Suspension guru help needed on "coil theory".........- Mtbr.com
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  1. #1
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    New question here. Suspension guru help needed on "coil theory".........

    Here's the question:

    Take a fork coil, say a Z1 heavy, and preload it to get pretty close to the same amount of sag that you would get from a Z1 x-heavy spring. Now, how will the the two springs behave? Should they behave identically, or will preloading a spring cause it to have more, or less, of a progressive response?

    Your typical coil, without preload, has a fairly linear rising rate, correct? Will preloading that spring simply shift the linear spring rate to the "right" or will it cause it's rate to become more progressive.

    The reason I ask is practical. I've got a Z1FR coil and it seems that the spring rate is just too linear; the fork blows right through most of it's travel on even small hits. It seems like tightening up the preload does little to help this. (I've played with oil heights and weights without luck.) When I'm on a steep downhill it seems that the weight shift causes the fork to sink through at least half of it's travel giving me only a small amout of useable travel to take up the hits. The fork ends up being harsh on the downhills as a result. I've already got the preload up pretty high but I've still got the problem. I'm thinking that the x-heavy coil may be the way to go but I fear that I'll loose the initial small hit sensitivity. (I guess I'm just to use to and air fork's progressive rate.) I'm #180.

    I'm also thinking about trying the air assist cap available as an aftermarket upgrade. Anyone try this? Good results? I hear that while you can keep the coil in the air assist side you can't preload the spring.

    Thanks in advance,

    Mike

  2. #2
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    Quote Originally Posted by Miker J
    Here's the question:

    Take a fork coil, say a Z1 heavy, and preload it to get pretty close to the same amount of sag that you would get from a Z1 x-heavy spring. Now, how will the the two springs behave? Should they behave identically, or will preloading a spring cause it to have more, or less, of a progressive response?

    Your typical coil, without preload, has a fairly linear rising rate, correct? Will preloading that spring simply shift the linear spring rate to the "right" or will it cause it's rate to become more progressive.

    The reason I ask is practical. I've got a Z1FR coil and it seems that the spring rate is just too linear; the fork blows right through most of it's travel on even small hits. It seems like tightening up the preload does little to help this. (I've played with oil heights and weights without luck.) When I'm on a steep downhill it seems that the weight shift causes the fork to sink through at least half of it's travel giving me only a small amout of useable travel to take up the hits. The fork ends up being harsh on the downhills as a result. I've already got the preload up pretty high but I've still got the problem. I'm thinking that the x-heavy coil may be the way to go but I fear that I'll loose the initial small hit sensitivity. (I guess I'm just to use to and air fork's progressive rate.) I'm #180.

    I'm also thinking about trying the air assist cap available as an aftermarket upgrade. Anyone try this? Good results? I hear that while you can keep the coil in the air assist side you can't preload the spring.

    Thanks in advance,

    Mike
    Not sure what year you have but mine is an 02' Z1 Freeride. I had the exact same problem - always blowing thru travel and terrible brake dive. I have BelRay 7wt. oil @ 50mm and X heavy green spings ( I weigh 190lbs.) I started w/ the stiffest springs so different springs were not an option. I ordered an air assist cap (stock on an X-Fly) You do lose preload adjustment but the air adds for adjustable compression. In all fairness I didn't accuratly measure the amount of air I was testing w/ as I used a High pressure pump that had a 0-300 psi gauge. I believe In had too much air as I had a harsh ride. I was told I could run up to 15 psi. I tried 4-5 psi. I came off a RS Psylo that was very progressive - I now have a Vanilla 125R that also feels very progressive. I posted the same question on the old forums and came to the conclusion that Zokes are very linear. I'd try the air assist just get a low pres. pump.

  3. #3
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    A few things to consider

    Quote Originally Posted by Miker J
    Here's the question:

    Take a fork coil, say a Z1 heavy, and preload it to get pretty close to the same amount of sag that you would get from a Z1 x-heavy spring. Now, how will the the two springs behave? Should they behave identically, or will preloading a spring cause it to have more, or less, of a progressive response?

    Your typical coil, without preload, has a fairly linear rising rate, correct? Will preloading that spring simply shift the linear spring rate to the "right" or will it cause it's rate to become more progressive.

