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  1. #1
    Thinks it's still 1991. 1987cp's Avatar
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    Question on adjusting a suspension fork (suspension n00b)

    My wife bought an '09 Globe Carmel 3 with a suspension fork and doesn't seem to be able to get it really stiffened up enough. I know essentially nothing about sproingy components, but she says the dealer's advice was that it should be adjusted so that it does not compress under the rider's weight but does compress when she hits bumps, and that the preload is adjusted by a knob on the right fork tine. Okay, makes decent sense so far. Except that the adjustment knob on the right-hand fork tine has been turned many full turns to the right and is now clicking every revolution as though it's at the end of an adjustment screw, and the fork still squats when she gets on. There does not appear to be any sort of adjustment on the left-hand fork tine, though if there were I imagine it would be for damping and not spring preload.

    This particular fork is labeled SR Suntour NEX-4100, for what that's worth. I downloaded a couple of PDFs from the Suntour website, but the only relevant info I've found is that the right fork tine has the spring in it, and we already knew that.

    Does it sound like we're doing something wrong? Do forks for "comfort" applications such as this bike sometimes have insufficient spring rates to provide the recommended performance characteristics? Or is there possibly some sort of adjustment procedure that we may be overlooking? The Specialized owner's manual is no help at all, as doesn't seem to even cover specific model ranges. I suppose (based on wild assumption) that it may be theoretically possible to disassemble the fork and substitute a higher-rate spring, but it seems silly to think that such a measure would be necessary.

  2. #2
    Senior Member JonathanGennick's Avatar
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    A fork should sag slightly under a rider's weight. The commonly accepted range is for a fork to sag 20-25% of its travel just from the rider sitting on the bike.

    Use a zip-tie to help measure sag. Put a zip-tie around one, upper fork stanchion. Snug it down to the bottom against the lower. Sit on the bike. Get on gently, without bouncing, but do put your full weight on the bike. Try to get as close to your riding position as possible. Then carefully dismount. Then measure the amount the zip tie has moved upwards.

    BTW, it is common with coil forks to swap out springs to accommodate heavier or lighter riders. Preload dials provide only a small range of adjustment.

  3. #3
    Thinks it's still 1991. 1987cp's Avatar
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    Thanks for the reply! I actually just thought of the spring-swapping concept on a whim, since it's a common thing for motor vehicles. We'll have to try your procedure and see whether we can in fact get it in range with the stock spring.

    If one were to swap springs, I suppose the logical place to start would be with the dealer that sold her the bike ... failing that, where would I look and how would I determine what springs are compatible with this fork?

  4. #4
    Senior Member DannoXYZ's Avatar
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    The dealer that told you the fork shouldn't compress with the rider's weight doesn't know squat about suspension or its adjustments. That should be a SR Suntour NEX-4110-700 on that bike and one should actually select a spring-rate and hi/low-velocity compression-damping so that the fork will just barely bottom-out when hitting the biggest bump a rider will encountre in their rides. You want to use up all available travel on the biggest bumps. This will give maximum absorption of the impact.

    Rebound is the other side of the equation and rebound needs to be balanced with the spring-rate + rider's weight. Higher spring-rates and lower-weight riders will need more rebound damping. So if you increase the spring-rate or preload, you'll need to use thicker fork-oil or modify the valving in the dampers.

    There's no "one" simple way to adjust a suspension fork as all the adjustments work in balance. If you adjust one thing, this causes a cascade of other adjustments as well. So start with:

    1. rider weight and terrain-type and riding-style
    2. select spring-rate for full suspension-travel on biggest bump, use preload for fine-tuning
    3. select rebound damping-rate to match spring-rate + rider's weight
    4. adjust low/high-velocity compression-damping (that's the shock's vertical speed, not the rider's horizontal speed)
    5. adjust low/high-velocity rebound-damping, most shocks have only one adjustment and that's for rebound.
    6. adjust "knee-point" where damper switches from low to high-velocity damping ratios

    You can download manual here: http://www.srsuntour-cycling.com/SID...tail&tnid=1604

  5. #5
    Senior Member JonathanGennick's Avatar
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    Quote Originally Posted by 1987cp View Post
    If one were to swap springs, I suppose the logical place to start would be with the dealer that sold her the bike ... failing that, where would I look and how would I determine what springs are compatible with this fork?
    I would begin with the dealer. I'm afraid I don't know enough about Suntour-brand forks to give advice beyond that. But a good dealer ought to know how to get different springs, if they are available.

    Don't be afraid to just take the bike and ask the dealer for some help. Helping you dial in a brand-new bike is part of their service, or at least it should be.

  6. #6
    I have senior moments... bikinfool's Avatar
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    The dealer's an idiot. Since preload's the only adjustment on that fork, spring swap (if you can even get an alternate spring) pretty much the only way to go. Wouldn't surprise me the preload adjuster already broke. Even for quality suspension forks, not much choice but factory springs, there's virtually no aftermarket alternatives.
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  7. #7
    Senior Member DannoXYZ's Avatar
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    There are ways to increase spring-rate by cutting off a section of spring and replacing it with PVC tubing. Very common technique when prepping street motorcycles for racetrack duty. Not likely to be needed for a hybrid bicycle being ridden mostly on the road.

    Use the zip-tie suggestion mentioned earlier to measure how much suspension-travel you are actually using. If you're not bottoming-out the fork, there's no need to increase spring-rate or preload.
    Last edited by DannoXYZ; 05-03-10 at 04:44 PM.

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