Wind deflector on roofrack

Submitted: Thursday, Mar 06, 2008 at 22:54
ThreadID: 55274 Views:9832 Replies:6 FollowUps:4
This Thread has been Archived
Just bought and fitted a second hand "Lowline" roofrack on my Pajero. At the front is a set of angled bars where a wind deflector is meant to fit - the original owner said he removed it as he didn't like it, but it wasn't clear why he didn't like it.

Do they make a difference to fuel economy when fitted? Noisewise, I can't hear any addition wind noise from the roofrack, empty, travelling at 100kmh - I haven't had a load up there yet to test any noise when loaded. Is the wind deflector more useful when travelling with a load up top? Or just a placebo for people who think they need them?

I know semi trailers have them on top of the cab, but that's because there's a metre high flat facing trailer poking about the cab...
Back Expand Un-Read 0 Moderator

Reply By: Member - Graham H (QLD) - Friday, Mar 07, 2008 at 00:14

Friday, Mar 07, 2008 at 00:14
Ive just bought a s/h ARB rack and there is a certain amount of wind noise manly near the rear.
On being quoted $132 for the wind deflector I thought $4 for a pair of ear plugs or just turn the radio up would be cheaper. Any thing in the wind will make a difference to fuel economy deflector or not.
AnswerID: 291311

Reply By: Member - Dennis P (Scotland) - Friday, Mar 07, 2008 at 01:55

Friday, Mar 07, 2008 at 01:55
Mate, the wind deflector has nothing to do with noise, it is more about aerodynamics. Works well on a Semi and probably to a smaller degree on a 4by towing a van.
Any noise you get from a roof rack is more to do with holes in the bar work causing a whistling effect.
AnswerID: 291318

Reply By: Wizard1 - Friday, Mar 07, 2008 at 09:08

Friday, Mar 07, 2008 at 09:08
Front wind deflectors on roof racks are a waste of time and money.

Think about it.

What happens when the wind is coming from the side?

What use is it when your roof rack is loaded and above the height of the deflector?

They are nothing but a placebo

AnswerID: 291348

Follow Up By: Member -Signman - Friday, Mar 07, 2008 at 09:25

Friday, Mar 07, 2008 at 09:25
Ahhh- why do race cars have air dams & spoilers..
Must be a placebo to make them look good !!

FollowupID: 556710

Follow Up By: Wizard1 - Friday, Mar 07, 2008 at 16:01

Friday, Mar 07, 2008 at 16:01
What an ill thought and naive comment from someone not qualified to make it.

You obviously know very little about areodynamics and why race cars use such devices.

Maybe if you did then you would realise that the downforce effect a spoiler or air dam produces to a car doing 200 km + has very little relevance to a roof rack on a 4WD.

I guess a mobile brick like a troopie would display next to no aerodynamics and downforce.

FollowupID: 556776

Follow Up By: Member -Signman - Friday, Mar 07, 2008 at 17:09

Friday, Mar 07, 2008 at 17:09
Hey Wizard,
Please don't 'assume' my knowledge of aerodynamics...
You would be VERY surprised....
The relationship of a wind deflector on a roof rack is (almost) directly related to a spoiler on a race car. It's called the Bernoulli Effect.
When this discussion was on the forum a while back- I actually mocked up a deflector, with it's shape equating to a section of the top surface of a Cessna 172 wing. This was fitted to the vehicle (in this case a Hilux)- and after a few runs on the strip at Camden airport, the optimum angle was approximating the angle of the windscreen. Of course the positioning and roof clearance to the leading edge would have some effect on this result.
We also determined that bonding the leading edge onto a 50mm tube gave even a more dramatic reduction on drag...
I still have the rig, and if you are slightly interested (or could understand the principle) I'd be happy to post.

FollowupID: 556787

Reply By: Member - Oldplodder (QLD) - Friday, Mar 07, 2008 at 10:04

Friday, Mar 07, 2008 at 10:04
I have a full length rack on my pajero.

It costs me 2 to 3l/100k in lost economy, depending how hard I push the speed. Big difference between 90 and 110 :O0

Was looking at fitting a deflector, since I noticed a lot of dead insects on the front of the rack when travelling.

But what I found worked best was moving the rack back a bit so it was behind the line of the windscreen by about 100mm. That way the air rising off the front of the car tended to go over the rack instead of hitting it. Reckon moving it made about 1l /100k difference.

At first I was tending to have the rack as forward as I could get it to distribute the load more evenly between front and back. Was nosier empty further forward too, so it must have been costing fuel.
AnswerID: 291361

Reply By: The Geriatric Gypsies - Friday, Mar 07, 2008 at 10:13

Friday, Mar 07, 2008 at 10:13
when towing my van and have the rack on i run 2 deflectors 1 on the front and 1 at the back to push the air over the van
does it help i believe it does
we have been towing vans for over 20 yrs and the same big deflector has been adapted to suit a variety of cars and 4bs and even with wind from the side or passing trucks i still believe it works

steve aka gg
AnswerID: 291363

Reply By: Member -Dodger - Friday, Mar 07, 2008 at 17:29

Friday, Mar 07, 2008 at 17:29
We have a full length ARB steel roof rack on the Patrol with a wind deflector and yes it did make a difference. Without the Deflector the fuel economy was increased by 4ltr/100k with the rack loaded and with the deflector this was decreased by 2tr/100 with loaded rack in other words an increase of 2ltr/100 over the vehicle without roof rack. all this whilst towing a 1.8t pop top off road van.The real gain however was that the dust was kept off the gear on the roof plus little dust got to the van.
As when we are on dirt or gravel roads there is a lot of dust to travel through when passing another vehicle in the opposite direction. Therefor for us it was Worth the exercise.
I used to have a handle on life, but it broke.

Cheers Dodg.

Lifetime Member
My Profile  Send Message

AnswerID: 291416

Follow Up By: Scubaroo - Friday, Mar 07, 2008 at 22:09

Friday, Mar 07, 2008 at 22:09
Thanks - those are meaningful figures. We're primarily going to use the rack for carrying a spare, and maybe firewood (without overloading it). The leading bottom edge of the rack is already mounted about 35cm back from the windscreen, but I can't move it to adjust anyway.

Haven't had it fitted long enough to notice a difference in economy, I guess if the economy skyrockets I'll knock up a test deflector and see if it makes a difference. Given it's mounted so far back I'll leave it be for now.
FollowupID: 556861

Sponsored Links

Popular Products (11)