More on wind deflectors

Submitted: Monday, Mar 10, 2008 at 11:05
ThreadID: 55390 Views:2458 Replies:8 FollowUps:7
This Thread has been Archived
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
I'll get there someday, or die wanting to.

Member
My Profile  Send Message

Back Expand Un-Read 0 Moderator

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.



AnswerID: 291895

Reply By: Member - Doug T (FNQ) - Monday, Mar 10, 2008 at 11:56

Monday, Mar 10, 2008 at 11:56
Indycars produce downforce equal to their weight at 190 km/h (118 mph), while an F1 car achieves the same downforce:weight ratio of 1:1 at 125 km/h (78 mph) to 130 km/h (81 mph), and at 190 km/h (118 mph) the ratio is roughly 2:1. Therefore, theoretically, F1 cars can drive upside down from 130 km/h (81 mph).[3]

.
still going strong with 836,179 K's

Lifetime Member
My Profile  My Blog  Send Message

AnswerID: 291898

Follow Up By: Member -Signman - Monday, Mar 10, 2008 at 12:21

Monday, Mar 10, 2008 at 12:21
A bit O/T Doug- but what did ya think of Paul Morris' comments..
To be in V8 Supercar- it helps to have a PHD (Parents Have Dough).

0
FollowupID: 557254

Follow Up By: Member - Doug T (FNQ) - Monday, Mar 10, 2008 at 12:49

Monday, Mar 10, 2008 at 12:49
Signman
Spur of the moment comment I feel, what was Courtney suppose to do when one gets shunted , Paul will when he see's the replays and and gets the officials report he'll settle down,
Was pleased with RK's performance too,but at the same time happy to see DJR getting results, even if I am a Holden supporter.
Well he is a Queenslander after all .

.

.
still going strong with 836,179 K's

Lifetime Member
My Profile  My Blog  Send Message

0
FollowupID: 557260

Follow Up By: Member - Roachie (SA) - Monday, Mar 10, 2008 at 13:43

Monday, Mar 10, 2008 at 13:43
I'll bet he was a bully at school!!!!
0
FollowupID: 557261

Follow Up By: Member -Signman - Monday, Mar 10, 2008 at 14:41

Monday, Mar 10, 2008 at 14:41
Sorry, this should've been a follow up- not a reply..

With Morris- it's not his money. It's the family bucks that supports his racing...
Same with Murphy, Weel (when he was around) The Kelly boys, Bright etc.

0
FollowupID: 557272

Reply By: Member -Signman - Monday, Mar 10, 2008 at 13:49

Monday, Mar 10, 2008 at 13:49
With Morris- it's not his money. It's the family bucks that supports his racing...
Same with Murphy, Weel (when he was around) The Kelly boys, Bright etc.
AnswerID: 291913

Follow Up By: Member - Doug T (FNQ) - Monday, Mar 10, 2008 at 16:01

Monday, Mar 10, 2008 at 16:01
Signman
Don't forget the money from Sponsers.


.
still going strong with 836,179 K's

Lifetime Member
My Profile  My Blog  Send Message

0
FollowupID: 557276

Reply By: Member - Mike DID - Monday, Mar 10, 2008 at 14:24

Monday, Mar 10, 2008 at 14:24
Turbulent airflow really increases fuel consumption - the idea of the deflector is to prevent the turbulent airflow caused by the flat front of a roofrack. That's why semi-trailers have the deflectors on the cab roof.

The reason sports car have an airdam below the front bumper with minimal ground clearance, is because the airdam improves power and fuel-economy by reducing turbulent airflow underneath the car.
AnswerID: 291916

Follow Up By: Member -Signman - Monday, Mar 10, 2008 at 14:39

Monday, Mar 10, 2008 at 14:39
You sure about Paragraph 2?????
"the airdam improves power" etc..

0
FollowupID: 557271

Follow Up By: Member - Mike DID - Monday, Mar 10, 2008 at 17:15

Monday, Mar 10, 2008 at 17:15
. . . . ok, to make it clearer "it reduces power losses resulting from drag."

(I'm not suggesting it works like a Hiclone !!!!!!)
0
FollowupID: 557285

Reply By: Member - Kiwi Kia - Monday, Mar 10, 2008 at 15:27

Monday, Mar 10, 2008 at 15:27
An air dam, deflector or airfoil can all be totally different items. A simple deflector may not cause any down pressure to be added to the vehicle. It may (as has already been suggested) just smooth out airflow and reduce drag to give added km/l or it may just deflect some air to reduce the swirling dust comming in behind the vehicle. I know of one vehicle where a small bead on the front of a roofrack bar has now reduced the wind noise to a bearable level, it used to be a real howler. Experiment and see.
AnswerID: 291932

Reply By: Member -Dodger - Monday, Mar 10, 2008 at 17:25

Monday, Mar 10, 2008 at 17:25
The air Deflector on my nissan is in line with the windscreen angle and as it is only 20mm above the roof at the bottom keeps the air that is forced up by the windscreen even higher thus helping and not really creating extra load. I think it is the opposite in actual fact. Just from my personal experience see pic below in members rig and profile.
I used to have a handle on life, but it broke.

Cheers Dodg.

Lifetime Member
My Profile  Send Message

AnswerID: 291951

Reply By: spudseamus - Monday, Mar 10, 2008 at 18:27

Monday, Mar 10, 2008 at 18:27
i was involved many yrs ago on evaluating those big prime mover air deflectors --you know the ones 3 curved sided thing that sat on top of the prime mover. Well on a trip to say Perth from Melbourne there was a fuel saving but was balanced by the wear on the steer tyers so in balance i would say theres better savings made by knocking 5 to 10 ks off your normal speed
AnswerID: 291961

Reply By: time waster - Monday, Mar 10, 2008 at 18:46

Monday, Mar 10, 2008 at 18:46
On our d/cab lux we had a caged rack 1200x1800 and we did two trips to pt lincoln and on one of them I made a wind deflector and I got an extra 70km out of the tank of juice which the tank held 65lt.

There was no noticeable difference in the wind conditions outside.

Christian
AnswerID: 291969

Sponsored Links

Popular Products (14)