My Eldiss Autostatus came with a roof box that had been removed. I am considering refitting the Box. it measures about 5ft wide by 3ft by 18 inches high. How much can I expect the box to effect fuel economy? The van does about 28mpg with steady driving on a run at the moment.
I think that is a difficult question to answer. I think it will very much depends on the speed you tend to travel at. When I towed a caravan I used to have a roofbox on the car and in Germany where you generally tow at lower speeds the economy improved but as soon as I entered France with higher speeds the economy was about the same with or without.. I appreciate that it dosen't amswer specifially what effect it would have on a motohome but suspect speed and driving style will be an important factor.
I would've thought with the amount of disruption to air flow caused by the "roof furniture" that MHs already have (aerials, roof vents etc),coupled with the fact that they only start off with the drag coefficient of a Porta-cabin anyway, the fitting of a roof box would make very little, noticeable difference...
If you are concerned, is there anyway of incorporating some form of deflector/"aerofoil", similar to Caravanners used to stick atop their cars...?
If you approximately measure the total frontal area of just the motorhome in square metres, then do the same with the frontal area of the roof box. Work out what percentage extra that the roof box will add, then your fuel consumption will be about the same percentage more.
Example motorhome is say 2m wide(?) x 3m (?) high gives frontal area of 6 square metres. The box is 5ft wide x 18 inches high is approx. 1.524 x 0.457 = 0.7 square metres.
This adds 0.12 % to your overall frontal air.
I would predict your new fuel consumption to be 28 mpg less 0.12 % or about 28 - 3.36 = 24 to 25 mpg.
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Thank's for the replies. I think the benefit of the box would be out weighed by the extra fuel consumption plus if I fit the box SWMBO would have to fill it with stuff we could do without if we didn't have the box. lol
Quote: Originally posted by ldpdmp on 21/12/2013
roof boxes will always lower fuel consumption no matter what. The faster you go the lower it will drop
I would have expected them to increase the fuel consumption.
it's true that a roof box will always increase fuel consumption but all things are relative, it is not like putting one on the roof of a mini. Motorhomes by their very nature usually have the aerodynamics of a housebrick and already have roof vents, aerials and sometimes a rack on the roof. after using ours with the box both on and off I would say the difference would be negligible (in our case completely indiscernible, 28 mpg on or off) and the benefits definitely outweigh anything else. Ours holds our table,chairs, cadac and everything else that we use outside
just make sure its secured to the roof, if it comes loose and hits anything you will be liable for any damage, they used to be a common site on motorhomes but you see far fewer these days, if it won't fit in the van then it stays behind thats what we do.
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Topic: Roof Boxes and economy
