BMW F900XR - Owner's Manual > Engineering details

General notes

To find out more about engineering go to: bmw-motorrad.com/technology

Antilock Brake System (ABS)

How does ABS work? The amount of braking force that can be transferred to the road depends on factors that include the coefficient of friction of the road surface. Loose stones, ice and snow or a wet road all have much lower coefficients of friction than a clean, dry asphalt surface.

The lower the coefficient of friction, the longer the stopping distance.

If the rider increases braking pressure to the extent that braking force exceeds the maximum transferable limit, the wheels start to lock and the motorcycle loses its directional stability; a fall is imminent. Before this situation can occur, ABS intervenes and adapts braking pressure to the maximum transferable braking force, so the wheels continue to turn and directional stability is maintained irrespective of the condition of the road surface.

What are the effects of surface irregularities? Humps and surface irregularities can cause the wheels to lose contact temporarily with the road surface; if this happens the braking force that can be transmitted to the road can drop to zero. If the brakes are applied under these circumstances the ABS has to reduce braking force to ensure that directional stability is maintained when the wheels regain contact with the road surface. At this instant the BMW Motorrad ABS must assume an extremely low coefficient of friction (gravel, ice, snow), so that the wheels will continue to rotate under all imaginable circumstances, because this is the precondition for ensuring directional stability. As soon as is registers the actual circumstances, the system reacts instantly and adjusts braking force accordingly to achieve optimum braking.

Rear wheel lift

Under very severe and sudden deceleration, however, under certain circumstances it is possible that the BMW Motorrad ABS will be unable to prevent the rear wheel from lifting clear of the ground. If this happens the outcome can be a highsiding situation in which the motorcycle can flip over.

WARNING Rear wheel lift due to severe braking

Risk of falling

• When you brake sharply, bear in mind that ABS control cannot always be relied on to prevent the rear wheel from lifting clear of the ground.

What is the design baseline for BMW Motorrad ABS?

Within the limits imposed by physics, the BMW Motorrad ABS ensures directional stability on any surface.

At speeds above 4 km/h, within the limits imposed by physics the BMW Motorrad ABS can ensure directional stability on any surface. Limitations inherent to the design principle mean that at lower speeds the BMW Motorrad ABS cannot provide optimum assistance on all surfaces.

The system is not optimised for special requirements that apply under extreme competitive situations off-road or on the track.

Special situations

The speeds of the front and rear wheels are compared as one means of detecting a wheel's incipient tendency to lock. If the system registers implausible values for a lengthy period the ABS function is deactivated for safety reasons and an ABS fault message is issued. Self-diagnosis has to complete before fault messages can be issued.

In addition to problems with the BMW Motorrad ABS, exceptional riding conditions can lead to a fault message being issued:

• Riding for a lengthy period with the front wheel lifted off the ground (wheelie).
• Rear wheel rotating with the vehicle held stationary by application of the front brake (burn-out).
• Heating up with the motorcycle on the centre stand or an auxiliary stand, engine idling or with a gear engaged.
• Rear wheel locked by the engine brake for a lengthy period, for example while descending on a loose or slippery surface.

If a fault message is issued on account of exceptional riding conditions, you can reactivate the ABS function by switching the ignition off and on again.

What significance devolves on regular servicing?

WARNING Brake system not regularly serviced

Risk of accident

• In order to ensure that the BMW Motorrad ABS is always maintained in optimum condition, it is essential for you to comply strictly with the specified inspection intervals.

Safety reserves

The potentially shorter braking distances which BMW Motorrad ABS permits must not be used as an excuse for careless riding.

The system is primarily a means of ensuring a safety margin in genuine emergencies.

Take care when cornering! When you apply the brakes on a corner, the vehicle's weight and momentum take over and even BMW Motorrad ABS is unable to counteract their effects.

Evolution of ABS to ABS Pro

- with ABS Pro OE

Until now, the BMW Motorrad ABS helped ensure a very high degree of safety for braking with the motorcycle upright and travelling in a straight line.

Now ABS Pro offers enhanced safety for braking in corners as well. ABS Pro prevents the wheels from locking even under sharp braking. ABS Pro reduces abrupt changes in steering force, particularly in panic-braking situations, counteracting the vehicle's otherwise natural but undesirable tendency to straighten up.

ABS intervention

Technically speaking, depending on the riding situation ABS Pro adapts ABS intervention to the motorcycle's bank angle. Signals for rate of roll and rate of yaw and lateral acceleration are used to calculate bank angle.

As the motorcycle is heeled over more and more as it banks into a corner, an increasingly strict limit is imposed on the brake-pressure gradient for the start of brake application. This slows the build-up of brake pressure to a corresponding degree. Additionally, pressure modulation is more uniform across the range of ABS intervention.

