Ergonomics of open cockpit, FF Single Track vehicles

Definition; “FF”

A single track vehicle with a seat base less than 20” above ground level at ride height, fitted with a seat back capable of supporting the rider. The front suspension should not be steered.

Application.

Single track vehicles.

Sources.

There have been articles published on the subject of the interface between the human and the machine, to my knowledge, since the middle of the last century when German aircraft engineers demonstrated the advantages of the reclining position over the prone position.

The subject became widely known as “Ergonomics” during the 1960's when car designers began to take it seriously. Any designer, engineer or user seeking optimal performance should be aware of it's importance and it is the principle failing of the motorcycle that it's designers have not done so.

In addition to my own interested reading the Quasar, Phasar and Voyager development programmes have allowed exploration of the subject.

Basic requirement

The principle advantages of FFs over motorcycles have been described as “Comfort, Handling and Safety” (Voyager rider summary results)

To qualify the term “Comfort” it is convenient to consider the two other conditions an open cockpit FF most closely resembles. These are the open air, standing in the street - and the open topped car.

If the level of comfort achieved by a pedestrian, assumed to be wearing clothing appropriate to the weather, can be maintained in the FF, and if that cockpit environment can be maintained at a similar level to an open car, then the rider can be said to be comfortable.

This implies that they will be seated normally, fully and securely supported by the seat, so that the steering is not used for support. It means that the cockpit area should be heated to a level at least as good as ambient, with no unpleasant draughts or buffet. Equally important, all the controls, including parking, refuelling and servicing access, should be easy and natural to use.

Relevance to specific design.

Jack Difazio (Front suspension pioneer);-

“Once you take the wind blast of your chest you'll worry about the cold draught down your neck”

Like most design areas there is no end to the improvements in Comfort that can be sought. The open cockpit type has the simple requirements noted above, full enclosure would need to achieve car-like levels of soundproofing and tranquillity to justify the loss of urban agility and convenience. A record breaker, or short circuit racer, would leave out heating and settle for a simple, secure seat.

The degree of comfort chosen will define the quality and possibly even the type of the vehicle. It might be regarded as the start point for a design process of any road vehicle.

Basic features.

The Seat.

The FF differs from other single track vehicles in it's seat height and type. The height is a response to the need to dramatically lower the CG. The type of seat, with a full seat back, is the feature that seems to cause motorcyclists most disturbance. Such seats, universal in all vehicles except motorcycles, are essential to comfort and handling.

By supporting the upper body they remove almost all the effort required to stay on a single track vehicle. Properly designed, they make good ride quality much easier to achieve. Finally, the extra support provided allows much greater control over the steering. The seat back, although run close by the front suspension, is the most important single component on an FF.

Even FF designers often have trouble taking this seriously, a seat back may not be as exciting to do as a four-valve, twin-cam cylinder head but may contribute more to performance satisfaction in use. Good comfort has been noted as a feature of several of my designs but in reality the common factor is the same Volvo seatback - from the 'legacy' 340 model.

This unit has everything a seatback needs in an extremely simple and lightweight package. During the Voyager project units were supplied for less than £30.00 and may be acquired from scrapyards for around £10.00. It has a 'tip-forwards' feature, allowing easy access to the passenger and rear compartments. There is a simple lumbar support adjustment, allowing correct support in different clothes and most important, rake adjustment.

Volvo spent more design time and money on this component than most individuals will on a complete prototype. Even if a different unit is used it would be wise to study this one as an example of excellent design. Other 'quality' cars also provide fine seatbacks and a trawl through scrapyards for an individual perfect fit is entirely sensible.

If a seat back is to be designed from scratch it should at the very least be free to flex from it's base. If rigidly mounted to the top there is a strong possibly that it will hit the rider between the shoulder blades over bumps, causing neck pain. Some trouble was taken to separate the top of the Banana seat from the structure during it's decade-long development.

Rake adjustment is the next important feature. It is very difficult to set this angle correctly at the design stage and in any case the angle that fits best in urban dodging may be steeper than that ideal for leisurely motorway cruising. Lumbar support adjustment is often regarded as a luxury but needs to be correctly set to support the upper body over bumps.

