Drag from roof box vs trailer
Submitted: Monday, Apr 23, 2007 at 13:53
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muzz63
Does anyone have any hard data on whether fuel efficiency/general performance is affected by carrying a roof box vs towing a trailer? I'd like to avoid the hassle of a trailer if I can but I've heard it argued that a loaded trailer still uses less extra fuel than a roof luggage box. I'm in a Forester so doing all road driving rather than serious off road.
Any help/advice is appreciated.
Cheers, Muzz
Reply By: Granpa Joe - Monday, Apr 23, 2007 at 16:09
Monday, Apr 23, 2007 at 16:09
It would depend more on the size of the roof top box as an eg:-I Used to take a tinny on the roof of my old turbo deisel 2.8 pajero up to
Urunga and back from
Sydney on occasions and found it to be cheaper whacking it upside down on a box trailer behind the 4WD as there was less constant drag on the vehicle. Doing 110kmh most of the freeway, it made a noticable saving by having it on the trailer instead of the roof.
Reducing the aerodynamic drag (footprint) at constant highway speeds will make a difference although it has to be a substantial amount to warrant a trailer especially if the trip envolves more hilly terrain and a petrol motor.
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Reply By: Member - Vincent A M (NSW) - Monday, Apr 23, 2007 at 18:51
Monday, Apr 23, 2007 at 18:51
All I can say is I use more fuel if the boat is on the roof .( I build boats on the south coast of NSW & deliver the same craft to
Sydney (have for 15 years) I travel the same way, same type of traffic,.. & use more fuel & one gear lower going up Mt Owsley than if I tow the same craft on a 350 kg trailer, the windage is the problem. I think you will find the forester to be worse my wife had the turbo wagon & it hated anything on the roof. good luck
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Reply By: Member - Roachie (SA) - Monday, Apr 23, 2007 at 20:09
Monday, Apr 23, 2007 at 20:09
In my experience, the answer depends largely on what type of terrain you will be travelling through and at what speed.
If you were driving up and down the
Snowy Mountains highway at legal speed limit, the weight of the trailer would add significantly to your fuel consumption. Even if you slow down to say 70 k/h, the weight factor is still gunna hurt.
However, if you had a roof rack loaded up, the wind drag factor at slower speed will have less effect.
However, say you were crossing the
Hay Plain (or Nullabor etc), then a properly loaded trailer will create less frontal area than a roof rack. At legal speed limit, there will be less impact on fuel economy from towing a trailer, than there would be from trying to jockey a block-o-flats which is 8 foot high.
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Follow Up By: Granpa Joe - Monday, Apr 23, 2007 at 20:17
Monday, Apr 23, 2007 at 20:17
Well said Roachie, That's exactly the point I was trying to explain.... depends if your climbing hills or rolling along on the flat.
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Reply By: AdrianLR (VIC) - Monday, Apr 23, 2007 at 20:21
Monday, Apr 23, 2007 at 20:21
We've had all three versions - roof rack, roof box and camper trailer. At highway speeds the roof rack with an irregular load was very noticeable (both in terms of performance and economy). The camper (around 650kg loaded) is only noticeable in hills but on the highway only marignally. The Thule roof box has no effect on performance or economy.
You need to position the box so that the curve of the windscreen continues into the front of the box or if this is not possible then behind the line of the windscreen. Vehicles were 2.8GU, Disco Td5 and Pajero DiD. Only had the full rack on the Patrol though.
Adrian
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Reply By: Russ n Sue - Tuesday, Apr 24, 2007 at 10:30
Tuesday, Apr 24, 2007 at 10:30
Jesus! We're buggered! In four weeks we take off with a
Kimberley Kamper loaded to the gills and a boat on top, as
well as a roof rack on the car with four Space Cases on it.
Sounds like we won't be driving past too many servos - even with the long range tank!
Cheers,
Russ.
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Follow Up By: Member - Stephen M (NSW) - Tuesday, Apr 24, 2007 at 13:00
Tuesday, Apr 24, 2007 at 13:00
Hi there Russ, was just having a look at your rig pics. How do you get away with where the rear spare is located obstructing you drivers side rear lights ?? Just curious thats all , or is the spare not normally in that position just looks that way in the photo's ??. Regards steve M
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Follow Up By: SA_Patrol - Tuesday, Apr 24, 2007 at 14:58
Tuesday, Apr 24, 2007 at 14:58
All Kaymar bars have some kind of lights at the bottom, looks like he has the LED strips you can just see the LH side.
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