    The reason I ask is practical. I've got a Z1FR coil and it seems that the spring rate is just too linear; the fork blows right through most of it's travel on even small hits. It seems like tightening up the preload does little to help this. (I've played with oil heights and weights without luck.) When I'm on a steep downhill it seems that the weight shift causes the fork to sink through at least half of it's travel giving me only a small amout of useable travel to take up the hits. The fork ends up being harsh on the downhills as a result. I've already got the preload up pretty high but I've still got the problem. I'm thinking that the x-heavy coil may be the way to go but I fear that I'll loose the initial small hit sensitivity. (I guess I'm just to use to and air fork's progressive rate.) I'm #180.

    I'm also thinking about trying the air assist cap available as an aftermarket upgrade. Anyone try this? Good results? I hear that while you can keep the coil in the air assist side you can't preload the spring.

    Thanks in advance,

    Mike
    Longer travel forks with the same percent of static sag such as 25% of travel has more brake dive. To slow brake dive you should try adjusting compression damping to be slower or using heavier weight oil if the compression damping is not adjustable. You will have a harsher ride for the trade off of using slower damping for increasing stability. And the amount of dive will be the same, just take longer to get compressed.

    You could use heavier coil springs to reduce the amount of dive travel used when steady braking downhill, but you'd loose total usable travel range if you aren't bottoming your current springs. And the speed of dive would be about the same without slowing compression damping.

    Air assist is like adding firmer springs. You can preload under the air caps staking shims or short springs of the same outside diameter as the springs. Be sure you don't shorten maximum travel by coil bind (bottoming coils before slider stansions are fully compressed to their limit).

    Preloading a softer spring with less preload will dive deeper in travel and bottom easier than using a firmer spring with less preload for the same static sag.

    Deeper static sag front and rear (or front only on hardtails) using a spring that doesn't bottom or higher oil level (higher bump stop air cushion) lowers the frame and reduces the amount of dive and improves higher speed bump compliance (as long as damping isn't too slow).

    If you have good sag (about 25 - 30%) and don't bottom the fork, you might try an inch higher rise bars, or taller stem, or shorter stem to keep your body weight further back reducing weight transfer onto the fork when braking, which will reduce that too much fork dive feeling when braking.

    - ray

  4. #4
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    Quote Originally Posted by derby
    Longer travel forks with the same percent of static sag such as 25% of travel has more brake dive. To slow brake dive you should try adjusting compression damping to be slower or using heavier weight oil if the compression damping is not adjustable. You will have a harsher ride for the trade off of using slower damping for increasing stability. And the amount of dive will be the same, just take longer to get compressed.

    You could use heavier coil springs to reduce the amount of dive travel used when steady braking downhill, but you'd loose total usable travel range if you aren't bottoming your current springs. And the speed of dive would be about the same without slowing compression damping.

    Air assist is like adding firmer springs. You can preload under the air caps staking shims or short springs of the same outside diameter as the springs. Be sure you don't shorten maximum travel by coil bind (bottoming coils before slider stansions are fully compressed to their limit).

    Preloading a softer spring with less preload will dive deeper in travel and bottom easier than using a firmer spring with less preload for the same static sag.

    Deeper static sag front and rear (or front only on hardtails) using a spring that doesn't bottom or higher oil level (higher bump stop air cushion) lowers the frame and reduces the amount of dive and improves higher speed bump compliance (as long as damping isn't too slow).

    If you have good sag (about 25 - 30%) and don't bottom the fork, you might try an inch higher rise bars, or taller stem, or shorter stem to keep your body weight further back reducing weight transfer onto the fork when braking, which will reduce that too much fork dive feeling when braking.

    - ray
    I found on my Z1 that it suffered from steady brake dive - spring rate not compression dampning was @ fault .I ran 3 forks back to back - Z1 Freeeide, Psylo, Vanilla 125R all w/ 20mm of sag. Travel was used up on all 3. Z1 was the only fork to exhibit such heavy/ steady dive. I guess the Z1 is very linear wheras the others are a bit progressive. I ran a 75mm x 25* stem & 2.5" riser bars but the best way to cope w/ dive was to position yourself over the rear of the bike.

  5. #5
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    I think that I have the information that you're looking for listed on my web site. Basically, a preloaded softer spring is not the same as a non-preloaded heavier spring.

    The preloaded softer spring will still be able to hit 25% sag, but will not have enough spring rate deeper into it's travel. Therefore, this combo feels like it is too 'linear' like you mentioned.

    A non-preloaded stiffer spring will likely still hit your 25% sag, but it will give you greater small bump sensitivity yet it won't blow through its travel during big hits and braking.

