Polygon Square One EX9 2017 (UPDATED)


UPDATE: después de hablar con Chris sobre la bici he revisado el modelo y pongo los nuevos resultados. La correlación con la realidad creo que es muy alta. El leverage rate es el cambio más destacado.

Esta bici ha generado muchos comentarios, pero obviando su  estética, el sistema de suspensión es algo novedoso en este mundillo. El nuevo sistema "R3act" es un basculante con dos bieletas, pero además el basculante se une con el cuadro mediante una deslizadera. Sí, no es un amortiguador oculto, ni un punto de giro escondido, ni un maletero para el bocata, es una simple deslizadera.

También me ha parecido muy llamativa su geometría. No es muy larga, pero tiene un reach muy largo, no tiene el pedalier bajo, pero si un stack bajo, el ángulo del sillín es más vertical de lo que pone, y los 66º de dirección no creo que sean un fallo, parece que todo está más que bien pensado para redondear el conjunto de la bici. Dicho esto, habría que probarla para opinar con fundamento. Todos los review que he leído dicen que pedalea increíblemente bien, vamos a ver:


Pues sí, parece que los de las reviews lo han clavado. Creo que esta curva ligeramente ascendente y con estos valores es lo mejor que se puede conseguir en cuanto al pedaleo. Perfecto en desarrollos cortos especialmente. La Yeti sobre el papel y según he leído pedalea muy bien, pero en este caso las comparaciones son odiosas. Puede decirse que es el sistema que mejor pedalea del mercado.


Valores correctos para el brake squat, un buen compromiso entre mantener la geometría e interferir poco la frenada con el trabajo de la suspensión.


En este apartado tiene unos valores muy altos relacionados al alto antisquat. Es especialmente notable en desarrollos largos, algo más de lo normal.


No solo del pedaleo vive el hombre, y aquí falla en mi opinión. Un leverage rate medio-alto pero con una progresividad correcta y una pendiente continua, algo bueno para poder usar muelle o aire. Lleva un Fox X2 y recomiendan llevar prácticamente abiertos todos sus ajustes, lo cual encaja con lo bien que pedalea y promete una gran tracción y agarre. Recomiendan un 25% de sag que va bien con el antisquat, y con tanto recorrido costará más apurarlo. Al final queda un resultado que puede funcionar muy bien.


Esta es la trayectoria que describe el eje a lo largo del recorrido (visto desde el perfil derecho de la bici). Aunque el novedoso sistema podría tener una trayectoria especial, no es el caso. Tiene hasta 6 mm de retroceso pero es prácticamente una línea vertical, una trayectoria muy común.

Como resumen, una bici muy particular y aunque a primera vista no lo parezca, con todos los detalles muy cuidados para que todo vaya en armonía. No la definiría como una bici de bikepark ni de freeride, si no como una trail con esteroides, polivalente y neutra. En breve más, mientras tanto espero vuestros comentarios.

13 comentarios:

  1. Demasiada complicacion con los links y el telescópico ese, para no aportar nada relevante a este mundillo. De juzgado de guardia lo del LR medio. Altisimo.
    Poca progresividad para una bici de tanto recorrido, y para más Inri... Con la incógnica solo despejable con el paso del tiempo, de la previsible poca rigidez, y la duda mas que razonable, ante la aparición con el tiempo de crujidos/ruidos diversos.

    El año que viene desaparece de su catálogo... Tiempo al tiempo.

    Saludos.

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  2. ¿Por qué sería el sistema que mejor pedalea del mercado? Por la curva creciente de %anti-squat con el recorrido? A mí no me termina de convender en ese aspecto. ¿Para qué vamos a querer poder generar fuerza anti-squat en zonas del recorrido tan avanzadas? Si el sistema se encuentra tan comprimido no se creo que se esté pedaleando. En cambio sí se impide que los valores de pedal-kickback sean inferiores, como pasa con curvas decrecientes de %AS con el recorrido.

    Estaría bien saber los valores de %AS en cada desarrollo, pero partiendo de un 32-10, y un 30-35% de sag que se puede llevar en esta bici, vemos en la primera gráfica que tendríamos un 140-150% de AS. En ese desarrollo al menos, el pedaleo tiende a extender un poco el sistema.

    Para mí el ideal creo que es tener un valor próximo a 100-110%, en la mayor cantidad de desarrollos, y en una zona de recorrido que no vaya más allá en exceso del punto de sag, y a partir de ese punto descender.

    Saludos y gracias por seguir haciendo más análisis.

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    Respuestas
    1. Pues eso, en nada descatalogada.

