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Introduction

The Dual Rod chainless bicycle concept was conceived as an alternative to the 150 year old bicycle chain. To most riders, the chain is probably the most disliked component of the bicycle, demanding constant maintenance and being prone to accelerated wear and unexpected failure.  Several alternative solutions have been introduced over the years, including a drive-shaft with bevel gears, rubber belts, and more unique designs such as the stringbike. All have their strengths and weaknesses. The Dual Rod strives to offer a more viable alternative, designed to perform well in the real world, while remaining efficient and reliable over time and use. The Dual Rod chainless design is currently in concept stage, and is patent pending.

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Design

The Dual Rod design borrows from mechanical principles used in steam engines and locomotives of the distant past. The rotary motion of the pedals is translated into push-pull (reciprocating) motion of the two drive rods, and then back into rotary motion of the rear axle, driving the rear wheel. The use of eccentrically pivoted bearings allows this power transmission without sacrificing the continuity and rigidity of the pedal axle or the rear wheel axle (as opposed to a possible crankshaft-like design), as well as keeping the mechanism narrow and relatively compact, allowing relatively straightforward packaging into existing bicycle frames.

Advantages

Bicycle chains are known for rusting prematurely, collecting dirt, stretching over time (and damaging the sprockets as a result), staining clothes, and sometimes falling off at the worst possible moment. A new properly lubricated chain can be around 98% efficient. However, without proper regular maintenance and constant lubrication its efficiency can quickly drop to 80% or less.

The Dual Rod chainless bicycle design uses sealed ball bearings, not unlike the ball bearings used elsewhere in bicycles today – for wheel hubs, bottom bracket, etc. This ensures long service life without any regular maintenance. This design extremely efficient and unlike a chain, remains this way over time. By design, it is much more robust and durable compared to a chain, with little chance for unexpected failures. And, it will never stain your clothing.

Efficiency

The Dual Rod design dictates a direct drive (1:1) ratio between the pedals and the rear wheel, thus demanding the use of an in-hub gearbox (or a similar solution) to make the chainless bicycle useful and practical. In itself, the bearing and rod mechanism is extremely efficient, losing almost no energy in the process of sending pedal power to the rear wheel. The primary cause of mechanical losses in such a bicycle would be the planetary gear sets used inside the gearbox. Still, the overall efficiency of this chainless design is comparable to a bicycle equipped with a derailleur and the accompanying chain tensioner.  However, unlike a chain that requires timely lubrication in order to keep its efficiency and integrity (and deteriorates over time even when perfectly maintained) the Dual Rod design allows the use of sealed ball bearings that remain highly efficient over time and can go many years without any maintenance whatsoever.

Weight

While the Dual Rod mechanism may look heavy, most of its components can be made out of lightweight materials. The drive rods can be made of aluminum, titanium, or more exotic options such as carbon fiber. Use of ceramic bearings can also reduce weight and slightly improve efficiency. Existing in-hub gearboxes are relatively heavy, ranging from 1kg for a simple 3-speed hub, to nearly 2kg of more advanced hubs such as  the Rohloff 14-speed SpeedHub. However, weight and efficiency are improving with every new generation of the in-hub gearbox technology.  Realizing its full weight-saving potential, a Dual Rod chainless bicycle weight can become on par with its chain, sprocket, and derailleur counterpart.

Applications

The Dual Rod chainless bicycle is expected to be first adopted by urban dwellers, as well as bicycle rental programs that are common in many cities today. Urban bicycles are often used for daily commute and their riders will benefit from the robustness and hassle-free nature of the Dual Rod. Operators of bicycle rental programs will certainly appreciate the reduced costs. Also, urban and rental cycles typically make do with 3, 4 or 5 speed gearboxes, which can be provided by a relatively simple and lightweight in-hub gearbox. As in-hub gearbox technology advances, the Dual Rod chainless design will become a natural choice for road and mountain bicycles as well.

Proof of Concept

The first ever functional Dual Rod chainless bicycle was built over the course of one year, in 2016. It was intended as a proof of concept, showing that the Dual Rod can actually be built, installed on a standard bicycle frame, and be successfully used (and sometimes abused) in real world conditions. Using a combination of custom made steel parts, off-the-shelf thin section bearings, and a Sturmey Archer XRF8 gearbox, it has undeniably fulfilled its purpose – demonstrating that the Dual Rod can be made a reality.  Made entirely of steel, it weighs just shy of 2kg, not including the 1.7kg of the 8-speed gearbox. Mass produced, the Dual Rod mechanism is expected to weigh under 1kg. Combined with a lighter in-hub gearbox, its weight becomes on par with the traditional system of sprockets, chain, derailleur and tensioner.

The Inventor

The Dual Rod was invented and designed by Uri Shaham, a self-taught engineer and inventor. Coming from a software background, Shaham co-founded IncrediBuild, a software company based in Israel, where he led R&D. His passion is in studying and understanding the first principles underlying complex systems, and finding ways to improve them. He has also designed and built the first functional Dual Rod chainless bicycle, featured on this website and Video.

Going Forward

The Dual Rod was created first and foremost with the vision of introducing a new exciting chainless bicycle design to the world. Also, it was created hoping that a major player from the bicycle industry would recognize its potential and be willing to bring it to market. It is currently in patent pending status, and not yet commercially available. Please follow this website and our Facebook Page for future updates.

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