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The completely new, weight-optimised exhaust system is made com¬pletely from high-grade steel and weighs only 8.5kg. The single-wall manifold system is connected to the silencer via a plug connection with tension spring. The attachment of a slip-on silencer is therefore easy and cheap because the catalytic converter is integrated into the manifold. The end silencer provided as standard is constructed as a two-chamber silencer in a combined absorption/reflection design. This offers a gas flow volume of 8 litres and is mounted half-way up the vehicle on the left side. The F 800 GS is fitted with a secondary air system which, in combination with the regulated catalytic converter, reduces the emission of pollutants (to Euro 3 requirements). Because of the modified valve timings and the associated lower raw emissions, there is no need for a SA system for the F 650 GS.
High-revving with great torque
It is not only the modern injection system that ensures excellent response from the F 800 GS twin; its low centrifugal mass also contributes to its agile power development. Even at the bottom of the rev range, the four-valve per cylinder twin, which has a bore-stroke ratio of 82 to 75.6mm, does not have a particularly short-stroke, quickly speeds up and releases a good 90% of the maximum torque in the broad range between 4 000 and 7500 min–1. Between 5 000 and 8 000 min–1, the engine develops its power dynamically, accompanied by a unique sound. The nominal performance data of the 798 cc twin – 63 kW/85 HP at 7 500 min–1 and 83 Nm at 5 750 min–1 – therefore gives an incomplete picture of the potential that is available in practice.
In combination with the low total weight and closely stepped six-gear trans¬mission, the engine accelerates from 0–100 km/h in about 4 seconds, and the top speed is over 200 km/h.
In this area, the F 650 GS comes close to the 800cc model. It copes with acceleration from 0–100 km/h in less than 5 seconds, and also reaches an impressive top speed of 185 km/h.
But it is not only the acceleration of the new GS models that is impressive; traction is also remarkable. The BMW development engineers have focussed quite deliberately on the smooth, confident development of power in the engine mid-speed range rather than on absolute peak performance. Sporting drivers will be surprised by the engine’s acceleration, while touring riders will enjoy the twin’s excellent traction with minimal gear shifting.
The parallel twin, which has been optimised for enduro operation, is not simply balanced between powerful torsion and dynamic acceleration. It also proves that good performance does not necessarily involve high fuel consumption. Driven over country roads, a consumption of well below 5 litres of Super unleaded petrol per 100km is perfectly possible. If required, the F 800 GS can also be equipped for use with normal petrol, which, however, reduces the peak performance by 1.5 kW/2 HP and slightly increases fuel consumption. This modification is carried out by selecting a characteristic map in the control software, and can be cancelled again at any time. The F 650 GS is designed for operation with lead-free normal petrol.BMW Motorrad can also provide, factory fitted, at no extra cost, a throttle version of the F 650 GS with 25 kW/34 HP at 5 000 min–1 and 57 Nm at 3 000 min–1, aimed specially at new drivers with graded driving licences. The power reduction is via a modified throttle valve.The sophisticated engine concept shows additional technical finesse in its peripherals. The water pump, for example, is on the right of the cylinder head and is driven by a cog wheel unit on the camshaft. The advantageous posi¬tioning of the pump – directly behind the cooler with integrated thermostat – means that only short hose connections are needed. The engine therefore looks particularly compact and tidy. An oil-water heat exchanger next to the easily accessible oil filter ensures that the engine warms up particularly quickly after a cold start. In addition, the heat exchange also limits the engine oil temperatures.
Rear wheel drive via robust O-ring chain
Because motorcycles suitable for off-road use are often used on unmade roads, they need a secondary drive that is not sensitive to dirt. Both GS models therefore have an O-ring chain with a division of 5/8 x 5/16.
A chain guide rail protects the aluminium rocker from damage. Four asymmetrical drive dampers provide shock absorption for the chain wheel bearer which is taken exactly over the full-floating axle via a grooved ball bearing. While the six-gear transmission is taken from the F 800 S/ST models and only the transmission output shaft has had to be modified to the chain drive, the end transmission ratio has been changed for both GS variants and modified for each model. The F 800 GS thus works with a transmission ratio of 1:2.625 (16/42 Z), and the F 650 GS with a ratio of 1:2.412 (17/41 Z).
A sturdy tubular steel frame
The tubular steel frame designed specially for the new GS models, built as a tubular space frame, offers a whole range of interesting details
which improve the extraordinary off-road qualities of the GS models. The
slim steering head, for example, which is integrated with total stability into the frame structure allows a steering lock stop of 40 (F 650 GS) or 42 (F 800 GS) degrees. The steering head is fixed using a completely new layout of gusset plates which have considerably reduced the design width without affecting the stability of the frame. The steering lock is also improved by positioning in front of the handlebar.
