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  1. #1
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    Coil rear shock spring rate question

    My bike is a true retro ride - '95 Cannondale Super V with the original 5.5" Fox coil shock in back. The spring indicates "750lbs". The suspension was spec'd for my weight by the shop that sold it to me, and the bike rides awesome.

    The shock has never been rebuilt, the spring looks like hell after 23 years of moderately hard use, and is of course steel, so if I upgrade to say a titanium one, should I stick with a 700- or 750lb spring (hard to find), or can the spring rate be lower? Would a 400- or 500lb spring work? What would be the difference in the ride?

  2. #2
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    Does the damper work? Spring sets your sag, damper keeps you there. If you liked it 23 years ago and your roughly the same weight and charging the same, I imagine the same spring rate will do well for you.


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  3. #3
    it's....
    Reputation: Strafer's Avatar
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    Doubt you can buy ti spring for such short stroke anyway.

  4. #4
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    Thanks - it takes a 3" spring, there are some out there -

    Yes, the damper works - so would there be a difference in ride quality if a 400lb spring was installed on the shock, in place of the existing 700lb spring?

  5. #5
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    Quote Originally Posted by noblefishing View Post
    Thanks - it takes a 3" spring, there are some out there -

    Yes, the damper works - so would there be a difference in ride quality if a 400lb spring was installed on the shock, in place of the existing 700lb spring?
    Spring rate is used to balance your body weight with the suspension rate. If you need a 750lb spring a 400lb one will be horribly under-sprung and can lead to premature frame failure. Until then it will ride like crap. Correct spring rate is determined by sag, although there are often charts or calculators available to help guess. If the rate was chosen for you and you haven't lost a bunch of weight then don't touch it. Springs don't wear out.

    In your other thread you said you've never bottomed it out. If that's the case you may want to move to a lighter spring. Be aware that coil shocks have a rubber bumper at the base and you won't necessarily feel the suspension bottom. You can push the bumper up (its inside the coil spring) and see how far you push it down over the course of a ride. Figure you want the rubber bumper touching the base plate if you've gone for a ride where the bike took some noteworthy rear impacts.

    Titanium springs are lighter weight. They weigh less. That's it.




    It's easy to sink more money in to an old bike than you'll ever recoup in improved riding experience. A Ti spring is probably the best possible example of this. IMO if it's over a decade old and you like it... keep it nicely maintained with fresh grips/tires/cables/brakes... and enjoy.
    "Things that are complex are not useful, Things that are useful are simple."
    Mikhail Kalashnikov

  6. #6
    Slower But Faster
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    All good advice above. I would seriously consider servicing the shock if you can find someone with parts for it. They need to be serviced just like your suspension fork.

    If you really have to have a titanium spring, https://www.ti-springs.com/ might be able to custom make you one (though they only list up to 650lbs on their web site).

  7. #7
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    Thanks all - I learned a lot - will stick with the steel spring, might put the air-oil shock off my parts SV on and send the coil shock in for service -

  8. #8
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    Related question: how do I know that my spring rate is correct when riding?

    I just switched to a coil shock for the first time, with a 400lb spring which is what several spring rate calculators suggested. Only had one ride on it before the snow arrived for real, riding in a bit of snow so was holding back but it felt pretty good. But... unless I try one spring rate higher and one lower, how do I know that the spring rate is correct and that I'm using all of the travel? It's easy to see travel used on an air shock with the stanchion o-ring but not possible on a coil shock.

    If the spring was too light, would I feel a bottom-out very noticeably on heavy hits? If it was a little too heavy then is it just impossible to tell? The bottom-out bumper is about 15mm thick so sliding it up and using it as a stroke indicator surely won't be effective because there would be no visible difference between all stoke used and 80% stroke used.

  9. #9
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    You can use the bumper to figure out if your sag is correct. Otherwise if you know how the bike feels with air and the coil shock is making the bike choppered out then you probably have too soft of a spring.

    Have you felt a harsh bottom out before? I do think it's a matter of feel. I guess you could mount a GoPro to watch your shock movement....


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