Thursday, Sep 01, 2016 at 10:11
The simple fact MUST be faced ..... ANY spring system without damping WILL oscillate. ..... This is simple physics and can not be avoided.
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People continue to dismiss the lack of shock absorbers (or more correctly
suspension dampers) on trailers and caravans as insignificant.
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ALL trailers without shock absorbers or a suspensions with significant inherant damping WILL oscillate If there is sufficient source of excitation.
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If that trailer is a short low box trailer, significantly lighter than the tow vehicle it will not cause any stability issues , it will just bounce up and down with little harm...... IF however it is a long, high centre of gravity trailer like a caravan, towed by a vehicle close to the trailer weight it can become a very big problem very quickly.
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The majority of trailer sway incidents are caused pretty much entirely by undamped spring systems.
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A road incident, (many times a windage incident) causes the trailer to deflect ..... compress
the springs on one side and extend on the other ........then because there is little or no damping in the system ...... the trailer hops from one side to the other as the undamped springs compress and expand ....... get the weight, spring rate, speed and lengths right ....... resonance occurs and the sway gets worse and worse till the combination overturns ...... there are many utube vids that show exactly this.
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If the
suspension had sufficient damping .... as pretty much all other road vehicles except trailers are required to have by law ...... the
suspension would deflect and rapidly return to the normal at rest situation in 1, 2 or at worst 3 cycles.
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Many factory standard road vehicles have significantly inclined shock absorbers ..... as much as 15 or 20 degrees ...... yes some of the trailer suspensions have shock absorbers at angles much steeper than preferable...BUT ... as long as the shock absorber is not starved for fluid it will continue to function as designed ..... most of the off road shock absorbers are specifically designed to continue to function at considerable angles.
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Yes there is the issue of mechanical dis-advantage with dramatically angled shock absorbers ...... IF the shock absorber does not travel in the same or similar path to the
suspension, there will be a mechanical disadvantage and a reduction in the damping effect.
If the shock absorber is angled at 45 degrees to the
suspension path ( not vertical) the mechanical advantage will be 1.2:1 ..... if the shock absorber is at 60 degrees to the
suspension path, the mechanical disadvantage (and the reduction in damping) will be 2:1.
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BUT ...... and the is a VERY BIG BUT ....... there IS STILL DAMPING where there would otherwise be NONE.
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If shock absorbers tolerant of working at angles and with sufficient damping where used to compensate for the mechanical disadvantage, a very effectively damped
suspension can result ..... this is why many off road independent suspensions have very large shock absorbers or double shock absorbers.
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Truth is .... quite small amounts of damping can considerably improve the stability of trailers and caravans .... it's not like we are trying to achive the wheel control that is needed to achieve expected ride and handling in a modern road car ...... we just need sufficient damping to stop the trailer oscillating and becoming critically unstable.
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People can disregard the elephant in the room issue of lack of
suspension damping on trailers and caravans.
But the fact remains, no other road vehicle is legal without sufficient
suspension damping.
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OH BTW .... compared to all the other gadgets, shock absorbers are very cheap.
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cheers
Cheers
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