Author Topic: Fork Spring Mod - Advice needed...  (Read 4853 times)

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Offline CRocker

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Fork Spring Mod - Advice needed...
« on: July 07, 2012, 06:39:20 pm »
OK...I'm feeling kinda dumb...I'm preparing to cut 4" off my stock fork springs ('97 forks)...and, I can't find a definitive answer...seems to be members in both camps...I'm not a racer...more of a sport touring kind of guy...200lbs...kneesavers and risers...just looking for a little help...

Which end should I cut 4" off?

Thanks!
« Last Edit: July 07, 2012, 06:45:26 pm by CRocker »

Offline Mettler1

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Re: Fork Spring Mod - Advice needed...
« Reply #1 on: July 08, 2012, 12:10:18 am »
  SiSF recommends  cutting the "B" end in your pic. Cut mine off the "tight wound end" also.
   If you install an Emulator your spacer size will be about 3". If no Emulator the spacer will be 4".  Don' forget fender washers on each end of the spacers.
« Last Edit: July 08, 2012, 12:13:19 am by Mettler1 »
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Offline CRocker

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Re: Fork Spring Mod - Advice needed...
« Reply #2 on: July 08, 2012, 12:39:38 am »
Fender washers on each end of the spacer?  What about that pre-load washer as a top washer?   Haven't done anything yet...so I could get a couple more fender washers...only grabbed a couple for the bottom of the spacers...

Offline Mettler1

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Re: Fork Spring Mod - Advice needed...
« Reply #3 on: July 08, 2012, 02:55:29 am »
  I think you are right about only needing 2 washers. I think I bought 4 washers just in case. I found out a long time ago if you don't have spares, "YOU ARE SCREWED". If you have spares you will never need them and couldn't find them if you did!! :truce:
'94 Concours 115,000 miles-- 7th gear,2MM,KB fork brace,Over flowtubes,Stick coils,Tcro shifter,GPS,SiSF'sTorque cams,SPOOKFAK,block off plates, SS brake & clutch lines,KB risers, FENDA EXTENDA, emulators, SiSF carb Spa, Delkevic exhaust, Murphs' knee savers +grips, etc

Offline CRocker

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Re: Fork Spring Mod - Advice needed...
« Reply #4 on: July 08, 2012, 02:57:48 am »
HA HA...BTDT! 

Thanks for the help!


Offline Daytona_Mike

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Re: Fork Spring Mod - Advice needed...
« Reply #5 on: July 08, 2012, 02:08:24 pm »
After you cut and then grind the spring as flat as you can on the cut end, drop that end into the fork tube first.
Normally aspirated engines have perpetual turbo lag
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Offline turbojoe78_MA

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Re: Fork Spring Mod - Advice needed...
« Reply #6 on: July 08, 2012, 08:16:18 pm »
Daytona_Mike,   I did the cut spring mod and put the cut end at the top, like before they were cut.

Is there a reason you feel it's better to put them in with cut side in first?
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Offline Daytona_Mike

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Re: Fork Spring Mod - Advice needed...
« Reply #7 on: July 08, 2012, 09:06:03 pm »
The end that is cut  will not seat perfectly  flat to the washers and could scrape and scratch on  the inside of the fork tube as the suspension moves up and down.
Putting the cut end at the bottom means it never moves off the bottom so it wont matter.
Normally aspirated engines have perpetual turbo lag
2000 Red C10 1052 kit 100+HP  + way more torque.
2008  C14 Silver Dammit Full AreaP- Flies are put back in SISF_Flash
2011  KLR650   688 piston ported and polished
2011  KTM 530    This thing is FUN!!

Offline GF-in-CA

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Re: Fork Spring Mod - Advice needed...
« Reply #8 on: July 08, 2012, 10:24:18 pm »
The end that is cut  will not seat perfectly  flat to the washers and could scrape and scratch on  the inside of the fork tube as the suspension moves up and down.
Putting the cut end at the bottom means it never moves off the bottom so it wont matter.

Mike, not sure I understand the reasoning here.  The lower end of the spring sits on top of the damper rod, which moves up and down.  The upper part bears against the end of the spacer, which is fixed relative to the fork tube.  It seems more likely that having the cut end at the lower end would scrape the inside of the tube where the damper rod slides.     :smiley_confused1:

Either way, it seems like if you break any sharp edges on the cut there shouldn't be a concern about scraping.
« Last Edit: July 08, 2012, 10:29:10 pm by GF-in-CA »
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Offline turbojoe78_MA

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Re: Fork Spring Mod - Advice needed...
« Reply #9 on: July 08, 2012, 11:39:19 pm »
The end that is cut  will not seat perfectly  flat to the washers and could scrape and scratch on  the inside of the fork tube as the suspension moves up and down.
Putting the cut end at the bottom means it never moves off the bottom so it wont matter.