If rake angle and lumbar support must be fixed it still makes sense to use a simple car seatback, with the angle set at the manufacturing stage so that the riders helmeted head just falls forward at a standstill.

The seatback of an FF is used differently from the car unit in one respect. The FF riders upper body will slide across the upper seatback in low speed manoeuvring and if the full range of FF rider body movement is considered it will be seen that there is a need to look around, and upwards, similar to a glider, or light aircraft pilot. In the absence of seatbelts this will be done by rotating and flexing the entire upper body and excessive lateral support, as provided by most 'sportscar' seats will be intrusive. Kart racing type GRP seats, with support right up to the armpits, will seriously intrude on the normal riding experience.

If seat belts are planned this movement requirement should be considered in their design.

The seat base is very simple by comparison. Fully sprung seat bases were used on 001, 002 and the production Voyagers but these are not noticeably more comfortable than the 'chopped foam' seats used on the Banana and FJ. These resemble motorcycle seats in structure, a rubber mounted steel base, with about 50mm chopped foam, covered with PVC 'leathercloth'.

It is necessary to shape the riders seat base to allow comfortable 'legs down' use. The well-known 'Tractor seat' is a good shape for the base. This supports the rider at the rear and the sides, with a raised horn between the legs, usually flowing into the engine cover between the knees, and the parts under the thighs are cutaway to allow the 'legs down' position.

The riders seat base, as is usual in cars etc., should slope upwards to the front quite steeply, so that the riders hips naturally slide into the back of the seat. It is absolutely worthwhile considering and defining these details by comparing and measuring available car seat units.

In the above assumes an interested individual considering the design of an FF. Thus the details of the ergonomics will be set to fit that individual. The designers of any production vehicle will need to go further to suit the majority of the population. It is normal to use a '90 Percentile Human Ergo' or standard human model to achieve this and although real 3D 'Ergos' as used by the auto industry are extremely expensive, 'Virtual Ergos' can be readily downloaded. The Voyager project, somewhat preceding commonplace computing, made a 2D Ergo many years ago, featured in some Comfortmax pictures.

Seat position.

The position of the seat in the vehicle impacts on the riding experience and possibly the handling. It is easy when converting a motorcycle to use the space often found just ahead of the rear wheel for the seat. The Banana and Arthur Middleton's Kawasaki conversion are classic examples of this and basic packaging will usually define the position of the rider.

This rearward positioning can lead to a rearwards weight bias, which in turn can cause snatch-locking of the front brake and excessive understeer although this can be minimised by packaging other components.

It also intrudes on the riding experience, especially at low speed. Although it is difficult to pinpoint an exact relationship, it seems that the rider is more comfortable if it feels as though the head is turning with the front wheel. If the front wheel is between the riders feet, as in the Voyagers and the Comfortmax, it is easy to achieve this feel. Steering on the Banana, by comparison, feels more remote.

This is a minor effect, unless urban use is to be common, however FJ is optimised to move the rider as far forwards as the Reliant engine will permit and I believe there is a detectable improvement in the feel of low speed handling. In an ideal situation, where packaging is not an issue, one might start by placing the riders head as near to the centre of the vehicle as possible.

Passenger provision.

If a passenger is to be carried there must either be a separate seat back for each occupant, or the seat back used by the rider must be transportable to support the passenger, whose body will also support the rider. This works well in practice and FJ has carried passengers right at the top of the 90% Euro range. This is clearly the most efficient way of packaging two humans.

Although the close proximity this system provides is commonplace on motorcycles and other single track vehicles, some designers regard it as unacceptable. The Ecomobile uses two separate seats and some system like this will be required if the occupants are to be physically separated. There is a penalty to be paid in weight, complexity and packaging for this feature.

Seat back transport.

A seat back capable of being adjusted to allow use by either a single rider or an additional passenger is a feature of the Quasar and several Phasars, designed by the late Malcolm Newell. The Quasar uses a hammock-style arrangement with a wide, upholstered leather 'strap' which can be adjusted to provide support for the rider or passenger. It major failing is that it provides no lateral support and I found that a skateboard, conveniently jammed behind the hammock, provided much better support in sporting use.

