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How tough are wind deflectors?


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The only convertibles I have owned are Land Rover soft top types so looking for some advise please, as I am sure many of you are aware I am currently building an overland trailer and getting close to the end now. One of the things I was advised to add was a deflector to stop stones and other detritus, breaking the rear windows etc.

stoneguard5.JPG

I have looked around and can’t find anywhere to buy one from or even look at one “close up” so going to have to make my own.

Do you thing that one of these types of deflectors would be up to the job? Or are they pretty flimsy?

http://cgi.ebay.co.uk/Audi-A4-Wind-Deflector-case-/290436561656?cmd=ViewItem&pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item439f5e3af8

Cheers, Jason.

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I would have thought you need a heavyweight cloth put on frame without tension so the cloth takes all the energy from the projectile and it drops straight to the ground.

Look you can even fill them with sand to keep your tent down in the wind!

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IMHO they are more than a bit flimsy - I would give them about 10 seconds at 30mph on a dirt track...

Are you thinking of using that sort of construction to allow the wind through? If so, then IMHO, the air behind the towing vehicle is a bit of a mess - very turbulent - and so I don't think that drag would be affected by using something more solid and cheap to replace (a frame with plywood inserts would be my suggestion).

But are they really needed? I know there will be loads of people who have had rear windows broken by stones bouncing off the trailer, but how many haven't? Some friends and I once towed a trailer behind a LWB Series IIa with no mud-flaps, 9000 miles to India - which involved hammering over a fair bit of rough/unmade and badly maintained roads, and although the trailer fell apart, we never broke a rear window.

Roger

Just to be clear: What I am describing as flimsy above is the wind deflector in the ebay link

Edited by ThreeSheds
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I started reading this thread thinking 'what are you on about'? I've got to the end, followed the links, and still think there is a large element of confusion.

To start at the top, the deflector shown in the OP appears to be mounted on the A frame of the trailer / caravan. It COULD protect the front windows of the caravan, but the text mentions 'rear windows'. Rear windows of what? How are they damaged by stones kicked up from any wheels?

I see another contributor has suggested the broken windows are on the rear of the towing vehicle, broken by stones bouncing off the front of the trailer. For this to happen, when the combination is travelling at 30 mph a flying stone would have to bounce off the front of the trailer, and in doing so gain a forward speed of GREATER than 30 mph so that it can catch up with the towing vehicles rear window that is moving away from it at 30 mph.

I'm not going to do the maths involved, I'm just going to reject the idea.

The Audi wind shield in the ebay advert is just that. A lot of modern open cars have them. They inhibit the air circulating round and blowing forward into the low pressure area behind the windscreen. This forward flowing air not only gives you a bad hair day, but can also cause the ends of your hair to literally whip your eyeballs. When you are suddenly blinded and in pain at 60 mph you are liable to more than a bad hair day, as is anyone in the vicinity of your out-of-control car.

I'm not saying that rear windows of towing vehicles don't break (if that is what experienced users say), I just doubt that it's caused by stones sent flying by the vehicle road wheels.

I'm not sure a debunking post is ever seen as 'helpful', but I hope it might help promote some clarity into the discussion.

Regards,

I

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David, as the stone leaves the rear vehicle wheel it will be accelerating from under the tyre. When it hits the trailer it will have some of this energy removed, but some will change direction.

I won't do the math either, but throw a stone against a wall, it will bounce back a bit. That change in direction is added to the 30mph of the trailer hitting it, like a bat, towards the rear of the vehicle.

I also don't know how often or how likely this is to happen.

Jason, it would need to be made of mesh or canvas to absorb the impact. How about some 20mm galv conduit? One length, a few elbows, frame made. For the netting I would use the scaffolders netting that you see around the sides of scaffolding. Usually green, fine weave, should be more than up to the job. Fold an edge, tie-wrap (zip-ties) on, job done :)

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I started reading this thread thinking 'what are you on about'? I've got to the end, followed the links, and still think there is a large element of confusion.

