En esta entrada voy a analizar a la nueva Rocky Mountain Maiden 2016, un modelo del que se empezaron a ver imagenes hace dos años, pero los prototipos estaban fabricados en aluminio y el modelo final está fabricado al 100% en Fibra de Carbono. El cuadro tiene 200mm de recorrido, es compatible con ruedas de 26'' y 27.5'' y tiene un sistema de ajuste para la geometría en el anclaje del amortiguador. A nivel de sistema Rocky Mountain utiliza una configuración tipo 4-Bar con el punto de giro un poco por encima del eje trasero. Desde un punto de vista legal no se inflinge la patente del FSR, pero hoy en día este tipo de "trucos" ya no son necesarios...
Como podéis ver en la tabla de excel y en las gráficas anteriores el sistema de la RM Maiden tiene una Eficacia de Pedaleo bastante baja, con unos porcentajes de Anti-squat en torno al 50% con unas ruedas de 27.5'' y en la posición Low. En la posición High los porcentajes suben un 10% y si hacemos un montaje con ruedas de 26'' los porcentajes suben un 30%. El Pedal-kickback (1º) es prácticamente nulo y el Brake-squat (21%) se mantiene en un nivel realmente bajo, consiguiendo un funcionamiento de la suspensión muy independiente durante las frenadas.
En la gráfica del LR vemos como el sistema es del tipo Progresivo (3.05-2.15), unas cifras muy buenas para un modelo de DH. El ajuste de la geometría influye un poco en los resultados, pero las diferencias son mínimas, no llegan a una décima en la gráfica del LR. En cuanto al amortiguador el cuadro utiliza un par de modelos de medida estandarizada (240mmx75mm)... Bos Stoy Rare en los modelos tope de gama y X-Fusion Vector en el básico y en principio no hay nada que objetar, es un LR que va a funcionar muy bien con un amortiguador de muelle y la decisión montar suspensiones Bos me parece muy acertada.
En la gráfica del LR vemos como el sistema es del tipo Progresivo (3.05-2.15), unas cifras muy buenas para un modelo de DH. El ajuste de la geometría influye un poco en los resultados, pero las diferencias son mínimas, no llegan a una décima en la gráfica del LR. En cuanto al amortiguador el cuadro utiliza un par de modelos de medida estandarizada (240mmx75mm)... Bos Stoy Rare en los modelos tope de gama y X-Fusion Vector en el básico y en principio no hay nada que objetar, es un LR que va a funcionar muy bien con un amortiguador de muelle y la decisión montar suspensiones Bos me parece muy acertada.
Un saludo.
11 comentarios:
Una bici sin demasiados compromisos... para bajar muy fuerte, y punto.
Me gustó al verla, y ahora sabiendo del palo que va, me encanta.
Saludos.
RM siempre se decantó por el lado de las "plow bikes", ya desde la época de la mítica RM9. Siendo ésta a niña mimada de Thomas Vanderham, se nota la tradición freerider, y que no está hecha principalmente para romper cronos...
RM siempre ha tenido bicis muy progresivas, pero todas eran Monopivotes con Bieletas por lo que la frenada era un punto debil. La nueva sin embargo tiene unas cifras espectaculares en ese apartado...
Un saludo.
Patents tend to impart a direction to discussion about the operation of a patented invention, channeling our thinking down paths that fit neatly with the demarcations set out in those patents. This is not necessarily a good thing - it is not hard to distinguish a "smooth-link" from a "horst-link" or a "lawwill-link" but whether the technical considerations/distinctions that permit these contrasts to be drawn are themselves of great value or allow us to delimit a meaningful range of valuable suspension performance characteristics is another matter. What is notable about this smooth-link bike is just how normal it is. A lot of horst-link bikes out there work a lot like it. Also, the somewhat low levels of anti-squat on this bike mainly derive from selecting a main pivot location (i.e. lowish) suited to RM's preference for very low levels of pedal kickback. A more pedaling neutral (i.e. with higher anti-squat levels) smooth-link bike would not be hard to design but the cost would be increased PK.