    There are a ton of combos to try though. I've tried heavy spring with no preload and a low oil height versus lighter spring with more preload and a higher oil height. My personal preference/weight seems to be best with light spring with more preload and 50mm oil height.

    Click on the link in my signature (sometimes my server sucks and it doesn't work. Just keep trying) and then click on the basic and advanced tuning links. There is a chart on the advanced tuning page that gives you a visual comparison of the springs (light vs. heavy; with more or less preload).

    Good luck.

    -Ryan
    I stopped driving my bike into my garage - I'm now protected with Roof Rack Ranger app for my iPhone.

  6. #6
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    Quote Originally Posted by Miker J
    Here's the question:

    Take a fork coil, say a Z1 heavy, and preload it to get pretty close to the same amount of sag that you would get from a Z1 x-heavy spring. Now, how will the the two springs behave? Should they behave identically, or will preloading a spring cause it to have more, or less, of a progressive response?

    Your typical coil, without preload, has a fairly linear rising rate, correct? Will preloading that spring simply shift the linear spring rate to the "right" or will it cause it's rate to become more progressive.

    The reason I ask is practical. I've got a Z1FR coil and it seems that the spring rate is just too linear; the fork blows right through most of it's travel on even small hits. It seems like tightening up the preload does little to help this. (I've played with oil heights and weights without luck.) When I'm on a steep downhill it seems that the weight shift causes the fork to sink through at least half of it's travel giving me only a small amout of useable travel to take up the hits. The fork ends up being harsh on the downhills as a result. I've already got the preload up pretty high but I've still got the problem. I'm thinking that the x-heavy coil may be the way to go but I fear that I'll loose the initial small hit sensitivity. (I guess I'm just to use to and air fork's progressive rate.) I'm #180.

    I'm also thinking about trying the air assist cap available as an aftermarket upgrade. Anyone try this? Good results? I hear that while you can keep the coil in the air assist side you can't preload the spring.

    Thanks in advance,

    Mike
    The two springs will not behave the same way. Preload only sets the "breakaway" of the coil. Once moving, the coil will behave in the same manner. If the fork feels too soft, don't preload it, don't fiddle with damping, GET THE HEAVIER SPRING. Compression damping, preload are all poor substitutes for correct spring rate. These are things to set once you have the correct spring to "fine tune" the fork or shock.

    THIS APPLIES TO ALL FORKS AND REAR SHOCKS...it is part of buying a coil fork or shock...expect to change the spring several times to find what is right for you.
    I AM HERE TO IRRITATE YOU SO THAT YOU POST MORE AND STAY OFF YOUR BIKE.

  7. #7
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    Physics problem

    Quote Originally Posted by derby

    If you have good sag (about 25 - 30%) and don't bottom the fork, you might try an inch higher rise bars, or taller stem, or shorter stem to keep your body weight further back reducing weight transfer onto the fork when braking, which will reduce that too much fork dive feeling when braking.

    - ray
    Having your weight farther back does not change the amount of weight transfer. The percentage of your weight that transfers depends on how hard you brake and nothing else. What does change is how much weight can be transferred before you go over the bars. In other words you can brake harder if your weight is farther back.

    If you brake just as hard in two situations but have your weight farther back in one, the difference is that you will start with less front sag and dive the same amount. That's assuming a linear fork. The air volume effect on 'Zokes and Foxes of course makes them progressive near bottom out.

  8. #8
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    Marzocchi more progressive than others

    The Marzocchi air sealed coil chambers with open oil bath produce an air assisted spring rate. The other forks that didn't bottom as much don't have the progressive assisted air spring effect so that the relatively linear spring is the only effect.

    One reason Marzocchis are so buttery smooth compared to Psylos coils and some others is the progressive air assist to resist bottoming, without preloading air and increasing stiction like air forks. Marzocchis can use lighter springs for the same travel without bottoming compared to others without sealed air assist. I think Fox coil forks uses air assist in a similar way.

    Sounds like heavier springs will get you more of what you want. You'll loose some bottom travel without lowering the oil level. You can't lower the oil level very much without starving the damping system, maybe 1/4-inch lower max. If you hear sucking sounds from your fork it probably has too low oil level. But a little oil height change makes a big difference in usable travel.

    And yes, Steve is correct. The weight transferred during braking doesn't change with a more rearward rider position. My point was a more rearward rider position when braking doesn't weight and compress the fork as much, having less weight on it (using the same spring and even with the same static sag). Notice the difference when braking while seated with bent arms while braking compared to standing behind the seat reaching further forward with straighter arms to the bars and braking. The fork will not compress as much and have more usable travel left for bumps while braking. Moving the bars back just 10 Ė 20 mm with a shorter stem makes a very noticeable difference in braking and quickens handling (the negative tradeoff is climbing is not so stretched out and pulls the front wheel up easier when you donít want it to Ė on-the-fly fork height lowering would help in those situations).