Advantages for the rider

The advantages of ABS Pro for the rider are sensitive response and high braking and directional stability combined with best-case deceleration of the motorcycle, even when cornering.

Traction control (ASC/DTC)

How does traction control work?

Traction control is available in two versions

• without provision for the bank angle: Automatic Stability Control ASC
• ASC is a rudimentary function intended to prevent falls.
• with provision for bank angle: Dynamic Traction Control DTC
• DTC regulation is more delicate and more comfortable thanks to the additional bank angle and acceleration information.

Traction control compares the front and rear wheel circumferential velocities. The differential is used to compute slip as a measure of the reserves of stability available at the rear wheel. If slip exceeds a certain limit, the engine management system intervenes and adapts engine torque accordingly.

BMW Motorrad ASC/DTC is designed as an assistant system for the rider and for use on public roads. The extent to which the rider affects ASC/DTC control can be considerable (weight shifts when cornering, items of luggage loose on the motorcycle), especially when the style of riding takes rider and machine close to the limits imposed by physics.

The system is not optimised for special requirements that apply under extreme competitive situations off-road or on the track. The BMW Motorrad ASC/ DTC can be deactivated in these cases.

WARNING Risky riding

Risk of accident despite ASC/ DTC

• Invariably, it remains the rider's responsibility to adapt riding style to riding conditions.
• Do not take risks that would negate the additional safety offered by this system.

Special situations

In accordance with the laws of physics, the ability to accelerate is restricted more and more as the angle of heel increases. Consequently, there can be a perceptible reduction in acceleration out of very tight bends.

The speeds of the front and rear wheels are compared and DTC, unlike ASC, also takes the bank angle into account in processing data to detect the rear wheel's incipient tendency to spin or slip sideways.

- with riding modes Pro OE

If the electronic processor receives values for the bank angle that it considers implausible over a lengthy period, a dummy value is used for the bank angle or the DTC function is switched off.

Under these circumstances the indicator for a DTC fault shows.

Self-diagnosis has to complete before fault messages can be issued.

The BMW Motorrad Traction Control can shut down automatically under the exceptional riding conditions outlined below.

Exceptional riding conditions:

• Riding for a lengthy period with the front wheel lifted off the ground (wheelie).
• Rear wheel rotating with the vehicle held stationary by application of the front brake (burn-out).
• Heating up with the motorcycle on an auxiliary stand, in neutral or with a gear engaged.

Minimum speed for activation of DTC

• min 5 km/h

If the front wheel lifts clear of the ground under severe acceleration, the ASC or DTC reduces engine torque in the RAIN and ROAD riding modes until the front wheel regains contact with the ground.

Front wheel lift-off detection allows brief wheelies when the DTC setting is DYNAMIC.

In DYNAMIC PRO riding mode, front wheel lift-off detection is switched off.

BMW Motorrad recommends turning the throttle grip back slightly when lifting the front wheel in order to reach a stable driving condition again as soon as possible.

In RAIN, ROAD and DYNAMIC riding modes, the DTC setting corresponds to the riding mode.

In the DYNAMIC PRO riding mode, DTC can be set differently.

Dynamic engine brake control

- with dynamic engine brake control OE

How does dynamic engine brake control work?

The purpose of dynamic engine brake control is to prevent the unstable riding states that can be produced by excessive engine braking moment acting on the rear wheel. Depending on the road condition and riding dynamic, excessive braking torque can produce a sharp rise in rear-wheel slip and impair directional stability. Dynamic engine brake control limits this slip at the rear wheel to a safe mode-dependent and bank-angle-dependent regulated slip.

Causes for excessive slip at the rear wheel:

• Riding with engine overrun on a surface with a low coefficient of friction (e.g. wet leaves).
• Rear-wheel hop when rider downshifts.
• Sharp braking during sporty riding.

In the same way as DTC traction control, dynamic engine brake control compares the wheel circumferential velocities of the front and rear wheels. Additional information on the bank angle enables dynamic engine brake control to calculate slip and the reserve of stability at the rear wheel.

If slip overshoots the applicable limit, the throttle valves are opened very slightly to increase engine torque. Slip is reduced and the vehicle is stabilised.

Effect of dynamic engine brake control

• In the RAIN and ROAD riding modes: Maximum stability.
• In the DYNAMIC and DYNAMIC PRO riding modes: High stability.

Dynamic ESA

- with Dynamic ESA OE

Dynamic ESA function

By interpreting ride height sensor signals, Dynamic ESA detects movements in the suspension and responds by adjusting the damper valves. The chassis and suspension will thus be adapted to the characteristics of the terrain.

