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Old 15th September 2020, 07:54   #1
macafee2
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Default Avoiding trailer and bumper collision when reversing

Avoiding trailer and bumper collision when reversing.
When reversing a car and trailer, what is the maximum angle the trailer can be at, before continued reversing will cause the trailer to eventually hit the car? 45 degrees?

Apart from using your eyes is there anything on the market to warn of imminent contact between trailer and car when reversing?

Got to be honest, when reversing at an angle this is always a concern for me.

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Old 15th September 2020, 09:26   #2
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Reversing a trailer with precision, does come with practice, and an understanding of the principles involved.

If you are anywhere near touching your trailer, with your bumper, then you have gone well past the point of being in control.

Like many things, reading about what to do can be more confusing than observing the geometry involved, in practise. A simple method is to use a model car and trailer, and “reverse” it on a table top. Nearly as good, is two model cars, lorries, or whatever; two blobs of blue tack and two paper clips, suitably bent.
The second car can be reversed, as if it was a trailer.

You will quickly see the point, or angle, where the trailer stops moving backwards, under control.
After this point, the car is reversing into the trailer (and trying to push it sideways) rather than properly reversing it.

The point is actually called “the follow through”, and it is where you change over from turning your steering wheel to the left (to turn the trailer right) to turning the steering wheel right (to continue turning the trailer to the right)

There are other factors involved.

1. The longer the distance from the tow ball to the trailer wheels, the easier it is to reverse the trailer.
This is because the follow through comes much later, or if you like, at a greater angle.
The hardest trailer to reverse is a 3 or 4 ft long box trailer, simply because you often can’t see it, and the follow through point is almost immediately after you start moving.

2. The distance between the towing cars’ rear axle, and its’ tow ball.

3. The wheel base of the towing car also has an effect, but not of any great significance.

As to a device to assist reverse towing, I don’t know if there are any on the market today, but years ago I couldn’t find any (pre internet)

Although I never did assemble the following, so not tested, I think it might work.

Essentially:-
Two short chains, permanently attached to the front corners of the trailer.
With a removable shackle, or possibly a large spring hook, connect them to two eyes, that are fastened as far as possible from the towing ball, directly onto the tow bar.
The length of the chain, stretched tight, determined by trial and error, to stop the trailer from pivoting on the ball; just before the “follow through angle”

All of this would need to be well engineered, as the forces involved are going to be considerable.

My apologies if this is already a recognised method,

Regards

Mike
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Old 15th September 2020, 09:55   #3
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To answer the OP's question, there is not a maximum angle, anything other than dead straight (ie exactly in line) will eventually cause a bumper touch.

As Mike says, you have to start corrections just as soon as the deviation starts, at the point of "follow through".
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Old 15th September 2020, 12:38   #4
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There is also the amount of space available to consider. When doing a " 3 point" turn,
one may need to get a lot closer to a jack knife position then normal. Had to do that a couple of times with the caravan before.

As for maximum angle, I guess my car and trailer and caravan and trailer will have their own maximum angles at which point it would not be able to continue to reverse no matter what was done with the steering wheel without jack knifing.

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Old 15th September 2020, 14:13   #5
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Reversing in a tight, or confined, space is where your experience really does come into play.

There is no ignominity in uncoupling and man-handling the trailer or caravan, if the manoeuvre is deemed (beforehand) as impossible, or simply too difficult.

Uncoupling once you are in trouble -- let’s be kind and say “I gave it my best shot”

You are correct in that the angle, where the trailer has jack knifed, will be different for different trailers.
However, for any one car / trailer it is a constant.

That makes me wonder if it might be possible to set up a visual line of sight, rather than the chains I originally referred to.

Maybe the corner of a caravan (or a corner marker on a boat or luggage trailer) which lines up with the edge of a piece of tape, stuck vertically on the car’s rear screen, and a third vertical rod, possibly mounted (temporarily) on the driver’s seat headrest.

Sitting facing forwards in the driver’s seat, should be constant enough, to then use the rear view mirror to ascertain that the edge of the caravan does not move beyond the line of the other two markers.

Again, apologies if this has been thought off before.

Regards

Mike
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Old 15th September 2020, 16:25   #6
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Originally Posted by BRG75 View Post
Reversing in a tight, or confined, space is where your experience really does come into play.

There is no ignominity in uncoupling and man-handling the trailer or caravan, if the manoeuvre is deemed (beforehand) as impossible, or simply too difficult.

Uncoupling once you are in trouble -- letís be kind and say ďI gave it my best shotĒ

You are correct in that the angle, where the trailer has jack knifed, will be different for different trailers.
However, for any one car / trailer it is a constant.

That makes me wonder if it might be possible to set up a visual line of sight, rather than the chains I originally referred to.

Maybe the corner of a caravan (or a corner marker on a boat or luggage trailer) which lines up with the edge of a piece of tape, stuck vertically on the carís rear screen, and a third vertical rod, possibly mounted (temporarily) on the driverís seat headrest.

Sitting facing forwards in the driverís seat, should be constant enough, to then use the rear view mirror to ascertain that the edge of the caravan does not move beyond the line of the other two markers.

Again, apologies if this has been thought off before.

Regards

Mike
Mike,
I was wondering if a sounder and two plunger type switches could be used.
As the "trailer" gets to "60" degrees the trailer comes into contact with the plunger, compresses it and provides power to the sounder. Same for it swinging the other way. Years ago retro fit car alarms had a plunger switch for the bonnet.

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Old 15th September 2020, 16:58   #7
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My father made up a magnetically mounted (on a short post) wide angle convex lorry mirror (set at 45 degrees approx) which he attached to the caravan A frame when connecting up. It was mounted high enough to see, through the rear view mirror of the car. It made reversing to the towball an absolute doddle. I suggested that he patented it but he never got around to it.A more permanent fixing might allow you to see the proximity of the rear of the car too?
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Old 15th September 2020, 17:48   #8
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Macafee2,
I think that is an excellent idea, and could certainly be developed; better than my sight lines.

Roverbarmy,
That's a very good idea, he probably should have patented it.
Down side is you won't see all the wives, as they straddle the A frame (don't really have them any more) guiding their husbands as they reverse up to the 'van.
On 2nd thoughts, the bracketry needed, might be just as ungainly.

Regards

Mike
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Old 15th September 2020, 18:49   #9
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Quote:
Originally Posted by BRG75 View Post
Macafee2,
I think that is an excellent idea, and could certainly be developed; better than my sight lines.

Roverbarmy,
That's a very good idea, he probably should have patented it.
Down side is you won't see all the wives, as they straddle the A frame (don't really have them any more) guiding their husbands as they reverse up to the 'van.
On 2nd thoughts, the bracketry needed, might be just as ungainly.

Regards

Mike
I do the directing and wife does the reversing. She sticks tow ball under tow hitch 99 % of the time so that all I have to do is lower hitch and it clicks into place.

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