Motorcycle ABS (Anti Lock Braking System) explained!

medha@Throttle|Updated: September 13, 2016 13:05

With the launch of new and international bikes, the term ABS is getting quite synonymous with the fast bikes we all have been looking forward to own.  So what exactly is ABS?  What does single and dual channel mean?  How does it work?  Well lets take you all around to know what ABS actually is and how life saving is this piece of technology for us bikers in the every changing road conditions that are most of the times not in favor of us.



What is ABS?

ABS means Anti Lock Braking System.  It is an automobile safety system that allows the wheels on a motor vehicle to maintain tractive contact with the road surface according to rider inputs while braking, preventing the wheels from locking up (ceasing rotation) and avoiding uncontrolled skidding.  It is an automated system that uses the principles of threshold braking and cadence braking which were practiced by skillful riders with previous generation braking systems.  It does this at a much faster rate and with better control than a rider could manage manually.


How does ABS work?

Wheel speed sensors mounted on front and rear wheel, constantly measure the rotational speed of each wheel and deliver this information to an Electronic Control Unit (ECU).  The ECU detects on the one hand if the deceleration of one wheel exceeds a fixed threshold and on the other hand whether the brake slip, calculated based on information of both wheels, rises above a certain percentage and enters an unstable zone.  These are indicators for a high possibility of a locking wheel.  To countermeasure these irregularities, the ECU signals the hydraulic unit to hold or to release pressure.  After signals show the return to the stable zone, pressure is increased again.  Past models used a piston for the control of the fluid pressure.  Most recent models regulate the pressure by rapidly opening and closing solenoid valves.  

While the basic principle and architecture has been carried over from passenger car ABS, typical motorcycle characteristics have to be considered during the development and application processes.  One characteristic is the change of the dynamic wheel load during braking.  Compared to cars, the wheel load changes are more drastic, which can lead to a wheel lift up and a fall over.  This can be intensified by a soft suspension.  Some systems are equipped with a rear wheel lift off mitigation functionality.  When the indicators of a possible rear lift off are detected, the system releases brake pressure on the front wheel to counter this behavior.  Another difference is that in case of the motorcycle the front wheel is much more important for stability than the rear wheel.



Single or Multi Channel?  Which one to choose?

Based on the entire ABS setup and functioning of it, the system is divided into one channel or multiple channel ABS.  As far as single channel ABS in motorcycles is concerned, it is dedicated to any one of the wheels and generally it is the front wheel because for effective braking the front brakes are considered more important.  According to Bosch, in its single channel "ABS Light" the wheel speed sensor present at the rear wheel of the motorbike plays very important role.  Although, there is no effective ABS present on the rear wheel in such kind of single channel setup but by the information obtained from the sensor present at the rear wheel the ABS modulates the braking of the front wheel to prevent the "Rear Wheel Lift-off".  

This situation can be occurred while applying front brakes forcefully as well as while rapidly down shifting the gears due to Engine Braking.  Normally such system that assists ABS to prevent the rear wheel lift off is known as RLP (Rear Wheel Lift-Off Protection).  The only thing is that the single channel ABS systems (As used in Pulsar RS200) is useful in keeping the bike cost low in markets like India.  But its always a safer bet to have a multi channel ABS system on the bike so that you even out all the negative possibilities and ride with complete peace of mind.