Dynamic ESA calibrates itself at regular intervals to ensure the system functions correctly.

Possibilities for adjustment

Damping modes

• Road: Damping for comfortable on-road riding
• Dynamic: Damping for dynamic on-road riding

Load settings

• One-up riding
• One-up with luggage
• Two-up (with luggage)

Riding mode

Selection

To adjust the motorcycle to the road condition and the desired driving experience, the following riding modes can be selected:

• RAIN
• ROAD (default mode)
• with riding modes Pro OE
• DYNAMIC

With coding plug installed:

• DYNAMIC PRO

For each of these riding modes, there is a matching setting for the ABS, ASC⁄DTC systems, for dynamic engine brake control and for throttle response.

- with Dynamic ESA OE

Dynamic ESA can be parametrised independently of the selected riding mode.

ASC⁄DTC can be switched off in each riding mode. The following explanations always refer to the driving safety systems that are switched on.

Throttle response

• In RAIN riding mode: the engine's throttle response is soft.
• In ROAD riding mode: the engine's throttle response is optimum.
• In DYNAMIC riding mode: the engine's throttle response is direct.
• In DYNAMIC PRO riding mode: the engine's throttle response can be parametrised to suit the rider's individual needs and preferences.

ABS

• Rear wheel lift-off detection is active in all riding modes except in the factory default settings of the DYNAMIC PRO mode.
• Rear wheel lift-off detection is reduced in the DYNAMIC riding mode to achieve an enhanced braking effect.
• In DYNAMIC PRO riding mode, ABS can be set up differently.

- with riding modes Pro OE

ABS Pro

• In the RAIN and ROAD riding modes, ABS Pro is fully available.

  The tendency of the motorcycle to straighten up when the brakes are applied with the machine banked for cornering is reduced to a minimum.

• In the DYNAMIC riding mode, ABS Pro is available only when the coefficient of friction is good. Assistance is less than in the RAIN and ROAD riding modes riding mode and instead, the system is set up to achieve maximised braking effect.
• In the DYNAMIC PRO riding mode, the factory default setting for ABS Pro is OFF.

ASC

• Front-wheel lift-off detection is active in the RAIN and ROAD riding modes.
• ASC is set up for on-road riding.
• ASC provides high driving stability in ROAD riding mode and maximum driving stability in RAIN riding mode.

- with riding modes Pro OE

DTC

Tyres

• DTC is set up for on-road riding with road tyres in all riding modes.

Driving stability

• In the ASC/DTC setting for RAIN, ASC/DTC intervenes early enough to achieve maximum driving stability.
• In the ASC/DTC setting for ROAD, ASC/DTC intervenes later than in the RAIN riding mode. This prevents the rear wheel from spinning whenever possible.
• In the ASC/DTC settings for RAIN and ROAD, the front wheel is prevented from lifting.
• In the ASC/DTC setting DYNAMIC, ASC/DTC intervenes later than in the ROAD riding mode, so slight drift can be induced when exiting corners and brief wheelies are also possible.

In the ASC/DTC settings RAIN, ROAD and DYNAMIC the ASC/ DTC setting corresponds to the riding mode.

In the ASC/DTC setting DYNAMIC PRO, ASC/DTC can be set differently.

Mode changes

The riding mode can be changed while the vehicle is stationary with the ignition on. It is possible to change it while driving under the following conditions:

• No drive torque on the rear wheel.
• No brake pressure in the brake system.

The following steps must be taken to change the riding mode:

• Close the throttle twistgrip.
• Release the brake levers.
• Deactivate the cruise control.

The desired riding mode is initially preselected. The mode change does not take place until the systems in question are all in the appropriate state.

The selection menu does not disappear from the display until the mode change has taken place.

Dynamic Brake Control

- with riding modes Pro OE

Dynamic Brake Control function

The Dynamic Brake Control function assists the rider during emergency braking.

Detection of emergency braking

• Emergency braking is detected when the front brake is actuated quickly and forcefully.

Behaviour during emergency braking

• If emergency braking is initiated at a speed above 10 km/h, the Dynamic Brake Control takes effect in addition to the ABS function.

Behaviour during accidental actuation of the throttle grip

• If the throttle is accidentally opened (throttle grip position > 5 %) during emergency braking, Dynamic Brake Control ensures the desired braking effect by ignoring actuation of the throttle grip. The effect of emergency braking is guaranteed.
• If the throttle is closed (throttle grip position < 5 %) while Dynamic Brake Control is in action, the engine torque requested by the ABS brake system is restored.
• If emergency braking finishes and the throttle grip is still actuated, the Dynamic Brake Control will reduce the engine torque to the driver's choice in a controlled manner.