Off-road, the small turning circle of the GS models is advantageous when the bike has to drive through trial sections at walking pace.
The manganese-alloy steel tubular space frame integrates the engine as a bearing element. The frame tubes are brought together in the area of the rocker bearings in forged steel parts. The frame tail made from rectangular steel pipe is integrated with the main frame via four screw connections and carries the new fuel tank (capacity 16 litres) which is positioned under the seat. The new design was not simply required because of the modified engine: in the front part of the bench seat the main frame and frame end are narrow – the seat itself and the covering of the suction silencer are very streamlined. This means that, in relation to the seat height, an incredibly short arc has been realised, which is the decisive dimension for the rider being able to touch the ground. The result is that the GS models provide perfect seating for tall and short riders, especially as the F 650 GS seat height can be reduced to 790mm (and with the lowering kit to 765mm).
Made-to-measure telescopic forks for both models
Because of the very long spring travel of 230mm, an upside-down tele¬scopic fork is the best choice for the F 800 GS. The overlapping of the fixed and sliding tubes is particular large with this design, particularly because the fixed tube diameter of 45mm ensures excellent bending strength. Plastic deflec¬tors combined with the front wheel covers provide protection against stones.
On the F 650 GS, a conventional telescopic fork with 43mm fixed tubes is used to provide a spring travel of 180mm.
Aluminium double-strut swing arm at rear
The rear wheel suspension of the GS models is similarly robust. It is based on an aluminium double-strut swing, die cast in a single piece. While the F 800 GS uses a directly hinged central spring strut with path-dependent damping and a spring travel of 215mm, the F 650 GS is fitted with a conventional gas pressure spring strut with a spring travel of 170mm. The spring pre-tensioning can be adjusted on both spring strut elements using a handwheel, making the rear wheel suspension easily adjusted for one- and two-person use. The tension stroke of the suspension can also easily be adjusted to individual requirements in both models.
Wheels and tyres for a specific purpose
The wheels are another point of difference. The F 800 GS travels on aluminium spoked wheels, size 21 x 2.15 at the front and 17 x 4.25 at the rear. The front wheel size of 21’’, which is normal in enduro sports, gives greater riding stability because of the greater gyroscopic forces, which can be an inestimable advantage on loose ground. In contrast, the road-orientated F 650 GS, designed as an entry level model, features cast aluminium wheels measuring 19 x 2.5 at the front and 17 x 3.5 at the rear. The smaller front wheel is a particular advantageous especially on asphalt because the cast wheels are slightly lighter than the spoked wheels. Both wheels come with road-capable enduro tyres as standard. For the F 800 GS, tyres with a marked stud profile are also approved. Refitting is easy if the motorcycle is to be used mainly off-road.
The tyre sizes are an indication proof that both vehicles have been tailored to a preferred area of use. The F 650 GS, for example, is fitted with tyres measuring 110/80-19 at the front and 140/80-17 at the rear. In contrast, the F 800 GS rides on tyres measuring 90/90-21 at the front and 150/70-17 at the rear. While the front wheel supports easy handling and minimises braking torque, the two rear wheel tyres take account of engine power difference
Braking systems matched to each model
The braking systems of each model are also matched to the intended purpose. Because the F 800 GS reaches higher speeds, the front wheel has two fully floating brake discs 300mm in diameter with double-piston sliding callipers. The F 650 GS’s single-disc brake of the same size also fulfils its requirements because it can also be set optimally. At the front, the steel-reinforced brake lines are routed in such a way that they do not push into the cockpit fairing when the telescopic fork is compressed. At the rear wheel, both GS variants are slowed by an identical 265mm disc brake with single-piston sliding callipers.
Modern two-channel ABS with improved rear wheel lift-off detection
If required, the GS models can be factory fitted with a two-channel ABS. The current generation of BMW Motorrad ABS is characterised by its compact design and low weight, and also by very short braking paths. The pressure modulator controls the optimum braking pressure in the regulating range via intake valves that are adjusted on a linear basis and are characterised by very fast, fine regulating intervals. The valves with infinitely variable cross-section openings also ensure that the rider only perceives a slight pulsing through the brake levers. In addition the BMW Motorrad ABS offers expanded diagnosis functions: the wheel rev sensors monitor the distance from the sensor wheel automatically and thus contribute to the machine’s outstanding safety. Riders who routinely ride off-road can deactivate the ABS system before off-road use.