Thanks for the explanation, makes sense to me.  Next time I do a fork oil change I'll flip them over.
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Offline CRocker

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Re: Fork Spring Mod - Advice needed...
« Reply #10 on: July 09, 2012, 12:52:15 am »
I guess I'm wondering now about flipping the spring upside down...I'm trying to think this through...since it is a dual rate spring, doesn't it transmit force from the bottom to the top...which is where the spring compression begins...and where the softer rate windings are?  So, if I flip it over, and place the softer rate windings at the bottom of the fork...wouldn't that compress the stiffer windings first?  Does this hurt anything?  Or, better yet...am I thinking correctly about this?  Or, will it even matter on the street?   :confuse:


Offline Daytona_Mike

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Re: Fork Spring Mod - Advice needed...
« Reply #11 on: July 09, 2012, 01:19:24 am »
The  rate of the spring wont change  with the spring upside down or not. The softest part of the spring will always compress first no matter where it is.
The damper rod is bolted to the lower fork tube so it cant move but then again the top of the spring  never leaves its position against  the fender washer and spacer and the upper fork tube travels  with it so,
after thinking about it  there is no real  difference  which way the spring is installed.
Sorry about that, just put the springs back in normally. I was thinking that because it is hard to get the end nice and flat after cutting it that the spring might bow outward a little and scrape on the inside tube.
If you had  emulators I would want the original machined end holding that emulator down flat so at this point just try and get the end ground flat.    Would it be possible to heat and bend the last coil so as to get close  that factory flat  grind? I suppose that might make it brittle.
« Last Edit: July 09, 2012, 01:28:17 am by Daytona_Mike »
Normally aspirated engines have perpetual turbo lag
2000 Red C10 1052 kit 100+HP  + way more torque.
2008  C14 Silver Dammit Full AreaP- Flies are put back in SISF_Flash
2011  KLR650   688 piston ported and polished
2011  KTM 530    This thing is FUN!!

Offline CRocker

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Re: Fork Spring Mod - Advice needed...
« Reply #12 on: July 09, 2012, 01:26:14 am »
Seemed like I kept coming back to that "Does it matter?" point...and, no, no emulators... :beerchug:

Offline Daytona_Mike

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Re: Fork Spring Mod - Advice needed...
« Reply #13 on: July 09, 2012, 01:29:49 am »
I agree, and Gary is right. It dont matter.
Normally aspirated engines have perpetual turbo lag
2000 Red C10 1052 kit 100+HP  + way more torque.
2008  C14 Silver Dammit Full AreaP- Flies are put back in SISF_Flash
2011  KLR650   688 piston ported and polished
2011  KTM 530    This thing is FUN!!

Offline GF-in-CA

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Re: Fork Spring Mod - Advice needed...
« Reply #14 on: July 09, 2012, 01:35:42 am »
I guess I'm wondering now about flipping the spring upside down...I'm trying to think this through...since it is a dual rate spring, doesn't it transmit force from the bottom to the top...which is where the spring compression begins...and where the softer rate windings are?  So, if I flip it over, and place the softer rate windings at the bottom of the fork...wouldn't that compress the stiffer windings first?  Does this hurt anything?  Or, better yet...am I thinking correctly about this?  Or, will it even matter on the street?   :confuse:

If it were me, I'd put the cut end up, but the spring doesn't care which way it goes to work properly.  As was discussed before, there MAY be a SLIGHT advantage with unsprung weight with the close coils up, but we're talking a few grams difference - virtually nothing, IMO.
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Offline CRocker

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Re: Fork Spring Mod - Advice needed...
« Reply #15 on: July 09, 2012, 02:16:04 am »
Thanks guys!  I'm sure I was just over-thinking parts of the process...and not thinking about other parts...I've filed the cuts down so they are smooth...gonna wash 'em off in the morning and put it all back together with the 10wt fork oil I had just put in a couple of months ago...maybe...I do have that bottle of 15wt fork oil in the garage...we'll see...

Anyway, thanks again for all your input!

 :beerchug:

Offline WillyP

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Re: Fork Spring Mod - Advice needed...
« Reply #16 on: July 09, 2012, 01:01:20 pm »
Lets see if it helps to put it this way:

Every turn of the spring has some 'give'. Since the spring is the same material and the same wire gauge from end to end, each turn contributes the same amount of softness. Therefore, the more turns in play, the softer the spring. Suspension travel is distributed equally among the turns, because they all contribute equally. So removing coils makes the spring firmer. To be clear, all of the coils, being of the same softness, close and open at the same time. For a single rate spring, end of story.

