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Fork Springs


I've got blue torn down to do a bunch of things. Fork service is on the list. The previous owner (Hi Fred!) cut the oem springs and installed with emulators. I've got some aftermarket springs that are marked 90#. Does anyone have any idea how these compare. I'm thinking of going with the aftermarket ones and see how that turns out.
Question; What do you want the new springs to do? (Harder or softer)
,,Have you set the sag?
,,Are you currently able to set it (with the available pre load)?
,,Are you using all the travel?
,,Use this to determine; Are the current springs too soft, or too hard?
Next; Find out if the new springs are harder or softer than what you currently have.
ie; Place a weight on top of each spring and see how much that weight compresses the spring.

If you don't want to go thru that, It wouldn't hurt to give them a try anyway. <grin>
(If they don't work, you can easily change back) 🥴

I have a set of Sonic Springs and have considered doing the same.
Forgotten how the Spring rate is noted on Motorcycle springs.
(Maybe someone can explain)
My Sonic's are marked 1.1.
On yours, 90 may mean 90 pound's (or Kg) of force per inch of compression?

Ride safe, Ted

PS: My Sonics came with a note on how long to make the spacer.
Their 13 1/2" long and the suggested Spacer length is 6 3/4" for 94 and up, 7 1/8" for earlier.
** If your using an Emulator, decrease the length by the length of the Emulator. (Approx 3/4")
Give me the length of your springs and we can determine if those dimensions might be useful.
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Well my assumption that the springs were cut is wrong. Once I cleaned the springs up and looked at the ends, I see 1.2. On the race tech website, it's saying to use 1 kg springs. I have a set of 90kg and a set of 1.2kg. I never set the sag. The spacer was short enough that there was basically little to no preload. The adjusters were all the way out. I thought it was a bit stiff so I'm inclined to try the 90's and see what I think. Looking more for comfort than performance. What do you think Ted?


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I have changed the title of this thread after discovering my mistake in assuming the 1.2 spring were cut. I expected the end would be polished smooth after being cut by the manufacturer. Maybe this thread can be useful by illustrating how springs are marked. I had not noticed either of the markings in the past. I've done too much assuming on this project. I assumed it had stock steering head bearings since it came with a set of tapered bearings in the spare parts box that Fred gave me. Imagine my surprise to see tapered bearings already installed when I opened it up. I'll clean and regrease and put it back together. Next will be fork seals, wipers and wheel bearings. Sorry for the confusion.🤦‍♂️
Something is wrong in your numbers.
It would be almost impossible to have a set of 1.2 Kg and a set of 90 Kg springs and not see the difference.
The 90's would be made from HUGE wire.
ie; If 1.2 Kg is needed, 90 Kg would hold up a battleship.
Bottom line; ya need to understand what springs you have.

To be comfortable, you need control of the damping, use full travel, and not have too much or too little sag.
(If your seeking improvement) ya need to "know" what you have, and what your accomplishing.
ie; What do you "want" the new springs to do? (Harder or softer)

To know the answers, You really need to ask yourself the questions I asked and do the tests.
Determine if the 90's are stiffer/weaker than the 1.2's.
See what the sag currently is.
See if your using "all" your travel.
Additionally, see if the damping is set correctly.

NOTE: Most people never do this, and just ride it as it is.
Or they change something and swear it's better. (Placebo effect)

Ride safe, Ted
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I don't know much about C10 stuff, but I would venture to say that the 90 is pounds per inch. Which is 1.6 kg/mm. Conversely 1.2 k/mm, is 67 #/in. Still a big change but if the 1.2 are soft, it might be worth a jump to 1.6.
Dug out the box for this pic. Looked in Fred's notes and he stated that they are 1.2 kg springs. Apologies for leaving the decimal point out. I can't check current sag as the forks are apart.


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Thanks Laker, that could have been the explanation.
But {with Bud's note},,, Ahh soooo, We now understand.
Y'all note that I'm not as dumb as I look. 🤪
ie; I knew that 90 vs 1.1 was a HUGE difference.

I understand that the forks are apart.
Just sayin' that change is best if you understand what ya changed, and (more importantly) what your trying to accomplish..

NOTE: All stock C-10 springs were on the soft side.
But they were progressively wound. (not a single set rate)
Smoother, but unfortunately this allows the bike to dive a lot when braking. {and sag too much if you weigh about 200#}
Because of that, the bike can bottom under hard braking or if you hit big/sudden bumps.
Because their not progressively wound, the .90's may be only slightly stiffer than the OEM's.

Ride safe, Ted

PS: I'm NOT a spring/suspension expert. Just sharing the little that I think I know.
Race tech spring calculator says, if you weigh 220, to use .98kg/mm or closest to that. It says stock is .4kg/mm. I think I'm gonna try the .90kg/mm springs and see how it works out. 15 weight oil from Murph. Oil level set to 158-160 mm or about 6.25 inches. Fork compressed, spring out. Emulators will be installed with blue spring set to 2 turns.