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Thread: fork spring question

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  1. #1
    P Monk
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    fork spring question

    Since I bought my /6 in 08, the only thing I have done is change fork oil once.
    I have never been real happy with the ride and am going to disassemble and do a rebuild on them.

    Supposedly the bike has progressive springs according to the previous owner. I am considering the heavier fork springs as recommended by Max.

    I am looking for just a little softer ride than I have now, but without creating a whole lot of fork dive.

    suggestions anyone?
    P. Monk
    My prized possessions. 74 R90/6 Mine! (also know by bride as the Black Hole). 09 R1200 GS. My wife, 1953 model who has survived aplastic anemia and a bone marrow transplant. My most prized possession is my relationship with Jesus!

  2. #2
    Registered User toooldtocare's Avatar
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    I do not understand the heaver spring to give a softer ride? Anyway, best to know what is in there first. Some springs came with spacers to increase their compression force. It may be enough just to remove it, if one is in there, or shorten it. Good luck.

    Wayne

  3. #3
    Administrator 20774's Avatar
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    Quote Originally Posted by toooldtocare View Post
    Some springs came with spacers to increase their compression force.
    Spacers don't change the rate of the spring...they just change the amount of sag that will be there once loaded. Unless the spring is a dual-rate spring, but even then you have to get the spring very much compressed so that part of the coils become coil bound...which then effectively changes the spring rate.
    Kurt -- Forum Administrator ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  4. #4
    Registered User toooldtocare's Avatar
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    Thanks Kurt. What I meant is, spacers increase the preload of the spring, thus increasing the force to compress it, same as on the rear shocks. This is only true if you have to force the top caps in place while compressing the springs, which I have had to do most of the time. I have tuned the rate and amount of dive on various bikes by changing the length of the spacers to suit me instead of always going with a heaver or lighter spring.

    Wayne

  5. #5
    Administrator 20774's Avatar
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    Wayne -

    I'm having trouble wrapping my head around that. If we're talking about a constant rate spring, that means it takes X pounds to compress the spring Y inches. Each inch requires the same force of X pounds...the total force is cumulative, so 2Y inches is 2X pounds. Is that the "increasing force" you're talking about?

    If we didn't have a spacer and the spring was not compressed a bit even with the rider sitting on it (unrealistic, I know), hitting a certain bump will cause the spring to deflect a given amount...I'll say the spring deflects 2 inches. Now say we have a spacer which compresses the spring just one inch...again, the spring wouldn't compress any more with the rider sitting on it. Go back down the road at the same speed, hit the same bump, the spring is going to deflect the same 2 inches. No additional force is required to deflect the spring in the latter situation with the spacer.

    Am I not understanding things correctly in this simple situation?
    Kurt -- Forum Administrator ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  6. #6
    Registered User toooldtocare's Avatar
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    Example: First, assume we are only working with a single fork bike. If you are talking two forks, multiply everything by 2. Also, we are talking constant wound springs, not progressive, they are slightly different.

    Steps

    1. A spring not under load just sits there. Apply force, say 50 pounds in our example, and it compresses 1 inch. To hold it there it there would take a constant 50 pounds, so you cannot let go.

    2. To compress it another 1 inch (2 inches total) let's say it takes an additional of 50 pounds. So now you are holding the 50 pounds you first applied to hold it down 1 inch, plus a second 50 pounds for the second inch to drop it 2 inches total, or 100 pounds to keep it dropped two inches.

    4. Now, put that spring in the fork without the spacer and assume that it does not compress when you put the cap on. Apply 50 pounds and it would drop 1 inch. Apply any force and it will start to drop, even an amount as little as 1 or 2 pounds and it will start to drop. This is the same as step 1. Add an additional 50 pounds of force (100 total) and it would drop 2 inches. The same as step 2.

    5. Now, remove the top cap and put a 1 inch spacer in, compressing the spring 1 inch inside, but not changing the length of the fork. The cap is providing that first 50 pounds. Same as step 1 again, but the bike stays all the way up.

    6. Now start to apply force. To even start to move it would take more than 50 pounds, because it is already preloaded to 50 pounds. Since you put 50 pounds on it to start it moving, you would have to put another 50 pounds (100 total) to drop it that inch. Remember, the fork only dropped 1 inch, but the spring inside 2 inches. Same as step 2 again.

    This is what you do when you turn the preload on your rear shocks, you partially compress the spring. This causes the bike to take more force to move, thus you can carry a heavier load.

    Does this make sense? Am I thinking right, or getting confused because I am comparing it to the rear shock?

    Wayne

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