    - ray

  9. #9
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    I was giving some thought to my fork (04 Z1 DO 1) the other day. It occurs to me there isn't really anything stopping me removing the right hand spring entirely and using the air preload valve to pressurise the right leg so that it acts as an air spring. It would tend to be more progressive than the coil + air preload.

    I really like linear suspension, so it's not something I plan on trying. It is a silly idea, but it might just work.

  10. #10
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    Good job! Ooh, ooh, ooohhhh! Good stuff!!! ................

    Thanks everone. That's just what I needed to know.

    The link to the "Marathon S site" was great. I'll save that one.

    I think I'll try one heavy spring and one x-heavy. (2 x-heavy coils seemed a bit stiff.) Now the question is, which side gets the x-heavy coil, the ETA or rebound side?

    Mike

  11. #11
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    Right

    Quote Originally Posted by Timbo
    I was giving some thought to my fork (04 Z1 DO 1) the other day. It occurs to me there isn't really anything stopping me removing the right hand spring entirely and using the air preload valve to pressurise the right leg so that it acts as an air spring. It would tend to be more progressive than the coil + air preload.

    I really like linear suspension, so it's not something I plan on trying. It is a silly idea, but it might just work.
    It becomes more difficult to get full travel without lots of sag using a constantly progressive rate progression. And brake dive is aggravated with progressive rate forks. Progressive rate only makes good sense for shorter travel XC suspension, front and rear for improving small bump compliance. With the spring options today a more linear coil progression will help reduce net brake-dive compression distance.

    What we need for suspension bikes is a two or three stage coil wind, or stacked coil springs. I can think of three springs rates that would be useful on mountain bikes. A short and firm bottom out spring, a long linear main spring, and a short soft small hit floater and preload spring. I had some Eibock MountainSpeed springs for the '96 Rockshock XC fork that had something like this combination.

    - ray

  12. #12
    Jm.
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    Quote Originally Posted by derby

    What we need for suspension bikes is a two or three stage coil wind, or stacked coil springs. I can think of three springs rates that would be useful on mountain bikes. A short and firm bottom out spring, a long linear main spring, and a short soft small hit floater and preload spring. I had some Eibock MountainSpeed springs for the '96 Rockshock XC fork that had something like this combination.

    - ray
    Marzocchi's been calling them "prowind" springs, in fact it takes that "multi-stage" concept even further, it's a variable rate spring, starts off lighter with coils further apart, and they get closer at the other end.

    My stratos S8 had a 3-stage spring setup. I can't say it was any better than my shiver, in fact the shiver performs a little better, and the stratos were always said to be a little too linear compared to marzocchis.

    I don't think that progressive springs aggrivate those problems you mentioned above. In fact, progressive suspension designs pedal better, dont bob as much, and resist those kinds of things better than linear forks and suspension designs do. The reason is that as it goes through it's travel, it is not a linear amount. Iinear isn't good for much of anything IMO, I can't think of where you really would want anything that is linear.

  13. #13
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    Prowind

    Quote Originally Posted by Jm.
    Marzocchi's been calling them "prowind" springs, in fact it takes that "multi-stage" concept even further, it's a variable rate spring, starts off lighter with coils further apart, and they get closer at the other end.

    My stratos S8 had a 3-stage spring setup. I can't say it was any better than my shiver, in fact the shiver performs a little better, and the stratos were always said to be a little too linear compared to marzocchis.

    I don't think that progressive springs aggrivate those problems you mentioned above. In fact, progressive suspension designs pedal better, dont bob as much, and resist those kinds of things better than linear forks and suspension designs do. The reason is that as it goes through it's travel, it is not a linear amount. Iinear isn't good for much of anything IMO, I can't think of where you really would want anything that is linear.
    Actually if the coil wire is the same but the wind spacing is closer at one end, the tighter spacing is the softer part of the progression. All the coil spring's winds work together, but the tighter winds twist easier with the more close to "linear" leverage angle between the coils, and the tighter wind eventually coil binds (depending on weight on it) and then the rest of the coils take over all the spring duty.

    Itís my experience that more progressive rate springs with the same travel and sag bob more easily. But otherís experience may differ.

