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BMW K1200S Suspension and Running Gear
source: BMW Press material
BMW K1200S Suspension and Running Gear
Suspension boasting the most advanced technology.
The K 1200 S has inspired BMW's suspension and running gear engineers to introduce a wide range of new ideas and concepts: The first point is that the rider can adjust the springs and dampers electronically at the touch of a button. An important world-first achievement, secondly, is the front-wheel Duolever while the lightweight Paralever has been further enhanced for the rear-wheel suspension.
The frame, again for the first time, comes in light alloy with inner high-pressure profiles visible from outside. The highly stable wheels, in turn, are particularly light and almost delicate in their design.
Together with the rider's seating position on the motorcycle, appropriate interplay of the suspension and the position of the engine ensures not only a low centre of gravity with ideal concentration of masses, but also well-balanced, ideal wheel load distribution of 50:50.
High-precision robot builds lightweight frame.
The central load-bearing component on the K 1200 S is the main frame forming a bridge structure. The frame itself is a welded, composite configuration made up of internal high-pressure moulded elements (IHU profiles) forming the curved profile sections at the side and extrusion-pressed profiles together with die-castings forming the frame head and the rear end with the swinging arm mounts. The K 1200 S is the first motorcycle with IHU-profiles directly in sight on the vehicle itself. A high-precision welding robot welds the components together to form one common extra-stiff unit at BMW's in-house Aluminium Competence Centre at the Berlin Plant.
With the engine being tilted extremely far to the front, the profiles on the main frame extend to the rear above the cylinder head as such, meaning that their shape is not dictated in any way by the width of the cylinder head. This ensures ideal design and configuration of the frame kept appropriately slim and slender (an advantage also provided by the newly designed Paralever around the swinging arm, which makes it possible to place the footrests lower down).
Despite the low footrests, the rider of the K 1200 S is able to lean over to an angle of more than 50 in bends thanks to the overall configuration of the suspension and engine. The low frame structure, together with the new front-wheel suspension, also serves to provide a very smooth and favourable inflow of forces, thus minimising the loads acting on the frame structure.
The main frame weighs a mere 11.5 kg or 25.4 lb. The engine is firmly bolted to the frame at six points and acts as a reinforcing element, without assuming any kind of load-bearing function. The light rear frame is made up of rectangular aluminium profiles welded to one another and is bolted on to the main frame at four points.
Reflecting the usual style and standard of a sports machine, the K 1200 S comes with only a side-stand in its usual, standard trim. A main stand is however available as special equipment and may be fitted easily and quickly on request.
A world-first achievement following a great BMW tradition: The Duolever for perfect front-wheel suspension.
The Duolever - BMW Motorrad's newly developed front-wheel suspension - stands for supreme riding precision and directional accuracy combined with equally superior suspension comfort and clear feedback from the suspension elements. The result is an unparalleled feeling of riding safety in every situation, even when the rider prefers a very ambitious, sporting style.
The original idea came from Norman Hossack--then implemented and developed to perfection by BMW Motorrad.
The front-wheel suspension is the most crucial component in giving a motorcycle ultimate riding precision and comfort. Recognising this essential criterion at a very early point in time, BMW Motorrad has introduced all kinds of innovations on the front-wheel suspension throughout the Company's history of more than 80 years: The first hydraulically dampened telescopic fork on a production motorcycle (1937), the longitudinal swinging arm ('50s and '60s), the long-stroke high-comfort telescopic fork ('70s) and the Telelever (1993) were and are milestones in motorcycle technology invented or at least further enhanced by BMW Motorrad and featured for the first time on BMW production machines.
To this day the Telelever is the only front-wheel suspension system able to achieve genuine success in the market next to the telescopic fork still dominating the scene. Indeed, the Telelever offers superior function and comfort features and is the absolute optimum for the flat-twin machines in BMW's Boxer Series.
With the K 1200 S being a high-performance sports machine, the engineers at BMW Motorrad set out from the start to find an even better solution with perfect kinematics. This was quite simply because the wheel elevation curve on all wheel guidance systems in production inevitably involves a certain compromise between the direction of spring response (comfort and fine response), the anti-dive effect when applying the brakes (residual spring travel and feedback when braking), the motorcycle's handling and riding stability.
