What the ECU does, therefore, is employ a much more complex algorithm that also analyses the rate of deceleration of the wheel's rotating speed. The ECU 'knows' how quickly the wheel can decelerate under normal braking, and if the wheel exceeds this known value, then there's a good chance it's about to lock up. The system still analyses both wheel speeds though, which is why you get a warning light if you wheelie an ABS-equipped bike. The computer doesn't know that you just hoisted an almighty half-mile monster-it just sees the front wheel slow down while the rear is still spinning fast, and it gets confused.
Once you have a reasonable control algorithm for the system, the next problem is cycling the hydraulic system on and off quickly enough. You need to be able to open a valve to drop the caliper pressure quickly enough to prevent the wheel locking, yet not so fast that the brakes go off too much. Similarly, you then need a pump unit that can very quickly re-pressurize the fluid to the caliper, without braking too hard. And you need this combined valve and pump setup to operate as quickly as possible, going through several on/off cycles a second. Too slow, and the brakes simply feel as if they've turned off-which is very disconcerting for the rider. But making valves and pumps operate this fast takes a lot of electrical energy and adds weight and size to the componentry, battery and generator.
Conclusion
Should we expect that all high performance bikes will come fitted with an ABS system in years to come? Presently we have the option, because under race conditions the experienced rider can still outperform the computer. That will almost certainly change one day, but for the time being enjoy your options and don't neglect weighing them. For the average street rider, a sportbike equipped with an ABS system could be the difference between crashing or staying safe and upright.
Sportbike ABS
BMW has been at the forefront of ABS development on bikes, and with the launch of its HP2 Sport last year, it claimed to have the first sportbike fitted with ABS.
Sportbikes offer special problems for ABS systems. First of all, they're less able to handle the extra weight and electrical power demands of the systems. Adding twenty pounds to a 375-pound, cutting-edge supersport machine is much more significant than adding twenty pounds to a 600-pound sport-tourer.
But the geometry and tire performance of a supersport bike also provides significant challenges. Basically, locking the front wheel is not the biggest problem when you're braking very hard on a sportbike with sport tires on a dry road. There's enough grip to lift the back wheel off the ground a long time before the front wheel will lock, so stability is the bigger problem.
Honda claims its new Combined-ABS system addresses these problems more effectively. It does this by combining the front and rear brake systems, with a sophisticated ECU controlling the balance of the braking efforts as well as preventing the wheels locking. Stomp hard on the rear brake lever, and the system applies the front brakes - stopping the bike in a controlled, smooth fashion. And if you're hard on the front brakes, the system also applies the rear - adding to the total braking effort and improving stability.
But on Honda's CBR600RR, the new system adds almost twenty pounds to the mass of the bike - making it amongst the heaviest of the 600 supersport class. It also adds a hefty chunk to the price of the bike: it costs $1000 more than the non-ABS version.