SRAM’S POWER PLAY?
A redesigned and repositioned battery could open the way to major performance gains
Some excellent sleuthing by our colleagues at sister site Bikeperfect.com has uncovered a patent application by SRAM for a new and radical e-bike motor that could – and we stress could – deliver big gains in weight and handling.
As we know, e-bikes are trying to juggle several opposing requirements: power and range with weight and handling. The more powerful the motor, the more energy it uses. The more energy it uses, the bigger the battery it needs. But weight is the enemy of agility and dynamic handling, and bigger batteries and motors are heavier and are more difficult to package. Which is part of the reason why lightweight, mid-power e-bikes are trending at the moment. But as we found out in our bike test last month, even the latest, ultra-expensive models are not without problems. Chiefly range, owing to the smaller batteries used to save weight. Experience has also taught us that full-power e-bikes with huge batteries (900Wh) can deliver remarkably agile handling, if given the right geometry, suspension and packaging.
SRAM’S patent looks to exploit the inefficiency of current motor and battery packaging to move the bike’s centre of gravity both lower and further back. Lowering the centre of gravity makes the bike more stable, particularly on steep descents, and helps with cornering. Bringing the centre of gravity further back also helps prevent the bike
SRAM’S PATENT SHOWS A CONCENTRIC MOTOR, SIMILAR TO TQ’S HPR50
wanting to tip forward under braking, but additionally makes it easier to lift the front wheel, which is critical when it comes to making a bike feel dynamic to ride.
Currently, big batteries are stuffed inside the down tube to bring power to the motor, but this puts the heaviest part of the system well in front of the BB and high in the frame. In SRAM’S patent, various configurations are shown, but all revolve around a similar theme; mounting the battery around the front of the BB at the base of the down tube. Instead of a cylindrical shape, SRAM proposes a battery that almost wraps around the front of the motor. It’s held by a protective cradle that swings forward to allow the battery to be removed for charging or exchange.
This leaves the down tube empty, which would allow, for example, in-frame tool storage, or, perhaps an internal range extender. Rather than cutting a hole in the down tube, it can be consistent in cross-section, which is the strongest and lightest solution.
But how does SRAM find room for a battery when most motors take up all of that space in front of the BB? Good question. Well the answer is that SRAM’S patent shows a concentric motor, known as a harmonic drive, similar to TQ’S latest