mar 17, 2003 at 19:59
I had the perspex and a stone bleep tered it. I am about to go to a piece of 2 ml aluminium and try and get it as close to the roof as possible, After watching the F1's, I should get down force and better handleing. HA HA!
But in theory is should work< if the air does not get under the rack,and it deflects over the load. and mine is 3/4 set at the back.
AnswerID: 15401

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