Breaking down the most common rider assistance functions.
Words: Matthew Shields
No matter what type of new motorcycle you are looking at these days, there will almost certainly be some type of rider aid that will change characteristics of the motorcycle or help you out when things go wrong. In this latest Q&A, we take a look at the most common rider assistance functions and breakdown how they work and how they can benefit you.
Q: What is a mode selector and how does it work?
A: Each manufacturer has an acronym or catchy name for what is essentially a switch that changes engine characteristics. Some machines have a system that allows you to switch between engine maps and alter spark timing and fuel delivery to change the speed and amount of power that is delivered. Other systems that have a ride-by-wire throttle change the relationship between the twist grip and the injectors so while you are doing the same thing at the handlebar, the power comes on differently. Those systems also allow power output to be moderated and can work in combination with other electronic systems like suspension and ABS to create a very different feeling machine all-round at the tap of a button.
Q: I’ve heard of a slipper clutch, but what is an assist and slipper clutch?
A: As its name suggests, the assist and slipper clutch aids riders with a lighter clutch pull and ensures the rear wheel doesn’t lock on deceleration. A&S systems in general use two types of cams (an assist cam and a slipper cam) to either drive the clutch hub and operating plate together or apart. Under normal operation, the assist cam functions as a self-servo mechanism, pulling the clutch hub and operating plate together to compress the clutch plates. This allows the total clutch spring load to be reduced, which translates to a lighter clutch lever feel when operating the clutch. When excessive engine braking occurs – as a result of quick or accidental downshifts – the slipper cam comes into play, forcing the clutch hub and operating plate apart. This relieves pressure on the clutch plates to reduce back-torque and help prevent the rear tyre from hopping and skidding.
Q: How is a quick-shifter of benefit to me on the road?
A: Although quick-shifters are designed to maximise acceleration on the race track, when used on road bikes they can give smooth, clutch-less gear changes which can be a godsend on a tight twisty road or in tricky riding conditions. Some systems operate up and down through the gearbox, but up-only tends to be the most common system you find on production bikes at present. The systems tend to operate by cutting the ECU when a gear change is detected and on down changes an auto throttle blip to facilitate a smooth change is present.
Q: How does ABS work and are all systems the same?
A: On a motorcycle fitted with an anti-lock braking system, the ABS control unit constantly monitors the speed of the wheels using wheel-speed sensors. If a wheel threatens to lock during hard braking or on slippery roads, the ABS regulates the braking pressure in a targeted manner, thereby ensuring optimum braking. In this way, the driving stability and manoeuvrability of the motorcycle is maintained, even where there are adverse riding conditions such as sand, gravel or water. Not every system is the same and, in general, vary through the amount of sensors they use. The most basic systems purely measure the difference between front and rear wheel speed, while the most advanced use an Inertial Measurement Unit (IMU) and can distribute brake pressure between front and rear wheels.
Q: How does traction control work?
A: Not every system is the same and, at the end of the day, it all comes down to the type and number of sensors a bike uses to detect rear wheel spin and intervene. The more basic systems use wheel speed sensors to monitor front and rear wheel speed and when it detects wheel spin, engine power is reduced to allow rear wheel grip to be regained. To reduce the engine power, systems either retard the ignition timing, skip fuel injection or electronically adjust the throttle if it is fitted with a RBW system. The more advanced systems, however, rely on separate ECUs with an accelerometer that measure lean angle and acceleration or multiple accelerometers and gyroscopes to give a more complete picture of what the bike is doing.
Q: We’ve heard about motorcycle stability control. How is this different to ABS and traction control?
A: MSC is in essence a combination of ABS and traction control with the primary objective of keeping the motorcycle safely on the road. The system constantly measures all key motorcycle data – wheel speed, lean angle, pitch angle, acceleration, braking pressure and many more. This data allows the system to recognise critical situations and intervene, thereby preventing the wheels from locking when braking, stopping the wheels spinning, mitigating the rear wheel from lifting, as well as making sure that the front wheel stays on the ground.