To start at the top, the deflector shown in the OP appears to be mounted on the A frame of the trailer / caravan. It COULD protect the front windows of the caravan, but the text mentions 'rear windows'. Rear windows of what? How are they damaged by stones kicked up from any wheels?

I see another contributor has suggested the broken windows are on the rear of the towing vehicle, broken by stones bouncing off the front of the trailer. For this to happen, when the combination is travelling at 30 mph a flying stone would have to bounce off the front of the trailer, and in doing so gain a forward speed of GREATER than 30 mph so that it can catch up with the towing vehicles rear window that is moving away from it at 30 mph.

I'm not going to do the maths involved, I'm just going to reject the idea.

The Audi wind shield in the ebay advert is just that. A lot of modern open cars have them. They inhibit the air circulating round and blowing forward into the low pressure area behind the windscreen. This forward flowing air not only gives you a bad hair day, but can also cause the ends of your hair to literally whip your eyeballs. When you are suddenly blinded and in pain at 60 mph you are liable to more than a bad hair day, as is anyone in the vicinity of your out-of-control car.

I'm not saying that rear windows of towing vehicles don't break (if that is what experienced users say), I just doubt that it's caused by stones sent flying by the vehicle road wheels.

I'm not sure a debunking post is ever seen as 'helpful', but I hope it might help promote some clarity into the discussion.

Regards,

I

Sorry for any confusion, I am currently building an overland trailer, when I started the project quiet a few people said that I should fit a stone deflector to stop stones thrown up from the Land Rover bouncing off the trailer and breaking the rear windows, as I am nearing the end of the project I started to look at them.

As I couldn't find one to look at or anyone who sold them I woundered if I could convert one of the Audi type to do the job and if they would be tough enough.

Yes it will attach to the A Frame, my thoughs behind it were a broken window could really spoil a trip and if I could add something on to my trailer now that would possibly save this trouble then it could be worth it.

Jason.

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David, as the stone leaves the rear vehicle wheel it will be accelerating from under the tyre. When it hits the trailer it will have some of this energy removed, but some will change direction.

I won't do the math either, but throw a stone against a wall, it will bounce back a bit. That change in direction is added to the 30mph of the trailer hitting it, like a bat, towards the rear of the vehicle.

I also don't know how often or how likely this is to happen.

Jason, it would need to be made of mesh or canvas to absorb the impact. How about some 20mm galv conduit? One length, a few elbows, frame made. For the netting I would use the scaffolders netting that you see around the sides of scaffolding. Usually green, fine weave, should be more than up to the job. Fold an edge, tie-wrap (zip-ties) on, job done smile.gif

Cheers Martin,

I did think about making a frame just looking at options, and I was woundering if there was an easy way, i.e. buy something and convert it... Scaffolders net is an option, I also have some brethable ground sheet which may also do the same sort of job or some canvas.

Would love to see an actual one up in person to figure out what it is made off etc....

Jason.

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If you box in the front of the trailer vertically and parallel to the A-frame rails so the body comes to a point at the front, the stones will bounce outwards rather than forwards (sorry cyclists) and you've gained some more storage space. It may or may not be more aerodynamic but that's down to turbulent flow between two essentially square boxes...

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If you box in the front of the trailer vertically and parallel to the A-frame rails so the body comes to a point at the front, the stones will bounce outwards rather than forwards (sorry cyclists) and you've gained some more storage space. It may or may not be more aerodynamic but that's down to turbulent flow between two essentially square boxes...

Cheers John,

But would building a box not affect the articulation?

I drive a 110 defender, aerodynamics have never really been that much of a consideration!!biggrin.gif so not worried about that side of things.

Jason

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But would building a box not affect the articulation?

Imagine two bits of something flat and verticalextending from the edges of the trailer to just behind the towball. I think it's a good idea myself...

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Imagine two 4x4ft sheets of plywood, nailed by their lower edges to the A-frame, onto the body at the rear edge and nearly touching each other at the front edge. I think you could clout the LR if you wind the trailer onto full lock and then lift the trailer wheel that's furthest from the LR (or drive steeply up a hill) but you could be cautious with the height - or how you drive!

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