Two-seat Phasars, with various powertrains, used a seatback mounted on telescoping tubes from the rear bulkhead. This provides better support as the seat back itself can be better shaped and a developed version might allow full adjustment of rake, lumbar support and position. The telescopic supports however intrude into the luggage space.

The concept was further developed in the Voyager series with an entire seatback transportable into either rider or passenger positions. The seat base resembles a 'King and Queen' seat, originally found on some American low-riders but also now common on large touring motorcycles. To allow the two occupants to fit together comfortably the passenger seat needs to be around 125mm higher than the riders seat.

002 and the Production Voyagers used the seat slides that come with the Volvo 340 seat unit, including the adjustment latches. These slides are inclined upwards to the rear so that the seat back is at the correct height at either end of it's travel. This system allows limited movement of the seat back to accommodate different solo riders. Similar slides were used in the Production design to transport the head fairing which covered the top of the passenger opening in the bodywork.

Some other prototype FFs also use slides to transport the seatback and it is clearly a solution worth considering in a two-seater design..

The major problem seems to be that. although convenient and easy to arrange, slides intrude badly on the packaging of components under the seat. The need for slides, and the carriage sliding on them, to be parallel, seriously constrains the shape of components which might otherwise be packaged more efficiently. The 'shelf' and side extensions on the top of the Production Voyager tail are principally there to accommodate the head fairing slides.

FJ accordingly used parallelogram arms to swing the seat back from it's single seat position up and rearwards to the rear seat position. Anchorages in either position are engaged by latches that transport with the seat back. The head fairing uses a single yoke to achieve the same end, although if a full parallelogram had been used it could have avoided the body damage done to the upper edge of the tail by the engagement latch in the head fairing during careless transfer to the rearward position.

These linkages have proved to be a better solution in terms of packaging and shaping the rear bodywork - this may be clear from photographs. It also allows the actual distance between the two seatback positions to be set entirely by ergonomic considerations; it is difficult to find car-type slides with sufficient range of movement. The common 'Drawer-type' slides do not provide sufficient location support at full extension. It is more difficult to provide adjustment of the seatback to accommodate different riders, making adjustable footboxes and hand controls more important in a production design.

More recently Honda have introduced a seatback, on a 250cc 'Urban utility' vehicle, which hinges back down flat so that a passenger may use it as a seatbase. It is good that Honda have finally fitted this essential device to one of their vehicles although it seems unfair that only the rider can experience the advantages, and then only when alone. Honda should be capable of designing a fully transportable seatback and it is to be hoped that they can afford the time to do so.

Footboxes.

In the absence of an Ergo the location of the footboxes in an FF design can again be found by sitting in cars. A friend with a tape measure will be needed. In a production design it will probably be found easier to make the footboxes and controls adjustable, rather than the seat. Even if slides are used to transport the seatback it is difficult to provide a full adjustment range. CVT FFs like the Comfortmax do not need foot controls, making a one-size-fits-all footbox quite easy.

The FF seating arrangement needs slightly better security than the car application. There may not be seat belts and the vehicle is subject to vertical accelerations during normal use. The normal agility of a low CG, HCS equipped, vehicle may provide enough vertical acceleration to unload the rider and in any case severe bumps may also cause problems.

The nearest vehicle to this is the racing kart, where heels cups are routinely used to allow the rider to hold themselves in the seat. The floor of an FF footbox needs to be set at an angle steep enough to provide a similar but more comfortable support. The Banana, in it's current form, most closely approaches this angle in the vehicles I have designed. It is considerably steeper than the Production Voyagers. FJ is somewhat inbetween, not steep enough.

This angle is not hugely critical, FJ is acceptable in moccasins, where the ankle can flex freely, but noticeably shallow in winter boots. The Production Voyagers had heel rests, like sportscars, intending the that the feet would rest on their heels, but resting the whole foot on a correctly angled plate is more comfortable and secure.

Width
The width between the footboxes is usually set by the space needed for suspension or wheel lock. If there is no machinery in the way the feet can be set at a natural sitting separation - typically 300-350mm.

Normally however packaging forces the feet further apart. FJ is already 415mm wide by the time it has front suspension and a wheel that steers. Adding 250mm to this, for the two minimum width 125mm footboxes, is what defines it's overall width. Some other FFs have even wider foot positions. This is not a problem ergonomically and any FF approaching standard door width will not trouble the rider with excessively wide foot positions - Unless the engine bay also forces the riders knees apart.

