Bulls E-Stream FS 2015

Despues de tres semanas analizando E-Bikes de XC-Trail por fin hemos llegado a los modelos de Enduro. Este año ningún fabricante se ha animado a fabricar una E-Bike de DH, por lo que estos modelos son los que mas se acercan a un usuario tipo al que le gusta mucho bajar, pero que no dispone de ningún Bikepark cerca de casa... En esta entrada voy a empezar analizando a la nueva Bulls E-Stream FS Enduro, un modelo con 160mm de recorrido, ruedas de 27.5'' y un motor Brose muy compacto con el que se consigue una geometría muy buena (66º-74º y 445mm de Vainas). 
Como podéis ver en la Tabla de Excel y en las primeras gráficas este modelo tiene un sistema tipo FSR con una Eficacia de Pedaleo muy alta. Los porcentajes de Anti-squat son bastante elevados en los desarrollos mas largos, pero no llegan a un nivel excesivo y tampoco se pueden rebajar mucho mas ya que en los desarrollos cortos el porcentaje de Anti-squat está en torno al 120%. El Pedal-kickback (15º) como es lógico también se va hasta un nivel bastante alto, mientras que el Brake-squat (66%) se mantiene en un nivel medio. 

En la gráfica del Leverage Ratio vemos como el sistema es muy progresivo (3.6-2.3). Unas cifras espectaculares, comparables a las de una Liteville 601 o una Young Talent Capra. La única diferencia es que este modelo utiliza un amortiguador un poco mas corto (200x57mm) por lo que el LR Medio está un poco por encima de lo habitual, pero esto en una E-Bike es algo casi inevitable, si tenemos en cuenta el tamaño del motor y de la batería es casi imposible utilizar un amortiguador de 216x63mm o de 222x70mm...      

Un saludo.

2 comentarios:

Unknown dijo...

Having examined the e-bike posts more closely now it seems to me that the Brose motor based bikes (this one and the Rotwild) have some significant advantages when compared to the Bosch and Yamaha based bikes. The Brose motor is more compact to start with and that doesn't hurt. Also, the Brose seems to be sufficiently bike specific to permit good kinematic and pedal kickback results to be achieved without having to resort to major changes to the drivetrain or the use of an idler.

It is shocking to see how major compromises in bicycle design, for example, the conflict between Anti-squat and pedal kickback, simply wither away when input torque gets a substantial boost. It might be concluded from the pedal kickback graph of the E-Stream that it is unremarkable in that respect but that would fail to take into account an important fact - the bike has greatly elevated AS levels compared to what is normally achievable for a bike of a similar design with similar levels of kickback. Indeed AS seems to be at levels much higher than are called for. That excess could easily be sacrificed in favour of kickback reduction and with minor changes to the E-Stream suspension linkage kickback could be rendered imperceptible without detrimental impact to the pedaling performance.

This notable improvement in the balance between different performance parameters comes as a result of what is possible when human effort gets amplified by means of electro-mechanical assistance. Being able to sustain generally higher gearing ratios (the driving cog of the motor whether Brose or Bosch rotating faster than the human driven crankshaft - okay, that is an assumption in the case of the Brose, which I have found little information on, but I don't see how the kickback numbers could be so low without some level of overdrive gearing) owing to the increased torque of the motor means that the goal of pedaling neutrality can be sought vigorously without fear of having to pay a high price in terms of pedal kickback.

Antonio, you may care to correct any mistaken assumptions that I have made. It is interesting to see so many of these bikes aiming at such high AS numbers, though. What do you think is going on there?

Un saludo

Antonio Osuna dijo...

Yes, Brose E-bikes are really nice, but right now there is only a couple of examples, so it's a bit difficult to understand how good it is going to be. On the other side Bosch has a lot of "strength in numbers"... we look at 30 models with Bosch motors, forget about most of them very easily and focus on the "top five", the good ones with nice kinematics and short chainstays... but wait a couple of years and you will see that Brose E-bikes are going to be even better.

Best Regards,


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