If you want electric bike power without buying an all-new e-bike, you'll need to look into add-on electric drives like the Rubbee and Bike +. And you can add the new ConoDrive to the list. This system is designed to keep bike weight as low as possible and give you maximum electric engagement when you need it and no efficiency drop when you don't.

The inspiration behind the ConoDrive is simple: Pedal-assist electric bikes are a great invention when the motor is spinning, but when the battery runs out, they're big, heavy slugs. All the added weight of the battery, motor and accompanying hardware, coupled with efficiency losses from pedaling through the electric drive instead of with a standard bicycle drivetrain, makes them more difficult to pedal, especially up hills.

The ConoDrive is designed to be a lighter, more efficient solution that brings electric assist to your bicycle of choice. It delivers terrain-smoothing motor power and is purportedly not as much of a burden as other pedelec bikes and add-on systems should you have to pedal home without battery power.

The friction-based, all-in-one pedelec drive mounts over top the rear tire, securing to both the rear axle and frame, much like a bike rack. In fact, the framework that surrounds the removable battery pack and holds the motor in place actually works like a bike rack, allowing you to secure panniers and cargo.

The ConoDrive's 250-watt motor spins a specially designed notched roller that fits snugly around the tire. This component is designed to provide firm, uniform friction on the tire, even in slick or steep conditions, allowing the motor power to blend seamlessly with your pedaling.

The handlebar-mounted computer lets you select power levels between 100 and 250 watts, and the motor power kicks in so long as your speed is under 25 km/h (15.5 mph) and pedaling cadence is over 30 rpm. When the battery is dead or motor power is not needed, you can move the cable-activated roller completely off the tire with a handlebar mounted switch, providing for smooth, normal pedaling.

It may look larger than the Rubbee 2.0 at first, but at 7.7 lb (3.5 kg), the ConoDrive is around half the weight. ConoDrive's designers are using aluminum alloy construction and a relatively light, compact 200Wh LiFePO4 battery to help keep that target weight low. That low weight, in turn, keeps the bicycle lighter and easier to maneuver so you're not muscling so much metal when battery power drops off. On the other hand, the ConoDrive is more than double the weight of the super-compact, disengage-able Velogical Velospeeder, so it's not the lightest add-on pedelec system we've seen.

While it's nice to know that the ConoDrive is optimized for manual pedaling, a recuperation feature helps keep the battery charged while on the road. The ConoDrive system acts as a dynamo, charging the battery during downhill coasting.

The story behind the ConoDrive's development is a little different than the average tech startup story. As the company explains, the design was originally invented by Spanish physicist José Fernandez, a cycling enthusiast who was looking to create a device to help him keep up with the younger, faster competitors in his cycling group on the hilly terrain of their rides. He looked to existing pedelec bikes as a solution but realized that the heavy weights, efficiency losses and restricted speeds of such bikes might actually slow him down more than help.

"On most grounds, I move easy faster than 25 km/h," Fernandez says, referring to the legally mandated top speed of a standard pedelec. "And with a [pedelec] bicycle with a weight of up to 28 kg (62 lb), no one can climb up the mountains!"

What Fernandez really wanted was a light pedelec drive that he could use to help pedal up inclines but disengage completely to pedal freely on flatter, easier ground without any efficiency losses. Such a lightweight design would also keep the bike well below that estimated 28 kg.

Fernandez developed the basic design and was happy using it for personal use. He had no intention of bringing it to market until he met up with German pedelec enthusiast and blogger Alexander Theis. Theis, who follows the latest electric bike technology on his blog Velostrom, liked the design so much that he struck a deal with Fernandez to bring it to market.

"After a test run with one of the prototypes I was perfectly enthusiastic of the driving experience," explains Theis. "As I heard that Mr. Fernandez wanted to leave it with the prototypes, I decided to take over the development of this propulsion system up to the series product."

Theis founded the ConoDrive startup and is now working to raise money on German crowdfunding site Startnext. His plan is to develop the production model over the course of the next few months and reveal it at the Spezialradmesse (Special Bike Show) next April. The €1,200 (approx. US$1,350) pledge level is sold out, but the ConoDrive is still available at the €1,500 ($1,675) level.

Because the unit is still in development, the specs are tentative, but Theis says that with the 200kW/10Ah battery, the motor can provide up to 120 km (75 miles) of range (or 1,200 m/3,937 ft of elevation gain). The prototype includes a 2.5-mm plug so that you can power a GPS or light off the ConoDrive's battery when you need. That battery takes between six and eight hours to charge with the prototype charger and includes replaceable cells so that you can replace a defective cell instead of the entire pack. The unit is currently designed to work with tires sized 700 x 25, and ConoDrive recommends the Schwalbe Marathon Plus tire.

The five-minute, English-subtitled video below provides a bit more detail about the ConoDrive and its benefits.

Source: ConoDrive

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