Roof Boxes

[Royston]

Fitting of a roof box,does this help in the towing dynamics, with regards to the airflow over the caravan, noticed that the Series 5 Bailey Senator range that the redesigned front is more upright, which much increase the air restance when towing.

With the ever increasing fuel prices just wondered if fitting one of the boxes would help to increase mpg.

Roy.

 

[rayc]

Roy, I towed with a Thule roof box for 3 years with a Mondeo Estste. I do not think the box helped fuel consumption at all and indeed it may have been heavier with the box on. I guess the only way to find out would be a lab type test and how much that would portray real life with different caravans is anybodys guess. As far as dynamics how would you know unless it was a pig to tow and fitting a box improved things greatly. I never experienced any problems towing with or without the box fitted.

 

[ProfJohnL]

Hello Roy,

The car manufacturers will tell you that even roof bars, open windows and sun roofs detract from the the aerodynamics of solo cars, so larger roof boxes certainly will.

Towing could be a different story, but it will depend on very careful setting up and as Ray says the use of wind tunnel or other high tech facilities to monitor the effects.

 

[Paul8]

When I use my roofbox I get at least an additional 5 MPG- only yesterday I saw 35 MPG over 150 miles when without I would only get 28-30 MPG.

This happens everytime I use it, so can vouch for the improved fuel economy. The outfit is a 2004 Mk5 Golf with 2004 Bailey Ranger 470/4. Just the two of us with the awning in the roof box.

 

[Lutz]

You're lucky if you are getting an improvement and any positive result that you're experiencing is pure chance. If you do the same with a different outfit, even if you only move the roof box back or forward a couple of inches, you could get the completely opposite result. Aerodynamics are a very complex subject and it's difficult to predict results without lengthy trial and error tests or the aid of a wind tunnel.

 

[Paul8]

It's nice to be lucky for a change- but a definate improvement when using the car's MPG computer. The MK5 Golf has fixed anchoring points for the roof bars (there are mounting holes in the door frames) and the roof box has fixed mountings for the front attachments too so I will have the box in exactly the same place every time.

It's only the fourth time I have used the box so i'll see what happens next weekend!

 

[blackrat]

Off down to Lake Garda in a few hours. Last year (same journey) averaged just under 20mpg on the car computer. This year is with roof box and a heavier van, so I'll report back in a fortnight or so as to there is any improvement or not.

gary

 

[blackrat]

Well, here we are back from there! Towing with roofbox gave an extra mile or two to the gallon. Not a lot, but the new van weighs around 250 kg more than the other. Big advantage of roof box was that the car boot was virtually empty, as was the caravan floor which made for easier tea stops. Got just over 20 mpg out of my Volvo 850 T5 when towing, and I was considering swapping it for a diesel, but the 'economy' seems to compare reasonably well with big car diesels, so I'll live with it for now.

Gary

 

[Paul8]

Last weekend I picked up the van from the dealer after service, without box, got 24 MPG over 30 miles. That afternoon went to site for weekend (50 miles away) with box and got 32 MPG.

I respect those that tell me it's luck but it does give an improvement for me!