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Antilock Braking System is now standard on cars, and is an increasingly available option on bikes.
There is no consensus that ABS works on bikes, and no real proof that it reduces crashes. But there is a lot of persuasive evidence.
ABS in Studies
Maids, for example, flubbed the chance to make a definitive finding on ABS. They discovered that bikes with ABS seemed to be under-represented in the crash numbers, but they discarded these data because they made a mistake in their control group recruitment. (This might be a good opportunity for a masters student to make a thesis, as the control group issue affected only the German part of the study, the rest of the data might be salvaged, and Maids is willing to share their database).
Promocycle of Montreal did some nice studies on braking, finding that ABS, under ideal conditions, added about one-tenth of a negative G to the average deceleration force of about three-quarters of a negative G. That's about a 15% bonus in stopping power, and ABS's real advantage is when the surface is wet or slippery, where you'd expect the benefit to be greater. Our calculations suggest that the average rider can emergency-stop from 60 MPH in 3.77 seconds (4.15 without ABS) or 193 feet versus 210 without ABS - that's a ten percent benefit that might save your life. Again, that's in perfect conditions, in the real world you'd expect much better.
The IIRS, Insurance Institute for Highway Safety, published a report that suggests an improvement in crash exposure of 38 percent. Isssues here include the fact that they monitored only a few mostly Japanese models, which generally have a higher rate of applying control changes than Beemers, so the ABS might not have been average in performance. Also, their increased helmet use might indicate that the ABS riders had a safer attitude. Or risk homeostasis might actually make the ABS riders more prone to taking more risks. The small sample size, lack of confidence in the statistics and the IIRS's rep for slipshod research also devalue these data.
Here's the Internet BMW Rider's account of Motorcycle Consumer News's tests. They like ABS. Though they note a small disimprovement in braking times in perfect conditions, in the wet ABS performance was brilliant. Stopping distance for the best rider (the track racer) was reduced by a third and the performance of the worst rider improved to be almost as good as the best. Although expert riders could always make the non-ABS bike stop quicker than the ABS bike, this difference was small, and ABS helped the less expert riders in the group stop significantly better. The disadvantage of ABS for the experts goes away quickly when conditions are not optimal. ABS seems like the great equalizer.
Expert Buying Decisions.
The Netherlands police force dropped their ST1300s in 2009 because of negative reports from the UK police, who found a high-speed wobble in their ST1300s over 90 MPH. This might have been due to user error in loading the saddlebags, or perhaps it is an ST design flaw. The Dutch went to Honda Transalps, but plan to dump them in favor of the Yamaha FJR1300 police version in 2010, because the Transalp doesn't have ABS, and the Yamaha does. Yamaha appears to be cleaning up worldwide with its police bike, because it is the ABS bike that's not an ST1300 with its alleged wobble or a Beemer with its heavy dry clutch and alleged maintenance issues.
Stateside, Harley Davidson seems to be selling to more police departments, despite its weak acceleration, partly because of it's recent decision to put ABS on all its 2010 models. They are taking advantage of disarray among the competition and Yamaha's poor police market penetration. This has to be a smart move from Harley.
We are aware of some demos put on by motorcycle manufacturers for police forces. Honda in the UK rode an ST1300 with ABS onto a sand pan at 70 MPH, and BMW have put on similar demos with several inches of water. We don't know what effect demos like this have on buying decisions.
As motorcycle cops are knowledgeable and particular about their rides, we think that police buyers do their homework and are savvy buyers. Their widespread preference for ABS is noted.
ABS and Emergency Braking Skills
We place some emphasis in our BikerED section on skills practice. Emergency braking is one of the important survival skills we like, as does MSF and other bike training organizations, and rightly so. Many bikers perform poorly in crash situations because they don't practice this skill enough. It's not something that you do every day, and like all such skills, it goes away if you don't practice it.
The problem with emergency braking practice is that it is itself dangerous. Maximum braking is achieved by applying both brakes to within an iota of the wheel lock points, for each wheel. Just a little additional pressure over the maximum on either of the brake controls will cause the corresponding wheel to lock. This situation is correctable, with skill and luck, but is itself dangerous, and even if it doesn't cause you to go down, it will make your emergency stop non-optimal. To complicate the matter further, your bike's brake lock points vary with the coefficient of friction of the road surface, which changes in the wet and on poor surfaces. The physics of the situation is lethal, and almost all non-professional riders are guaranteed to perform less than optimally in an emergency stop without ABS.
Here's a summary of the emergency braking problem from Steve Munden. Nicely put.
If you have ABS, emergency stopping becomes simple. You start straightening up the bike, and you jam on both brakes to the max, making sure your handlebars and the bike are straight by the time you stop. Problem solved. The bike and the ABS takes care of the rest. Who wouldn't want that in an emergency situation?
This doesn't mean that riders with ABS can skip quick-stop skills practice. A quick-stop, even with ABS, will only come naturally if you've been practicing.
You can improve your braking performance slightly beyond the ABS braking maximum by manully adjusting the brake control pressure, and Lee Parks insists that when he was testing bikes for Motorcycle Consumer News that he could consistently outperform the Promocycle braking performance, with or without ABS. No doubt, but Lee Parks is a brilliant, highly competitive track rider and the average leisure biker has no hope of attaining his level of virtuosity. The bike brake testing was performed in perfect conditions, which rarely occur on real roads, the rider can do some practice runs, and he knows in advance where he should start braking.
What ABS does
ABS senses wheel rotation multiple times per second and, if the wheel rotation reduces excessively under braking, indicating that locking is imminent, it pulses the brake pressure up to 10 times per second (depending on manufacturer). This prvents lock-up and keeps the wheel rotating.
ABS does nothing at all for wheel instability caused by lateral (sidewards) sliding or excessive acceleration. It is up to the rider to control these factors, and to keep the bike straight and upright during braking.
ABS: worth the price.
We have little doubt that, except for true experts, operating in perfect conditions, most riders in ambient conditions will perform much better in emergency stopping with ABS
The accumulation of evidence looks like ABS does work on bikes, and that it probably saves lives.
We'd like to see ABS available on more models of motorcycles, and perhaps the current cycle crash causation study will include enough ABS-equipped motorcycles in its exposure data to be able to settle the matter for once and for all. We think that if ABS was a proven lifesaver, the operation of the market and the product liability issues would lead to greater availability and reduced costs.
In the meantime, if you are buying a bike, and ABS is an option, we recommend you get it.