GS fork spring lengths

[jellywrestler]

i've got a chopper that had what i think are cut down honda forks (720mm) and i'm trying to build some new forks for it. i'm starting with NOS GS1000G tubes, not sure of the coirrect damper rod lengths, have posted a Q on here earlier and now i find i have 420 which maybe too long, i have read some fork springs for large GS's are in the mid 300mm range, can anyone confirm please?
i do have a couple of books which confirm miniumu length, can anyone tell me new length please?

 

[RichDesmond]

Length of fork springs, at least for damper rod forks, doesn't matter much. You just a cut a spacer to give you the correct static preload, about 3/4".

 

[jellywrestler]

Length of fork springs, at least for damper rod forks, doesn't matter much. You just a cut a spacer to give you the correct static preload, about 3/4".

i don't have any to start with so may as well buy the correct length first if that makes sense.hence the query

 

[RichDesmond]

i don't have any to start with so may as well buy the correct length first if that makes sense.hence the query

No. There is no off the shelf "correct length" in your situation. If you have none to start with you're best off buying some in the proper rate for your application. Any stock spring set from that era is going to be way too soft.

 

[bwringer]

Rich, do you have any good links that explain the basic physics of springs as used in motorcycle suspension?

There are several aspects of springs in suspension that are somewhat counterintuitive, such as the fact that the length of the spring is largely irrelevant (within the physical limitations of the material). Spring rate can be a very confusing topic.

 

[RichDesmond]

Rich, do you have any good links that explain the basic physics of springs as used in motorcycle suspension?

There are several aspects of springs in suspension that are somewhat counterintuitive, such as the fact that the length of the spring is largely irrelevant (within the physical limitations of the material). Spring rate can be a very confusing topic.

I don't know of anything that addresses that directly. We have a couple of tech articles up on the website, the preload one is slightly relevant.

http://www.sonicsprings.com/catalog/tech_articles.php?osCsid=b89a5e655d772bdef0fea934fb02e837

You're right though, it can be confusing and counterintuitive. People hear two different things, "if you cut off part of a spring off it will be stiffer" and "length doesn't matter as long as the rate is the same". And they are both true.
In the first case, the coil spacing and wire diameter are the same before and after the cut, so the rate does change. In the second, if we want to make a shorter spring and have it be the same rate we either decrease the coil spacing or the wire diameter, or both.
I've also had people who think that a longer spring will feel different than a shorter one even if they are the same rate. It can be hard to convince them that that's not true.

 

[Guest]

I used GS1100GK forks on my GT750. They are longer & have more travel than the stock GT750 forks.
I used a Progressive Suspension lowering kit to get the correct ride height & spring rate.
Progressive Suspension had a lot of useful info that made the decision fairly straightforward.


Started by using their website selector tool to determine their recommended spring for the forks.
http://www.progressivesuspension.com



They provide the spring specs so you can get the corresponding specs.
http://www.progressivesuspension.com/pdfs/7100-105.pdf



Not exactly sure what you have & what to recommend as the next step. Hope this info helps.