Help on installing progressive springs

[mladen]

Hello!

I need help on installing progressive springs on my AT 1998. I don't know which way is the right to put them in the fork. The more densed side down or up?

Thanks for your help!

[Hagalaz]

IIRC, the tighter coils go to the top.

[Pussyhorse]

Yup, tighter coils at the top.

[mladen]

Thanks a lot for the answers!

I was pretty sure that the tighter coils go in the bottom. I'm glad I asked for an advice!

[Rubberchicken]

The trick is that you want the unsprung bit (i.e., the wheel) to be as light as possible, and the tight bit of the spring is heavier than the open bit.

[mladen]

My english is limited, so i didn't quite understand the part "The trick is that you want the unsprung bit (i.e., the wheel)". I understand that the tight bit of the spring, which is heavier is up, but I didn't understand why is this better, considering that we are always loking to pack the heavier things low as possible?

[Dilbert]

You need the softer end at the wheel so it rides easily over bumps, the top tighter bit does not compress at all, it is only when the travel of the spring is much more that it then starts to try and compress the tighter part of the spring.
if you had the tighter bit at the bottom it has to transmit the small forces of minor bumps through the tight bit of the spring first and this does not work as well.

[mladen]

Aaaaaaaa, now I understand! It's all clear now.
Thanks for the explanation.

[icenian]

You need the softer end at the wheel so it rides easily over bumps, the top tighter bit does not compress at all, it is only when the travel of the spring is much more that it then starts to try and compress the tighter part of the spring.
if you had the tighter bit at the bottom it has to transmit the small forces of minor bumps through the tight bit of the spring first and this does not work as well.

Erm... surely, as far as the spring in concerned, the two ends move closer together, so the coils are compressed, and this will be the same whichever way up it is

There will be some inertia from the mass of the spring, which will resist movement; and this will be less with the tighter coils at the top as less mass is being moved as the wheel rises/falls; but that's not due to resistance from the compression of the spring.

I understood that the progressive rate is because the closer wound coils start to bind. I'm not up to explaining this! A quick google turned up this convincing sounding explanation - Jenna will be along in a minute to tell us if it's true or not

http://www.gti-vr6.net/library/suspe...planation.html

Take a "simple" 100 lb/in straight-rate spring, composed of 4 identical
evenly spaced coils. Apply 100# of force. The spring compresses 1".
Each coils compresses 1/4". Add another 100# and the spring compresses
and additional 1" (2" total) and each coil is now compressed an
additional 1/4" (1/2"total). This continues linearly until the coils
begin to bind (at which point you no longer have a spring). From
observing this spring, we can deduce that each coil has a rate of 400
lb/inch.

[...]

What makes a spring progressive is a geometry where some of the coils
bind up partway through the anticipated travel. For instance let's take
our original spring and play with the coil spacing. Let's wind it so
that the first two coils only have 1/4" of air between them while the
other two coils have substantially more. Put 100# on the spring, it
compresses 1". But at that point, two of the coils can't compress any
more. Add another 100# and it only compresses 1/2"; i.e. the rate of
the spring has doubled to 200 lb/in!

[Jenna]

yep makes no odds which way up to how it works in general, putting the tighter wound end to the top will reduce weight marginally at the wheel but then the weight of the extra coils will compress the lighter ones and to some extent counteract the effect of the progressive nature.... lol bit **** or bust!

http://www.atvscene.com/video/evalua...6/springs.html


goes some way to explain the theory.