Quote:
Originally Posted by bradleyland
Looks pretty cool, but appears that it would be heavy compared to a traditional full-suspension setup. The reinforced baseplate that the rear sub-frame mounts too looks like a real behemoth as far as bike parts go. Then again, you're going to be hauling around a sizable Li-Ion pack and electric motor, so the weight added by this system is probably trivial in proportion to the electronic drive components.
This is the cool part:
"In accordance with the principle of four-joint kinematics with a virtual rotary axis around the spindle, the BMW drive unit swing arm is guided in such a precise way as to prevent the relative position of the mid-motor spindle unit from deviating in relation to the main frame."
In plain ass english, the geometry of this suspension is set up so that the rear swing arm rotates around the electric motor's spindle. This is important since this is also where the crank connects. Hence, the crank won't be jarred by bumps in the road/trail. You can get this in an electric mountain bike already, but you have a standard chain derailleur, which also functions as a tensioner. That's the real innovation here: you can use this with a fixed drive system and no tensioner.
Which brings us to this: this is a fixed ratio driveline. I guess when you have electric assist, you don't need the lower gears to get started, you simply use the electric motor for torque assist, then rely on human power at speed. Language in the write-up seem to support this:
"As the proportion of human driving force is relatively small, there is no unpleasant rocking movement when accelerating or breaking."
For a mountain bike with FS, this seems really optimistic though. When you're on an uphill, you need a lower ratio. There's just no way you're going to make it through a sizable ascent on the ratio pictured in the press photo. The battery pack will be depleted in no time. If you're just going to ride around a city, then why bother with FS at all? I would venture that you're better off saving all the weight and complexity, going with a rigid rear frame.
Never the less, this is a really tight looking design, and having a modular rear swing arm means that manufacturers could afford to offer this system on a much wider range of cycles 
EDIT: I looked in to this "Carbon Drive" system, which I wasn't familiar with before. It looks like they use internally geared hubs to achieve variable ratio drive. Seeing that my price ceiling for a MB is around $3,000, I never really shop the upper end of the scale where this stuff sells. Mea culpa. |
Very nicely explained there, I am certain many appreciate that effort!