There's more than one truth to HPV suspension, but in this article we'll elaborate on the choices that were made developing the WAW as a single person ultralight vehicle. General principles from the automotive industry have limited use for a vehicle with a mass several times smaller than it's payload, and limited power. On the other hand, the hefty torque on a trike's rear wheel in cornering makes velomobile rear suspension differ from a bicycle suspension.
Large travel suspension on a driven wheel causes a number of undesirable effects I can hardly get into now (more info on many HPV web pages: see pedal-induced bob, pogo, squat, torque-reactive etc., or this article in Flemish about suspension geometry optimization ), commonly summarized under the term 'suspension loss'. Active suspension mechanisms also add considerable weight to a bike - in the case of a three wheeler this extra weight quickly multiplies due to the large torsion moment. Some inherent problems can be solved by a cunning geometry and an increasing number of pivots, but again at the cost of even more weight and complexity.
You can be fast or you can be comfy...
But you can't be both, is an ancient saying in the bicycle world. Suspension losses and extra weight are to be weighed against shock absorption. For a downhill bike, the ergonomic benefit of full suspension outweighs the loss. Fast road bikes, however, will benefit most from a light, small travel suspension, especially on the driven wheel where transmission efficiency matters. This isn't meant for the big bumps but it eliminates road vibration, the main cause of rider fatigue - and nerve damage! A body in effort will happily cope with jolts and bumps it wouldn't appreciate in rest, e.g. in an automobile. The recent development of curved seat stays for road bike frames are a good example of light and fast suspension design. (or a bad one for that matter, as they're often in carbon fibre, which has a lot of qualities but bending isn't one of them.)
The WAW builds upon the same efficient suspension design principles that have been applied by fast road bike designers for over a century:
Pneumatic suspension, or a good fat tire which has a fantastic 'shock absorption to weight' ratio. Only since about a decade we have got tires that combine minimal rolling resistance with a comfortable tire pressure. A contemporary good 50 mm tire like the Schwalbe Big Apple or Marathon Racer is super smooth ànd fast at 4 bar.
Frame suspension, or passive suspension: commonly known by the curved bicycle front fork. The advent of composite frame building radically changed the way we look at suspension. With almost no weight penalty, it is now possible to build durable and lossless small travel suspension reconciling transmission efficiency and ergonomics.
The WAW's semi-monocoque base is made of aramid fibre, better known under the commercial name of KevlarR, in our case TwaronR. Aramid fibre composite has tremendous energy absorption capacity (famous by the bullet-proof vests) and we put its elastic and dampening properties to good use. In fact the aramid fibre rear architecture performs like a leaf spring and dampener (by hysteresis) in one. Road shock and vibration energy is diverted and largely neutralised on its way from the wheel to the rider.The geometry of the rear suspension is such that no compression is possible along the chain line, so the WAW rear suspension induces no loss at all! We believe our Aramid suspension is the lightest, most efficient form of suspension for a velomobile.
'Saddle' suspension: in our case, the geometry and material of the seat. Like the coachwork, it's a smart mix of aramid and carbon fibre, anatomically shaped to support the curves of a back in action and eliminate pressure points. A 20 or 30 mm thick Ventisit seat pad caters for ventilation and adds comfort. For an ultraplush ride, the rear part of the seat can be suspended on XPE (elastic foam) blocks. This provides the ultimate comfort but again the laws of physics kick in so there's some loss of efficiency. Most riders are happier with the very efficient aramid suspension.
Frame geometry: a bump in the road exerts a force on the wheel, that wheel is some distance away from the rider so in physics we consider a moment (torque) around the rider. Therefore the further a wheel is away from the rider, the less he will feel the shock. This is, by the way, one of the main reasons large wheels are perceived as more comfortable than small wheels: the contact point is just farther away -> less torque and more frame absorption. Second, a trike is inherently more comfortable than a twowheeler: a lifting of a front wheel can also rotates the rider, this time along the longitudinal axis. The same principles apply: without even taking into account any frame springing, each impact on one of the front wheels is literally halved.
Active front suspension: The non-driven front wheels' suspension is a lot more compact, so there we use a traditional McPherson strut from our colleagues Velomobiel.nl: coil springs and friction dampening/damping. Thanks to the extremely low center of gravity and maximal wheel base, the WAW does not need a torsion bar to avoid excessive roll while cornering.
Speed is comfort is speed.
Along these principles, the WAW has been designed and optimized through many iterations over the years. We aim for the best balance of performance and comfort, of ergonomics and transmission efficiency.