Saturday, Oct 24, 2015 at 18:37
you do
well to mention the 505
sedan ...... but it can be argued that it is semi-trailing and long arm and a hell of a lot better engineereed than what we are finding under caravans and trailers..... but back to that later.
The other major two problems with most of the nasty light trailer independent
suspension is the swing arm is too short and the front pivot point is too high .... .... yeh and
the springs and shockabsorbers are located at the extreem rear of the arm.
OH and the shock absorbers are tilted in the oposite direction the the
suspension travel making them less effective.
In pretty much all unmodified automotive suspensions the swing arms, wishbones or springs are close to horisontal in the at rest position, with the axle centre close to the same horisontal plane as the front pivot or attachment point or in the case of dual wishbones the inner and outer povots are close to horisontal as practicality will allow.
This minimises bump steer, other geometry changes and keeps the spring seats or pivots as close to paralell as possible.
In addition most wishbone or swing arm suspenson have their spring attachment points between the pivot and the axle ...... this means that the spring has to travel considerably less than the axle ..... and because of this springs can be shorter and they are easier to keep in their seats. .... in some dual wishbone designs the axle travels twice or more what the spring
seat does.
So back to the Pewgot.
If you google up Peugeot 505 sti rear
suspension, you will find some good pictires and comparing them with the jayco video it will show exactly the problems.
On the 505
1/ Most conspicuoulsy, the pivot points are in more or less the same horisontal plane as the axle when at rest.
2/ this can be argued ..... the 505 sti rear
suspension looks to me to be semi-trailing.... its not dramatically semi-trailing ...... but it is all the same ......... in that the front pivot points are not perpendicular to the longditudinal axis of the car .......this introduces negative camber as the suspenion compresses ... ... and may I expect to be more intended to correct for bumpsteer.......... some of the traier
suspension I have seen are semi-trailing ..... ....the jayco does not appear to be.
3/
the springs and less importantly the shockabsorbers are inbetween the pivot and the axle, this means far greater
suspension travel for a given spring compression ..... the longer the spring the less stable it is. ..... the shockies will remain more or less vertical thru the whole
suspension travel and will never be disadvantaged.
Per-go have had a very long reputation for soft, long travel suspensions that hold the road very
well ..... they have used some strange
suspension arrangements over the years .... arrangemenst that other makers have failed with miserably...... it is not the type of
suspension ..... it is the attention to detail that gets them results.
look at the differences between these two suspensions and you should be able to see pretty much everything that is wrong with the independent suspensions offered on trailers.
Possibly THE single biggest source of
suspension problems on trailers is the pretty much complete failure to deal with the flat straight box section chassis.
pretty much no trailer manufacturer will even attempt lower the front attachment point of a leaf spring to get it in the right attitude and to maximise suspenion travel... hell they are mostly too stingey to fit shackles at the rear unless it is an "off road suspension"
They certainly are not interested in building stepped or curved chassis designs even when a flat floor is not required ......
cheers
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