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Subject Topic: roof box as spoiler when towing Post Reply Post New Topic
Persondebcon
13/5/2009 at 12:50pm
 Location: west yorks
 Outfit: Caravanett View debcon's Profile View Profile   Reply to debcon Reply   Quote debcon Quote  
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what are your thoughts as to fitting the roof box on the car (when towing caravan) so as to act as a spoiler and increase fuel consumption ?

Or has anyone got any hard evidence for or against this

regards debcon 


Person664DaveS
13/5/2009 at 1:03pm
 Location: Shropshire
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Why would you want to increase fuel consumption? Decrease maybe!

Box on roof= more drag+ more weight = less mpg!



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DS-There's more to life than football!!!


Karim
13/5/2009 at 1:05pm
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It will just create more drag & as you say, increase fuel consumption. In order to reduce drag air would have to be directed cleanly past car & over caravan roof but due to the large gap between car/caravan anything on car roof will just create more turbulence & hence more drag.

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Salaam


Personneil and lena
13/5/2009 at 1:15pm
 Location:  Dumfries
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Definately use more fuel when had one fitted my mpg dropped by 1-2 miles per gallon when towing caravan


PersonZafiral
13/5/2009 at 1:16pm
 Location: Kent
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Salaam

That explains why the windjammers from the 70's never continued. 



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All year Dorset!!!


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PersonDavid Klyne
13/5/2009 at 4:44pm
 Location: Milton Keynes
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I beg to differ here. Last year on our  trip round Germany and the first time using a roof box I did notice a marginally improved fuel economy. This, of course, could have been something to do with the  lower towing speed allowed. However I have not noticed a massive difference and certainly not worse.  The only  real probllem  is what to do with the thing on site! I just leave it on and accept economy solo will not be as good.

David


Personbev+jon
13/5/2009 at 4:52pm
 Location: N Yorkshire
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i noticed no difference to mpg when towing , less flies plastered to the front of the caravan though.solo with it on , 4 up fully loaded mpg dropped by around 4mpg.

 


PersonLegsDownKettleOn
13/5/2009 at 5:06pm
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When towing, the drag of the roof box is not as significant as it is solo as you create a vacuum behind it which draws the caravan in, cancelling out much of the drag of the roof box. I would not expect it to reduce fuel consumption though, but increase it less than a roof box would increase the fuel consumption when solo.

A roof box will not work as well as a wind deflector as it has a gap underneath it. Also for a wind deflector to work properly it should be mounted tight to the caravan and also finish flush around the roof and sides of the van. This is rarely if ever the case. If the deflector is not fitted correctly, the aerodynamics will do all manner of strange things. To put this in perspective, look at the aerodynamics of this years McLaren F1 car. With all their experience and money, they have got the aerodynamics badly wrong this year. They cannot blame their problems on the engine either as Jenson Buttons Brawn is using the same engine and he has won 4 races out of 5 this year.

When all is said and done, I am no aerodynamicist, but I do know that you cannot take something pointy and stick it on your roof expecting it to improve the aerodynamics.


PersonGrampian91
13/5/2009 at 10:48pm
 Location: Midlands
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Roofbox kills my MPG when towing.

Wide halfords one. I might try going slower next year, See if it helps.


Personbazzerg
14/5/2009 at 12:17am
 Location: lincoln
 Outfit: sterling eccles jewel kia sportage View bazzerg's Profile View Profile   Reply to bazzerg Reply   Quote bazzerg Quote  
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I tow an avondale dart 556/6 with a Kia sportage. I recently bought an awning with fibre tech poles annex etc all of which weighs in at 68kgs. So I stuck all this gear in a top box I bought in Spain 5 years ago when my estate car was full of wine and needed to get our luggage, and kids, home. If anything I noticed when towing to Yorkshire that the drive was better with the box on the roof, acceleration was better, feul consumption appeared better, it is hard to tell, the Kia lets you put upto 12 ltrs in tank after the pump at the station cuts out firts time...It definatly seemed to go better with the box on the roof, and will use it in the future, but perhaps with the awning etc in van and the bags in the box. My rear seat is taken up by a GSD (german shepard dog) and the boot by duvets towels etc that I dont leave in van in case of that damp smell......not that my van is damp!



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just because I am paranoid it doesnt mean I am not being followed.


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Persongazmister123
14/5/2009 at 10:24am
 Location: Redditch Worcestershire
 Outfit: Mooveo Motorhome F camper & Static View gazmister123's Profile View Profile   Reply to gazmister123 Reply   Quote gazmister123 Quote  
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We are contemplating putting our roof box on for our next trip, new roof bars arrived today so will let you know about MPG



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Never take life seriously. Nobody gets out alive anyway.



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