Caution, this bike is no longer available: The Street Machine Gt recumbent with steel frame and rigid seat has been replaced by the Street Machine Gte. These pages are only online for archive purposes.
The Street Machine Gt's No-squat suspension concept
A good bicycle suspension spoils you with comfort. It increases safety as control and road grip are improved. But best of all, you save energy: a good suspension enables you to ride faster!
This is because every unabsorbed shock transforms a certain amount of your propulsion energy into movement of bike and rider in a vertical direction. In other words, wasted energy. With the Street Machine Gt, however, only the wheels follow the profile of rough tracks, meaning that a greater proportion of your energy is efficiently transformed into forward motion. Suddenly you'll even enjoy dirt roads.
But the true quality of a bicycle suspension shows up only when riding heavily loaded or climbing steep hills.
We have designed our rear suspension using our No-squat concept: the combination of a very rigid rear triangle with the sophisticated positioning of the point of pivot, and an extremely rigid pivot point completely prevents activation of the suspension by force on the pedals.
Try this experiment: compare the suspension mechanisms of different recumbents under various conditions: smooth tarmac, pavements and dirt roads. Find a short steep hill, load the rear rack and lowrider with heavy bags and ride up as hard as you can. You can check for movement in the rear suspension by putting a hand on the spring element as you put pressure on the pedals (be carefuly not to put your fingers into the spring!). You will easily be able to tell if your energy is being wasted in unwanted compression of the suspension. You'd rather prefer moving forward?
No-Squat - the theory
The term "No-Squat design" stands for optimized gear and suspension technology. There are two major effects that need to be considered:
The jerk at the pedals caused by sudden tightening or loosening of the chain when the suspension activates it's called pedal induced bobbing, and is quite unpleasant for both hinges and muscles. Good design maintains a constant chain length when suspension responds, no matter what size gear is used.
The moment you put force into the pedals, other dynamic forces combine to give a resulting force, which in turn causes leverage to take effect at the pivot. According to whether the chain moves above or below the pivot point, the pedalling force compresses or decompresses the rear suspension. As you'll never put the same amount of force into the pedals, the load will vary, leading to vibrations in the rear triangle. This effect is called initial compression response and many bike designers, including those who design mountain and trekking bikes, attempt to place the pivoting point within the chain's play.
In practice even such simple constructions sometimes suffer from undesirable vibrations which must be compensated for by a lot of damping in the spring. Unfortunately, more damping also means that the suspension responds less. Additionally, the damping causes energy to escape as heat - energy which was meant for propulsion. Remember: good suspension doesn't cost energy, No-squat saves muscle power.
The simple approach we just took ignores the fact that a bicycle is a dynamic system with acceleration forces. A deeper analysis requires a trip into physics. As a part from the forces on the chain, we also need to consider the responsive force at the rear wheel (as the bicycle undergoes acceleration) and the intertia forces of bike, rider and luggage, with all parameters in addition being dependent on gear sizes. Things get even more complicated if hub gear systems are being used... let's stop the lesson for now, for further details we recommend reading appropriate literature or visiting an HP Velotechnik suspension technology course :)
Finally, when the designer has gone through all the theory and made his calculations, he'll often notice to his disappointment that the chain would have to be placed where that fat frame tube was planned. Or at the designated place for the bottle cage... ;)
With the Street Machine Gt, the SilentRing-equipped sprocket keeps the chain at an optimum distance to the pivoting point, giving very effective suppression of vibration. The chain is not really returned but runs nearly straight, so that you can utilize all your pedalling force effectively.
Why use damping at all?
The dynamic forces mentioned vary with size and weight of rider and luggage, and of course a design can not consider every possible combination equally. Additionally, it often happens that a certain safety distance to other parts must be maintained as the chain swings when in use. The Street Machine Gt's teflon chain tubes find another use here since they keep the chain very smooth.
However, the main reason for using damping are is the rider's movements on the bike. If, for instance, the rider uses his torso to climb a hilly road or if the rider's legs go rhythmically up and down, additional forces may be induced into the suspension. The Street Machine Gt suppresses these forces with a light damping when suspension decompresses. Choose the optional spring element DT-Swiss SSD225 and you can customise damping with a small adjustment knob to optimize the bike to different load and road conditions.
Damping during compression should be set to a very small amount so that suspension can respond easily to even the the smallest unevenness. As a recumbent rider you're here in a better position than the normal bicycle rider: on a recumbent you pedal forwards, rather than downwards but the forces on the suspension are downwards, therefore your pedalling action doesn't interfere with the action of the suspension.
All too complicated?
If this all sounds too complicated, don't worry. The outlined theory's been built right into your Street Machine Gt. Enjoy the ride and concentrate on the landscape in a relaxed fashion. Look forward to the next pot-hole. Your daily ride to work will suddenly become a pleasure...
Want to give it a try? Your Street Machine dealer will be happy to invite you for a test ride. Or read more about the details of the Street Machine Gt.