Finding the right coil spring


Got a question about coil springs: when do I need to step up to a heavier weight? I’m running an older Vanilla TC rear shock with a 550 lb spring. 500 lbs was definitely too light. 550 will work, but with a lot of turns to the preload collar. I’m not 100% on my damping settings, but it seems to work pretty well a few clicks in from full fast. Is there a compelling reason to go purchase a 600 lb spring?

Thanks. Scott.

The more you click, the more I can post. Lee Likes Groceries dot com!

Hey Scott,

1. Set your sag. On most bikes, in your normal riding position, you want the shock to sag 1/3 through the travel (check your bike’s manual to be sure). If you need more than a couple turns of preload, you need a stiffer spring.

2. If you still bottom harshly and frequently, add compression damping.

Sounds like you need a stiffer spring.

— Lee

5 replies
  1. turbo says:

    Hey Scott,

    here is my humble opinion if you want to save money (buying springs till you get the right one :)) and time (changing one spring after another):

    – stifness of spring vary on damping system of your frame, i.e. largest difference you can find between single pivot systems and the others – for single pivot you need much more stiffer spring!!!

    – stifness of spring also depends on your riding style, but you can compensate it by more air preload – for DH is much more better higher SAG (more than 30%, of course it’s individual), for FR is better smaller SAG, i.e. around 25%.

    On the net you can find some “spring rate calculators” – you have to feed them with numbers like your weight, travel of your shock (not frame, those are different numbers!), type of shock, riding style (actually SAG number) etc. …

    Maybe sounds difficult, but a time ago i was in same situation (tuned Manitou Metel by disabling propedal, because it sucked, after that i needed stiffer spring).

    Good luck!

  2. Scott says:

    Lee, Turbo-

    Thanks for the input, but there’s still something I don’t get. You both say I want ~30% sag, which I can get with the current spring and many turns of preload. Lee then says I should run a stiffer spring because I have “more than a couple turns of preload.” I’ve heard this before, and this is why I asked the question, but I don’t understand why a stiffer spring will be a benefit to me.

    From what I can recall of various things I’ve read in the past, too much preload on a coil spring can make it hard for the damping to keep up. This sort of reasoning makes sense to me along the same lines as heavier riders need more damping. However, I’ve got plenty of damping left on this shock. In fact, if I turn the dials all the way in, I can lock it out on either the compression or the rebound circuit. Given this, will I still get better performance out of a stiffer spring? Why?

    Checking with the manufacturer won’t help as I made the bike (just finished a couple of weeks ago) ;-D
    BTW, I’ve done a couple rides around Golden (_rides_ not shuttles for you Apex shuttle monkeys) and it was working well there, but that’s not a “real” test. Yesterday I took it to Keystone where it worked pretty well IMO. I do have to add the caveat that I while know what geo I like, I’m not well “cultured” when it comes to suspension. That said, especially with the current 5″ fork on the front (upgrade planned), the rear travel was not slowing me down at all.

  3. leelikesbikes says:

    Look at the writing on your spring. Let’s say it says 2.80 x 500.

    That means the spring rate is 500 pounds per inch, and the spring is designed to compress 2.8 inches.

    Say your shock has a 2.75-inch stroke. Your spring is too light, so you turn the preload collar way in — say 0.25 inches.

    You’re out riding, and you push your suspension all the way through the travel. Do you get 2.75 inches of stroke out of the shock? No. You get 2.55 inches, then the spring starts to bind up. Harsh.

    If you turn the preload collar more than a few turns (more than the difference between your shock stroke and the intended spring compression), you’re eating into your suspension travel.

    — — —

    If you’re smart enough to build your own frame, I’ll assume the actuation ratios, spring curves and all that are dialed. If they’re not, that could really screw things up.

  4. Scott says:

    Aha. Travel reduction as the spring compresses. I hadn’t thought of that. That’s the problem with me being a physicist vs. an engineer. I’m sorta “trained” to think of things in terms of ideal springs that just compress, well, ideally. I imagine I might hear the spring making horrible noises if this were happening. Then again, any time I bottom the suspension there’s probably plenty of other noises (chain, rocks, etc.) to mask that. It may be that I haven’t bottomed the suspension yet as I am a wuss (though I have bottomed the fork — zip tie), but I haven’t noticed the rear being harsh at all on big hits, so maybe I’m getting lucky?

    I wouldn’t call the spring curve 100% dialed, but it’s simple enough that there’s not all that much to do with it. Single pivot, *slightly* rising rate that’s almost straight, which I’ve found that I like pretty well: First single pivot I made had adjustable shock position and I figured I’d determine what I like by just riding, changing shock position, and seeing if I liked it better or worse. The problem with that was that I didn’t think through all the clearance issues well enough so I was forced to use a hateful, falling rate position. Learned that lesson (too well) and suspension bike #2 was a linkage bike with a rising rate. I say too well ’cause the rising rate was too much: soft when pedalling but still kinda harsh on big hits. So far the close to straight rate’s been where it’s at, at least coupled with ~7″ of travel and my level of skillz.

    Thanks for the explanation of the spring compression effect.

  5. JV says:

    Just a thought on Fox’s coil springs: Their quality control dictates that springs fall within 15% of the stated rate – ie, a 500lb spring coming out of the factory could range from

    That could explain any discrepancy in setup, especially when switching between two springs and expecting congruency between the ranges.
    For example, say your
    500lb spring REALLY is 425 (thus waaay too light at 15% from stated weight)
    550lb spring REALLY is 495 (still too light, lots of turns on preload at 10% less than stated)
    You might want to try a different 550.

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