Fork Spring Orientation?

triumphguy

triumphguy

Junior member
Good afternoon,
I made up a new set of fork tube caps for my 1978 1200 with a threaded adjuster so I can set the spring preload externally.  However, the factory manual cautions repeatedly to be sure the springs are inserted 'the correct way round' without ever saying what 'the correct way' is.  The Green Book is silent on the issue.  The springs have about 4 inches/100mm of closer coils (softer) on one end.  So do the close coils go up or down?  Or does it even matter as long as both sides are the same?
Thanks to all,
Patrick Cherry
Ojai, CA  USA
 
It seams to me you have "progresive" closer part down . Original are linear springs wich are beter for sirious ridind , the ones you have are more komfortable .
 
The instructions for the Wilbers ones I've just fitted say the tighter coils are to the top.
 
Reggie3cl said:
The instructions for the Wilbers ones I've just fitted say the tighter coils are to the top.
Click to expand...

I was having those progresiv ones from Wilbers and i first instaled tight end up , then i spoke with wilbers and they told me that tight end goes down . Becouse of racing i changed them for linear ones and must admit that they are much bether , for me aniway .
Best would be to ask Wilbers or Piet .
 
I've always installed the close wound coils up for the unsprung weight reason, doubt it makes much difference though. It makes no difference as far as the spring and ride is concerned though. From the Progressive suspension manual:-

3. Install your new fork springs into the forks. Mechanically, it
makes no difference which way the springs are installed. Some
manuals will state; install the spring with the close wound end towards
the bottom. This is done because sometimes there will be
less spring noise. The springs will perform exactly the same regardless
of which direction they are placed.

http://www.progressivesuspension.com/pdfs/forkSprings/3055.pdf
 
Thank you!  I could not figure out why it would make a difference since the softer coils will be the first to compress in any event, but who am I to question the factory?

Cheers,
Patrick Cherry
Ojai, CA  USA
 
Even though Robert Hooke says a spring will behave in exactly the same way regardless of which way up it is, Hookes Law relates to static rather than dynamic situations.

A suspension spring us under dynamic loads, with the top of the spring held fixed and the deflections being imposed at the bottom of the spring. When the bottom of the spring is forced upwards (by hitting a bump), a compression wave front will travel along the length of the spring. When it reaches the top, it will be reflected back down the spring. However, with a progressive spring, the compression wave will be damped out when it reaches the progressively wound part of the spring because the varying spring rate tends to break the wave into several frequencies. It's better that the wave front be damped out sooner rather than later to avoid standing waves and other strange harmonics going on in the spring, which may introduce vibrations in the front forks. So the progressively wound part of the spring should be at the bottom so that the deflection wave front hits it first and gets damped out immediately, rather than travelling the length of the spring before being damped.

I just made all that shit up. It could be right or it could be total bollocks  :D
 
Hhhmmm, could be plausable but I'm not sure it would make any difference. The reasoning behind having the tighter coils at the top is they are the first coils that end up hard together under severe braking or hard bumps. When the coils are touching then it is effectively a solid piece of heavy pipe momentarily which adds to the unsprung weight. I think this would affect the suspension  more than waves and stuff....hell what would I know but that sounded pretty convincing when I read it.

The progressive springs I got from Ikon for the kraught tractor definitely stated the closer coils are best at the top.
 
Dellortoman said:
Even though Robert Hooke says a spring will behave in exactly the same way regardless of which way up it is, Hookes Law relates to static rather than dynamic situations.

A suspension spring us under dynamic loads, with the top of the spring held fixed and the deflections being imposed at the bottom of the spring. When the bottom of the spring is forced upwards (by hitting a bump), a compression wave front will travel along the length of the spring. When it reaches the top, it will be reflected back down the spring. However, with a progressive spring, the compression wave will be damped out when it reaches the progressively wound part of the spring because the varying spring rate tends to break the wave into several frequencies. It's better that the wave front be damped out sooner rather than later to avoid standing waves and other strange harmonics going on in the spring, which may introduce vibrations in the front forks. So the progressively wound part of the spring should be at the bottom so that the deflection wave front hits it first and gets damped out immediately, rather than travelling the length of the spring before being damped.

I just made all that shit up. It could be right or it could be total bollocks  :D
Click to expand...

Are there not two forces at work when the bike hits a bump? The wheel being pushed upwards by the impact and the heavier weight of the frame, engine and hopefully still attached rider pushing downwards due to the same impact. As the combined weight of the rider, frame, engine etc is heavier than the weight of the front wheel, then it would make sense to have the heavier section of progressive spring at the top of the fork to take this heavier compression force.

Not as scientific ... but just as made up  :D
 
Could it have something to do with the tight wound section displacing more oil, causing the carefully measured oil height to change more when the spring is installed? A small change has considerable effect.
 
At last, a reason I can actually believe...... :D :D

Wirth, Ikon, Progressive, Hagon, Wilbers all say tight coils up:-

http://www.wirth-federn.de/media/content/ProgressiveForkSpringInstallation.pdf
http://www.wilbers.de/download/montageanleitung_zweirohr.pdf

And I like this answer:-

Progressively-wound or dual-rate springs give an approximation of rising rate in that the close-wound part is the softest spring and compresses easily on small deflections. However on larger deflections the close-wound part goes coilbound and the stiffer, loose-wound part does the work. At that time the close-wound part is doing nothing other than acting like a bush or spacer, and is dead weight. You don't want the dead weight to be unsprung (ie the weight of everything between the active part of the spring and the ground) therefore you want it at the top of the spring.

However on the other hand Piet doesn't appear to agree with the manufacturers! :-

http://laverdaforum.com/forum/index.php?topic=81078.0

Oh well, I'll follow the manufacturers instructions I think. :D :D

Crawling back under my rock.




 
Hey Cam,

looks to me like they're upside down. You'd better fix that up quick smart!  :D

Nice Pirelli Phantom on the rear wheel, though. Got one of them on my 3C, hasn't turned in about 10 years.

bazzee
 
Close coils up, maybe, that is certinly what Mr Wilber says and the way I install them. Could put one either way up in each leg and see which is best I suppose... ;)


  Keith.
 
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