Height
If the knees are significantly further apart than the feet, because of such a wide engine bay, there is a possibility that they will tend to fall apart in a relaxed sitting position. this is uncomfortable and places them outside the cockpit. The problem is reduced if the feet are below the seat base. As the wheel centre (and front suspension arms) are around 320mm from the ground and a typical seat height is around 450mm, there is space to arrange this. Sweeping back angled footboxes also assists keeping the knees tucked in.

Detail.
It is normal to include a high friction surface to the footbox floor, and also a small raised ridge along the outer, but not the lower, edge, usually not more than 10mm high. These increase foot security in the event of hitting big bumps or during accidents where rider location is important.

The 'leg clearance' cut outs, mentioned in the submission on safety performance, and aerodynamics, should start immediately behind the footbox, with the rear edge designed to avoid sharp corners or edges.

The outer edges of the footboxes are the widest and strongest part of the front of the vehicle. They protect the legs from impact and trapping if the vehicle is on it's side. These structural demands, including high friction surfaces as noted in the safety notes, should be integrated into the footbox design.

Hand Controls.

Type
A wide variety of hand controls have been used on different FFs without seriously intruding on their riders conciousness. With one exception the standard motorcycle control set is adequate for FF use.

The exception is the twist grip throttle. Although suitable for a motorcycle it demands that the handlebar be gripped hard enough to keep the twist grip open against the throttle return spring. It was noted that, riding the Banana at speed on motorways, this gripping effort was the highest muscular effort being used. To the extent that, in long runs, it was the limit on comfortable use.

An HCS equipped FF should require virtually zero steering effort at speed. Exactly as in a car, the hands will merely hang on the controls. A similarly low effort throttle control is required. The Voyager solution has been a right hand trigger throttle lever. This was easy on these Reliant-engined FFs, where the car-type carburettor has a single throttle disc. 001, with a slide type motorcycle carburettor was also acceptable. This solution allows easy simultaneous use of the throttle and front brake, as in changing down into a corner while braking and also permits very fast throttle-to-brake transitions. It may not be the only low-effort throttle solution but it sure beats a twist grip!

The trigger throttle also frees the design of the actual hand grips and this was use to provide 'pistol grips' which support the whole hand in a natural, relaxed position. Other controls are similar to the motorcycle set, although combined light/horn/indicator and ignition/start/engine kill switches from cars were selected for their superior ergonomics and protected in a waterproof hand control yoke.

These details may seem excessive compared with the universal motorcycle set. However they pass the definitive ergonomic test - they're unnoticeable - and the motorcycle set does not.

Position.

Height
The requirement for rider security and the braking performance mean that the hand controls need to be higher than they are in a car, where seat belts help with the braking loads. Again, racing Karts provide a good insight with hand positions nearer shoulder height than the centre of the chest. The Production Voyager riding position was largely copied from the Ford Sierra and even with the hand controls at their highest adjustment point it is clear that they should be higher. FJ and the Banana are better in this respect.

Individual designers can get a good idea of the correct position by kneeling on the ground and supporting their upper body on slightly bent arms, there is a position of natural balance where the head and chest are balanced on the hands and this relationship will be correct for handling braking loads.

Width.
Total vehicle width will closely confine the width of the hand control and the 660mm-720mm width range of most of my designs is narrower than normal motorcycle handlebar width. Fortunately HCS allows far narrower handlebars, in terms of control effort, and the Voyager hand controls have generally been set to provide comfortable clearance to the inside of the cockpit, itself close to the full width of the vehicle. Other designers have used hand controls where the minimal width is set by packaging the motorcycle control set.

The Comfortmax is interesting in this respect. It's standard, rather wide handlebars are clearly necessary to control the original scooter but the increased steering authority given to the rider by the seat back gives an initial impression of excessive leverage and over-control, until the limits of the telescopic forks are reached and it becomes quite useful again.

Adjustment.
It has proved important to be able to correctly adjust the hand controls. Pistol grips should be adjustable for angle, to allow the wrist to form a natural angle. It is also very useful to be able to adjust the hand control for height and distance to shoulders. During development of a new vehicle other problems, damping, springs, engine set-up etc., tend to obscure ergonomic details and it may be some months before it's realised that the hand controls are uncomfortable, or fail to provide good security. In a production design adjustability of the hand controls seems essential.

