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Topic: Bike rack on rear of van

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michael

24/2/2010 at 9:34pm
Location: Lancashire
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of interest

http://www.towingstabilitystudies.co.uk/stability-studies-simulator.php

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the only silly question is the one you do not ask.

JTQU

24/2/2010 at 10:23pm
Location: Hampshire
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Quote: Originally posted by Rune Caster on 24/2/2010
So when everyone says pendulum effect they are referring to movement in the horizontal plane around what is the (in aeronautical terms) yaw axis and not to the up and down movement (which should be)controlled by the nose weight?

In this case predominately "yaw" about the axles centre, and coupled to this some "rolling" due the height of the bikes above the ground.
The yaw of course driving "snaking" which will not be helped by the increased rolling. "Pitching" amplitude will be reasonably controlled by the tow vehicles rear suspension, but the ride will be considerable less comfortable than without the rack/bikes mass.

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path20

24/2/2010 at 10:23pm
Location: Lancashire
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Thanks everybody. We will definitely not be having a bike rack on the back.Michael's link finally made our minds up.Your comments have been very helpful.Better safe than sorry.

michael

24/2/2010 at 10:39pm
Location: Lancashire
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i use one like this only a 4x4 type,carry two and one inside van.

http://cgi.ebay.co.uk/Paddy-Hopkirk-Dartmoor-3-Bike-Cycle-Carrier-Low-Mounted_W0QQitemZ220383048840QQcmdZViewItem?rvr_id=&rvr_id=&cguid=f69956921260a0aad3a57525fefe3ed3

300

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the only silly question is the one you do not ask.

mtgin

24/2/2010 at 11:29pm
Location: Leeds
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We've had a bike rack fixed on back of our Bailey ranger for 3 yrs now and have never had a problem with stability or snaking.We've toured all over UK,France and Italy and always take our bikes with us.The rack was fitted by dealer when we bought van and they said it would not affect warranty if fitted by them.We wouldn't be without it

Greendemon315

25/2/2010 at 9:43am
Location: Blackburn Lancashire
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Pendulum effect Is definitely seen in pitch and yaw. It is less noticeable in roll, but is still there.

Weight far from the axles is a really bad idea.

Jim

Opensauce

25/2/2010 at 1:10pm
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Quote: Originally posted by michael on 24/2/2010

of interest
http://www.towingstabilitystudies.co.uk/stability-studies-simulator.php

Totally misleading, the snake is induced by transfering possibly 40% of the weight of the entire test rig to the rear. 2 bikes on a rack would probabley weigh 40kg which on a 1500kg caravan would amount to 2.6% of the weight of the caravan, so insignificant.

The fact that large amounts of Dutch/German caravanners use rear mounted racks suggests that provided your caravan has mounting points a rear mounted rack is quite safe.

michael

25/2/2010 at 2:30pm
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more here

http://www.towingstabilitystudies.co.uk/stability-studies-research.php

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the only silly question is the one you do not ask.

JTQU

25/2/2010 at 4:32pm
Location: Hampshire
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Quote: Originally posted by Tentz on 25/2/2010

2 bikes on a rack would probabley weigh 40kg which on a 1500kg caravan would amount to 2.6% of the weight of the caravan, so insignificant.

Think its time to blow the dust off your physics books.

What is missing in this statement is an understanding the the "pendulum effect" is determined by the square of the distance from the point of rotation, its not simply a ratio of weights or more correctly mass.
As the bikes are as far rear as you can get them on the van then squaring that distance has more than an "insignificant" effect.
The continentals realise physics might be relevant and typically place the axle further back from the hitch than we do.
If instability is not provoked then you can tow oblivious to the lurking problem, its when you, a passing vehicle, or simple side gust move things from static to a dynamic situation that inertia has its day.

Opensauce

25/2/2010 at 5:03pm
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Quote: Originally posted by JTQU on 25/2/2010
The continentals realise physics might be relevant and typically place the axle further back from the hitch than we do.

You can discuss the physics all you like but if you google image various UK & continental makes of caravans & look at them side on you will see that the above statement is not correct.

Greendemon315

25/2/2010 at 7:20pm
Location: Blackburn Lancashire
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Still a very bad idea...

Jim

mtgin

25/2/2010 at 9:33pm
Location: Leeds
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Well i know nowt about physics but the rear bike rack works for us!!

Grampian91

26/2/2010 at 2:02am
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Makes a mockery of the theory,
Load all heavy items low down and as close to the axle as possible.

What does a bike weigh 10 - 15kg? plus the weight of the rack.
A couple of bikes and a rack will be a large percentage of the caravans loading margin.

Not something i would consider.

JTQU

26/2/2010 at 7:27am
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Quote: Originally posted by Grampian91 on 26/2/2010Makes a mockery of the theory,

No not really as the issue is just a dynamic one. They can get away with it until something nudges the van to swing then that's when it all will start going wrong. And if its near the natural yaw frequency of the unit then wrong, big time.Something like the bow wave of a passing vehicle, one of those nasty wheel track grooves found in some roads, a side gust of wind or having to swerve to avoid an idiot [the one I know all about!]. If you can plod on without ever encountering this sort of thing you will be fine; I just think the risk of using an inherently unstable unit is not worth it.

Le Phantom

26/2/2010 at 8:02am
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I just think the risk of using an inherently unstable unit is not worth it.

To me what you have said there is the bottom line.

Greendemon315

26/2/2010 at 10:21am
Location: Blackburn Lancashire
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Agreed. One day it will bite you.

Jim

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