Fork Spring Mod

[bikerphil]

Decided to do a little experimenting with the factory straight wound springs on my 79 Special. For the last couple of years I've been running Progressives and I had the originals just sitting around. The Progressives to me are way too soft, even with a 4" long PVC spacer in the top.

First I chopped 20% of the length of the springs off, making these factory springs 20% stiffer.



Then I heated the cut ends up with a torch and pressed them flat to compress the end coils so they could be ground down flat.



I installed the springs with a 4.5" PVC spacer to make up for the lost spring. Took her out for about 100 miles of testing and I am very happy with the handling. No front end diving (without air) and definite improved handling. Running 3/4" of spring preload now instead of the previous 2" with the Progressives. JMHO, straight wound springs rule! Cost of mod, $0.

[XS1100 Newbie]

Will that work with my special?

[bikerphil]

I don't see why not. I'm very suprised this mod worked out as well as it did. Each spring only took about 10 minutes to do. I'm just waiting to see if someone will chime in and say this is not a good idea for some reason.

[yamahansolo]

Go for the gold valve emulators!!!! My bike handles a billion times better. If you don't want to spend the 150 on them there are 40 knockoffs on mikes xs. I have been out running my friend with an 04 r6 easy. You pedople have to try them

[fredintoon]

Will that work with my special?

Hi Newbie,
the fork springs that Bikerphil shortened were the originals from his '79 Special, so, yeah. That is, yes, shortening a spring makes it stiffer. OTOH, Crazcnuk has often claimed that most bikes sold in North America come with springs that are too hard and damping that's too soft.
Presumably those Gold Valve Emulators improve damping and perhaps that's a better thing to do?

[yamahansolo]

Trust me they are incredible

[Cobia]

Nice mod, Phil

Always thinking about how to make them better, within the budget!!!

[bikerphil]

Go for the gold valve emulators!!!! My bike handles a billion times better. If you don't want to spend the 150 on them there are 40 knockoffs on mikes xs. I have been out running my friend with an 04 r6 easy. You pedople have to try them

Yep, I have those knockoff ones in the FJ forks on my Standard and they do work well.

[bikerphil]

Crazcnuk has often claimed that most bikes sold in North America come with springs that are too hard and damping that's too soft.

Fred, I'll agree on the soft damping but not about the springs being too hard, at least for my weight, 175 lbs. If the springs are correct for your weight, the fork caps should be able to be threaded on very easily, only compressing the spring about 3/4" with the correct rider sag adjustment.

[Drumagician]

I believe that you did not gain any spring stiffness other than the 0.5" increase in spacer length you added. Every spring has a inherant spring constant "k" and it cannot be altered unless you deform (meaning change its equilibrium state or length) the spring. Now the force that the spring exerts back is dependent upon the "COMPRESSED" length of the spring. The change in handling is merely due to the stiffer stock springs and the 1/2" extra preload you added with the spacer.

[crazy steve]

...I'm just waiting to see if someone will chime in and say this is not a good idea for some reason.

I think it's a great idea if it works, particularly for the cost, but I will add this personal observation. I've cut springs down numerous times (only one bike, usually cars, sometimes with recommendation from suspension 'gurus'), and while it always worked well initially if done right, every single damn spring I cut ended up 'sagging' on me sooner or later.

Why that is, I can't say. I tried to get a satisfactory explanation and never did, so I'm pretty gunshy about cut springs these days. So you may want to keep an eye on ride height....

Of course, YMMV

[bikerphil]

I believe that you did not gain any spring stiffness other than the 0.5" increase in spacer length you added. Every spring has a inherant spring constant "k" and it cannot be altered unless you deform (meaning change its equilibrium state or length) the spring. Now the force that the spring exerts back is dependent upon the "COMPRESSED" length of the spring. The change in handling is merely due to the stiffer stock springs and the 1/2" extra preload you added with the spacer.

What I forgot to mention is the Progressive springs are 20 1/2" long and require a 4" spacer for the Special's fork application. The Special's factory spring length is a little over 24" long and do not require a spacer. Now I cut about 5" off the factory spring and replaced it with a spacer which has to make it stiffer. I can tell just by compressing the forks. The general rule is: Shorten a straight wound spring by 10% and it becomes 10% stiffer.

Next project is to build a tool to measure fork spring rates.

[Bullet]

Yep, I have those knockoff ones in the FJ forks on my Standard and they do work well.

Do these fit in the XS Special forks as well ?

[Drumagician]

So what would happen if you just added your spacer without cutting the spring? Do you think it would be stiffer than it is currently? If so, why not just add a 1-2" spacer and not cut anything to achieve the same spring rate?

[Drumagician]

Please don't think that I am arguing with you. If there is something to be learned here, I would like to learn it.