what do you fork gurus reckon?

[cl1ve2004]

got a pair of unused stock fork springs from my 2005 FZ6 ..a bit longer ( 10mm) than the 1000 spring, and coils look


less tightly wound..any point trying them out on the thou ?? or is it just me pis*ing in the wind for the sake of it??

[PieEater]

IMHO I really wouldn't. The stock springs are not firm enough as it is and replacing them with less tightly wound springs would just make things worse. The fact that they are slightly longer may make up for some of the difference in tension but I doubt it would be anywhere near enough to make it a viable option. Others may disagree..........

[NorthWestern]

If the wire diam is the same and there are less winds then they will be stiffer springs.  If that is what you are after then seeing as its a quick job it would be worth a try.

[cl1ve2004]

Thank you for the input guys..The gauge of wire is slightly less on the FZ6 (the thou is 5.25 and FZ6 5.05) my silly logic was ..the thou springs have done 25k and the FZ6 nothing ..so maybe the tension has lessened on the thou springs??
Cheers

Clive


here's a pic anyway   thou at lower of photo

[PieEater]

If the wire diam is the same and there are less winds then they will be stiffer springs.

I don't understand the logic in that, surely with less winds on the spring it will be weaker not stronger !?! With progressive springs you have a section that has less winds that compresses more easily and a section with more winds that is firmer.

[NorthWestern]

The more winds you have (given the same length) then the length of wire used is longer, hence it is "softer".  It is the same principle of cutting a section of spring off to stiffen it.

[cl1ve2004]

I'm learning all the time from you guys !!!!

I reckon I'll give 'em a run..

[PieEater]

The more winds you have (given the same length) then the length of wire used is longer, hence it is "softer".  It is the same principle of cutting a section of spring off to stiffen it.

I still don't understand it but you are right - http://www.motorcyclistonline.com/making-sense-motorcycle-suspension-springs-tech-tips-mc-garage-technology

[NorthWestern]

You can think of it as a spring is simply a convenient way to bend a metal rod.  The more winds you want the longer the rod has to be to make a spring of the same length.  If you gripped a rod at both ends with your thumbs pointing to each other, to bend it you want to raise both your thumbs up.  It is much easier to do that the longer the rod is.  Progressive springs have tight winds at one end so as the spring compresses these collapse onto each other which locks off those winds effectively shortening the rod.  This is the same as starting with your hands wide and then moving them closer together on the rod, it will become harder to bend.

[Andy W]

You can think of it as a spring is simply a convenient way to bend a metal rod.  The more winds you want the longer the rod has to be to make a spring of the same length.  If you gripped a rod at both ends with your thumbs pointing to each other, to bend it you want to raise both your thumbs up.  It is much easier to do that the longer the rod is.  Progressive springs have tight winds at one end so as the spring compresses these collapse onto each other which locks off those winds effectively shortening the rod.  This is the same as starting with your hands wide and then moving them closer together on the rod, it will become harder to bend.

Wow!    I'm lost so I'll just believe ya!   

[Fazerider]

Assuming the steel of the springs have similar properties a given length of the thou spring will be about 8% stiffer because it depends on the square of the diameter. As has been pointed out though, the total length of that spring is greater because it has more turns.
You could experiment by securing one end and hanging a weight from the springs in turn to see which is stretched more.

[stet]

Shame to contradict on my first post, but the stiffness of a round cross section torsion bar (spring is a coiled torsion bar) is proportional to the fourth power of the torsion bar diameter. As a result a slight increase in diameter results in a large increase in stiffness.

[Fazerider]

Shame to contradict on my first post, but the stiffness of a round cross section torsion bar (spring is a coiled torsion bar) is proportional to the fourth power of the torsion bar diameter. As a result a slight increase in diameter results in a large increase in stiffness.

Ah... my mistake. Can't quite get my head around how it's a torsion spring, but you appear to be correct.
That would make the thou spring about 17% stiffer if all other variables are the same. And even if you do measure the spring rates it probably doesn't help much since the springs are different lengths and the FZ6 one looks as if it'll hit the stiffer rate a bit sooner.

[stet]

It is not intuitive- I had to look it up. In fact I thought it was the third power.

[stet]

Shame to contradict on my first post, but the stiffness of a round cross section torsion bar (spring is a coiled torsion bar) is proportional to the fourth power of the torsion bar diameter. As a result a slight increase in diameter results in a large increase in stiffness.

...
That would make the thou spring about 17% stiffer if all other variables are the same. And even if you do measure the spring rates it probably doesn't help much since the springs are different lengths and the FZ6 one looks as if it'll hit the stiffer rate a bit sooner.

Yes the thou spring is 17% stiffer, but I recon the thou is roughly 14% longer, so the effective base rate would be about the same for both springs. As you say, it looks like the FZ6 would hit the stiffer rate sooner.

There is another aspect too: the FZ6 is the weaker (mechanically) of the two springs so I would not recommend using an FZ6 spring in a thou, although this is based on theory rather than any practical experience with the two springs.