Pedelecs in the recent years have developed into bicycle category of its own. In terms of technology by their increasingly powerful electric motors that smoothly add to your pedalling force up to 25kph and adapt that support even more exactly to the rider’s needs, as well as in terms of design with new frame shapes and functions.

The frames of STEVENS pedelecs, meticulously shaped by load-specific hydroforming, not only nicely integrate the motor. They can also handle any forces thrown at them by acceleration, braking and hard pedalling.

Ride stability is further enhanced in all STEVENS PowerTube Pedelecs by using tapered steerer forks (diameter increases towards the lower end of the shaft). Another feature of STEVENS pedelecs are reliable and powerful hydraulic disc brakes, well-matched shifting components and bright LED lights.

To enhance ride stability even more, for current model year 2018 Bosch eBike Systems suggests integrating the battery into the downtube. To do so, STEVENS’ supplier has developed the PowerTube battery, which is compatible to all ebike motors from Bosch and fulfils all the manufacturer’s requirements in quality, ride characteristics and ease of operation. In addition, riders of STEVENS pedelecs will benefit from the qualified service offered by STEVENS dealers and proven by many tests in several magazines.

The new battery, like all previous Bosch PowerPacks, offers 500 Watt-hours (Wh) of capacity and is conveniently compact with its dimension of 349 x 84 x 65 mm – so small in fact, that a second back-up battery easily fits inside your panniers or backpack. At 2.8 kg (6.2 lbs) it is also one of the lightest batteries on the market.

For Better Handling, Better Protection And Clean Lines
Better serviceability by easier handling: A two-step mechanism ensures safety when removing or reinstalling the Bosch PowerTube battery. After unlocking the battery will pop up by about 2 cm (.75”), so it can easily be grabbed. The safety mechanism prevents the battery from falling out. A PowerTube battery could also be removed from the side or from the bottom.

Yet, STEVENS’ designers intentionally opted for an upward-facing compartment because this enables an easy and comfortable removal of the battery in a few steps. The PowerTube battery can also remain on the bike and be charged via a charging port integrated into the seat tube.

Placing the battery on top of the downtube for example still is a practical and well-proven solution, but integrating the new PowerTube battery into the downtube offers additional benefits.

Generally speaking: The lower and the more directly below the rider a bike’s center of gravity, the more natural is a bike’s handling. Placing it inside instead of on top of the down tube already results in a technical advantage. The new location for the battery especially benefits STEVENS pedelecs with a Forma frame. The low-instep models’ ride characteristics are improved by moving the battery and its weight from the pannier rack to the inside of the downtube.

Being enclosed by the down tube the battery now is also better protected than before. And last but not least: By integrating the battery and the larger surface of the down tube you get a lot more room for design ideas to unify form and function in one great lifestyle product.

Completely New Design Developed in Hamburg
For the new pedelecs STEVENS’ engineers and designers at our company’s headquarters in Hamburg have developed some totally new frame shapes. They combine all major requirements – integrate the battery into the downtube – with all the well-proven sporty ride characteristics of a STEVENS bike.

The goal was to develop a concept that is aesthetically pleasing, fulfils all kinds of needs in terms of stability and comfort and offers convenient solutions for handling and maintenance. The new PowerTube pedelec frames are all proprietary designs like for example the protective battery cover and the integrated charging port at the seat tube. Housing the battery inside the downtube and easy access to all cables simplify maintenance a lot.

Tested According To Zedler Advanced Plus
All STEVENS PowerTube frames have passed a test protocol according to the ”Zedler Advanced plus” standard by the Zedler Institute for Bicycle Technology and Safety [Link]  - a protocol that by far exceeds all usual legal standards for stability for bikes.

Compared to the ISO Standard test, in the ”Zedler Advanced plus” the frames have to repeat all dynamic test cycles under higher loads. In addition disc brakes are tested to check the disc mounts’ strength followed by an impact test where a 22.5kg (50lbs) test weight gets dropped onto the fork from a height of 52cm (20.5”). Only after all frames have passed these tests without failing, they get cleared for serial production.

To Please The Eye And More Legroom
One of the basic questions was whether to insert the battery vertically or horizontally – both is possible. The decision was made in favour of vertical placement: First of all, for aesthetical reasons since it enables an organic transition from the down tube to the steerer tube and bottom bracket area. Then also the sleeker frame offers the rider more legroom. The seat tube adapts as far as possible to the rather square shaped design. This makes room for a charging port. Towards the top where the seat post is inserted, the seat tube tapers into a round cross section.

Clear Design, Practical Details
Seat and chain stays also adhere to the boxy design language of the main triangle. For frames to be equipped with gear hubs and belt drive like the E-Courier Luxe the redesign of the opening in the frame was the engineers’ top priority. This opening in the right chainstay is necessary to install the indivisible drive belt. This opening now is flush with the chainstay.

The adjustable dropout (used to tighten drive belt or chain on bike with gear hubs) also is now better integrated into the frame and better to reach for mechanics. The dropout area also contains mounts for the hydraulic disc brake as well as a kickstand. Here the engineers opted for an inward-facing kickstand mount. This way the mount does not protrude from the chain stay. This not only provides a clean appearance but also more heel clearance.

When developing the frames it was important to the STEVENS engineers that these would accommodate tires up to 47mm width. The wider Schwalbe tires nicely integrate into the wider overall frame design. Due to their larger volume they offer more cushioning and due their larger contact patch also more traction while maintaining most of its smooth-rolling characteristics. The fact that a bicycle tire’s rolling resistance is influenced more significantly by its profile than its width is already included in the algorithm of the Bosch range calculator.

Battery Cover
To securely store the battery inside the downtube a cover is needed. This lid is a proprietary STEVENS development. One challenge in its design was to take into account that it not only needs to be waterproof and fit tightly but can also securely hold a lock or a large water bottle.
Many a cyclist in the Hamburg area might have been bewildered to encounter a STEVENS pedelec prototype carrying a water bottle filled with 3kg (6.6lbs) of nuts and bolts to test the how the lid and its water bottle bosses would withstand high loads. Both held up well on extended rides over bumpy roads and daily commutes.

Just like the lid the motor cover also is an in-house STEVENS design. It provides more space for the cables connected to the motor.

More Than A Carrying Handle
Above the motor of all PowerTube pedelecs there is an extra strut. Especially in the Forma frames it works as a reinforcement to add lateral stiffness. In the diamond and trapezoid frames the frame itself would already be sufficiently stiff, yet the strut is shaped to work as a handle. In addition to its original function it can be used to carry the bike up and down the stairs from and into the cellar or to put it on the bike rack on a car. This way form follows all kinds of different functions.