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    2. Josep, debo rectificar. He revisado el modelo ya que el slider no lo había interpretado bien, fallo de novato. Al final queda un antisquat un pelo más alto pero un leverage rate muy correcto. Creo que no está tan mal el "R3ACT" y tiene margen de mejora.

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    3. FSiano: Se relaciona un poco con el comentario que te hice en el post de la Norco, que fue espeso jaja Lo ideal en la teoría es un 100% en todo el recorrido pero en la práctica, como dices, para conseguir recorrido al pedalear tienes que aplicar bastante fuerza. Además tu CDG se moverá continuamente y no poco, por eso con este tipo de gráfica puedes dar los zapatazos que quieras que no debería tener apenas balanceo. Como muy pocas se parecen, por eso lo digo. Lo comentaba en Pinkbike, que aunque no es un monopivote se comporta como tal, y si te fijas en cualquier monopivote puedes ver gráficas parecidas.

      Pero claro, en un buen sistema no solo tiene que ser perfecto el antisquat. Si tenemos en cuenta todos los aspectos del sistema, yo preferiría sobre un 100% hasta la mitad del recorrido más o menos y que luego descienda. Esto es cuestión de gustos pero hay que saber interpretarlo.

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  3. Hola MrBlackmores, Josep,

    My best regards to you. It's a while since we have talked.

    It is evident that the bike pedals well. (Don't forget the Craftworks ENR though, which provides a similar pedalling performance without a lot of pedal kickback.) While much of this stable pedalling performance comes down to the AS profile that may not be the only basis for its stability under hard pedalling - there could be and probably is stiction in the sliding link. A better telescoping link implementation could fix that though.

    A stranger thing about this bike that is being widely reported is its supposed i) ground hugging ability,and its capability to ii) easily soak up rough terrain iii) without noticeable pedal feedback. Now, when iii) gets combined with the other two points credulity gets stretched. So, it is important to understand what is happening. Maybe, a very light shock tune or a rearward axle path could help to explain i) and ii) but then it gets hard to understand who no one is reporting a pedal feedback issue. This needs a closer look.

    MrBlackmores, I hope you can include the axle path diagrams in your analysis so that we are in a better position to judge some of these claims.

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    1. Welcome Chris! Interesting the stiction, the seal is a Skf which has a low stiction and the interior seems empty (I think it only has the valve in the upper axle if interior pressure builds up), so this isn´t a big issue in my opinion. Check this interesting link: https://www.bikerumor.com/2017/04/12/a-new-era-of-kinematics-naild-r3act-2play-suspension-makes-the-polygon-square-one-ride-like-nothing-else/. After reading again this review I think I can improve my model.

      I think the traction comes from the open tune of the Fox and high LR. They say that the recommended sag is 25%. Add long travel and I suspect that a few tokens on the shock, and the result is big traction, no bottom outs and usable and active travel. It´s a tricky bike.

      PD: Craftworks ENR kinematics are awesome.

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    2. I have updated my model and the results. The biggest change is on the leverage rate and now it looks really good.

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    3. Well that is an interesting set of results and not entirely what I expected. I just want to absorb them for the moment.

      On the topical matter of telescopics in suspension design, though, I wasn't at all concerned about pressure in the sliding link on the EX9. My concern is the humdrum one - tubular telescoping/sliding mechanisms are one of the best bad ideas that the world of engineering has ever had. Despite the usefulness and simplicity of the mechanism engineers are invariably compelled to shield the sliding part behind other more robust parts in order to iron out the turbulence of forces that might be experienced by the sliding part. The rocker component driving a shock, for example, in addition to its leverage rate related function also serves to reduce friction arising from side loads on the shock shaft as it telescopes into and out of the damper. Occasionally, the need for simplicity and the lack of viable practical alternatives means that telescopic mechanisms get used in contexts where they might be exposed to an unpredictable and even violent jumble of forces. That is the case with bicycle and motorcycle forks which operate in an untamed world of forces. Good engineering can reduce side loading but not eliminate it. As one of two links joining the swingarm to the frame on the EX9 surely the sliding link will suffer side loads and frictional issues in the same way as a fork.

      And, there is anecdotal evidence to support the proposition that there is friction coming from somewhere in this linkage. Mike Levy, in his Pinkbike piece, running the shock open (n.b. the shock is said to have 60% less damping than a standard shock) reported, in a review that was glowing in other respects, that rebound damping was quite a bit slower than he would have imagined (when riding with the shock open) and that the result was "a ride that feels anything but dynamic". I struggle with the idea that a bike with an extremely light shock tune and a normalish LR curve could have anything other than a rapier quick feel. Friction in the sliding link would be my guess as to why things are slower than expected. Am I barking up the wrong tree?

      Josep, a thought that may interest you. This bike could represent a path previously not taken in mountain bike design. Based on early reports about the EX9, which must be considered unreliable, but are nonetheless interesting, pedal kickback is not upsetting the rhythm of riders or causing any loss of composure. So, there may be another way to meet the essential ride goals that you have outlined over the years, if any of the claims about this bike hold water. Of course, it would be good to answer the question of whether riders sensitive to pedal kickback really will find positive characteristics in the way the bike rides. So, perhaps, if you get a chance, you might care to demo the bike and let others reading this blog know what you think.

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    4. @Chris, yes that bushing/bearing bind in the telescopic member is an interesting possibility. It would be interesting to cycle this suspension with the shock removed, to feel what it is like when under very little load, but it seems that under load the bushings in the telescopic unit could nearly lock up. Purely on a front/rear plane, if you look at what pedal loads will do, they will tend to load the back side of the telescope, whereas bump loads will tend to try to flex the telescope in the opposite direction. This means that under hard pedal loads the telescope would tend to lock, due to friction. Then when a bump load of equal force to the pedaling load was encountered, it would neutralize the load on the telescope, and allow the suspension to move without excess friction. If hitting a huge bump when coasting, as you would on a downhill run, the telescope would try to lock out in the opposite direction, which would add significant friction compression damping, proportional to the bump force.

      Basically what I am saying is that bushing bind in the telescopic unit has the potential to magnify the normal resistance to movement that you would expect with a bike that has 100% anti-squat values, as it would add additional friction damping that would be proportional to the sum of pedal and bump loads.

      This video is a good illustration of the potential of bushing bind to lock out a telescopic system: https://youtu.be/_WlRqcAQr2w

      BTW, great information here from both Mr.Blackmore and Chris, thank you guys for taking such an interest in figuring out what is truly going on with this bike!

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    5. @TheKaiser I read your comment several days ago but didn't have an opportunity to respond until now. You have brought some very well considered points to this discussion. And, yes, some bowing of the telescopic linkage one way or another on the front/rear plane could be what accounts for a significant part of the strange combination of characteristics reported about the R3act suspension linkage. I suspect that way you have broken things down (linkage distortion due to acceleration vs linkage distortion occasioned by bump force/wheel deflection) is on the right track.

      I note, you have deliberately left transverse (i.e. side to side plane) forces out of the picture you have drawn. That make's analytical sense but the effects of any deflection of the rear wheel - sideward movement or twisting out of normal alignment with the front triangle - will need to be taken into account to get the full picture. It seems to me that any deflection of the rear wheel will exert a lot of force on the telescopic slider due to the wheel acting as a lever.

      The kind of frictional forces we are talking about here will probably rise and fall on short to very short time intervals viz. severe stiction may only be momentary but it could still have a significant impact on suspension performance. To put that another way, linkage bowing and twisting will likely start to correct itself after an initial elevated degree of resistance following a spurt of acceleration or the compression of the suspension by a bump. Even transverse wheel deflections which would probably raise friction in the linkage a lot would have a reducing frictional impact as the wheel begins to spring back from its deflected/flexed state into its normal alignment.

      I would say that the kind of approach you have outlined (suitably expanded) could go a long way to explaining the strange combination of suspension/ride characteristics that have been reported in reviews of the EX9. I suspect that you might agree with me (I had a good look at the the video on the advantages of the Lefty fork) that stiction is a bad thing even when there are those arguing that its effects are good e.g. the supposed XC-like ride of the EX9 while pedalling (if indeed stiction is partially responsible for that ride characteristic). You might also agree that with a more appropriate telescopic mechanism riding on needle bearings (which is really what the bike should have) much of the stiction problem could be overcome. With a low friction telescopic linkage, moreover, damping could go back to where it belongs - the shock absorber! Even if linkage stiction/resistance were viewed in a positive light (which would not be the right way to view it) there is no way the complicated combination of forces acting on the telescopic link during a hard charging ride through steep and rough terrain could somehow automatically work themselves out in a result that always provides the right amount of resistance (i.e. frictional damping) for optimal traction. This is what has been claimed about the R3act suspension design and the claim is nonsense.

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  4. Bufff, qué valores de pedal-kickback tan elevados!

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    Respuestas
    1. Sí, es con diferencia lo peor del sistema. Veremos si en el futuro pueden conseguir mejores valores.

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