Help choosing spring size- Mtbr.com
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  1. #1
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    Help choosing spring size

    I just picked up a 2008 Giant Reign X1 with a Fox DHX 3.0. It currently has a 550x2.75 spring on there. When I sit on the bike, it compresses a lot. I've tried turning the collar down some, but that doesn't seem to help, and I don't want to turn it down too much more.

    I searched the forums a bit, and am wondering if my calculations for selecting a spring are correct. I'm about 225lbs with gear, the stroke length is suppose to be 2.25, and the wheel travel according to Giant is 6.7 inches.

    Using this site: http://www.tftunedshox.com/info/spring_calculator.aspx, it says I should have a 700 lb spring if I want 28% sag . Does that sound about right?

    And looking at jenson usa, I should get the 700lbs/2.3. I assume the stroke length is fine if its larger, seeing as the current spring in there is even bigger.

    In summary

    1. Do I have the right spring weight?
    2. Should I go for a larger spring?
    3. The TF site says Manitou springs work in Fox shocks. They are 1/3 the price as the Fox springs (the 650x2.25 is $10), worth saving the $ or stick with Fox?

    Thanks in advance for any advice.

  2. #2
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    hmmm...now I'm confused. If I put in the 2.75 stroke length, it says I need a 470, which means the current spring should be enough. Why does it sag so much when I sit on it.

  3. #3
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    quick back of the envelope calculations (and gut feeling), 700# seems like a lot for the setup you described. Fox's calculator puts you at 542 (which obviously doesn't really exist, but 550 is close). What are you getting for sag now?

    as for you other questions: Assuming you really do have a 2.25" stroke damper, you can use a longer spring, or not, it doesn't matter. The "weight" is pounds/inch of compression, so with a 2.75" spring, you just won't get the last 0.5", but the rate is the same. I'm a little surprised the longer spring will fit on your damper, so I'd double check that 2.25" damper stroke is really what you have. When you put 2.75 in the calculator, you are telling it you have 2.75" of damper stroke, which it treats as if you had a lower leverage ratio, and thus need a lighter spring.

    Manitou springs have a larger diameter than Fox, which means they can (but often don't) hit the reservoir when the shock compresses (and the OD of the spring increases). I've never had a problem, but others have.

  4. #4
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    Quote Originally Posted by Joules
    quick back of the envelope calculations (and gut feeling), 700# seems like a lot for the setup you described. Fox's calculator puts you at 542 (which obviously doesn't really exist, but 550 is close). What are you getting for sag now?

    as for you other questions: Assuming you really do have a 2.25" stroke damper, you can use a longer spring, or not, it doesn't matter. The "weight" is pounds/inch of compression, so with a 2.75" spring, you just won't get the last 0.5", but the rate is the same. I'm a little surprised the longer spring will fit on your damper, so I'd double check that 2.25" damper stroke is really what you have. When you put 2.75 in the calculator, you are telling it you have 2.75" of damper stroke, which it treats as if you had a lower leverage ratio, and thus need a lighter spring.

    Manitou springs have a larger diameter than Fox, which means they can (but often don't) hit the reservoir when the shock compresses (and the OD of the spring increases). I've never had a problem, but others have.
    Oops. I just had my wife check again, its not 2.75 - I was at work and was going off the top of my head. The current spring is actually 550x2.35.

    Maybe I better step on the bathroom scale again too.

    I'm going to try adjusting it again tonight. Maybe try the 600 spring if it still seems to soft.

    Thanks for your help.

  5. #5
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    The 2.35 on your spring isn't the shock stroke, it's the compression to bind length of the spring. It means the spring can compress 2.35" before the coils bind.

    Your rear suspension is a 3:1 ratio. With a ratio that pretty high, I can definitely see you needing a 700# spring at your weight. Don't forget you want the spring preloaded as little as possible.

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