Wind deflector on roofrack

Ahhh- why do race cars have air dams & spoilers..
Must be a placebo to make them look good !!

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.

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.

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.