    - ray

  14. #14
    Jm.
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    Quote Originally Posted by derby
    Itís my experience that more progressive rate springs with the same travel and sag bob more easily. But otherís experience may differ.

    - ray
    Yeah, that's my experience too, but that's exactly the same as the "multi-stage" spring you suggested. A soft inital spring, a long linear main spring, and a heavier bottom-out spring is going to do the same thing as having a progressive stack.

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    Coils further apart lighter?

    Coils on a spring "further apart" are actually the stiffer part of the coil spring rate. Closer together is the "softer" rate.

    Spring rate is a funny science. Stack two 20 lb springs on top of each other and you end up with a 10 lb rate. That's because for each inch of travel, each of the stacked springs only travels 1/2". Weird huh?

  16. #16
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    Spring Characteristics

    After reading all the posts, I see there are a lot of people that know a lot about forks. But there was misconception I wanted to clear up.

    No matter what kind of combination of springs you stack together, or how you vary the stiffness throughout the length, a spring only has one coefficient of stiffness. And that coefficient remains constant throughout the entire deflection. So if you stacked a low stiffness spring (Kl) on top of a high (Kh), the resulting stiffness (Kr) would be:

    1/Kl + 1/Kh = 1/Kr

    That Kr can then be used in the equation:

    F = K*x

    where F is the force and x is deflection. The only difference is that in the full spring, the whole thing would compress equally. Where in the stack, the softer spring would compress more than stiffer, with the sum of the two equalling the same deflection. Now, perhaps this makes a fork feel more supple under small stutter bumps, I don't know. Theory and practicality often collide.

    But one thing is for sure, every metal spring has a linear spring rate, as seen in the second equation. The progressivity characteristics each fork displays must be from something else. I know (and I'm sure everyone else knows) Marzocchi's advertise progressivity adjustment through oil level height, allowing more or less air, which does have a progressive spring rate, to be compressed. Same idea with the air assist feature, only with above atmospheric pressure at no load. Progressivity could also come from the valving. I have absolutely no idea how these advanced damper valves work, so I'm just gonna stay away from that.

    So in answering the original question, cranking down the preload just takes the 20mm of deflection you would put on the fork and transfers it to the internals. So the fork stands taller, and requires a bit more force to find the bottom, but stiffness is unaffected.

    Hope this helps. There are so many other variables to talk about; different springs in each leg, spring in one, air in the other (interesting idea Timbo), oil weights and heights, custom valving, yada yada yada. But now were talking vibrations analysis, not just basic physics. I'd love to trade ideas (learn and teach) and answer rebuttles if anyone is interested.

    Happy Trails

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    Soft and stiff spring can act as a progressive rate spring.

    Quote Originally Posted by UP Dude
    After reading all the posts, I see there are a lot of people that know a lot about forks. But there was misconception I wanted to clear up.

    No matter what kind of combination of springs you stack together, or how you vary the stiffness throughout the length, a spring only has one coefficient of stiffness. And that coefficient remains constant throughout the entire deflection. So if you stacked a low stiffness spring (Kl) on top of a high (Kh), the resulting stiffness (Kr) would be:

    1/Kl + 1/Kh = 1/Kr

    That Kr can then be used in the equation:

    F = K*x

    where F is the force and x is deflection. The only difference is that in the full spring, the whole thing would compress equally. Where in the stack, the softer spring would compress more than stiffer, with the sum of the two equalling the same deflection. Now, perhaps this makes a fork feel more supple under small stutter bumps, I don't know. Theory and practicality often collide.

    But one thing is for sure, every metal spring has a linear spring rate, as seen in the second equation. The progressivity characteristics each fork displays must be from something else. I know (and I'm sure everyone else knows) Marzocchi's advertise progressivity adjustment through oil level height, allowing more or less air, which does have a progressive spring rate, to be compressed. Same idea with the air assist feature, only with above atmospheric pressure at no load. Progressivity could also come from the valving. I have absolutely no idea how these advanced damper valves work, so I'm just gonna stay away from that.

    So in answering the original question, cranking down the preload just takes the 20mm of deflection you would put on the fork and transfers it to the internals. So the fork stands taller, and requires a bit more force to find the bottom, but stiffness is unaffected.

    Hope this helps. There are so many other variables to talk about; different springs in each leg, spring in one, air in the other (interesting idea Timbo), oil weights and heights, custom valving, yada yada yada. But now were talking vibrations analysis, not just basic physics. I'd love to trade ideas (learn and teach) and answer rebuttles if anyone is interested.