So, is there anything seen in the charts here that is a kind of fingerprint that identifies qualities unique to the smooth-link? Certainly, the smooth-link does allow anti-rise to be kept to a very low level across the range of travel. It is not hard to see how this happens. Because, the smooth-link uses an articulated swing arm with a high swing arm link pivot (the one forward of the rear axle) as the main pivot dips during suspension compressions the lower suspension arm forms a relatively sharp angle sloping downwards from the swing arm link pivot. Broadly speaking, the sharper that angle is the lower the level of anti-rise will be. It is relatively sharp on a smooth-link (compared to a horst-link, say) and on this bike RM has amplified this characteristic by pushing the swing arm link pivot further forward further sharpening that angle during suspension compressions. There is one additional requirement to keep the levels of anti-rise low and it is applies equally to horst-links as well - the rocker linkage (upper link anchored to the frame) must be relatively long and set close to horizontal at SAG. This fact can be easily checked - see the Specialized Demo 2015 and Norco Aurum Carbon 2015 also on this site. If the rocker is short or there is a downward sloping angle from the seatstay pivot of the rocker link down to the rocker pivot anchored to the frame, already at SAG (which further increases during suspension compressions), then there will normally be a less flat AR curve. A look at the AR curve of the Range bears this out.
First post of two
Is this flat and very low AR curve an especially valuable characteristic for DH bikes? Maybe, but I am far from convinced. Just as the need for neutral pedaling (a critical design goal for suspension bikes) must give way to the need for PK to be limited on larger suspension compressions, so too the need for braking traction at or around SAG (test simulations done by Antonio have lent support to the widely held notion that low AS is beneficial for braking traction) must give way to the need for the suspension to respond on larger compressions as expected (per its specific design) because it is the suspension response that will be, it seems to me, the main factor governing traction in that situation. If, out of some terrible necessity, a rider must apply and release their brakes in very rough sections of trail with the suspension already compressed, having any changes to suspension geometry and operation imparted by dabs or grabs at the brake, is the last thing you would want. Low AR in this situation seems to me to be more of a curse than a blessing. The problem here is that low AR seems to be good around SAG whereas somewhat higher AR seems to be preferable deeper in travel. Actually, a rising AR graph is not so uncommon - it is found on the aforementioned RM Range and quite a few horst-link bikes (Ghost, Rotwild, Transition and Specialized trail bikes) and Trek and Dave Weagle are designing their ABP and Split Pivot bikes to exhibit exactly that characteristic. It is the overall design of those bikes that holds the most interest in my view.
I can see one design brief where the smooth-link in particular might offer some important benefits, though. The smooth-link might work well as an alternative to the high pivot horst-links or high pivot Trek ABP linkages we are starting to see on e-bikes (with or without diverted chainlines). The design features of the smooth-link already mentioned may help in achieving a reduction of AR or some improvement of the AR curves for bikes of this sort.
Second post of two
Un saludo
Chris
AR Curves depends so much on the upper link design that there is no need to talk about how the Smoth Link affects this parameter.
The biggest difference between Smoth Link, Split Pivot, FSR and lets call it NRS style 4-bars it's the Anti-squat curve. If you design four bikes with the same level of AS around sag and you look at the curves you will see that the Smoth-Link bike has the flattest one, then you have SP, FSR and NRS, a system that works pretty much like a Virtual Pivot, and that's a good point in my opinion.
The only place where SL makes sense is in E-Bikes frames as you said, and last year we saw one design following this idea (Flyer Uproc).
Best Regards,
Tony.
Hi Antonio,
Your mention of NRS surprised me. Why is Antonio mentioning that? Isn't it just ancient history? So, looking into things a bit I noticed your mention of the Simplon Kibo in your tutorial on FSR wheelpaths and then read your recent blog entry on the bike. That bike, which is very NRSish, is indeed fascinating as you say. It shows that the interrupted NRS/NRS-like story is far from over. And on that score, if I'm not mistaken, the carbon version of the same bike takes things even a bit further in that direction. Will you be doing an analysis of that bike?
Un saludo
Chris
Why is the anti-rise always positive if RMB claim that the instant center is behing the wheel initially?
keep up the good work!
Many people remember NRS as the system that worked without sag, but that`s more about the shock than kinematics, because you can get the same results with any system... Turn up the AS to 200% at the begining of the travel and use a special shock that works well at 0% sag... To me it's about keeping the main pivot very low (Straight chainstays are the best structural solution...) and getting a good AS by moving the HL as low as you need it to be. It's not as pretty as having a small HL, but it works really well.
About the Maiden... The IC is behind the wheel (very far away...) and it's also "Underground" so Anti-rise ends up being positive.
Best Regards,
Tony.
Madre mia de mi alma, si la nueva Slayer sigue esta tendencia, adapatada a algo más ligero.
Por la fotos que hay en la web, el amortiguador serà suuuuper largo.
Saludos.
La verdad es que el prototipo tiene muy buena pinta, pero casi todos los puntos de giro están medio ocultos asi que ya veremos como sale el análisis...
Un saludo.
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