Just to add something to the mix,
there might be something in it, when i put my roof box on my unit becomes more stable, so if the roof box is making the differance would a roof box be money better spent.
When i got the angle right the caravan stability was amazing. Aerodynamics are a major part of unstable caravans. There will be others who rubbish what i am saying But think about it. If you have done everything else IE Nose weight/Loading/Tyre pressure so on & it still tows like a pig. Then Aerodynamics could be the problem.
I have an aftermarket Webasto tilt/slide glass sunroof in my Mondeo estate. If you open it fully it tilts up and the back and then slides backwards above the roof like a windslammer but obviously not at as steep an angle.
I was amazed a couple of years ago when I discovered purely by accident 'cos the roof happened to be open that with the sumroof fully open my mpg went up by approx 5 mpg.
Only any good in nice weather and a sunroof like mine costs a lot more than a windslammer though.
And yes, I had one back in the day too. On top of my Cortina towing an old Swift Doublette with single glazed glass windows, no fridge, no hot water, no mains..........
Hi I tow with a crv and tow a 1800 kg van and with an old style windslammer on I get between 2 and 3 mpg improvement in consumption. The critical bit is the angle of deflector between car and van. My slammer fits on rear roof bar but ideally could be a bit further back.
Also for those who are in 6th at 60mph towing, you are bordering on labouring the engine and increasing mpg, which some do report, my onboard computer tells me I'm better in 5th on the flat at 62ish and 6th on a slight downslope.
This might be true for your car, but it is not for mine. The onboard computer tells me to change up to 6th at 50mph whilst towing. I normally tow at lorry speed, ie 56mph, and I rarely need to change down. Invariably if I drive in 5th consumption drops. Going to Italy last year the car averaged 38mpg towing almost entirely in 6th.
We still have our Dutch-made aluminium roof deflector that we used in the 1980's with a Vauxhall Astra Mk1 estate and a Vauxhall Carlton Estate towing a Sprite Alpine.
The instructions were pretty explicit, fit as far back on the car as possible, angle the deflector so that it aligns just over the top of the caravan.
It gave us a usable top gear in the Astra and made cruising in the Carlton much easier. Fuel consumption improved on both cars.
We have a Discovery 2 V8 now, and our trailer/RV is 22ft long and a fair bit higher than a standard caravan, so might be worth trying the deflector out again.
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Topic: purpline aeroplus windslammer
