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How can we improve the ergonomics, the shifting performance and the resilience of a bike? This is the question we have asked ourselves, discussed it with our team riders and we came to the conclusion that a great tuning potential lies in the accessories - more specifically in the shifting system. The frames are technically mature by now, in recent years there have been huge leaps forward concerning materials, weight, stiffness, comfort and performance. But almost all mountain bikes still shift with a traditional derailleur. This principle exists since around 1930. While there were some changes, they have always been more of an evolution, real revolutions were scarce. Still today riders have to drag along up to three chainrings and 10 sprockets.
However, derailleur gears have undoubted advantages, which we’d like to continue building on with the project 1.44². These advantages are the very low weight and the wide range of gear ratios available. Well maintained chains offer an outstanding level of efficiency and gear parts can be can changed quickly.
An alternative to derailleurs are drive trains. The benefits of drive trains are obvious: The shifting speed is much faster and more direct than with derailleurs, one can shift while pedaling as well as when stationary, the maintenance effort is reduced and the reliability is higher. This is because there is no derailleur, which allows an easy chain-guide assembly. The chain can no longer jump and chain sucks can be prevented. However, the current drive trains on the market are too heavy for many bikers, their efficiency is too low and its use is limited by the lower gear ratio. There is still much potential for innovation and further development.
How can we combine the advantages of both systems? By constructing a hybrid solution in which each part eliminates the disadvantages of the other and increases the benefits. First, the question arises, which features in both systems work best and for what they can be best used for. With this type of reasoning it quickly becomes clear that the front derailleur of a derailleur system is too slow and too unprecise – a chain suck while racing can mean the difference over victory or defeat. In addition, the large chainring can be disturbing when you face large steps or logs. A derailleur on the crank requires a relatively large space, which in turn is reflected in a higher Q-factor. A low Q-factor (that is a small pedal spacing), allows more ergonomic pedaling. Therefore the aim was that the bike can be ridden with only one chainring.
A drive train with more gears translates to a more complex mechanism, and thus a higher weight. The goal is to construct a drive train with as few gears as possible but just as many as necessary. In recent years, the combination of three chainrings combining a big 44 and a small 22 chainring has been established. With this combination the achieved gear ratio is 200%. For that purpose, a cassette is combined with many
sprockets and small gear jumps. In this way one obtains a small gear ratio for climbs, while still having the possibility to put pressure on the pedals during the descent.
In order to allow the Q-factor to remain as low as possible, it is a logical step to put the gears to the rear. In this way we have maximum space available on the bottom bracket for new pivot points of rear rocker arms, the derailleur mount is therefore no longer required, we can obtain the lowest possible Q-factor and we have the basic framework for a racing gear with optimized ergonomics. The derailleur remains at the rear. Thus we achieve the maximum gear ratio, obtain low weight and rapid shifting performance. The hub in connection with the 11-36, 10-speed cassette guarantees a maximum gear ratio of 674%. By comparison, a circuit with three chainrings (44/32/22) and the same cassette gets you a ratio of 654%, a double-crank (42/28) even only 490%.
Our gear hub has a total of three speeds: a 1:1 direct gear, in which the gear ratio is solely the result of the actual number of teeth on the chainring and cassette. With the 32 mm chainring, the hub can be mainly operated in the direct gear, without loss of efficiency. In addition, there is an overdrive and a gear reduction ratio, each of which is approximately a factor of 1.44 (or 1 / 1.44). There is an overdrive mode in which the wheel travels 1.44 times as many revolutions per minute as the cassette. During the gear reduction, the cassette rotates nearly 1.44 times faster than the wheel. Therefore, you can calculate the overall gear ratio of the hub: 1.4359 ² = 2.06. The gear hub has a gear ratio range of 206%. Thereby the gear ranges are based on a classic triple crank. The rider therefore does not require a period of familiarisation with the equipment.
In contrast to previously known gear transmissions for mountain bikes, the project 1:44 ² is based on race gearing, combining lightweight with the highest efficiency. With this kind of weight, we are on the same level as the Shimano XT. The target weight for the hub: 630 grams – this weight includes the rear hub, two chainrings and front derailleur. Altogether this a component which will offer maximum performance, even on the most demanding race tracks.
|Fork:||Gabel DT XRC 100|
|Front wheel:||DT Swiss XCR 1250|
|Rear wheel:||Canyon 3-speed gear hub, DT Swiss XRC 300|
|Crank:||THM Clavicula, Tune Triebtreter (32)|
|Rear derailleur:||Shimano XTR 10-speed, Custom Shifter|
|Front brakes:||Formula R1 Carbon|
A major disadvantage of many gearing mechanisms is their low efficiency rate. An important design goal was therefore to achieve best possible efficiency. The overall efficiency of a transmission system depends on the performance of the chain and gears. We have taken a close look at both systems and have optimized each on their own. The chain efficiency decreases significantly when you increase the chain angle. In other words, when you use a small chainring with 22 teeth the angle of the chain, when connecting to the gear, is higher than that of a chainring with 32 teeth. This makes the chain efficiency up to 1% lower. By using the 32 mm chainring, we not only offer very good chain efficiency, but through the extended lever arm we also reduce the chain tensioning force by 30% compared to a 22-chainring. The result is reduced loads on the chain, sprockets and rear triangle.
To maximize the efficiency of the transmission, we decided to use the planetary gear design. This design combines maximum strength and highest efficiency with low weight and a compact design. In order to minimize bearing friction in the gear, we used highly resistant needle bearings as storage for the four planets instead of the frequently utilized slide bearing. To ensure that the cogs inside the hub are continuously covered with an oil film, we have designed the hub so that the entire transmission is constantly lubricated. The low viscosity oil - that is relatively thin oil - is atomized to fine droplets by the movement of the gears over and over again and can thus penetrate into all the spaces and lubricate the entire hub.
The spur gearing ensures a low rolling friction between the cogs. This means that the teeth are parallel to the axis. With this design no axial
forces appeared under strain, in contrast to a helical gearing, in which the gears are on an incline to the axis. Thus, the design features to support the axial forces can be eliminated. Efficiency losses due to friction through axial forces can be circumvented. The theoretical disadvantage of less smoothness is not noticeable at speeds as low as those of bicycles.
For longer life and higher durability, we have hardened the cog flanks; by this we mean the outer layer of the cogs. In the so-called case-hardening process, the individual components are placed in a carbonic atmosphere at elevated temperature. In this way, carbon diffuses into the upper layers. The surface of the steel's composition is changed and then hardened through specific temperature control. The result: a wear resistant surface with great tenacity in the core, which is good for the dynamic load capacity, since the cogs keep their elasticity on the outside.
The project 1.44 ² offers a view into the future. How could an efficient shifting with maximum lightweight components and an ergonomic pedal position be viable? By looking into the future, it is conceivable that frames will be optimized for cranks with a single chain ring. Structurally this would create new opportunities to build more advanced frames - as the designers would have more freedom in the bottom bracket area. The shifting times of the hub in project 1.44 ² are so short that during the race one does no longer have to think about the shifting system. You can power down a descent in overdrive mode, pedal through uphill and then quickly switch into neutral or the mountain gear. Now you can better concentrate on the terrain, especially in technical off-road races. With the race gear hub of the project 1.44² we show a way how the shifting system of the future might look.