Wheel on Bonnet = Aerodynamic improvement

[rrturboD]

Here is proof, for those who want to read it all I have attached the full South African University research paper, ....for the rest of us here is the main findings:

"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 (Ed: ute)."

[jakeslouw]

Some countries study the Higgs boson......

we study the IMPORTANT STUFF! :p :D

[TimNZ]

"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 (Ed: ute)."

Wow! I knew roof racks didn't help your fuel economy, but think of how many vehicles you see getting around with empty roof racks on :eek:

[Davo]

Whew! What a read. They really should make a snappy 2-minute Youtube video instead. :D That's great stuff, and well worth the work they put into it.

[superquag]

Wonder how much drag you'd get with a pair of RHINO racks (two single bars).


Dunno if I want a spare wheel on the bonnet of my Classic....:o

[newhue]

duno but it would be better than those big boxy roof tents.

[ugu80]

Dunno if I want a spare wheel on the bonnet of my Classic....:o
Try opening the bonnet with a spare wheel on it!:spudniklifter:

[jerryd]

Maybe that's why mine is so thirsty :eek:

[pop058]

Maybe that's why mine is so thirsty :eek:

I didn't think it mentioned chickens in the report :p

[460cixy]

That big cock on the bonnet would have to help

[JDNSW]

I have often thought about installing a set of vortex generators along the front edge of the bonnet on my 110 - should have a similar effect to spare, but neither heavy nor blocking your vision.

John

[TheEntertainer]

Hi,

Thought you may find this interesting, well tha attached doc on the defender aerodynamics.

Cheers

The Entertainer

[p38arover]

Threads merged.

[pannawonica]

Thank you most interesting ! I have always beleived that towing a trailer empty or loaded was a more economical way of moving stuff. Generally on longer runs 1k miles I find it only increases fuel burn by around 1.5 litres per 100Km's. However I do understand trailers are not practical in all circumstances.:D:BigThumb:

[luke68]

Rhino Bars on my Disco is about 1.5-2L/100km worse off. Put them on for a while as I was carrying pipes and other stuff for renovations. After renovations left them on and after a while ( A few fills of the tank) I noticed that I was getting less out of a tank of Diesel than before. Took the Rhino Bars off and fuel ecenomy back to normal.

Cheers
Luke

[gusthedog]

I too have rhino bars. I was thinking of fabricating up a wind deflector that follows the roofline and lifts the wind over the bars. I have three bars and at the rear I was going to put a canvas bag on a platform when travelling. I was also thinking about designing a wing to push the air over said bag. Was thinking alloy for the wings. To get the shape of the roof I was going to use plastic conduit held in a wooden frame and then transfer this shape to the alloy to get the correct roofline. They quite often use conduit to get nice curves in home made boat building so I thought It would work in this application too.

Now if I can just finish of the fence, the veggie garden, put in a new back lawn, build a chook pen blah blah blah..... I'll have some time to make them!:D

[Hymie]

So am I better off having a road tread tyre or an off road tread tyre on the bonnet?
Will the blocks on the off road tyre create vortices that will affect consumption?

[Dougal]

Thank you most interesting ! I have always beleived that towing a trailer empty or loaded was a more economical way of moving stuff. Generally on longer runs 1k miles I find it only increases fuel burn by around 1.5 litres per 100Km's. However I do understand trailers are not practical in all circumstances.:D:BigThumb:

Here in NZ the legal towing speed is 90km/h and without 100km/h. I can tow an empty trailer at 90km/h and get exactly the same 10km/l as I get on the same trip with no trailer.

This experiment happened because I drove 500km with a trailer to get something that didn't arrive. So I drove 500km home again with the trailer in tow. I had to make the trip anyway, the trailer was the extra bit.

My best estimates of bikes on a bike-rack on the back is 1 litre/100km extra, bikes on a roofrack 2 litres/100km.

[Bush65]

Maybe that's why mine is so thirsty :eek:
Put the hen on the front and shackle 2 roosters back near the windscreen - should fly up the hills then :D

[460cixy]

Looks like I better get a spare wheel mount for the bonnet no where to mount it at all on the tray back gives me the ****s

[ramblingboy42]

Try opening the bonnet with a spare wheel on it!:spudniklifter:

did it nearly every day for years first parading vehicles in the army.

[Judo]

This document is amazing. Bumping for others to see who missed it in the past! :)

If you want to skip straight to the point, page 31 of PDF (which read page 21 on document page).

[simmo]

It's interesting I suppose, but a bit academic, the test was conducted at equivalent to 187km/hr, and the Reynolds number was fairly constant after 165 km/hr. It tells us what we already know; a roof rack increases fuel consumption, the actual percentage is not really accurate because most of us will rarely exceed 110 km/hr. It was interesting about the aerodynamic improvement with a spare wheel on the bonnet of the defender. It would not apply to many cars, because the defender has a fairly unique shape in modern times, and probably the poorest Cd of any car made in the last 25 -30 years. Volvo 2 series was often criticized for boxy (but practical) shape, & poor Cd. Volvos reasoning was Cd is a secondary importance to practicality for cars that spend most of their time below 100km/h. They must have got something right because it didn't stop them selling 2 series for 25 years. I notice on my tdi landy sitting on 95 -100kms hour with fully loaded 2.2 meter roof rack I still get less than 11 liters per 100km. I recently bought bonnet for carrying a spare wheel so I'm looking forward to an improvement. :D

[PhilipA]

Land Rover have always known that.
I was rereading an older LRO in the dunny, and came across an article by one of the Defender engineers who stated just that.
Regards Philip A

[gusthedog]

This thread has always cracked me up :D

Blokes who drive cars shaped like fridges worrying about aerodynamics :Rolling: :wasntme:

[DiscoDB]

This thread has always cracked me up :D

Blokes who drive cars shaped like fridges worrying about aerodynamics :Rolling: :wasntme:

...or turning the fridge into a brick.

Would have been fun to study.

But no test for spare tyre on bonnet plus short roof rack at back...can this cancel each other out?