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  1. #1
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    Experts, help me understand suspension behaviour on my bike...

    Wasn't sure where to post this, it's more linkage related than shock but I guess the experts all lurk here so... I currently have a Devinci Banzai, it’s a “horst link/ICT” type frame with 5.75” of rear suspension and a 7.875x2.00 shock.

    I’ve read all sorts of things about compression ratio, rising, falling rate, length of the rocker, axle path, etc. Unfortunately my technical knowledge and capacity to understand the technical stuff is quite limited, I guess my IQ is not that great or I'm too old! Hahaha

    From what I understand, my frame has a relatively medium to low compression ratio. The main pivot on my bike is right above the crank like Turner’s and Ellsworth’s but I have a short rocker link compared to Ellsworth’s bikes.

    Now, you are probably asking, what the heck does he want.

    Well, I’ve been thru 3 different air shocks on this bike, the latest being a Push’d RP3 custom for me which is supposed to be one of the best. I’m still unsatisfied with the performance of my rear suspension when going downhill, especially on small bumps but a bit also on medium to large stuff. Basically I have no experience with bikes aside from my old Giant NRS and my friend’s Giant VT. We can skip immediately the NRS but as far as the VT is concerned, it’s the version with the Swinger 4way and it is really quite a bit nicer then mine when going downhill. It feels much plusher, especially on small bumps.

    So I am trying to understand my suspension design to see if it could be the culprit or if it is the shock, or even the geometry. It’s definitely not my bearings; those are awesome needle bearings that feel like running on butter when I take off the shock. Also my suspension action is awesome for going uphill, no bobbing at all but it absorbs everything, never looses traction.

    Do you guys think that with a rocker link like mine, this could lead to a “stiffer” suspension movement then if it had been conceived with a long rocker link like Ellsworth’s? Is it the geometry since the seat tube places me relatively over the crank compared to the VT so the weight transfer is not as much on the rear? Is it because that type of suspension would perform better with a non platform shock? Or is it just because that type of suspension will never provide the bump absorption smoothness you get from a single pivot linkage like the VT? Would a VPP design be plusher then horst link/ICT designs by nature?

    Sorry if this is a long post. Hope some of you can share your thoughts or theories on how my suspension should in theory be performing.

    Thanks much.
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  2. #2
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    Quote Originally Posted by BanzaiRider
    Wasn't sure where to post this, it's more linkage related than shock but I guess the experts all lurk here so... I currently have a Devinci Banzai, it’s a “horst link/ICT” type frame with 5.75” of rear suspension and a 7.875x2.00 shock.

    I’ve read all sorts of things about compression ratio, rising, falling rate, length of the rocker, axle path, etc. Unfortunately my technical knowledge and capacity to understand the technical stuff is quite limited, I guess my IQ is not that great or I'm too old! Hahaha

    From what I understand, my frame has a relatively medium to low compression ratio. The main pivot on my bike is right above the crank like Turner’s and Ellsworth’s but I have a short rocker link compared to Ellsworth’s bikes.

    Now, you are probably asking, what the heck does he want.

    Well, I’ve been thru 3 different air shocks on this bike, the latest being a Push’d RP3 custom for me which is supposed to be one of the best. I’m still unsatisfied with the performance of my rear suspension when going downhill, especially on small bumps but a bit also on medium to large stuff. Basically I have no experience with bikes aside from my old Giant NRS and my friend’s Giant VT. We can skip immediately the NRS but as far as the VT is concerned, it’s the version with the Swinger 4way and it is really quite a bit nicer then mine when going downhill. It feels much plusher, especially on small bumps.

    So I am trying to understand my suspension design to see if it could be the culprit or if it is the shock, or even the geometry. It’s definitely not my bearings; those are awesome needle bearings that feel like running on butter when I take off the shock. Also my suspension action is awesome for going uphill, no bobbing at all but it absorbs everything, never looses traction.

    Do you guys think that with a rocker link like mine, this could lead to a “stiffer” suspension movement then if it had been conceived with a long rocker link like Ellsworth’s? Is it the geometry since the seat tube places me relatively over the crank compared to the VT so the weight transfer is not as much on the rear? Is it because that type of suspension would perform better with a non platform shock? Or is it just because that type of suspension will never provide the bump absorption smoothness you get from a single pivot linkage like the VT? Would a VPP design be plusher then horst link/ICT designs by nature?

    Sorry if this is a long post. Hope some of you can share your thoughts or theories on how my suspension should in theory be performing.

    Thanks much.
    There's nothing that is going to make a VPP design plusher by nature, there is just no variable that will make it feel better.

    Traditionally, low pivot bikes (FSRs and the "faux bar" bikes like ventanas) feel "plusher' than high pivot bikes like many cannondales and santa cruz bikes. This is due to the fact that when you are pedaling the high pivot bike, the torque from your pedaling fights the suspension, making it feel choppy and harsh (add the bad braking effects of a single pivot and it can feel even worse on certain terrain).

    On the other hand, the higher pivot bikes tended to do a little better on bigger hits (when you're not pedaling) due to a more rearward axle path. This is not cut and dry though, as many of these single pivot bikes had falling rate designs and without a linkage to make them progressive, they may or may not have fared any better in this particular situation. These days the shock technology makes up for this a little bit, but it doesn't address the first paragraph at all, so you'll still get some "choppy" and harsh feel in the suspension on high pivot bikes, shocks can't help with this.

    So what you are describing is almost to the opposite of the "general" rules, but these do not always apply on a case by case basis.

    First of all, the rate of your bike could be to blame. There's a wide variety of shocks out right now, and out of all the ones that I've tried, the fox DHX-Air, DHX-Coil and RP3 are worth talking about. The different sizes of air chambers and other factors will make these shocks perform differently on different bikes. So a bike may have a suspension rate that is "tuned" to work with a pretty linear shock. In other words, the bike is progressive, and adding a small-volume air shock like an RP3 may be overkill for progressiveness, making the bike feel very harsh at speed. On the other hand, a bike designed for a progressive shock like the santa cruz bullit, will feel like crap if you put a linear coil shock on it. The original bullits had the fox RC shocks, and you had to run a very high spring weight to keep from bottoming the falling-rate design, and this caused the low speed performance to be crappy, and while the excessively high spring rate would keep it from botting, it simply caused it to ride like crap in all other areas.

    So, if you have a bike that "can accept" a coil or air shock, it doesn't mean that both will work equally well, the "rate" of your bike may work better with a more progressive shock, or a less progressive one, and if you use the wrong one, it will feel like crap.

    The reason why the rate and amount of progressiveness is important is that a progressive bike will be able to run more sag, get much better low speed performance, and still be able to resist the big hits due to the progressiveness. This kind of bike will usually ride more into it's travel, and that fact allows it to feel very plush on the small stuff, even at high speed. This can go both ways though, as I have described above. I've ridden them all, and I feel a good progressive design really leads to a compliant feeling bike, but you can get "fooled" by a falling rate design as long as you don't hit a big enough bump or jump it too high, because the falling rate really allows it to go into the travel and eat up medium sized bumps, so just because one bike feels better at slow speed may not tell the entire story.

    I've tried 2 air shocks on my Turner 6pack. One was the RP3 and the other was the Fox DHX-Air. These shocks were extremely different, and on different ends of the spectrum. The RP3 was very harsh overall, in my opinion it is overdamped. This makes it pedal pretty well, because the damping resists motion, but it makes it ride harsh over all sorts of bumps, and the progressiveness of this air shock (a smaller air volume=more progressive) coupled with the progressiveness of my bike simply makes it ride like crap. It's too progressive, and there's too much damping. If you want a firm and "snappy" feeling bike, the RP3 does deliver on this, and it doesn't bob much, especially in the "more compression damping" settings. Good for race-type bikes, bad for my trail/freeride bike.

    The DHX-Air on the other hand was on the other extreme, too linear IMO. The air chamber is bigger (which means less progressive) and the damping at certain times feels like it is too light. This causes the DHX-A to feel excessively "plush" on certain mid-sized bumps. It has a hint of harshness on extremely small bumps just because it is an air shock, but this effect is hardly noticable. I'm extremely picky about my suspension, and I believe that this should NOT be a factor to consider when thinking about this shock. The low speed performance of the DHX-A is excellent overall, so while I can detect the slightest amount of stiction, I do not believe it is a detriment here. The excessively low amount of damping though allows the shock to blow through the travel on medium sized bumps, and while it feels very plush at a certain speed, if I go faster it seems to blow through the travel too fast, and at the end of the travel it "ramps up", so going fast over medium-sized bumps makes it feel pretty crappy, because it's trying to use up too much travel on one bump, and there isn't enough travel left over for the next bump. I tried the DHX-A with the same settings and sag that I use with the DHX-C, and from there I tried different settings, but the key is that with the SAME settings, the DHX-A did not ride the same. If you don't ride extremely fast at mach9, the DHX-A might be for you, especially if you like a real plush low speed and medium speed feeling.

    The DHX-C was just right, in between the above two shocks, but that doesn't mean it's perfect. At speed it seems to get a little harsh on some impacts, a little "spikey". Better than progressive/manitou SPV stuff, and better than the curnut that I ran on my foes. I think that it can be better though, I want to try the marzocchi Rocco and the Ohlins rear shock. I simply want my rear suspension to work as well as possible, and I don't give a damn how bad it pedals.

    What I really think is to blame is the current focus on "pedaling platforms" and "compression damping" that acheives better pedaling. What we are basically talking about here is low speed compression damping. Sometimes with a blowoff, and sometimes with a "threshold" in the case of SPV. What low speed compression does though is that it KILLS the ability of the bike to absorb small ripples and bumps, and it just makes it ride like crap through this stuff. A lot of people are ok with sacrificing some of the suspension to get better pedaling, but make no mistake; An increase in the compression damping, or a "platform" WILL sacrifice some suspension ability. There is no way around it. Most bikes will bob with the amount of compression damping that is required for maximum suspension performance. The DHX-C/A do a very good job of providing a decent tradeoff, and more in the direction of compliant suspension IMO than the SPV type stuff, but it's not quite far enough for my likings (then again, I'm never really satisfied!). This craze may be finally blowing over with stuff like the new Marzocchi Rocco, which is supposed to have very minimal compression damping. Also keep in mind that air shocks (on the most part, except for the DHX-A) are intended for XC bikes, so the compression damping and platform can be generally higher or more extensive than with a coil shock that is intended for freeride/DH. So that's why the RP3 has way more compression damping than many coil shocks.

    I'd advise you to try a decent coil shock, DHX-C, Marzocchi Rocco, Avalanche, not romic, not a progressive, not a manitou swinger. The last three have an exceptionally high amount of compression damping that may not improve your ride at all.

    Another thing that is worth noting; If you get a "pushed" shock, it depends on what you tell them, as to what the outcome is going to be. If you tell them you want to improve the pedaling, they will increase the low speed compression, and they use some very good parts, pistons, blowoffs, etc, but in the end, better pedaling is more low speed compression, and you can get the "overdamped" effect still. The other way to go about this is to tell push that you want the plushest and most compliant suspension, and you don't give a damn about pedaling. They can set it up to have much more minimal compression damping, and increase the oil flow. When dealing with Push, these two different approaches will mean an extremely different riding shock.

    Although it's hard to tell if the rate of your bike is conflicting with the shock, another thing that will make a bike feel like crap is misaligned suspension, either at the shock or somewhere else where something is binding. It's rare, but it happens.
    Last edited by Jayem; 11-21-2005 at 08:46 PM.
    "It's only when you stand over it, you know, when you physically stand over the bike, that then you say 'hey, I don't have much stand over height', you know"-T. Ellsworth

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    Well earned posts.

    Jayem, I am not sure that I can add to this one. Well done.


    p.s. Where did that TE quote come from? What a riot.

  4. #4
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    Quote Originally Posted by damion


    p.s. Where did that TE quote come from? What a riot.
    Go to the website, look at the Moment bike, click on all the videos on the left. It is an exact quote.
    "It's only when you stand over it, you know, when you physically stand over the bike, that then you say 'hey, I don't have much stand over height', you know"-T. Ellsworth

    You're turning black metallic.

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    Wow Jayem, thanks for all this info, quite a post!

    I’m not worried about anything being misaligned on my suspension. As I said, it runs like butter without a shock and I already repacked the needle bearings on all pivots with grease.

    Also, my current RP3 has been Push’d with instructions to minimise the platform and make it as plush as possible. I’m sure it is the best it can be, the shock/linkage works great on absorbing any type of bumps going uphill.

    Thanks for your suggestion, I guess I really need to take a risk and order a 4th shock for this bike, this time a coil without platform. I hope it is the solution.

    I’m still a bit curious about understanding how my specific linkage can be compared to others. You say that traditionally low pivot feel plusher than high pivot when pedalling. That I think is a given and on my frame, when pedalling, there is absolutely nothing left to be desired. I think the Giant VT is a low single pivot type but not horst link like mine so when going down and not pedalling, in theory, it should feel very similar to mine as far as bump absorption.

    The way I interpret your text, with the right type of shock, my linkage, when not pedalling, should be absorbing bumps the same way as any other linkage, or am I completely out to lunch? For example, the longer rocker length that Ellsworth uses, does that influence only the behaviour of the suspension when pedalling?
    How do you determine the rate of the suspension? I’m a bit surprised that the designers of my frame have designed a frame that would be “tuned” for a linear shock when no shocks like that was proposed at the time they came up with it on the market (2004, a Fox Talas Propedal or Manitou 3way coil were the shock options).

    Anyway, thanks again for this discussion. I appreciate your comments.

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    Also check that your pivots aren't too tight. My friend's DeVinci Wilson with a Fox DHX 5.0 felt like absolute crap, we figured out that a couple of the pivots were so tight that it was making the travel too "sticky". Loosened and properly re-tightened the pivots, and the bike felt great.

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    Thanks for the advise but no problem there either. I keep the pivot bolts "almost" loose to make sure it is butter smooth.

    Quote Originally Posted by watermoccasin
    Also check that your pivots aren't too tight. My friend's DeVinci Wilson with a Fox DHX 5.0 felt like absolute crap, we figured out that a couple of the pivots were so tight that it was making the travel too "sticky". Loosened and properly re-tightened the pivots, and the bike felt great.

  8. #8
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    Quote Originally Posted by BanzaiRider
    Thanks for the advise but no problem there either. I keep the pivot bolts "almost" loose to make sure it is butter smooth.
    BR,

    Before you get a new shock, I suggest talking to Jimmy or Darren at PUSH to see if they can revalve the RP3 to your liking. I think they can make it work better if they get some feedback from you.

    SP
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    could it be in the wheels and tires? saddle/seatpost? flex in the vt's rear triangle?

    the linkage setup on your bike looks like it requires more force at the wheel to turn the pivot than on the vt where the linkage is near tangent to the path of rotation.

  10. #10
    MK_
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    Maybe before you go out and shell out your money on another shock, you ought to download a piece of software called linkage. You'll need to take a photo of your frame from a side and then you mark the pivots with markers and the sofware calculates the linkage rate, wheel path, etc. You'll have a good idea of what type of shock will work the best. Also, air shocks have an inherent problem of having little mid stroke support. They aren't too linear, as implied above, they simply have a flat section of force vs. stroke curve in the middle. What it translates to is that it takes some force to get it to initiate, then it takes very little to make it go deep into the stroke, before it begins to ramp up, like all single chamber air springs do. The end result is a super plush ride at a cost of low rear end/bottom bracket. This is particualarly true of large air volume shocks like the DHX air. A standard RP3, having a small air chamber, ramps up a lot quicker than the DHX air. Both are very hard to bottom out. This is surprising, given how much stroke they eat up on medium size bumps, but the ramping air spring assists the bottom out. DHXair has added benefit of having the remote reservoir with additional bottom out control which offsets the lesser ramp up of the air spring. It also results in more controlled rebound as the air spring being less ramped up doesn't shoot the rear wheel back out with nearly as much force as the RP3. Coil shocks are very linear, therefore in order to provide the same bottoming resistance of the spring as air shocks there is a small tradeoff in small bump performance. Air shocks also take the cake in medium size impacts due to the flat section of the spring curve. Coilovers do offer a lot more mid stroke support, so you ride higher in the rear. DHX coil BO control helps a lot with bottoming, but overall, my DHXair rides a lot plusher than my DHX coil did. I am running an air shock in the front, so the lack of mid stroke support is pretty equal on both ends, which makes for a super plush ride, however, on big step downs, rollers, etc. I wish I was on a coil fork.

    _MK
    Last edited by MK_; 11-22-2005 at 03:55 PM.

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    Quote Originally Posted by MK_
    Maybe before you go out and shell out your money on another shock, you ought to download a piece of software called linkage. You'll need to take a photo of your frame from a side and then you mark the pivots with markers and the sofware calculates the linkage rate, wheel path, etc. You'll have a good idea of what type of shock will work the best. Also, air shocks have an inherent problem of having little mid stroke support. They aren't too linear, as implied above, they simply have a flat section of force vs. stroke curve in the middle. What it translates to is that it takes some force to get it to initiate, then it takes very little to make it go deep into the stroke, before it begins to ramp up, like all single chamber air springs do. The end result is a super plush ride at a cost of low rear end/bottom bracket. This is particualarly true of large air volume shocks like the DHX air. A standard RP3, having a small air chamber, ramps up a lot quicker than the DHX air. Both are very hard to bottom out. This is surprising, given how much stroke they eat up on medium size bumps, but the ramping air spring assists the bottom out. DHXair has added benefit of having the remote reservoir with additional bottom out control which offsets the lesser ramp up of the air spring. It also results in more controlled rebound as the air spring being less ramped up doesn't shoot the rear wheel back out with nearly as much force as the RP3. Coil shocks are very linear, therefore in order to provide the same bottoming resistance of the spring as air shocks there is a small tradeoff in small bump performance. Air shocks also take the cake in medium size impacts due to the flat section of the spring curve. Coilovers do offer a lot more mid stroke support, so you ride higher in the rear. DHX coil BO control helps a lot with bottoming, but overall, my DHXair rides a lot plusher than my DHX coil did. I am running an air shock in the front, so the lack of mid stroke support is pretty equal on both ends, which makes for a super plush ride, however, on big step downs, rollers, etc. I wish I was on a coil fork.

    _MK
    Good info MK_ and your analogy with forks makes me think about something also.

    I used to run a Talas up front and basically I found it's behaviour in a sense similar to how I find my rear now and the way you describe it. The Talas was a great fork but somehow it left something to be desired as far as bump absorption, it was a bit choppy on small hits and did blow through it's mid travel pretty fast. When I changed it for the Marzo AllMountain1 I was surprised by how much better the coil fork felt on the downhill to my taste.

    Being an old guy, my first cars were those old Buicks with coil spring that always felt butter smooth. That's how my Marzo feels upfront but the rear feels a bit more like my current Honda CRV, efficient but choppy! haha

    I'll try to download that linkage program when I have time.

  12. #12
    MK_
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    Quote Originally Posted by BanzaiRider
    I used to run a Talas up front and basically I found it's behaviour in a sense similar to how I find my rear now and the way you describe it. The Talas was a great fork but somehow it left something to be desired as far as bump absorption, it was a bit choppy on small hits and did blow through it's mid travel pretty fast. When I changed it for the Marzo AllMountain1 I was surprised by how much better the coil fork felt on the downhill to my taste.
    There's something else at play here as the concept behind the TALAS is to make it perform like a coil shock. The issue with the talas is that it never ramps up, so you either have to set it up firm to resist bottoming or plush and you can't get rough with it or it will bottom out. AM1 is a mix of coil and air, so it is has all the benefits of coil, yet it ramps up like an air shock at the bottom of the stroke. AM1 has much better compression damping characteristics as well. Your TALAS experience much be based on improper setup, wrong oil levels, or something different entirely.

    _MK

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    Quote Originally Posted by BanzaiRider
    Wow Jayem, thanks for all this info, quite a post!

    I’m not worried about anything being misaligned on my suspension. As I said, it runs like butter without a shock and I already repacked the needle bearings on all pivots with grease.

    Also, my current RP3 has been Push’d with instructions to minimise the platform and make it as plush as possible. I’m sure it is the best it can be, the shock/linkage works great on absorbing any type of bumps going uphill.

    Thanks for your suggestion, I guess I really need to take a risk and order a 4th shock for this bike, this time a coil without platform. I hope it is the solution.

    I’m still a bit curious about understanding how my specific linkage can be compared to others. You say that traditionally low pivot feel plusher than high pivot when pedalling. That I think is a given and on my frame, when pedalling, there is absolutely nothing left to be desired. I think the Giant VT is a low single pivot type but not horst link like mine so when going down and not pedalling, in theory, it should feel very similar to mine as far as bump absorption.

    The way I interpret your text, with the right type of shock, my linkage, when not pedalling, should be absorbing bumps the same way as any other linkage, or am I completely out to lunch? For example, the longer rocker length that Ellsworth uses, does that influence only the behaviour of the suspension when pedalling?
    How do you determine the rate of the suspension? I’m a bit surprised that the designers of my frame have designed a frame that would be “tuned” for a linear shock when no shocks like that was proposed at the time they came up with it on the market (2004, a Fox Talas Propedal or Manitou 3way coil were the shock options).

    Anyway, thanks again for this discussion. I appreciate your comments.
    Well, yes, with the right type of shock, you should be able to get the bike to perform to your liking, but the problem is that you don't know the actual amount of "progression" that the suspension has. It could be linear, falling rate, or progressive. The only real way to know is to plug it into that linkage program, which will give you an idea as far as that is concerned. Sometimes you can "eyeball" whether or not a bike is progressive, but you have to have a good idea of what is going on with suspension designs. I don't recommend "eyeballing" it.

    The longer rocker arm should have no impact on bump absorption.

    The point of my post was to point out most of the variables at play. I can't tell you whether your bike is progressive or linear, but I did lay out a lot of general rules and characteristics.

    On the subject of the talas, it pretty much abides by the same criterial that I used to describe the DHX-Air. It blows through it's travel rather fast, feels nice on some smaller sized bumps due to this fact, but blows through the travel easy on the steeps, and at high speed the excessive amount of travel used can make it feel crappy due to not enough travel for the next bump being available. If you set up the talas with enough air-spring force to not dive, it rides much harsher due to being excessively sprung. The talas is amazingly plush in some situations, but it's always seemed like fox went way too far in the direction of "linear action" with the talas.
    "It's only when you stand over it, you know, when you physically stand over the bike, that then you say 'hey, I don't have much stand over height', you know"-T. Ellsworth

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  14. #14
    TNC
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    Your air/coil comments.

    Quote Originally Posted by MK_
    There's something else at play here as the concept behind the TALAS is to make it perform like a coil shock. The issue with the talas is that it never ramps up, so you either have to set it up firm to resist bottoming or plush and you can't get rough with it or it will bottom out. AM1 is a mix of coil and air, so it is has all the benefits of coil, yet it ramps up like an air shock at the bottom of the stroke. AM1 has much better compression damping characteristics as well. Your TALAS experience much be based on improper setup, wrong oil levels, or something different entirely.

    _MK
    MK, you have some great observations there on the air/coil issue. On rear shocks, I always thought the Stratos Helix series was on to something with an oil damped shock suspended by a coil spring with an added air chamber. The coil handled all of the first 2/3 of the stroke, and the air chamber had a huge influence on the last 1/3 of the travel. Obviously the bottomout control was pretty awesome, and the rest of the shock worked fairly well. I would have loved to see Fox or one of the other biggies take this idea to the extreme with their technology.

    On front forks I have long thought the same principle of air/coil hybrids should apply. A couple of '04 Z150SLs that I have were turned into this type of fork. I used a Z1FR1 coil spring and a Z150 HSCV cartridge in each fork and kept the Doppio leg intact. The characteristics are as you described...the best of the both worlds of coil and air. It's plush without blowing the through the travel and has outstanding bottomout qualities. I don't find it surprising that more of these hybrid type forks are appearing.

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    Quote Originally Posted by Jayem
    Well, yes, with the right type of shock, you should be able to get the bike to perform to your liking, but the problem is that you don't know the actual amount of "progression" that the suspension has. It could be linear, falling rate, or progressive. The only real way to know is to plug it into that linkage program, which will give you an idea as far as that is concerned. Sometimes you can "eyeball" whether or not a bike is progressive, but you have to have a good idea of what is going on with suspension designs. I don't recommend "eyeballing" it.

    The longer rocker arm should have no impact on bump absorption.
    OK great. I took a picture tonight so tomorrow I should have time to check out this linkage software. Hope you don't need an engineering degree to use it! haha
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    Quote Originally Posted by TNC
    MK, you have some great observations there on the air/coil issue. On rear shocks, I always thought the Stratos Helix series was on to something with an oil damped shock suspended by a coil spring with an added air chamber. The coil handled all of the first 2/3 of the stroke, and the air chamber had a huge influence on the last 1/3 of the travel. Obviously the bottomout control was pretty awesome, and the rest of the shock worked fairly well. I would have loved to see Fox or one of the other biggies take this idea to the extreme with their technology.
    It was good for some situations.

    I used the helix pro on some of my linkage bikes, and holy cow it felt like crap, way too progressive. First of all, there was a progressively wound spring, secondly the progressive air assist shock that needed a certain psi or the oil would seep into the chamber and you'd loose damping, combine these with a progressive bike and you get a hell of a lot of progressiveness. On the other hand, if you wanted a coil shock for your trek Y bike or other falling-rate single pivot, they were the only logical choice for the longest time.

    Not a bad shock, but only worked for certain bikes IMO. Outlasted my romic easily, I used it on the same bike that the romic came standard on, and due to how much the romic was back at the factory getting fixed, the stratos spent a lot more time on that bike.
    "It's only when you stand over it, you know, when you physically stand over the bike, that then you say 'hey, I don't have much stand over height', you know"-T. Ellsworth

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    Quote Originally Posted by BanzaiRider
    OK great. I took a picture tonight so tomorrow I should have time to check out this linkage software. Hope you don't need an engineering degree to use it! haha
    Personally, I'd put a decent coil shock on there. I have a friend with a PUSHed RP3 on a 5" ventana, and I still spank him on the downhills because my 6" bike is so much plusher on the small ripples and stutter bumps at speed. Our bikes have low-pivots, both have a rocker-linkage like your bike, and there really shouldn't be that much difference in the stutter-bump performance between a 5" bike and a 6" bike, but because he's running an RP3 and I'm running a DHX coil, there's a pretty significant difference in how both ride on small bumps.

    I think a marzocchi rocco, avalanche, ohlins, or the DHX-coil would make the most difference in this respect, but I'd say the first 3 would probably be the biggest difference. A lower cost option would be to find an old vanilla RC, and send it to Push and have them install their piston and set it up for you, that would be the most cost efficiant most likely.

    As I said before, the only air shock that I've ridden that didn't feel like it was orientated for XC and was pretty darn push overall was the DHX-A, except that it seemed to go a little too far in this direction and sacrificed some other aspects of the ride.
    "It's only when you stand over it, you know, when you physically stand over the bike, that then you say 'hey, I don't have much stand over height', you know"-T. Ellsworth

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  18. #18
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    That's why...

    Quote Originally Posted by Jayem
    It was good for some situations.

    I used the helix pro on some of my linkage bikes, and holy cow it felt like crap, way too progressive. First of all, there was a progressively wound spring, secondly the progressive air assist shock that needed a certain psi or the oil would seep into the chamber and you'd loose damping, combine these with a progressive bike and you get a hell of a lot of progressiveness. On the other hand, if you wanted a coil shock for your trek Y bike or other falling-rate single pivot, they were the only logical choice for the longest time.

    Not a bad shock, but only worked for certain bikes IMO. Outlasted my romic easily, I used it on the same bike that the romic came standard on, and due to how much the romic was back at the factory getting fixed, the stratos spent a lot more time on that bike.
    I said it would be interesting to see Fox and some others give a new twist to the concept. I think it's the concept that has some merit. I just think the air and coil combination that makes your AM1 work so well could be applied to rear shocks...though I guess that Fox and others are heading in that direction with the boost chamber and SPV technology. Funny you mention an old Y-bike. I had that shock on one, and it was a good combo. It also worked quite well on an MRP equipped FSR Enduro which didn't make as much sense...what with the more progressive rate on the Enduro.
    Last edited by TNC; 11-22-2005 at 10:48 PM. Reason: text

  19. #19
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    Quote Originally Posted by Jayem
    I think a marzocchi rocco, avalanche, ohlins, or the DHX-coil would make the most difference in this respect, but I'd say the first 3 would probably be the biggest difference. A lower cost option would be to find an old vanilla RC, and send it to Push and have them install their piston and set it up for you, that would be the most cost efficiant most likely.
    From another post, it seems like Marzo has the 2nd edition of the Rocco to come out soon and that version will have the TST. If it works like the fork version then it's perfect...

  20. #20
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    Quote Originally Posted by BanzaiRider
    From another post, it seems like Marzo has the 2nd edition of the Rocco to come out soon and that version will have the TST. If it works like the fork version then it's perfect...
    No, if you are going for maximum plushness I'd pass up the TST and go with the standard rocco. More chance of making your bike better IMO.
    "It's only when you stand over it, you know, when you physically stand over the bike, that then you say 'hey, I don't have much stand over height', you know"-T. Ellsworth

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    Well it depends. When you set the TST on the forks to the first click it has absolutely no "platform/compression" impact, it's pure butter. It's when you set it at the second or third click that it has a compression effect. If the Rocco TST works the same as the forks then for me it would be kind of an insurance policy. If it bobs too much in the full open mode, I could give it a click or two when going uphill then wide open for the downhill...

    Quote Originally Posted by Jayem
    No, if you are going for maximum plushness I'd pass up the TST and go with the standard rocco. More chance of making your bike better IMO.

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    Axle Path

    Quote Originally Posted by BanzaiRider
    Wasn't sure where to post this, it's more linkage related than shock but I guess the experts all lurk here so... I currently have a Devinci Banzai, it’s a “horst link/ICT” type frame with 5.75” of rear suspension and a 7.875x2.00 shock.

    I’ve read all sorts of things about compression ratio, rising, falling rate, length of the rocker, axle path, etc. Unfortunately my technical knowledge and capacity to understand the technical stuff is quite limited, I guess my IQ is not that great or I'm too old! Hahaha

    From what I understand, my frame has a relatively medium to low compression ratio. The main pivot on my bike is right above the crank like Turner’s and Ellsworth’s but I have a short rocker link compared to Ellsworth’s bikes.

    Now, you are probably asking, what the heck does he want.

    Well, I’ve been thru 3 different air shocks on this bike, the latest being a Push’d RP3 custom for me which is supposed to be one of the best. I’m still unsatisfied with the performance of my rear suspension when going downhill, especially on small bumps but a bit also on medium to large stuff. Basically I have no experience with bikes aside from my old Giant NRS and my friend’s Giant VT. We can skip immediately the NRS but as far as the VT is concerned, it’s the version with the Swinger 4way and it is really quite a bit nicer then mine when going downhill. It feels much plusher, especially on small bumps.

    So I am trying to understand my suspension design to see if it could be the culprit or if it is the shock, or even the geometry. It’s definitely not my bearings; those are awesome needle bearings that feel like running on butter when I take off the shock. Also my suspension action is awesome for going uphill, no bobbing at all but it absorbs everything, never looses traction.

    Do you guys think that with a rocker link like mine, this could lead to a “stiffer” suspension movement then if it had been conceived with a long rocker link like Ellsworth’s? Is it the geometry since the seat tube places me relatively over the crank compared to the VT so the weight transfer is not as much on the rear? Is it because that type of suspension would perform better with a non platform shock? Or is it just because that type of suspension will never provide the bump absorption smoothness you get from a single pivot linkage like the VT? Would a VPP design be plusher then horst link/ICT designs by nature?

    Sorry if this is a long post. Hope some of you can share your thoughts or theories on how my suspension should in theory be performing.

    Thanks much.
    Some bikes excell at something and others at something else, combine that with the variety of trails must of us ride and the only solution is to own more than one bike

    Jayhem mentioned axle path (great post Jayhem) on his initial response, but then his and all other posts focused entirely on shocks. Different shocks will vary how your bike rides, but axle path also influences how the suspension feels on different conditions.

    Haven't checked, but I am certain that your friend's VT probably has a more rearward axle path, making it feel plusher on the downhills. You did not mention how the VT compares to your bike on the uphills, I would guess probably not as good, because the more rearward axle path feels better while ascending.

    No matter what shock you try, there is another factor, wheelpath. And the only way to change it is......with a different bike.

  23. #23
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    Quote Originally Posted by Pedro
    Haven't checked, but I am certain that your friend's VT probably has a more rearward axle path, making it feel plusher on the downhills. You did not mention how the VT compares to your bike on the uphills, I would guess probably not as good, because the more rearward axle path feels better while ascending.

    No matter what shock you try, there is another factor, wheelpath. And the only way to change it is......with a different bike.
    Looking at the VT linkage, I don't see any rearward wheel path component. The main pivot is right at the bottom bracket. It looks like it is a low monopivot with a linkage driven shock. In any case, it is true that you can't beat rearward wheel path for the plush feeling over square edges, but you can optimize the feeling of the suspension of your current steed by installing and setting up a proper shock which matches the characteristics of the linkage the best.

    _MK

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    Quote Originally Posted by Pedro
    Jayhem mentioned axle path (great post Jayhem) on his initial response, but then his and all other posts focused entirely on shocks. Different shocks will vary how your bike rides, but axle path also influences how the suspension feels on different conditions.

    Haven't checked, but I am certain that your friend's VT probably has a more rearward axle path, making it feel plusher on the downhills. You did not mention how the VT compares to your bike on the uphills, I would guess probably not as good, because the more rearward axle path feels better while ascending.

    No matter what shock you try, there is another factor, wheelpath. And the only way to change it is......with a different bike.
    The reason I didn't mention the axle path since then was because it really depends on the type of bumps we are talking about, as to what effect that the axle path has.

    A more rearward axle path will help absorb big hits, like slamming into a square edged bump at high speed. A more vertical path may feel a little harsher in this respect.

    When talking about small bumps, braking bumps, basically the small trail variations at high speed, we shouldn't see much difference in the performance, these won't have a huge rearward component with them, so it just isn't going to be a real difference in my experience.

    The giant VT is a low pivot singlepivot bike. The axle path of the VT should be very similer to the axle path of an FSR bike. When you are going to get a significantly "different" axle path is when the pivot point is significantly different, as with a high pivot bike (bullit, orange, etc) or when you have a dual-linkage bike that has a specific axle path that is a lot different than the one on the FSR, like you might find with a VPP.

    For absorbing small bumps at high speed, IMO the rate of the suspension is ultimately important, because you have to have soft initial travel to absorb those small bumps. Usually more sag=plusher on the small stuff, so setting up the sag correctly is going to have a very big impact here.
    "It's only when you stand over it, you know, when you physically stand over the bike, that then you say 'hey, I don't have much stand over height', you know"-T. Ellsworth

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    Air pressure?
    Banzai, I didn't see you mention pressures you've tried.
    This year I went from a Float R to a Float AVA propedal shock on my '01 FSR, and I'm getting more of the travel, now that the propedal platform (and the larger volume AVA) lets me run a bit less pressure, while still pedaling decently. I've heard the RP3 is supposed to have more volume than the AVA, so I would drop psi incrementally to see if the ride improves, and find the lowest psi you can use before the shock gets too soft to pedal well.

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    Quote Originally Posted by fsrxc
    I've heard the RP3 is supposed to have more volume than the AVA, so I would drop psi incrementally to see if the ride improves, and find the lowest psi you can use before the shock gets too soft to pedal well.
    That's not true. The AVA has more volume, and to boot, it has adjustable volume. I have a friend here that has fox connections, and he has an AVA sleeve for his RP3, and he ran it like that last year. It most definitely increases the volume with the AVA, and the AVA could work a lot better by allowing him to make the spring curve more linear, but since he's tried a lot of air shocks already, I'd say just skip that and go for the coil.

    And one more thing for banzia, I know you said you were going to wait for the "TST" rocco, but go back and see what I was saying about the air shocks and suspension components that are in this "platform/pedaling" fad. The TST doesn't really do this to any big extent, but it does have a pretty stiff blow-off for the compression damping, which means real fast hits at high speed could be kind of "choppy", as they are with the AM1. The AM1 does a pretty nice job at most speed ranges, but given what you've outlined as your priorities and what you've already experienced, I think going for the current "piston and shims" rocco would still have the highest probability of improving the ride. My priorities sound a little close to yours, and it is basically; Make the suspension run as well as possible, I'll choose a suspension design that doesn't pedal terribly, but if it bobs a little I don't really care, because I want the suspension to be the #1 priority. I'll make up the difference in bobbing by getting stronger and live with that part.
    "It's only when you stand over it, you know, when you physically stand over the bike, that then you say 'hey, I don't have much stand over height', you know"-T. Ellsworth

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    Quote Originally Posted by fsrxc
    Air pressure?
    Banzai, I didn't see you mention pressures you've tried.
    This year I went from a Float R to a Float AVA propedal shock on my '01 FSR, and I'm getting more of the travel, now that the propedal platform (and the larger volume AVA) lets me run a bit less pressure, while still pedaling decently. I've heard the RP3 is supposed to have more volume than the AVA, so I would drop psi incrementally to see if the ride improves, and find the lowest psi you can use before the shock gets too soft to pedal well.
    Thanks but I've tried everything from 20 to 35% sag...

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    Quote Originally Posted by Pedro
    Some bikes excell at something and others at something else, combine that with the variety of trails must of us ride and the only solution is to own more than one bike

    Jayhem mentioned axle path (great post Jayhem) on his initial response, but then his and all other posts focused entirely on shocks. Different shocks will vary how your bike rides, but axle path also influences how the suspension feels on different conditions.

    Haven't checked, but I am certain that your friend's VT probably has a more rearward axle path, making it feel plusher on the downhills. You did not mention how the VT compares to your bike on the uphills, I would guess probably not as good, because the more rearward axle path feels better while ascending.

    No matter what shock you try, there is another factor, wheelpath. And the only way to change it is......with a different bike.
    I didn't have time to try the software to check out my frame's configuration. The VT climbs very well as long as you stay seated. However, if you stand it blows through the platform of the Manitou 4way air. On mine seated or standing it climbs great. I think that's always been a given that a horst link climbs very well.

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    Quote Originally Posted by Jayem
    And one more thing for banzia, I know you said you were going to wait for the "TST" rocco, but go back and see what I was saying about the air shocks and suspension components that are in this "platform/pedaling" fad. The TST doesn't really do this to any big extent, but it does have a pretty stiff blow-off for the compression damping, which means real fast hits at high speed could be kind of "choppy", as they are with the AM1. The AM1 does a pretty nice job at most speed ranges, but given what you've outlined as your priorities and what you've already experienced, I think going for the current "piston and shims" rocco would still have the highest probability of improving the ride. My priorities sound a little close to yours, and it is basically; Make the suspension run as well as possible, I'll choose a suspension design that doesn't pedal terribly, but if it bobs a little I don't really care, because I want the suspension to be the #1 priority. I'll make up the difference in bobbing by getting stronger and live with that part.
    Yap that's right. A few years ago I had a Giant NRS and I got a CaneCreek Cloud9 shock to replace the original Rockshock. It did bob a bit with the Cloud9 but barely, however it felt way better on the downhill. I guess I'm just a bit afraid about the regular Rocco since I never had a coil shock before and the only experience I have with them is a parking lot ride on a big DH Kona that was bouncing like mad with each pedal stroke!

  30. #30
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    ICT extends while braking

    Quote Originally Posted by BanzaiRider
    Wasn't sure where to post this, it's more linkage related than shock but I guess the experts all lurk here so... I currently have a Devinci Banzai, it’s a “horst link/ICT” type frame with 5.75” of rear suspension and a 7.875x2.00 shock.

    I’ve read all sorts of things about compression ratio, rising, falling rate, length of the rocker, axle path, etc. Unfortunately my technical knowledge and capacity to understand the technical stuff is quite limited, I guess my IQ is not that great or I'm too old! Hahaha

    From what I understand, my frame has a relatively medium to low compression ratio. The main pivot on my bike is right above the crank like Turner’s and Ellsworth’s but I have a short rocker link compared to Ellsworth’s bikes.

    Now, you are probably asking, what the heck does he want.

    Well, I’ve been thru 3 different air shocks on this bike, the latest being a Push’d RP3 custom for me which is supposed to be one of the best. I’m still unsatisfied with the performance of my rear suspension when going downhill, especially on small bumps but a bit also on medium to large stuff. Basically I have no experience with bikes aside from my old Giant NRS and my friend’s Giant VT. We can skip immediately the NRS but as far as the VT is concerned, it’s the version with the Swinger 4way and it is really quite a bit nicer then mine when going downhill. It feels much plusher, especially on small bumps.

    So I am trying to understand my suspension design to see if it could be the culprit or if it is the shock, or even the geometry. It’s definitely not my bearings; those are awesome needle bearings that feel like running on butter when I take off the shock. Also my suspension action is awesome for going uphill, no bobbing at all but it absorbs everything, never looses traction.

    Do you guys think that with a rocker link like mine, this could lead to a “stiffer” suspension movement then if it had been conceived with a long rocker link like Ellsworth’s? Is it the geometry since the seat tube places me relatively over the crank compared to the VT so the weight transfer is not as much on the rear? Is it because that type of suspension would perform better with a non platform shock? Or is it just because that type of suspension will never provide the bump absorption smoothness you get from a single pivot linkage like the VT? Would a VPP design be plusher then horst link/ICT designs by nature?

    Sorry if this is a long post. Hope some of you can share your thoughts or theories on how my suspension should in theory be performing.

    Thanks much.
    I've been playing with modeling 4-bar floating brake geometry lately using some stiff cardboard and thumbtacks, with which I can quickly change the link lengths and leverage alignments. Try it, it is very revealing.

    Basic rear brake reaction is that the link (or monopivot swingarm) that the caliper is mounted to will rotate in tension force in a forward direction with the rear wheel while braking.

    One basic fact became obvious. Unless the 4-bar swing links crossed between the pivot points, all floating brakes (calipers on the rear link) cause the frame to rotate forward or at least tensions the frame in a forward rotation direction. Forward frame rotation tension (also called suspension extension tension or force) resists suspension compression from bumps.

    Combine the floater brake extending tension with any shock compression resistance like platform damping common now with most suspension designs that bob significantly while pedaling, and you’ve got two factors resisting smaller bump compression while braking.

    Playing with the modeling tool it became obvious that some 4 bar alignments have greater leverage rotating the frame within the usable range of travel while rear braking. When the rear link is relatively more aligned with the upper swing link such as your bike there is significantly greater than 1 to 1 forward frame rotation leverage compared to the rear caliper link force, producing less freedom to move with compression inputs.

    You asked about the difference from you bike’s design to the Ellsworth designs. The longer upper link of the most resent year Ellsworth design change and older Dare have are more close to 90 degree pivot angles and significantly closer to 1 to 1 frame extending leverage with the rotation input from the caliper link. None of the Ellsworth designs are anywhere near neutral tension rear braking, but the latest variety are less extending in frame tension than most other ICT compliant alignments. All non-ICT Horst Link and FSR designs ever produced are lower extending leveraging and closer to neutral reacting than any Ellsworth or ICT design ever produced (try the cardboard and thumbtack modeling, you can feel the difference, it will be obvious).

    Moving your body weight more rearward will help reduce extending inputs allowing compression from smaller bumps to be more compliant. An inch shorter stem would make a very noticeable difference. Lowering the seat for extended seated downhill helps reduce extending leverage around the front wheel when front braking.

    If easily adjustable, reduce platform and compression damping when going downhill.

    - ray

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    Quote Originally Posted by derby
    I've been playing with modeling 4-bar floating brake geometry lately using some stiff cardboard and thumbtacks, with which I can quickly change the link lengths and leverage alignments. Try it, it is very revealing.

    Basic rear brake reaction is that the link (or monopivot swingarm) that the caliper is mounted to will rotate in tension force in a forward direction with the rear wheel while braking.

    One basic fact became obvious. Unless the 4-bar swing links crossed between the pivot points, all floating brakes (calipers on the rear link) cause the frame to rotate forward or at least tensions the frame in a forward rotation direction. Forward frame rotation tension (also called suspension extension tension or force) resists suspension compression from bumps.

    Combine the floater brake extending tension with any shock compression resistance like platform damping common now with most suspension designs that bob significantly while pedaling, and you’ve got two factors resisting smaller bump compression while braking.

    Playing with the modeling tool it became obvious that some 4 bar alignments have greater leverage rotating the frame within the usable range of travel while rear braking. When the rear link is relatively more aligned with the upper swing link such as your bike there is significantly greater than 1 to 1 forward frame rotation leverage compared to the rear caliper link force, producing less freedom to move with compression inputs.

    You asked about the difference from you bike’s design to the Ellsworth designs. The longer upper link of the most resent year Ellsworth design change and older Dare have are more close to 90 degree pivot angles and significantly closer to 1 to 1 frame extending leverage with the rotation input from the caliper link. None of the Ellsworth designs are anywhere near neutral tension rear braking, but the latest variety are less extending in frame tension than most other ICT compliant alignments. All non-ICT Horst Link and FSR designs ever produced are lower extending leveraging and closer to neutral reacting than any Ellsworth or ICT design ever produced (try the cardboard and thumbtack modeling, you can feel the difference, it will be obvious).
    Hum that's very interesting ray. I'm not sure I'm quite up to your level but let me swing this and maybe you can tell me if I understood correctly.

    From what you say, I think I can translate it from a feel I get when riding my bike. When pointing downhill, most of the time you immediately apply "some" level of braking from both sides. I've noticed that when I apply the rear brakes, even without applying the front, the rear tends to lift up so I assume that this is what you refer to as "cause the frame to rotate forward"? And if I remember well, that behaviour was less or not obvious at all on my friends Giant VT. I also think my frame is an ICT type but with a short rocker.

    So that would mean that my frame linkage is somewhat the culprit in creating this choppy feel on the downhill! And I was right in a sense to question about those very long rocker links that Ells frame use on the Moment or the new Rogue/Dare.

    Quote Originally Posted by derby
    Moving your body weight more rearward will help reduce extending inputs allowing compression from smaller bumps to be more compliant. An inch shorter stem would make a very noticeable difference. Lowering the seat for extended seated downhill helps reduce extending leverage around the front wheel when front braking.
    Those suggestions will be difficult to implement. The front of my bike is already pretty "light" feeling, if I shorten the stem I'll be flipping backwards on the uphill!!! Same for moving my saddle backwards. I already lower the seat when I do some DH but on regular technical trail riding I need to be relatively high for pedaling efficiency.
    Quote Originally Posted by derby
    If easily adjustable, reduce platform and compression damping when going downhill.
    That would only be solved by buying a Marzo Rocco shock. I already have a Push'd RP3 with minimal platform configuration.

    Thanks a lot for this info ray. It really make sense and is helpful in understanding a bit more.

  32. #32
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    brake jacking occurs whether you use the front brake or rear. it's simple, when you decelerate, your weight moves forward. because of suspension movement, you get more total shift than from a solid frame, unsuspended bike. if you want a rear shock that can cope with unloaded conditions such as under braking while still maintaining ride while loaded, you could rig up a dual shock (or dual pressure) system which is tied into your braking system. otherwise, do what everyone has always done while riding downhill; hang your butt off the back.

    then again, if your suspension is a unified triangle type (little more than a suspension seat post which is totally unresponsive unless you're sitting), you're stuck.

  33. #33
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    Are you sure?

    Quote Originally Posted by drunkle
    brake jacking occurs whether you use the front brake or rear. it's simple, when you decelerate, your weight moves forward. because of suspension movement, you get more total shift than from a solid frame, unsuspended bike. if you want a rear shock that can cope with unloaded conditions such as under braking while still maintaining ride while loaded, you could rig up a dual shock (or dual pressure) system which is tied into your braking system. otherwise, do what everyone has always done while riding downhill; hang your butt off the back.

    then again, if your suspension is a unified triangle type (little more than a suspension seat post which is totally unresponsive unless you're sitting), you're stuck.
    I don't claim to be an expert on the topic, but I thought brake jack/brake squat was induced from rear braking. Now obviously when you brake with the front, the front fork dives some and the rider's CG tends to want to be projected forward, but I didn't think this was the same as brake jack/squat. Maybe we're just talking semantics here.

  34. #34
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    Quote Originally Posted by TNC
    I don't claim to be an expert on the topic, but I thought brake jack/brake squat was induced from rear braking. Now obviously when you brake with the front, the front fork dives some and the rider's CG tends to want to be projected forward, but I didn't think this was the same as brake jack/squat. Maybe we're just talking semantics here.
    i'm no expert either.

    brake jacking simply refers to the lifting of the rear of a vehicle due to weight transfering to the front of the vehicle under deceleration. suspension squat is a result of acceleration in which the rear of the vehicle squats from weight being transfered back. has to do with inertia, things in motion wanting to stay in motion, things at rest wanting to stay at rest.

    you get fork dive under deceleration regardless of which brake used. it's a result of brake jacking, more weight being carried by the front. you see it more when you use the front brake because the front brake is your primary and most powerful stopper. the faster you decelerate, the more the fork dives.


    as far as the op is concerned, i still think the vt has better initial leverage on the shock resulting in better small shock absorbtion. whereas the long rocker link in his bike seems to increase leverage through the travel thereby requiring a low initial leverage setting..

  35. #35
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    "brake-jack"

    Quote Originally Posted by drunkle
    i'm no expert either.

    brake jacking simply refers to the lifting of the rear of a vehicle due to weight transfering to the front of the vehicle under deceleration. suspension squat is a result of acceleration in which the rear of the vehicle squats from weight being transfered back. has to do with inertia, things in motion wanting to stay in motion, things at rest wanting to stay at rest.

    you get fork dive under deceleration regardless of which brake used. it's a result of brake jacking, more weight being carried by the front. you see it more when you use the front brake because the front brake is your primary and most powerful stopper. the faster you decelerate, the more the fork dives.


    as far as the op is concerned, i still think the vt has better initial leverage on the shock resulting in better small shock absorbtion. whereas the long rocker link in his bike seems to increase leverage through the travel thereby requiring a low initial leverage setting..
    For many years trail bike magazine writers have used the term "brake-jack" to describe monopivot rear braking reaction in bumps.

    Like Drunkle says "jack" is a term meaning rising or extending action. But as riders experienced on many types of rear suspension know, the monopivots do not rise in the rear very much if at all while braking as long as there's traction (the fork dives without the rear rising).

    While there is traction nothing about the bike rises while braking with a monopivot, only the front end dives lower. There is mechanical tension leveraged with the monopivot swingarm from friction with the rear wheel while braking than pulls or tugs the frame downward, while deceleration and front brake reaction try to rotate the frame forward, with the net result of little change in rear suspension level.

    But if the rear tire skips or skids, a rear monopivot suspension suddenly rises to near topout until traction is regained and the rear brake and swingarm reation lowers the frame back down. Repeating skipping over stutter bumps or tightly repeating bumps makes the jacking effect most noticeable.

    The sudden rise when traction is lost doesn't typically occur using a floating rear brake such as horst link or the ICT type. The floating rear brake link geometry is mildly to moderately extending (rising) in mechanical braking reaction with the frame. As soon as the brakes are applied the rear suspension will rise to the level of sag that deceleration weight shift produces. So when traction is lost it can't rise or lower significantly enough to notice.

    - ray
    Last edited by derby; 11-25-2005 at 12:22 PM.

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    Quote Originally Posted by derby
    For many years trail bike magazine writers have used the term "brake-jack" to describe monopivot rear braking reaction in bumps.

    Like Drunkle says "jack" is a term meaning rising or extending action. But as riders experienced on many types of rear suspension know, the monopivots do not rise in the rear very much if at all while braking as long as there's traction (the fork dives without the rear rising).

    While there is traction nothing about the bike rises while braking with a monopivot, only the front end dives lower. There is mechanical tension leveraged with the monopivot swingarm from friction with the rear wheel while braking than pulls or tugs the frame downward, while deceleration and front brake reaction try to rotate the frame forward, with the net result of little change in rear suspension level.
    ah... so if the rear is counter acting the front in this situation, removing the front forces (allowing the front wheel to roll free) would in fact result in a net downward force at the shock, ergo, "brake squat"... i had not considered such a possibility, but i suppose with a swing arm, the maximum wheelbase could be at a point somewhere in the range of the swingarm's path of travel. under rear braking, the wheel would find equilibrium at the maximum wheelbase corresponding to swingarm position somewhere in its range of travel... assuming braking - forward momentum > shock.


    But if the rear tire skips or skids, a rear monopivot suspension suddenly rises to near topout until traction is regained and the rear brake and swingarm reation lowers the frame back down. Repeating skipping over stutter bumps or tightly repeating bumps makes the jacking effect most noticeable.
    since braking forces are dependant on traction, loss of traction = loss of braking force = braking - forward momentum < shock. so the shock immediately returns the swingarm to that state of equilibrium = pogo...


    The sudden rise when traction is lost doesn't typically occur using a floating rear brake such as horst link or the ICT type. The floating rear brake link geometry is mildly to moderately extending (rising) in mechanical braking reaction with the frame. As soon as the brakes are applied the rear suspension will rise to the level of sag that deceleration weight shift produces. So when traction is lost it can't rise or lower significantly enough to notice.

    - ray
    for this, i think it has more to do with the verticle or linear path of travel of the wheel through it's suspension movement in a linkage setup rather than whether or not the brakes are "floating", based on my reasoning of the system reaching equilibrium at max wheelbase length under braking. with a linkage setup that provides a verticle wheel path, braking forces can't extend the wheelbase...

  37. #37
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    That is an awesome looking bike Banzai!

  38. #38
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    Banzairider, maybe this is a stupid question, but what percentage sag are you running?
    Last edited by paddlefoot64; 11-26-2005 at 08:24 PM.
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    Quote Originally Posted by paddlefoot64
    Drinkle, maybe this is a stupid question, but what percentage sag are you running?
    It's an excellent question, because not all bikes will sag the same, you could get away with more sag on a progressive bike than you could on a falling rate bike, and because of this, the one with more sag will undoubtedly feel plusher on the small rippples and bumps at speed.
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  40. #40
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    Path matters for braking

    Quote Originally Posted by drunkle
    ah...

    for this, i think it has more to do with the verticle or linear path of travel of the wheel through it's suspension movement in a linkage setup rather than whether or not the brakes are "floating", based on my reasoning of the system reaching equilibrium at max wheelbase length under braking. with a linkage setup that provides a verticle wheel path, braking forces can't extend the wheelbase...
    Nice visualization of the mechanical dynamics.

    The path effect can be the same or different between monopivots and floating-brake multi-links. Multi-links can be designed with the same paths as monopivots such as the ICT designs, and more acutely changing direction radius paths than monopivots, such as VPP types. Multilinks don't have the monopoly on "vertical path". Very low monopivots have paths that are more "vertical" than many multi-links.

    For braking the direction of the path during rebound is most reactive to grip and traction factors.

    For braking the path doesn't matter significantly if there is very little travel, but in moderate to bigger bumps or sharper hits it does matter how the path complements whether the tire maintains contact. There's no problem maintaining traction on the compression of a bump with the entire forward and gravity inertia loading the tire for more grip and maintaining traction.

    But upon spring rebound and tire bounce over the top of a bump the direction of path rebound matters. A wheel path that begins rebounds rather straight down or even in a rearward direction such as a low monopivot or FSR multi-link has an advantage over a wheel that rebounds with a forward direction such as a higher monopivot or Lawwill multi-link.

    The more rearward compressing (and forward rebounding) path such as high monopivot or Lawwill complies well while compressing, the wheel doesn't need to accelerate as quickly on the bump face. While compressing, the chain-stay increases in length, and less kick from the bump is felt compared to a more vertical path (spring rate and damping condition the difference in feel). But on rebound the wheel must accelerate while the path is drawing the tire forward faster than the frame and rider, and while the bump falls away there is even less grip to accelerate the wheel to maintain traction. Add rear brake friction and the rear wheel skips and skids most easily with the more rearward compressing (forward rebound) paths.

    The ability to rotate the caliper link (or swingarm) is dependent on high traction and the amount of modulation (the amount of brake lever input). So the path matters whether you can apply more brake lever input. The more "vertical" and especially the more rearward rebounding paths have a traction advantage. So these path designs allow more rear brake input and the resulting effects form caliper link (or swingarm) tensioning.

    Theoretically a floating brake with the same path as a monopivot won't "jack" or pogo as easily when traction is lost. However, riders of the new Turner TNT "faux-bar" linkage change from the prior year ICT floating brake design with no other changes on the bike or terrain are not noticing braking differences switching the designs back to back, some even reporting that the monopivot is a little better. Maybe they are being too careful with their modulation and that more "ham-fisted" panic like late braking will produce the theoretical differences. Turners "faux-bar" monopivot and ICT designs are both virtually the same, rather low monopivot-like in path dimensions. The lack of noticeable rear braking differences implies that the path matters more for rear braking traction than differences in caliper swingarm or floating-link rotation tension induced compression or extension reactivity. Not to say that the floating brake is useless, just not as important a factor in quality braking as some manufacturers of floating brake link designs promote.

    For more on the difference of floating axle vs. monopivot differences see the Turner forum. There are many reports now by riders with time on both linkage configurations on the same frame.

    - ray

  41. #41
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    Damn, Derby...I never really gave any thought to the principle and influence of the rebound wheel path. It's seems ignorant not to have thought of what is an obvious occurence. We focus so much on the axle path and its characteristics during compression that I'll bet a lot of us don't give near as much thought to how that path is influencing the bike on rebound. Then again, maybe I'm the only dummy here who just experienced this "light bulb goes off" moment...LOL!

    I have to admit that even though I'm not totally dense, I usually get my opinions on how these physics/geometry lessons merge with reality through the seat of my pants...and I guess how my seat and brain are communicating. While I understand the basic principles of suspension technology and a few of the more complicated ones fairly well, for some reason the effect of the rebounding wheel path had escaped my notice as to obviously how big a factor it is during certain aspects of the bike's operation. I don't know why my brain picked this time to make such an obvious and critical realization, but it did, and perhaps it was your articulate description of it that enabled me to see it. Thanks. It sheds a lot of light on many aspects of my personal bikes' characteristics and to many general suspension issues discussed here.

  42. #42
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    Quote Originally Posted by tim_54321
    That is an awesome looking bike Banzai!
    Thanks, it's funny I've had people telling me that a few times but I myself don't find it that great! I prefer flashy silver! haha

  43. #43
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    Quote Originally Posted by derby
    Nice visualization of the mechanical dynamics.

    The path effect can be the same or different between monopivots and floating-brake multi-links. Multi-links can be designed with the same paths as monopivots such as the ICT designs, and more acutely changing direction radius paths than monopivots, such as VPP types. Multilinks don't have the monopoly on "vertical path". Very low monopivots have paths that are more "vertical" than many multi-links.
    i'm not sure i agree that swingarms and linkages can mimic each other. swingarms travel in an arc, any vertical movement would be an approximation rather than a definate. use a swingarm long enough and the world seems flat at close distances. likewise, use a linkage setup that places the axle pivot on the axle itself and it behaves like a swingarm... because it is a swingarm.

    anyway, the generalization was made to simplify distinction of the design differences with regards to axle path.

    For braking the direction of the path during rebound is most reactive to grip and traction factors.
    ...
    i can totally understand what you're saying here, it again address the importance of axle path in suspension design.


    The ability to rotate the caliper link (or swingarm) is dependent on high traction and the amount of modulation (the amount of brake lever input). So the path matters whether you can apply more brake lever input. The more "vertical" and especially the more rearward rebounding paths have a traction advantage. So these path designs allow more rear brake input and the resulting effects form caliper link (or swingarm) tensioning.
    ...
    and here, you point out the necessity for rider skill and adaptation to the mechanical behaviour. like, the difference in driving technique given a front engine car and a rear engine one.

    for a linkage that increase wheelbase from x to top out, it seems you would have reduced resistance to top out resulting in increased weight transfer and reduced rear wheel braking. as well as reduced bump sensitivity. it doesnt seem like that kind of behaviour would be of any advantage over a decreasing wheelbase/increased braking set up. just a different set of problems/compromises.


    For more on the difference of floating axle vs. monopivot differences see the Turner forum. There are many reports now by riders with time on both linkage configurations on the same frame.

    - ray
    i know that any bike pro given a huffy could blow me away on my centuple link, variable gravity, rising ego, unobtainium tubed, tranverse directional purple people eater. at the same time, i wonder how much of the perceived difference can be attributed to gucci factor.

  44. #44
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    I know you'd like to try the new M Rocco but there is a shock that would be a good comprimise. A Fox RP3 "high volume" as it is on te RM Slayer 2006. I'm wondering if it' s a OEM shock only...
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  45. #45
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    to reiterate

    Quote Originally Posted by BanzaiRider
    Thanks, it's funny I've had people telling me that a few times but I myself don't find it that great! I prefer flashy silver! haha
    That is a cool bike. I wanted one until I found out they wouldn't be available in the US.
    But to reiterate what another poster said - Definitely talk to the guys at Push. You didn't buy a one time shock service, your money got you a valuable resource. I'm sure if they know you're not completely happy with your Push'd shock, they'll do whatever it takes to get you there.
    There aren't many places that have customer service like Push - it'd be a shame to let it go to waste.
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  46. #46
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    When I was mentionning the VT below as feeling great and plush, it is the version with the 4way not 3way. Considering how my friend's VT rides with a 4way, I would say ditch the 3 way and get a 4way or DHX-A...

    Quote Originally Posted by granny.gear
    The VT has a very progressive linkage. My problem with my VT is it never allows you to use the travel. I guess coupled with the 3-way Swinger, that makes thing worse. I know the 5" setting is not as progressive and you can use more travel, but it never feels as good as the 5.75" setting which is far more progressive. I have been steadily dropping the SPV on the Swinger and finding new life in it. Seated pedalling isn't that much worse.

    I'm trying to get it to use the travel on the rough rocky trails but it is hard. It will end up packing in, but never using full travel. I run 35% sag.

    Why would Giant spec the 3-way swinger for this bike (with the already very progressice rate linkage)? It's not a huckers bike and isn't slack enough for 'freedriding'.

    Any shock reccomendations for rough rocky trails with no jumps or significant drops?

  47. #47
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    Correction to my post

    Quote Originally Posted by derby
    I've been playing with modeling 4-bar floating brake geometry lately using some stiff cardboard and thumbtacks, with which I can quickly change the link lengths and leverage alignments. Try it, it is very revealing.

    Basic rear brake reaction is that the link (or monopivot swingarm) that the caliper is mounted to will rotate in tension force in a forward direction with the rear wheel while braking.

    One basic fact became obvious. Unless the 4-bar swing links crossed between the pivot points, all floating brakes (calipers on the rear link) cause the frame to rotate forward or at least tensions the frame in a forward rotation direction. Forward frame rotation tension (also called suspension extension tension or force) resists suspension compression from bumps.

    ....

    - ray
    After more cardboard and modeling 4 bar brake tests I must post a correction to this thread too.

    The correct facts are that anytime the rear caliper link IC is in front of the front wheel axle (or behind the rear wheel axle), then the rear braking extends the suspension. When between the axles frame compressing tension is produced by rear braking.

    I don't understand it completely, but that's the consistent effects from testing. It is as if the IC reacts exactly like a monopivot will in the same position when braked at any moment.)

    Some configurations are more reactionary than others. Of the more common HL and ICT most are near the front axle line or behind and would be mildly frame compressive at sag. Only those with more parallel linkages would produce significant extending reaction.

    Banzi Rider's bike has an IC behind the front axle at top out and moves further behind at sag or deeper in travel. It is not extending in rear brake mechanical reactivity.

    Other factors such as platform shock resistance most likely are causing the lack of small bump sensitivity when braking downhill. All bikes exhibit lessening small bump sensitivity in the rear suspension when unloaded of weight when braking. Platform shocks exaggerate the loss of sensitivity when unloaded of rider weight.

    Sorry for the misinformation earlier.

    - ray

  48. #48
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    Quote Originally Posted by derby
    After more cardboard and modeling 4 bar brake tests I must post a correction to this thread too.

    The correct facts are that anytime the rear caliper link IC is in front of the front wheel axle (or behind the rear wheel axle), then the rear braking extends the suspension. When between the axles frame compressing tension is produced by rear braking.

    I don't understand it completely, but that's the consistent effects from testing. It is as if the IC reacts exactly like a monopivot will in the same position when braked at any moment.)

    Some configurations are more reactionary than others. Of the more common HL and ICT most are near the front axle line or behind and would be mildly frame compressive at sag. Only those with more parallel linkages would produce significant extending reaction.

    Banzi Rider's bike has an IC behind the front axle at top out and moves further behind at sag or deeper in travel. It is not extending in rear brake mechanical reactivity.

    Other factors such as platform shock resistance most likely are causing the lack of small bump sensitivity when braking downhill. All bikes exhibit lessening small bump sensitivity in the rear suspension when unloaded of weight when braking. Platform shocks exaggerate the loss of sensitivity when unloaded of rider weight.

    Sorry for the misinformation earlier.

    - ray
    Hey that's good info ray. One thing for sure is that my seat angle puts me quite a bit forward compared to the Giant VT. So when going downhill, if I stay seated my weigth is definitely less on the rear then the VT. When I go behind the saddle it moves back the weight but not as much as when you are on the seat. Well anyway, everything points out towards the shock so it seems to more and more clear that this bike does not need any kind of compression resistance. I will most probably try out a Cloud9 finally because the piggyback coil shocks will most probably not fit. The Cloud9 will be a cheap way of confirming if our theory is right! Thanks again, I appreciate your feedback.

  49. #49
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    Great discussion.

    My experience has been with a KHS faux bar and a Giant VT.

    A couple of questions:

    The VT is an extremely low single pivot where the pivot is right at or slightly below my little chainring. It seems to me the lower the pivot the better. Right or wrong???

    With a faux bar don't you get more "brake jack" when you use canti mounts vs a disc since the braking forces are at different points??

    Looking at the Devinci, it seems like your head angle is very slack. How does the bike steer? I use a zokes xc fork on my bike with adjustable travel, lockout, coil and air chamber combo and ETA for long uphill climbs. Perhaps the front fork is messing with your rear susspension?? I would think a too tall fork would weight your bike improperly.

  50. #50
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    Quote Originally Posted by richwolf
    Looking at the Devinci, it seems like your head angle is very slack. How does the bike steer? I use a zokes xc fork on my bike with adjustable travel, lockout, coil and air chamber combo and ETA for long uphill climbs. Perhaps the front fork is messing with your rear susspension?? I would think a too tall fork would weight your bike improperly.
    Yes, it is very slack (66 degree HA) but strangely enough, it steers great both on tight singletrack, fast turns and steep downhill. Might be because the tob tube is relatively short (22.2). However, going steep uphill, the front lifts really easily if I don't sit right at the front of my seat and lean on my handlebar.

    In a sense you are right with the fork but probably not in the sense you mean. If my fork messes with my rear suspension it must be just about feel. The Marzo AM1 feels so plush that it makes me realize much more that my rear end is a bit bumpy. When I was using a Fox Talas up front, I was concentrating much more on the "bumpy" feel of the front end so I was not realizing that my rear was like that also.

  51. #51
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    Quote Originally Posted by BanzaiRider
    Yes, it is very slack (66 degree HA) but strangely enough, it steers great both on tight singletrack, fast turns and steep downhill. Might be because the tob tube is relatively short (22.2). However, going steep uphill, the front lifts really easily if I don't sit right at the front of my seat and lean on my handlebar.

    In a sense you are right with the fork but probably not in the sense you mean. If my fork messes with my rear suspension it must be just about feel. The Marzo AM1 feels so plush that it makes me realize much more that my rear end is a bit bumpy. When I was using a Fox Talas up front, I was concentrating much more on the "bumpy" feel of the front end so I was not realizing that my rear was like that also.

    Well if it were my bike I would put a coil on it that was adjustable and that you could buy different weight and rate springs for it. I would also like the shock to be air adjustable as well and have both rebound and compression damping. I would probably get a high end Stratos.
    I would then put on a Zokes fork like you got but with ETA on it for those long uphill grinds. 66 degrees is way too slack for uphills if you have a lot of those to deal with.

  52. #52
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    Quote Originally Posted by richwolf
    Well if it were my bike I would put a coil on it that was adjustable and that you could buy different weight and rate springs for it. I would also like the shock to be air adjustable as well and have both rebound and compression damping. I would probably get a high end Stratos.
    I would then put on a Zokes fork like you got but with ETA on it for those long uphill grinds. 66 degrees is way too slack for uphills if you have a lot of those to deal with.
    My AM1 has ETA and I do use it often!

    As for the shock, I've concluded that this frame needs a non platform shock, ideally a coil. However, in another thread I've also found out that most "reservoir/piggyback" shocks will not fit because the reservoir will hit the down tube at full compression. So either I spend a lot for a custom remote reservoir shock like Stratos or Avy, I just try out a cheap Cloud9 or I buy a new frame. I'm still at the decision process! haha

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