Tyre pressure monitoring (RDC)

- with tyre pressure control (RDC) OE

Function

A sensor integrated into each tyre measures the air temperature and the air pressure inside the tyre and transmits this information to the control unit.

Each sensor has a centrifugalforce tripswitch that does not enable transmission of the measured values until the motorcycle has accelerated to a defined minimum speed for the first time.

Minimum speed for transmission of the RDC measured values:

• min 30 km/h

The display shows -- for each tyre until the tyre-pressure signal is received for the first time. The sensors continue to transmit the measured-value signals for some time after the vehicle comes to a stop.

Time for transmission of measured values after vehicle comes to a stop:

• min 15 min

An error message is issued if wheels without sensors are fitted to a vehicle equipped with an RDC control unit.

Tyre pressure ranges

The RDC control unit distinguishes between three tyre pressure ranges matched to the vehicle:

• Tyre pressure within permitted tolerance.
• Tyre pressure close to limit of permitted tolerance.
• Tyre pressure outside permitted tolerance.

Temperature compensation

Tyre pressure is a temperature-sensitive variable: pressure increases as tyre-air temperature rises and decreases as tyre-air temperature drops. Tyre-air temperature depends on ambient temperature as well as on the style of riding and the duration of the ride.

The tyre pressures are shown in the display as temperature compensated and always refer to the following tyre air temperature:

• 20 ºC

The air lines available to the public in petrol stations and motorway service areas have gauges that do not compensate for temperature; the reading shown by a gauge of this nature is the temperature-dependent tyre-air pressure. As a result, the values displayed there usually do not correspond to the values displayed in the display.

Pressure adaptation

Compare the RDC value on the display with the value in the table on the back cover of the rider's manual. Then use the air-line gauge at a service station to compensate for the difference between the RDC reading and the value in the table.

Example

• According to the operating instructions, the tyre pressure should be: 2.5 bar
• The following value is shown in the display: 2.3 bar
• So pressure is low by: 0.2 bar
• The gauge on the air line shows: 2.4 bar
• You must now increase tyre pressure until the value is: 2.6 bar

Gear Shift Assistant

- with shift assistant Pro OE

Gear Shift Assistant Pro

Your vehicle is equipped with Gear Shift Assistant Pro, a system originally developed for racing and now adapted for the touring sector. It permits upshifts and downshifts without declutching or closing the throttle in virtually all load and rpm ranges.

Advantages

• 70-80 % of all gearshifts on a trip can be done without using the clutch.
• Less relative movement between rider and passenger because the shift pauses are shorter.
• It is not necessary to close the throttle valve when shifting under acceleration.
• When braking and downshifting (throttle valve closed), engine speed is adjusted by blipping the throttle.
• Shift time is shorter than a gearshift with clutch actuation.

In order for the system to identify a request for a gearshift, the rider has to move the shift lever from its idle position in the desired direction against the force of the spring through a certain "overtravel" at ordinary speed or rapidly and keep the shift lever in this position until the gearshift is completed. It is not necessary to increase the force applied to the gearshift lever while shifting is in progress. Once the gearshift has completed the shift lever has to be fully released before another gearshift with the Pro shift assistant can take place. When shifting gears with the Gear Shift Assistant Pro, the rider has to keep load state (throttle twistgrip position) constant before and during the gearshift. A change in the position of the throttle twistgrip during a gearshift can cause the function to abort and/or lead to a missed shift. Gear Shift Assistant Pro provides no assistance for the gearshift if the rider declutches.

Downshifting

• Downshifting is assisted until maximum rpm for the target gear to be selected is reached.

  This prevents over-revving.

Maximum engine speed

• max 9000 min-1

Upshifting

• Upshifting is assisted until idle rpm for the target gear to be selected is reached.
• This prevents the engine from dropping below idle speed.

Idle speed

• 1250+-50 min-1 (Engine at regular operating temperature)

Adaptive Headlight

- with adaptive head light OE

Function

In addition to the bulbs for low beam, high beam and daytime riding light, or side light, the headlight has two separate LED elements complete with their own reflectors. The LED elements are activated as a function of bank angle in addition to the low-beam headlight, enabling the headlight to illuminate the inside of the bend as the motorcycle banks for cornering. The adaptive cornering headlight is optimised for bank angles up to 25 º.

The adaptive cornering headlight is activated under the following conditions:

• Bank angle is more than 10 º.
• Speed is higher than 10 km/h.
• The low-beam headlight is switched on.

See also: