Spot Rollik 557 2016

Spot Brand es una pequeña marca artesanal que siempre se ha dedicado a fabricar cuadros en acero y titanio, especializandose además en modelos tipo Singlespeed. La Spot Rollik 557 por lo tanto es una autentica rareza dentro de esta marca, es su primer modelo de doble suspensión (140mm de recorrido y ruedas de 27.5'') y por si esto fuese poco se han atrevido a fabricarlo en fibra de carbono y a realizar un diseño bastante original con un sistema de suspensión tipo Pivote Virtual. El sistema Living Link utiliza una configuración muy similar al del DW-Link, pero evita entrar en conflicto con la patente de Dave Weagle gracias a la utilización de una lámina fléxible de carbono con la que se elimina un punto de giro en la bieleta inferior...

Como podéis ver en la tabla de excel y en las gráficas anteriores la nueva Spot Rollik 557 tiene una Eficacia de Pedaleo bastante alta. El sistema tiene unos porcentajes de Anti-squat altisimos y esto quiere decir que cuando pedaleamos con fuerza el sistema va a extenderse, provocando en algunos desarrollos una pequeña oscilación debida a este exceso de Anti-squat. La gráfica ademas es muy plana, muy parecida a la de un DW-Link por lo que modificar el porcentaje de Sag no va a cambiar el funcionamiento. Los porcentajes en los desarrollos mas cortos están en torno al 120% (Una cifra muy alta, pero que no llega a ser excesiva), y en los desarrollos mas largos no se suele pedalear con tanta fuerza, pero aun asi el sistema tiene unos porcentajes de Anti-squat excesivos. La llegada de los nuevos grupos de doce velocidades va a ayudar un poco, pero utilizar un desarrollo de 34T o de 36T no va a resolver el problema. El Pedal-kickback (25º) como ya os podéis imaginar se mantiene en un nivel muy alto, al igual que el Brake-squat (95%), como suele ser habitual en los sistemas de Pivote Virtual.

En la gráfica del Leverage Ratio vemos como el sistema es del tipo Progresivo-Regresivo (2.8~2.5~3.0). Lo habitual en este tipo de modelos es encontrarse una gráfica en la que el primer tramo representa el 70%-80% del recorrido y en la que el tramo regresivo solo afecta a la parte final del recorrido, algo muy facil de compensar con un amortiguador de aire... En este caso el sistema tiene una gráfica prácticamente simétrica, con un tramo regresivo muy importante que va a influir mucho en el comportamiento del sistema, creando un tramo medio muy firme y un tramo final facil de aprovechar. En cuanto al amortiguador este modelo ha sido uno de los primeros en pasarse al "Metric standar" (210x55mm), los primeros prototipos utilizaban amortiguadores Fox tuneados para conseguir esta medida, pero supongo que los modelos de serie utilizaran versiones estandarizadas... En fin, en mi opinión estamos ante un modelo bastante especial, en el que tanto el sistema como la geometría (67º-76º) están muy enfocados hacia las subidas. Los recorridos son bastante generosos, pero creo que este modelo está enfocado hacia un uso tipo Trail. El sistema se sale un poco de lo habitual, pero aun asi creo que hay gente a la que le puede dar muy buen resultado.

Un saludo.

4 comentarios:

Unknown dijo...

Antonio,

Does the reference to the DW-link mean that this linkage is to be analysed in the normal terms that apply to any dual short link? I ask this question because it is not obvious to me exactly how to approach the analysis of this thing. Is it a dual short link or a flexy single pivot? I'm not entirely sure. I'm not even sure that the analogy to either a four bar or single pivot is quite right. Anyway, I'd be interested to know how you approached the analysis of the linkage.

Also, beyond the dry analytical point just raised, isn't there a another basic problem with this new linkage? Why is the structural flexion inherent in this linkage any better than the bad flex of an insufficiently stiff frame or linkage? Spot bikes are claiming high lateral stiffness. Well, maybe, but I would like to see that confirmed in the experience of riders. Also, even allowing the bike may be laterally stiff it is still possible that the "leaf spring" could contort into unpredictable shapes, an S shape (in side view), say, on one suspension compression and some other shape on another. All of this in rapid succession. That would be bad flex. It seems to me that something like that is possible and maybe even likely.

Un saludo
Chris

Antonio Osuna dijo...

I've placed the rear pivot of the lower link in the middle of the flex plate. To me it's clearly a Virtual Pivot. The exact position of the "Flex Pivot" it's really difficult to find, but it doesn't matter too much, AS and LR stay pretty much the same if you move the pivot a bit to the front or to the rear.

Rear-end stiffnes it's probably good too. The flex plate is very short but very wide and I don't think it can be twisted.

Best regards,
Tony.

Unknown dijo...

I would agree that the reservations expressed so far about the Rollik's suspension are just that, worries about how things work not proof of defects.

Spot Bikes say the flex plate resists flexion/bending and recoils to flat, that is it is spring like, with the maximum resistance and strongest recoil coming at the point of maximum flexion - around mid-travel. It is not clear how strong these spring-like forces are but they do add to or modify the spring rate in some degree. Before mid-travel that is probably a good thing - the satisfactory designed LR escalation of the Rollik is enhanced with a more progressive spring rate (due to the effect of the flex plate) than the forces graphs probably convey. Would I be right in saying that you haven't factored anything like that into the graphs, Antonio? So, that would probably mean escalation is excellent in practice, before mid travel.

After mid travel things change. Even as the shock spring continues to compress and resistance increases the flex plate is already in a state of recoil (i.e. it is moving to a flatter less flexed state as the suspension continues to compress). This is also probably a good thing because the effect would be to incrementally retract any excess spring resistance above that from the shock in the section of travel where such an excess wouldn't benefit suspension function - a bit of extra support from the flex plate around SAG and mid travel is good but its effect should diminish thereafter.

The two problems I see are, first, that the flex plate, in the deeper reaches of travel opposes suspension rebound - as the shock moves into rebound the flex plate starts to flex again and counter (to some degree) the proper action of the suspension i.e. it counteracts the recoil of the shock spring as it extends towards the mid-travel point. The odd strongly regressive LR curve in the latter half of travel may be an acknowledgement of this problem - it may allow greater extension at the rear wheel (wheel displacement) despite a sluggish rebound at the shock shaft (shaft displacement).

The second problem is an excess of rebound force as the suspension rebounds past mid travel and towards SAG. Once again, the flex plate is in a state of recoil and it must elevate rebound force in consequence. Perhaps this is a lesser issue than the one already mentioned, though, because at least the rebound force reduces (after maximum flexion at mid-travel) as the bike moves towards SAG. Sadly, the flex plate will have some extensive rebound force even at SAG which won't be completely expended until the suspension tops out. I doubt that would be much of an issue though, in practice, because correct shock adjustment for SAG will be naturally compensated in a degree equal to the ambient 'preload' from the flex plate acting on the suspension. The more troubling point is that, insofar as the flex plate exerts an influence on rebound response, the rebound forces rapidly shift from being heavily muted, just above mid travel, to being maximally elevated, just short of mid travel. This might produce an unsettling spike in rebound force at the mid travel point of maximum flexion of the flex plate as the suspension rebound response turns from muted to forceful.

Un saludo
Chris

Antonio Osuna dijo...

I never take into account the spring force of flex plates, mainly because it's impossible to know the spring rate and the preload of the system just by looking at a picture or even when you have the blueprints...

In a system like this you have two springs and one damper, but the damper controls both springs, even if it's only "attached" to one of them... the system has one DOF so the two springs work as a team and you only need to care about the sum of both springs...

Here we have an air shock that is probably going to take ~90% of the job and a flex plate that it's going to take the rest. The flex plate bends in the first part of the travel and relax a bit at the end, but it doesn't come back all the way, I've just checked and it bends back only 50% of it's maximum travel. Anyway, this type of spring rate complements pretty well the spring rate of the shock so it's not a problem at all.

Best regards,
Tony.

 

Google Translate

Buscador

Archivo

Etiquetas