More on wind deflectors
Submitted: Monday, Mar 10, 2008 at 11:05
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brushmarx
There was a thread last week (55274) where the merits or otherwise of wind deflectors on roof racks were discussed.
Comments were mixed and apparently the deflectors seem to both work, and not work, depending on the comment makers.
Irrespective of the possible savings in fuel economy, the down force of the deflectors must be adding to the effective weight of the vehicle and subsequent
suspension, friction and tyre wear.
I would suggest that one and a half square metres of deflector at 45 degrees at say 80 km/h would have to add heaps of kilograms of downforce. The dead weight of the roof load could be doubled or worse with the added live load of the deflector.
Any comments or theories in this subject?
Cheers
Ian
Reply By: Member -Signman - Monday, Mar 10, 2008 at 11:23
Monday, Mar 10, 2008 at 11:23
The key word in your post is 'deflector' .
The object of the exercise is to migrate the air away from the cross bars and the side rails of the rack- and the load.
The effective angle of the deflector varys at various speed. At, say, 50kph, an angle of 15 deg. at 80 this angle increases to about 35 degs, and at 100kph 40 degrees.
IF the deflector is set at the optimum angle at the desired speed, the is no down pressure- in fact it creates a slight lift.
In saying that, because we travel at 80 to 100kph- that would be the velocity to attain a static angle. Lower speed would not have the pressure to have any great effect on the steeper angle.
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