    Happy Trails
    Nice explanation. Just thought I'd add one thing.

    Many steel coil springs are designed with progressive rates. These springs are usually barrel shaped. The fatter less stiff coils will run out of travel first and the rest of the travel will be taken up by the stiffer coils. The same thing could happen by stacking a stiff and soft spring if you designed the soft spring to hit it's compressed height before you ran out of overall travel.

    Air springs are much more progressive...so are elastomers. You can vary the progressivity of an air spring by changing the volume of the reservoir. You can have an air spring the pushes a piston backed by a coil spring and get an even more linear rate.

    Heck, you can even have falling rate springs that work with overcenter mechanisms. You will find falling rate springs in clutches, so that the hold down force is less than the clamping force.

    There are all kinds of tricks you can do with materials and mechanisms. It gets more complicated as you take the dynamics into consideration and try to reduce the responsiveness to bioloading while not hindering the response to environmental loading.

    Fun stuff.

    Danny

  18. #18
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    A real short soft spring

    Quote Originally Posted by Jm.
    Yeah, that's my experience too, but that's exactly the same as the "multi-stage" spring you suggested. A soft inital spring, a long linear main spring, and a heavier bottom-out spring is going to do the same thing as having a progressive stack.
    I'd want a long linear main spring with about an inch or less really soft spring for extra small bump compricance like when climbing. Maybe a short 1 inch really firm spring for bottom out, but maybe it's not needed.

    Whatever it would take to get a bit of progression in the first 25% of travel but linear below sag.

    I guess that would be old school suspension. Platform shocks are initially digressive in compression then turn linear (or progressive if air). Although I suspect a short soft spring stacked on a linear spring might still reduce wallow and squat but better smooth out the mild harshness Iíve felt with every platform shock Iíve tested so far on short travel bikes.

    - ray

  19. #19
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    Falling rate spring?

    Quote Originally Posted by Disaster
    Nice explanation. Just thought I'd add one thing.

    Many steel coil springs are designed with progressive rates. These springs are usually barrel shaped. The fatter less stiff coils will run out of travel first and the rest of the travel will be taken up by the stiffer coils. The same thing could happen by stacking a stiff and soft spring if you designed the soft spring to hit it's compressed height before you ran out of overall travel.

    Air springs are much more progressive...so are elastomers. You can vary the progressivity of an air spring by changing the volume of the reservoir. You can have an air spring the pushes a piston backed by a coil spring and get an even more linear rate.

    Heck, you can even have falling rate springs that work with overcenter mechanisms. You will find falling rate springs in clutches, so that the hold down force is less than the clamping force.

    There are all kinds of tricks you can do with materials and mechanisms. It gets more complicated as you take the dynamics into consideration and try to reduce the responsiveness to bioloading while not hindering the response to environmental loading.

    Fun stuff.

    Danny
    Isn't the clutch using linkage to produce the sprung falling rate?

    It is fun stuff!

    - ray

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    The main clutch plate spring itself is a slotted cup type spring.

    Quote Originally Posted by derby
    Isn't the clutch using linkage to produce the sprung falling rate?

    It is fun stuff!

    - ray
    Cup springs are falling rate. Similar to the little cup shaped rubber jumping toys made for kids. You pop them inside out and they slowly return until they hit the magic point where the return force multiplies and they snap.

    The other spring in the system is the one that returns the linkage (pedal, arms, cables etc.) When I worked in the heavy truck industry I patented an overcenter clutch linkage return leaf spring. Heavy trucks have very heavy clutch springs. I've seen them run over 100 pounds! The simple little leaf spring I designed used the overcenter principle to lower the efforts about 10%.

  21. #21
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    In car racing some teams created falling rate springs by combining two different springs in a stack, so that when one spring coil-binds the remaining spring had a *lower* rate than the two together (something about Super Touring cars with a stiff initial roll rate but that could suck up the corner curbing hits while passing etc without upsetting the car too much) I don't know the math but the combined rate of two stacked coils is not as simple as just adding them together.

  22. #22
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    Any Harshness?

    Interesing with the stacked springs. So the softer one clashes and the stiffer one takes the rest. Is the clash noticable? I always figured it might feel like a knock when it hit. But I suppose if you did a linearly varying spring stiffness through the length of the spring, the clash would slowly move its way down the spring, yes?

  23. #23
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    Some springs like this have a plastic/rubber wrap on the binding coils so maybe coil clash is a factor...

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