Adjustability generally is seen as something as a luxury on single track vehicles but to return to Jack Difazio's quote, it is the key to eliminating irritating discomfort, cramps, aches and pains, the ergonomic equivalent of the draught down the neck. A vehicle which fits well, causing no discomfort, will be used. An uncomfortable one will either be modified or abandoned.

Heating.

This essential feature, normally entirely absent on single track vehicles, will cause some technical difficulties due to that fact. There are no heater assemblies in production designed for such vehicles. However, if water cooling is used for the engine there will almost inevitably be a hot water pipe which can be used to supply a custom made heat exchanger. Even a manifold heater line can be used, after the manifold, for a heater matrix, but the main coolant circuit can be tapped into if needed.

The heater matrix will probably need to be custom made simply because of packaging problems. This is not particularly expensive, radiator repair companies are fairly common and a wooden pattern, with hose connections defined, will usually suffice. The heater outlet should be into the area under the hand controls. If the cockpit is reasonably well protected from buffet this will distribute hot air right up the riders front and out to the hands. The matrix should basically be as big as there is room to fit it, with good ram air supply from the front of the vehicle. The Voyagers use the front wheel bay for the heater intake but the headlight opening might be just as good.

Although not fitted originally several owners have added a small fan to the heater matrix for use at a standstill and it has been noted in in the submission on Aerodynamics that the cockpit pressure increase these fans generate keeps rain out of the cockpit at a lower speed.

None of the heaters fitted so far provide enough heat to trouble riders in an English summer. Users tend to turn the fan on in October and turn it off in April, but a really effective heater, basically bigger than those tried so far, might need to be controlled to supply cold air in summer. designing the control system and air supplies is quite difficult due to the need for fairly large air passages and very constricted space.

Like the seat back, detailed heater design seems to be thought insufficiently exciting by designers to be worth real consideration but for the user heating will make the vehicle genuinely useful in all conditions. Even with the matrix fitted to the Voyagers it's possible to park, step out of the cockpit and realise that it's cold out there....

Rider Access.

Further irritations that justify attention at the design stage concern access to the cockpit and the servicing areas. The Quasar is quite difficult to enter and leave but even simple open cockpit vehicles can present obstacles. It is worthwhile considering entry and exit while finalising bodywork and seat arrangements. If the vehicle is to be entered while balanced there needs to be a way of holding it up while entering. If it is intended to be on a stand it must be possible to operate these stands from the cockpit.

The Voyagers all use lever operated centre-stands to make this easy. The Banana demonstrates that the operating lever should be on the left hand side, opposite the front brake. If there is a side stand it needs to be well forward, like the riders feet, so it can be easily reached.

Servicing access

Access to basic service areas, oil, water, ignition, carburettor should be as simple as a car. It is appropriate to use car type latches for this and under any bonnet in a scrapyard a wide variety of simple, rugged, cable or rod operated latches are available. Dzus, for one, also offer similar latches as catalogue items. Although this is also an area ignored by motorcycle designers the easy access provided by such latch systems mean that servicing and development adjustment will be carried out. As a result the vehicle will last longer and work better.

Less routine areas, charging, cooling, any wearing parts will eventually need attention. If these are easily accessible this will be done in the routine course of vehicle maintenance. This will hugely increase the chances of the vehicle surviving for long enough to justify the cost and time spent in building it. There are number of companies supplying latches and fasteners, the Voyagers use very effective and lightweight “Swell latches” from the American company “Southco” but study in scrapyards will provide many alternatives.

As a general rule servicing access panels should be removable without tools.

Conclusion.

Ergonomics, the science of comfort, is almost completely ignored on motorcycles or scooters and is therefore an unfamiliar area to many single track vehicle designers. However all designers have a body to experiment with and most have access to a variety of cars providing a rich seam of design solutions. There was never any excuse for the appalling ergonomics of motorcycles but given the similarity of the FF cockpit to that of a car it would be ludicrous to ignore the subject in FF design.

Royce Creasey
Feb. 1005
Copy free for credit