For a variable rate spring, everything above still applies. Until the suspension closes the coils so much that the tighter wound coils are completely closed. At that point, they can no longer collapse any further, so they no longer contribute and softness to the overall spring rate. So as these tighter coils become closed, they are taken out of play, and act like a solid spacer, and the spring has less softness.
« Last Edit: July 09, 2012, 01:03:32 pm by WillyP »
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Offline CRocker

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Re: Fork Spring Mod - Advice needed...
« Reply #17 on: July 09, 2012, 05:22:17 pm »
Well put...

Thanks WillyP!

Offline Strawboss

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Re: Fork Spring Mod - Advice needed...
« Reply #18 on: July 09, 2012, 11:54:01 pm »
I'm reading here and am I'm thinking, can I use 4 inches of my stock spring instead of spacers in addition to the sonic springs and emulators?
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Offline BBroj

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Re: Fork Spring Mod - Advice needed...
« Reply #19 on: July 10, 2012, 12:47:17 am »
I've read and thought about this mod quite a bit. One question never seems to get asked or answered, does this limit the overall suspension travel? It seems like it would, but I'm not sure how much. If you are cutting 4 inches off of the tightly wound end of the spring, you would only loose the amount of travel represented by those 4 inches of the spring, right? Anyone know about how much that is and how noticeable it is on the road?
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Offline CRocker

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Re: Fork Spring Mod - Advice needed...
« Reply #20 on: July 10, 2012, 02:07:30 am »
I've read and thought about this mod quite a bit. One question never seems to get asked or answered, does this limit the overall suspension travel? It seems like it would, but I'm not sure how much. If you are cutting 4 inches off of the tightly wound end of the spring, you would only loose the amount of travel represented by those 4 inches of the spring, right? Anyone know about how much that is and how noticeable it is on the road?

BBroj...I would love to be able to answer that...but, I'm changing too many things at once to be able to give you a good A/B comparison...have to get ready for a 2500 mile ride next month...I have the forks back together...but, with 15w fork oil instead of the 10w I had in it before...and, I'm changing tires (Shinko 733/734 Wing sizes)...and rear shock (C10 with 15w suspension fluid)...I'd be glad to tell you how it is after all the changes are made...but, that wouldn't address your question...I dunno...lots of people on this forum seem to like the spring mod...

Offline WillyP

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Re: Fork Spring Mod - Advice needed...
« Reply #21 on: July 10, 2012, 03:38:14 pm »
I'm reading here and am I'm thinking, can I use 4 inches of my stock spring instead of spacers in addition to the sonic springs and emulators?

If you did it would soften the suspension. How much? hard to say.

I've read and thought about this mod quite a bit. One question never seems to get asked or answered, does this limit the overall suspension travel? It seems like it would, but I'm not sure how much. If you are cutting 4 inches off of the tightly wound end of the spring, you would only loose the amount of travel represented by those 4 inches of the spring, right? Anyone know about how much that is and how noticeable it is on the road?

You could measure each space between the coils you cut off, add that up to get a rough measurement.
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Offline BBroj

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Re: Fork Spring Mod - Advice needed...
« Reply #22 on: July 10, 2012, 03:54:07 pm »
Someone who has done it could get an exact measurement. Simply run a long bolt or threaded rod through the cut off section, use washers and nuts as needed to compress the spring completely and measure its length. Subtract that from the initial 4 inch length (or whatever it was) and that's the loss in overall travel.
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Offline GF-in-CA

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Re: Fork Spring Mod - Advice needed...
« Reply #23 on: July 10, 2012, 05:18:25 pm »
The only way this would limit your overall travel is if the spring is cut short enough for the coils to get completely compressed before the suspension hit its stops, which is referred to as coil binding.  If the coils don't bind, the travel is limited by the upper fork tube bottoming out inside the lower fork tube.  You can get a pretty good idea if the coils will bind by first measuring the length of the cut-down spring, counting the total number of coils, and measuring the diameter of the coil wire.  Then multiply the number of coils by the wire diameter and subtract this number from the length of the spring along with the estimated preload distance.  This will give the amount of compression required to bind the coils.

maximum compression = total length - (number of coils) X (wire diameter) - preload distance

If the maximum compression is more than the total suspension travel (5.5" for the Connie), the coils won't bind and you will retain full travel.


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Offline CRocker

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Re: Fork Spring Mod - Advice needed...
« Reply #24 on: July 11, 2012, 04:29:30 am »
Uhh....pretty sure I'm just going to put the front wheel back on and take it for a ride to see if I like it... :beerchug: