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  1. #1
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    Advantages of single pivot suspension

    I've only ridden a couple of FS bikes, both of the multiple pivot variety. I'm interested in getting a new Rush this next spring. What are the advantages and disadvantages of single pivot versus the latter?? Thanks in advance!!

  2. #2
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    Only 1 set of pivots to clean/lubricate

  3. #3
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    I don't know specific details other than it's easier to mantain for obvious reasons, but let me tell you it really works. I've had a Specialized FSR and while it was a nice bike going down I always felt a lot of pedal bob going uphills. Now I've a Rush and I'm surprised on how good it climbs, it always find the traction and I can't feel any pedal bob, in fact my bike came with a Fox RP23 shock but I never use the propedal lever. It feels more plush than the FSR too.

    In the end I guess it depends on what do you want to do with the bike. For overall trailriding conditions the Rush is hard to beat IMO. If you plan to jump anything over 3' I think there're better bikes out there.

  4. #4
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    Pretty much pure trail riding. I don't plan on the wheels leaving the ground to often! I was in my LBS the other day checking on the price of the new 08 5z. Even the guys that worked there were suprised by the decent component for the price. 1699.00 Not to bad considering the Fox suspension and X9!!

  5. #5
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    Some reading....

    http://www.rdrop.com/~/twest/mtb/pathAnalysis/

    Yes, I noticed it too...Cannondale seems to be able to offer quite good bikes at good prices. For example for a price of a Heckler frame (it's a hack of a frame, don't take me wrong) you can get a complete Cannondale bike.

  6. #6
    All Lefty's, all the time Moderator
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    SP bikes offer a more curved axle path, which in turn, allows you to pre load it for log crossings, leaping etc. It also settles you into the bike in a hard turn, as opposed to a multi link, which tends to leave you sitting high up on the bike, in the same situation. I dig 'em
    This is a Pugs not some carbon wannabee pretzel wagon!!

    - FrostyStruthers



    www.mendoncyclesmith.com

  7. #7
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    Depending of the pivot location, the SP eats bumps with more ease than a Sumo wrestler eats anything and provide good traction on steep climbs as the rear tire wants to stick to the ground... It's the case on the Rush and the Prophet... Another single pivot aficionado here!

    DAN.GEROUS.NET : MOUNTAIN BIKING : CYCLOCROSS : ROAD :

  8. #8
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    Over the years I have owned some 4 bar HL bikes, including a Titus Racer X and Turner 5 Spot, a low single pivot (Titus Locomoto) and high forward single pivot (Orange 5) in addition to a Rush and Scalpel. I feel that other things such as geometry and suspension setup in terms of rates and damping are far more critical to ride than the kind of suspension design. In addition other factors such as frame rigidity are also important.

    The article Nonojoe posted is really worth reading. What it really clearly shows that ties in with my own experience is there is no free lunch and perfect suspension design. Each has its own advantages and drawbacks. The Rush with its higher forward pivot has a good path for bump absorption, it also tends to extend more with pedalling in the small and middle ring. This is good for climbing under some situations because it helps offset the forward weight shift that produces suspension movements, it also makes the bike more responsive to pedal input, the drawback can be on some loose rocky surfaces you have to be more carefull about a smooth pedal stroke because the suspension is not as active.

    I wouldnt buy/not buy a bike because it has a single pivot, four bar, faux bar etc, etc, I would buy it because it fits me and my riding. I should also add that having a great local shop that sells and services your bike is the most important factor of all.

    Kevin

  9. #9
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    I have had a Gemini for 4 years with Coil & Romic; Single Pivot, no-platform.
    It was plush, and Gemini was said to be good at climbing compared to others in those days, for a long time I was happy with the bike didn't question the bobbing and didn't realize its design was outdated.

    This year, I tried Santa Cruz Blur with VPP and Fox RP23. I'm now a convert. I was very impressed that I'm climbing better than I did with my Hardtail. No bobbing, yet good traction. I don't have to worry about roots and bumps, and lines I take. I just crank and crank. There is a good reason that Specialized and Santa Cruz (or Intense) vigorously defend their Horst Link and VPP patents, and other bike companies are having a difficult time trying to work around that. The technology works. I wonder when those patents will expire so that Cannondale can build killer multi-link bikes.

    Remember, the riding characteristic of Single Pivot bikes depend on having a good platform rear unit, and the height of the pivot.

    Like Kevin said in above, Rush & Prophet have the pivot between the middle ring and large ring. This means when pedaling with granny or middle ring the chain tension acts to extend the swing arm thus reducing the bobbing. But if you're pedaling in the large ring, say on the flat road, it acts to compress thus inducing the bobbing.

    Just something to think about.

  10. #10
    Unit 91
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    I understand your analogy, but I think your comparison is somewhat invalid. You compared a Gemini to a Blur. Those are two completely different bikes in terms of how much travel they have and the weight of the bike. A comparison to a Rush would have been a little more correct. Just my opinion.

    And about all the fuss about SP vs. linkages...just ride the damn bike. (my opinion once again)
    Bikes

  11. #11
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    Rush is in 10cm rear suspension category. How much different the path and behavior of rear wheel can be on such short travel frames? Not by much...

  12. #12
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    You guys are right, my comparison on Gemini to Blur is not exactly relavent with regards to the orginal poster's question in purchasing of Rush

    I just wanted to illustrate the advantages or disadvantages of Single Pivot system on its theory as this discussion was about.

    I believe what I described about Single Pivot with regard which chainring still applies to Rush. Especially with the big ring, the bobbing can be solely controled by the SPV or ProPdal, TerraLogic, etc.

    Pedal induced bobbing the rider feels in itself is usually only a few centimeters of vertical movemnet, while less than a centimeter miniscule horizontal reduction in chain length. What's crucial in design is wheather chain tension acts to extend or compress the swingarm.

    No doubt Rush must be a great bike for the price, and I'm a big fan Lefty.

    The article linked above by nonojoe was indeed a good read.

    BTW, Mendon's statement got me curious.
    --------------
    SP bikes offer a more curved axle path, which in turn, allows you to pre load it for log crossings, leaping etc. It also settles you into the bike in a hard turn, as opposed to a multi link, which tends to leave you sitting high up on the bike, in the same situation. I dig 'em
    --------------

    I need some help understanding how -- in SP-- preloading helps for leaping, or also how the bike settles into during the hard turn. What is pre-load anyway? I've never really quite figured it out with my Gemini and tickered with it.

    Thanks so much.

  13. #13
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    Quote Originally Posted by TheProphet
    And about all the fuss about SP vs. linkages...just ride the damn bike. (my opinion once again)

  14. #14
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    Quote Originally Posted by Astroboy
    BTW, Mendon's statement got me curious.
    --------------
    SP bikes offer a more curved axle path, which in turn, allows you to pre load it for log crossings, leaping etc. It also settles you into the bike in a hard turn, as opposed to a multi link, which tends to leave you sitting high up on the bike, in the same situation. I dig 'em
    --------------

    I need some help understanding how -- in SP-- preloading helps for leaping, or also how the bike settles into during the hard turn. What is pre-load anyway? I've never really quite figured it out with my Gemini and tickered with it.
    Preload:
    Think about an athlete getting ready to jump vertically: She must first move her mass downward (crouch) and then spring upward pushing her legs from a bent position to an extended position. Next think about someone on a pogo stick: In order to get off the ground, the 'rider' must throw their mass into the pogo spring, thus compressing (preloading) the spring. This movement is similar to the athlete crouching to prepare to jump. After the pogo spring compresses, it immediately rebounds. If the rider extends their legs simultaneously (like the jumping athlete), the pogo spring will propel the rider much higher off the ground than the athlete jumping without the aid of the spring. It is the combination of the leg extension and the spring rebound that gets the greatest jump.

    In an effort to eliminate suspension compression from chain tension, 4-bar and VPP bikes are designed such that the forward component of the rear axle path is minimized. The rear axle paths for these designs are more vertical or even backward. This is good because you can pull on the chain (pedal) without wasting any energy on compressing the suspension. This has another effect as well, if a linkage bike rider leans back toward the rear axel, the suspension compression should be minimal, because of the suspension is not designed to compress in that direction. Some think that this is also good because they think that only ground forces (bumps) should have effect on the suspension.

    Single pivot designs have an axel path that curves forward relative to the rider under compression. The inherent problem with this design is that chain tension also pulls the axel forward to some degree, thus wasting pedaling energy on compressing the suspension. While frame designers were working on linkage to solve this problem, rear shock manufacturers developed platform damping to minimize this problem. So which is the better solution?

    As described above, if a rider leans back into the rear suspension on a linkage bike, the resulting suspension compression should be minimized by design. This is why Mendon stated that when you come into a hard turn, the linkage design will not allow you to settle into the suspension but instead will "leave you sitting high up on the bike."

    Now back to the pogo-
    If the rider preloads the suspension on the linkage bike and unleashes a 'jump' as the shock rebounds, the axle path will cause the spring to push vertically or even backward, which is not in the direction that the rider wants to travel. Conversely, if the rider preloads the suspension on the single pivot (and breaks through the pedaling platform), the rider's mass moves back into the curve of the axle path. When the spring rebounds, and the rider jumps, the combined result propels the rider upward and forward, which is the desired direction of travel. This is why Mendon stated that the single pivot design "allows you to pre load it for log crossings, leaping etc."

    This doesn't mean that you cannot jump a linkage bike. Remember, even the athlete without a pogo can get off the ground. What it does mean is that you cannot use the linkage bike suspension to enhance the jump like the single pivot design does.

    My personal experience: I've primarily ridden ridden Cannondale single pivots - Jekyll, Raven, Super V. A few years back I saved my pennies and bought an Ellsworth ID because I believed that the linkage design and the greater travel might improve my riding. After a year of trying hard to like it, I realized that the ID was a big mistake. I could never make the Ellsworth do what the Super V could do. I eventually figured out how to get the greater travel from a Super V frame (the 'Uber V') and I never looked back. The Uber V with a Fox DHX air outperforms any other bike I've ridden.

    One other interesting note: For what it's worth, the November '07 Mountain Bike Action has a review of the new Tomac Snyper 140. The conclude by mentioning that the new Tomac ranks up there with their other two favorites: the Santa Cruz Heckler and the Foes 2:1 XCT 4. All three of these bikes are single pivots. Makes me wonder how they'd like the Uber V, which has similar pivot placement to the Foes and the Tomac.

  15. #15
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    First of all, thanks so much to rw420 for dedicating the time for writing the post above, and I admire how it's illustrated nicely.

    I understood the part where the forward axel path ( in SP bikes) helps in jumping forward, while the backward axel path acts against, but I'm still confused with other points.

    1) I see -- in the cases of compressed pogo spring or athlete with bent knees that there is potential energy which could be released for jumping.

    However by the look of the coil unit equipped on my Gemini, the spring looks to be linear. The preload adjuster is -- in essence -- a spring compressor. If I dial it. It's like the pogo spring compressed and stays locked, or knees bent but cannot extend. I don't see how the energy can be released and exploited.

    Doesn't a regular coil spring have a linear rate? My understanding is that -- if it takes 10 pounds to compress the first inch of travel for a given spring, then it takes the same additional 10 pounds for each inch of travel thereafter until the end of the stroke.

    I have an equivalent preload adjuster mechanism on the rear of my motorcycle. When this step-teeth looking adjuster is dialed, it compresses the spring. What this does is to set the initial spring rate prior to the riding in anticipation of the aggressive riding condition, the presence of a cargo or a passenger, etc. However, in order for this to function, the spring must be rising rate -- progressive spring. This spring is wound tighter at one end, and spaced apart at the other end.

    Yet my Gemini has preload adjuster even though the spring is regular linear spring; it's wound with even interval. The regardless of the preload (pre-compressing), the spring rate should stay the same.

    --------------

    2) What does it mean to "settle" into suspension while cornering? Why is it beneficial? I may unsaddle and pull my hip back during the descending or cornering, so that I don't flip over my handlebar, or so that the front can steer freely, or so that the front tire won't have too much weight and understeer. Whether SP or Linkage, if I lean back, the weght bias shift backwards to the rear wheel, thus compressing the rear swingarm. Why would there be a difference?

    What am I missing here?

    Thanks so much.
    Last edited by Astroboy; 10-20-2007 at 12:23 AM.

  16. #16
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    I noticed it was funny how I could bunnyhop higher on my heavier Gemini than I do with Blur (lighter by about 9 ~ 10lb). I thought I just wasn't used to my new ride, or the longer stroke of the Gemini was letting me to compress deeper and to set up for the jump.

    Well, from this thread I learned that the axel path is also a factor in bunnyhop. Cool.

    I did some further reading and learing: on the anti-squat behavior of some of the multi-link sysmtems, on the development of the DW-Link, etc. It's a huge maze of information.

    I should let those designers to work it out...

    Let's "ride the damn the bike(s)" and enjoy.

    I love both my Gemini & Blur.

    You'll definitely be happy with your Rush.
    Last edited by Astroboy; 10-20-2007 at 12:48 AM.

  17. #17
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    There is a lot of info here but I have to play the myth buster. It is important to note that the axle path of the Rush actually swings back and up through the intial stages of travel. This makes the rear respond pefectly to small bumps. Through the middle stages of travel the axle path moves almost vertical and only during the late stages of travel does the axle start to move forawrd. It has to move forward at the later stages or chain growth becomes to much.

    I thought it was propaganda until I saw a recent clinic. My Cannodale Rep showed me a demo where he put a Rush in a bike stand and replaced the rear wheel with a pencil. He then took a bike box and put it close enough to let the pencil touch. He would actuate the swingarm to show the axle path. The Rep then repeated the process with the a Specialized Stumpjumper. You would be surpised at how similar the axle paths were. He also pointed out that Specialized has dropped the "vertical wheel path" argument from their marketing. They seem to have realized what Cannondale already knew. A real vertical wheel path is not a good thing.

  18. #18
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    Thanks for sharing the story. I'll be excited to cram a pencil in my dropout later, and literally be able to see the VPP's and my Gemini's axel path.

    I think I now khow how the preload adjuster ring is crucial in setting up the proper sag in relation to the axel path for the Gemini.

    For Cannondale Single-Pivot variety, by using the preload (or the spring rate, or the air spring pressure), the optimal axel path is achieved, when the bike w/ rider's weight, at the static sag, is set to have its pivot location slightly above the front-to-rear axel horizon.

    I didn't understand before, what it meant to have a X percent of proper sag and why.
    The visuals help me greatly -- I'm a slow learner.

  19. #19
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    re: sag...if trails only had bumps (forces that compress the rear shock) then you really would not need sag but trails also have depressions. So, it is important that a rear shock be able to extend slightly as the rear wheel drops into them. Traction and comfort are greatly improved with sag. It is recommended that you run 20-30 percent of a shocks total stroke as sag. Closer to 20 for XC riding and closer to 30 for Trail Riding.

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