They found the right basic idea and philosophy in the Hossack fork developed by British inventor Norman Hossack back in the '80s: front-wheel suspension with two longitudinal arms in parallelogram arrangement. Studies conducted by BMW Motorrad at the time of Hossack's invention showed that this configuration can offer its advantages only in interaction with suitable wheel geometry - meaning that for reasons of the package alone it was not suitable for BMW Motorrad's motorcycle and engine concepts back then. But when the first ideas on the concept of the R 1200 S started to take shape, the engineers took another close look at Hossack's wheel guidance principle, developing and optimising its kinematics and ultimately reaching production standard.
Structure and kinematics of the Duolever.
The kinematics of this new system now named the "Duolever" fulfils several contradictory requirements all in one: A rectangular pivot made up of two almost parallel longitudinal arms turning within the frame holds the wheel bearing and allows the necessary lift motion. The wheel bearing, a light casting made of high-strength aluminium alloy, is connected to the longitudinal arms by two ball bearings and is therefore able to convey the steering forces and motion required. The straight line connecting the two ball joints forms the steering axis, an assembly resembling a pair of scissors serving to convey steering movements and disconnect the entire unit from wheel lift. The handlebar is mounted conventionally on the head of the frame and may be turned the usual way. A central spring strut pivoting on the lower longitudinal arm, finally, provides the suspension and damping effect required.
The two longitudinal arms are suitably aligned to one another, allowing the wheel to follow an almost ideal motion. Thanks to the kinematic configuration of the overall system, wheel elevation follows an almost straight line, with castor and wheelbase hardly changing regardless of spring travel. The wheel elevation curve as such is angled slightly to the rear, allowing the wheel to follow bumps and unsmoothness on the road in a natural process both when under pressure and in the rebound mode, thus evading undue forces and impacts from the surface.
In combination with the low-friction rotational movement of the longitudinal arms, spring response remains smooth and consistent even under high lateral forces or when subject to severe bumps. And the set-up of the suspension can be kept firm and taut without any noticeable reduction of comfort, thus maintaining the standard expected of a sports motorcycle.
With wheel forces being supported at a low point by the longitudinal arms (which keeps the lever arm versus the wheel contact point short and efficient), forces and momentum are fed into the frame in a smooth, favourable process reducing the load acting on the frame as such. The front-wheel suspension itself combines maximum stiffness with minimum weight, since the shape and contours of the wheel mount can be chosen as required thanks to the die-cast structure, thus being adjusted perfectly to force and momentum curves. The individual choice of wall thickness tailored to loads and forces helps to reduce the weight of the entire structure without making any concessions in terms of strength and stiffness. And following the main direction of force application, finally, the longitudinal arms are subject to forces primarily in their own longitudinal direction, that is tensile and compression forces, meaning that through their configuration alone they are particularly stiff and sturdy.
Weighing just 13.7 kg or 30.2 lb, the entire construction is about 10 per cent lighter than a comparable Telelever. The geometric configuration of the spring strut support allows a slightly progressive effect, with overall spring travel of 115 millimetres/4.53 (60 mm/2.36 inbound, 55 mm/2.17 rebound). At 32 right and left, the handlebar angle maintains the usual standard.
Through its kinematic configuration, the Duolever provides an anti-dive effect when braking - and the special point is that this effect remains largely consistent throughout the entire path of spring travel. Longitudinal forces acting on the front wheel when applying the brakes cause virtually no compression of the spring, only the dynamic distribution of wheel load resulting in a slight dive effect giving the rider the usual feedback on how hard he is applying the brakes, that is the feeling he is already used to with a conventional telescopic fork. Ultimately, therefore, the Duolever combines the feedback from the front wheel so desirable to the sport rider with the comfort and safety benefits of brake dive compensation.
Paralever swinging arm and lightweight driveshaft.
