Motorcycle Anti-Lock Braking Systems (ABS)
By David Tong
Anti-lock braking systems (ABS) were developed for one simple reason: rapid stopping under challenging traction conditions, while retaining steering control. People who have driven older cars understood that brakes could lock the wheel, which would stop turning, resulting in a skid that could cause a loss of control.
Aircraft were the first vehicles to receive anti-lock braking systems, way back in the late 1920s. These systems and subsequent ones developed through the 1960s were mostly mechanical, and there was little cross-pollination between automobile and aircraft usage until the 1970s.
Bosch and Mercedes-Benz installed an electronic-based system in 1936, which given my respect for German technological prowess, surprises me not. In the early 1970s, both Chrysler and Lincoln offered electronic ABS as options on their luxury cars, the Imperial and the Continental Mark III. By the late 1970s, several Mercedes-Benz cars offered optional ABS and by 1986 all BMW automobiles were equipped with ABS.
Just three short years later, in 1989, BMW installed their ABS-1 system on their K100RS-Special sport touring motorcycle. I owned one and rode it some 50,000 miles. By then, the system had computer control, using a perforated wheel hub sensor to detect brake locking on one front disc and the rear disc. The system was not linked, so the front and rear brakes operated independently.
It was a fairly heavy system at 22 pounds and the cycle time (the speed at which it cycled when detecting a locking wheel) was pretty slow and jerky. However, it was utterly reliable, which from a product liability perspective is important for a manufacturer offering it for the first time on a motorcycle.
I tested it several times to check its function by stopping from speeds up to about 80 MPH. ABS is an all or nothing rider input; you simply nail the brakes and the electronics do the rest. There are old videos still online showing two BMWs, one with and one without ABS, both supported by outrigger frames and wheels, hitting their brakes hard in an area doused with water.
The standard Brembo brake calipers of the era are nothing like the four or six piston units of today in either speed or power, but when you saw the non-ABS bike veer onto the outrigger wheel out of control, and watched the ABS bike come to a reassuring upright halt, you got the message.
Just five years later, BMW's ABS-II system debuted on their R-1100 series flat twins as optional equipment. This had four piston Brembos and a far faster cycle time. The system weighed less than half of the earlier version and was neatly tucked out of sight.
The rest of the motorcycle world watched and waited until the Japanese manufacturers adopted ABS in the early 1990s. In the late 1990s, both Ducati and Triumph adopted ABS.
The systems on motorcycles have conceptually developed in parallel with automotive systems. ABS computers have been enhanced to provide anti-skid during hard acceleration and cornering. Often called traction control systems (TCS), these adaptations of the original braking assistance now nearly eliminate traction issues on motorcycles so equipped, even when leaned over. I need not tell you what a great safety boon this is.
The last BMW I owned, a 2002 R1100S sport bike, had a further development of ABS with electronic power braking assist, while retaining independent front and rear wheel brake function. This system removed nearly all feel at either lever and was touchy, feeling like an over-boosted set of disc brakes on older cars. If there was an electrical interruption or the ignition was switched off, the system would not allow normal braking. I did not like this system at all.
BMW played with similar systems on their touring bikes and refined them, using linked brakes. However, the company has since backtracked somewhat. In some models they have removed the front/rear brake linking. This is good, because most experienced motorcyclists want their brakes to operate independently. Other companies, mostly Honda, have continued with the development of more seamless integration of front/rear braking force distribution.
BMW broke into the police motorcycle market with ABS equipped bikes and law enforcement agencies world-wide saw the advantages, especially on the rainy roads of the Pacific Northwest. They held a marketing advantage for nearly a decade, before Honda's ST1300 and Harley-Davidson's Electra-Glide police bikes started to sell in any numbers to police agencies.
Currently, one of the most popular police motorcycles is the Kawasaki Concours 1400 sport-tourer and, of course, it has a full suite of traction management controls. Agencies started to require it in all requests for bid, because of the additional safety factor.
BMW was also the first to offer racing quality ABS and TCS, on its S1000RR racing motorcycle. This allows an expert rider to brake to the threshold of traction before it engages. It allows maximum acceleration, prevents most wheelies and allows some two-wheel drifting to use all of the available traction.
Several of BMW's huge "dual-purpose" GS bikes have an ABS off switch. Many experienced dirt riders want to manage braking and traction, because of the far different traction issues on dirt.
With the exception of the electric-assisted brakes on my last Beemer, I consider ABS an unmitigated plus. After a long day of riding, one's reactions are dulled by fatigue and here in Oregon, as well as elsewhere, wildlife or domestic animals can make a sudden appearance. ABS is a godsend in such circumstances. It can also save your bacon when you roll up to a greasy intersection's stoplight, preventing you from falling over. While I have not ridden a bike with an integrated TCS, I suspect that it will also help keep a rider off the ground.
One caveat: when I owned ABS equipped bikes, I ALWAYS let the dealer maintain the system, even though I would do all the other standard maintenance myself. This way, the ABS (Hall effect) sensors that detect the near instantaneous wheel stoppage are gapped properly. In addition, the biannual brake fluid replacement can be properly pumped to remove air bubbles or contaminants in the system that could affect brake piston or check valve function. Do this for your own peace of mind.
The best thing is, if you are a skilled rider and have practiced hard braking, you can still use your brakes to the traction threshold manually, should the ABS system fail for any reason. Technology can be a great thing!
Copyright 2015 by David Tong and/or chuckhawks.com. All rights reserved.