The Effect of Vehicle-Roof Rack Configurations on the Aerodynamic Drag Coefficient

[PUCHG]

Hi

Please read this very interesting thesis done by a Stellenbosch student.

To express the technical impact of the research the results are first briefly
discussed. By placing a tyre (spare wheel) on the bonnet of a Land Rover
Defender decreases the vehicle’s aerodynamic drag by roughly 8%. The best
position for a short roof rack is at the most rear position on a vehicle. The addition of an unloaded roof rack can increase fuel consumption with roughly 21% for the Land Rover Defender and 26% for the Toyota Hilux Bakkie. All of this information shows potential to reduce the fuel consumption of vehicles carrying roof racks.

Download complete file here:

http://www.mb4x4.co.za/files/Roofrack_Report.pdf

username: 'user', password: 'u5er'

[PUCHG]

The interesting part is basically that the spare-wheel on the bonnet decreases the vehicle’s aerodynamic drag by roughly 8%, thus making fuel economy better by quite a margin.

This will also apply to a G. However I have only seen one G with a spare-wheel on the bonnet.

[Arnold Ross]

Hi Anton

Very interesting article. I saw in the conclusion what you are referring to.

Obviously - first price is not to have a roof rack at all! And that is what I always try and achieve! I think the same thing that they say about the best winch (the one on your friends car!) applies here! Last time we went to Mozambique I manage to get my brother to take my Jerry cans on his roof rack!

Thanks again for the link.

Regards,

Arnold

[Andrew]

Interesting.

Without the science my gut feel agrees. A have a lightweight roof rack that is a heavyweight fuel thief - even unloaded.

[Pete460332]

I have seen the devastating effects of a bonnet mounted spare wheel in the case of an accident. The wheel goes straight through the windscreen / A pillars and causing major personal injury. You don't want to that .

I have not read article yet but drag reduction will be dependent on speed so a fixed number is meaningless unless a speed is quoted.
Peter

[amzimmy]

I've seen some results of a "wind-tunnel" experiment some while back, that was tested on a G-Wagen. I can't remember and I can't find the article again, but the graphic was something like this, the best position would be about 25 to 30cm behind the edge of the windscreen surface:

btw. I do not challenge nor dispute the article!

amzimmy

[Doug Nel]

Strangely, my fuel consumption has not changed when adding my roof rack, RTT, 3 Jerry cans and 2 spare wheel. Not sure why. I have averaged 20-21l/100km in the 11 years that I have owned my G.

[Riaan Harman]

Strangely, my fuel consumption has not changed when adding my roof rack, RTT, 3 Jerry cans and 2 spare wheel. Not sure why. I have averaged 20-21l/100km in the 11 years that I have owned my G.

280GE thats the reason