Shaft drive is absolutely indispensable on a large BMW motorcycle and was therefore the obvious drive system from the start also on the K 1200 S with its power unit fitted crosswise. Indeed, this not only reflects an old BMW tradition, but also - and in particular - offers well-known functional advantages: The truth is that a chain requiring careful service and maintenance is simply not appropriate these days on a top-end sports motorcycle for superior riding pleasure also on long distances. The challenge in developing the K 1200 S was to minimise the higher unsprung masses of a driveshaft as opposed to a chain, making sure that the rider does not even feel any such effect. And the ideal way to do this was with BMW Motorrad's new universal driveshaft unit complete with its Paralever swinging arm presented for the first time in early 2004 in the R 1200 GS. Much stiffer and lighter than its predecessor, and slim and dynamic in its appearance, this lightweight construction is a perfect match for the concept of the new K 1200 S. In its design and construction it has been modified to meet the needs of the four-cylinder power unit and it is appropriately dimensioned for the extra power of the engine. The pivot angle at the output point from the gearbox has already been described in the Drivetrain Chapter.
The main components of this new construction are the axle drive unit and the swinging arm itself. Made of a high-strength cast aluminium alloy, the Paralever swinging arm is particularly light simply because, in its design and dimensions, it is tailored precisely to the load conditions and requirements encountered on the K 1200 S.
Despite its low weight, the Paralever swinging arm is stiffer and stronger than conventional arms used on the suspension. In geometric terms it is designed to provide 90 per cent dive compensation.
The pivot point of the swinging arm has been moved to a new position beneath the front universal joint on the driveshaft. This, in turn, helps to keep the mounts suitably slender and ensures that the footrests are particularly low down on the motorcycle.
The pivot arm itself rests on a bearing in the stiff main frame formed at this point by a highly stable cast light-alloy structure. The support point for the rear-wheel drive housing lies above the swinging arm, providing the possibility to fit the brake calliper at the bottom. The advantages provided in this way are a better thermal balance and easier removal of the wheel.
The swivel point for the axle drive housing in the swinging arm is below the axis of the driveshaft, the entire system of six pivot points in all being designed kinematically to avoid any effective changes in length on the drivetrain throughout the entire range of spring travel. The advantage in this case is that there is no need for any additional compensation for length and tolerance.
The spring strut pivots via a lever assembly with about 30 per cent progressive action near the swinging pivot point and is supported by a boom on the main frame. The progressive action provided in this way gives the suspension a sensitive response combined with enhanced traction and sufficient reserves for riding with a passenger.
In its basic design and configuration, the final drive housing has been carried over from the R 1200 GS. At the same time it is closely aligned to the inner contours of the angle drive unit, thus avoiding any empty spaces or free areas inside. Precisely calculated, the crown wheel is very light in the interest of minimum weight and optimum smoothness, and the wheel flange is made of aluminium again in the interest of low weight. Through its large diameter, the wheel flange gives the wheel perfect support, again helping to save weight around the hub of the rear wheel.
The visual highlight of this compact and elegant lightweight construction is the 50-millimetre bore of the axle tube in the axle drive housing which, through its large surface and flow effects, enhances the dissipation of heat from the final drive. With the entire axle drive unit being filled with oil for life, there is no further need for an oil change. Like on the R 1200 GS, the driveshaft is made of two concentric tubes with a piece of elastomer in between to provide a reverse damping effect. The shaft itself runs without oil in the swinging column.
The first-ever motorcycle suspension with electronic management--adjustment of the suspension at the touch of a button even while riding.
The suspension system features high-quality gas-pressure spring struts front and rear. Spring travel is 115 millimetres or 4.53 at the front and 135 millimetres or 5.31 at the rear. In its basic configuration fitted as standard, the rear sprung strut allows infinite adjustment of the inbound stroke for optimum damping and infinite adjustment of the spring base by 10 millimetres or 0.39, enabling the rider, simply by turning a wheel, to set the suspension to different loads.
As an option (special equipment at extra cost) the rider is able to adjust both the suspension and damping most conveniently simply by pressing a button on the handlebar. Referred to as ESA or Electronic Suspension Adjustment, this system provides the option to adjust the suspension set-up with maximum comfort even while riding. Indeed, this is the first electronic suspension adjustment system on a motorcycle worldwide, serving to adjust both the spring base as well as the damper inbound and rebound strokes on the rear wheel and the inbound damping effect on the front wheel.
To make operation of the system as simple as possible and to avoid the risk of misadjustment, all the rider has to do is enter the motorcycle's current load condition ("solo", "solo with luggage", and "rider with passenger and luggage"). Then the system will adjust the spring base electrically by itself.
Depending on his style of riding, the rider also has the choice of the Comfort, Normal or Sports mode. Taking this input, the electronic control unit then chooses the appropriate damper rates based on optimum parameters pre-set in the motorcycle's Central Electronic System (CES).
In all, this provides a choice of 9 different variants, with the rider being able to change the damper setting (Comfort, Normal, Sports) while riding simply by pressing a button. For reasons of function and safety, the spring base can be re-set only when the motorcycle is at a standstill.
An electric motor complete with its own transmission serves to vary the spring base as required, while the damper rate is modified by small step motors on the damper itself.
Wheels and tyres--strong but delicately designed lightweight wheels in futuristic design.
The cast light-alloy wheels were specially designed as brand-new highlights on the K 1200 S. Light but at the same time very stable, the wheels come with special spokes designed with the help of a new, biontic calculation model taking the wide range of load requirements into account. The big advantage of such biontic calculation models is that they make allowance for structural principles and concepts of the same kind as in nature: Proceeding from load data and tightening parameters at the fastening points, such models calculate the optimum shape and design of a component in an iterative, step-by-step process. The aesthetic benefit provided in this way is that both the front and rear wheel look light, delicate and dynamic. But despite these similar looks, the wheels are quite different in their structure and layout.
On the front wheel the brake discs rest directly on a stable wheel spider without any carrier elements in between. The five radial arms of the spider extending out of the hub split up like forks to support the rim consistently via 10 cast spokes. With the forks being split up tangentially and the spokes following a radial configuration, the front wheel offers excellent radial stability even under high wheel loads.
A further advantage of this configuration is that it effectively resists the main load caused by high circumferential forces when applying the brakes.
This special design of the wheel tailored to load conditions helps to keep the spokes particularly slender and delicate, not only reducing the weight of the wheel, but also giving the entire wheel structure a light and almost "transparent" look. On the rear wheel the rim is also supported by 10 spoke arms in similar orientation. The difference is that in this case the spokes do not fork out, but rather extend all the way to the wheel hub. The brake disc itself is bolted on to the wheel flange.
Dirty fingers and inconvenient hassle in checking tyre pressure are now a thing of the past: Because now the tyre valve is integrated into one of the spokes at the side, ensuring convenient access in nearly every position of the wheel. Wheel dimensions are 3.5 x 17 at the front and 6.0 x 17 at the rear, running on tyres measuring 120/70-ZR17 and, respectively, 190/50-ZR17.
Brakes--high-performance EVO brake system and integral ABS featured as standard.
The K 1200 S comes with BMW Motorrad's widely lauded EVO brake system already featured in other flat-twin and K-Series models. The brake hoses are steel-clad for extra strength and safety, brake disc diameter of 320 millimetres/12.60 at the front and 265 milliemtres/10.43 at the rear ensuring maximum stopping power even at very high speeds and with the motorcycle carrying a heavy load. And in numerous tests, this sophisticated system has also proven its further benefits such as faster build-up of brake pressure than any other system as well as brake operating forces kept to a minimum. The bottom line, therefore, is that BMW's EVO brake system - with EVO standing for Evolution - is one of the safest and most effective brake systems in the market.
On the K 1200 S this sophisticated brake system comes as standard with BMW Integral ABS already well-known from other BMW models, in this case in the sporting partly integrated version. "Partly integrated" means that both brakes (in the front and rear wheel) are activated whenever the rider pulls the handbrake lever, while the footbrake lever acts only on the rear-wheel brake.
Integral ABS has been modified to match the sporting configuration of the K 1200 S, and its control functions have been enhanced to a standard even higher than before. With the sports rider requiring a brake system that allows fine dosage and application of the brakes, the K 1200 S offers precisely these qualities, virtually eliminating the risk of the motorcycle rolling over even when braking all-out - an advantage ensured by the low centre of gravity and the particular geometry of the suspension interacting with the kinematic configuration of the Duolever. As a result, the ABS control system is able to capitalise on maximum tyre grip and friction even when the rider applies the brakes all-out, which guarantees supreme safety even in the most extreme braking manoeuvres.
The customer looking for a motorcycle without ABS is able to order his K 1200 S as an option without the ABS brake system, with an appropriate reduction in price.
Ride Fast - Ride Safe !
There is no road to happiness, happiness is the road