Front Fork Springs

Just got an 86 Maxim 700 with 31000 kl. Leaking fork seals. Got them apart and found the springs in the forks had been out at one time. Can anyone tell me which way the tight coil goes , up or down, dont have a repair manual yet. Thanks.

 

Doesn't matter - just do them both the same way.

Just for fun, here's a quote from some Progressive fork springs install manual:

It makes no difference which way the springs are installed.
Many manuals will say to put the tight wound end at the bottom, this is done sometimes as there will be less spring noise. However, the springs will perform exactly the same regardless of which direction they are placed.

 

Thanks Altus, will install with the tight coils down. Ed This is one GREAT site.

 

If you put the tight end up you end up with a bit less unsprung weight. Less unsprung weight=good.

Might not be enough to notice, but I always do them that way.

 

the books (factory and aftermarket) tell you to put the tight coils up top.

Like everyone said, it REALLY doesn't matter to the performance of the spring as long as they're the same; I believe Carl is right as to why they say to put the tight coils on top.

 

Okay - I'm not an engineer, but I've done a lot of physics.... and that there just doesn't make sense.

For the actual definition, here's the wiki on "Unsprung Mass"
Unsprung Weight

In short, unsprung weight is the mass of the suspension, wheels and other components directly connected to them, rather than the remainder that is supported by the suspension (sprung weight).

Okay - so how exactly does turning the springs around change the figure?

 

Because the tight end is "more dense" and the bottom half to one-third of the spring itself is unsprung weight? (That's my reasoning anyway...)

I did it because the book said so.

 

When you did your physics your calculations were based on a weight (point mass really), a spring and potentially a damper. In your calculations you probably assumed no mass to the spring or damper because it makes the calculations really complicated.

If you think about a conventional spring in the fork and the dynamics it's pretty easy to realize that the very bottom of the spring moves with the wheel and is completely unsprung. Likewise the very top of the spring moves with the frame and is completely sprung.

Working your way up from the bottom of the spring it's mass goes from mostly unsprung through 50/50 sprung/unsprung to mostly sprung.

By having the tight coils at the top you shift that extra mass to the mostly sprung end of the deal. In fact, those coils collapse pretty quickly and it becomes a heavy spacer that is completely sprung (top) or unsprung (bottom).

Aren't you glad you asked? :wink:

 

YEAH. What Carl said.

I was thinking about this after my last post, and the "percentage" of the spring that is sprung vs. unsprung changes as the suspension compresses or extends doesn't it? In other words, the "point" at which the mass of the spring goes from unsprung to sprung moves up and down as the suspension works, doesn't it? Or does it always remain at the center of the SPRING, moving only because the length of the spring is different?

I don't know, I'm thinking out loud... Carl?

 

I've been told that with a conventional spring you treat it as 50/50 and the center of mass at the center of the spring. My math is not up to proving this but it sounds reasonable.

The proper way to treat a progressive is as a stack of springs (in fact on quads and rear suspensions it is often done with a stack of springs). As each spring collapses it becomes a rigid body and it's spring rate gets dropped from the equation.

 

So with a conventional spring the "transition point" only moves relative to the whole assembly but remains (more or less) at the center of the spring itself.

Therefore on a progressive spring you'd actually get a SERIOUS change in the "transition point" once a section of the spring collapses to the point where it becomes a 'spacer.'

Interesting. Makes a case for putting the tighter coils up top.

 

I wish to thank all you gentelman for the lesson in sprung- unsprung weight. Never looked at it that way before. Thanks

 

I'd like to thank those guys for the headache I just got.

 

Actually - yes - makes perfect sense now that I'm not halfway into a bottle of rum, and I take the time The springs would be unique in that they are both sprung AND unsprung - likely using the centre of mass for the spring itself, no?
So given that - I could see why to have them at the top.
So it comes down to:
At the top - bit less unsprung weight, but possibly a bit noisier.
At the bottom - bit more unsprung weight, but possibly a bit quieter.

 

+1!

haha