You've seen the fancy videos, the technical breakdown info-graphics and read the first person accounts about how completely awesome APRC is. But if you're not a racer, why should you care? Technology from racing has been improving the street riding experience for decades. In the 1960s racing technology brought us powerful four cylinder engines with a ton of reliable smooth power. In the 70s we got disc brakes, providing linear, reliable stopping force. In the 80s we got aluminum frames and the addition of fairings (the 80s were kind of awesome for motorcycles). In the 90s we got good tires and ever improving suspension. The next step in this evolution? Electronic traction control, or APRC. When you're riding on the street, you sometimes might be able to catch or hold a slide, and when you do, you feel like a superhero. Riding away from that corner, you breath a sigh of relief because you didn't highside. How about having that feeling in every corner, just for fun? You can with APRC.
The principles of traction control are pretty simple: Monitor wheel speeds, gear selection, RPM, throttle position, lean angle and crankshaft acceleration to determine whether or not the rear wheel has traction and if not, reduce power until it does. Collecting and processing the data isn't hard. The trick is in deciding how to handle a loss of traction.
APRC is the blanket name given to all the electronic systems on the RSV4. It includes traction, wheelie and launch control, as well as the quick shifter. Launch control is frankly too loud (and likely too hard on the clutch) to use on the street. Sure, it'll work just fine, but every cop within a 6 block radius will know exactly what you're up to. The quick-shifter works so seamlessly that you forget about it after just a few minutes. Why don't all sportsbikes come with this feature? Wheelie control takes some stress out of riding a powerful bike, but I turn it down to it's lowest setting and shift up when the front wheel gets more than a foot off the ground. It's still there to catch you if you make a mistake though.
After spending some time with APRC's traction control, I think I've figured out how it works. The secret is in the tires. Motorcycle tires are fairly complicated pieces of technology. Think about this for a minute: Just how does a tire work leaned over at 55º? Not many people can give you a straight answer to that question. Things are simple when a tire is perpendicular to the road. There's only one diameter and force is applied relatively uniformly. No one but drag racers seem to have trouble with straight-line acceleration though.
When a tire is leaned over, its circumference is not constant. Measure around the middle of the tire, then around the very edge. There's a huge difference in size.
Imagine the contact patch being forced into the road surface by the your and the bike's weight and how the application of torque effects both weight distribution and traction. The tire will squish and deform and only a very small part of it will actually match speed with the road. You see, even though the tire flattens out where it contacts the road, those different circumferences still apply. Only one is going to match up with road speed. The rest will all have to slip in proportion to how much larger or smaller they are.
None of this is static either. On corner entry, almost all of the weight is on the front wheel. Traction control can't save you from a low-side (and neither can ABS if you ask the impossible). As you trail off the brakes and pull the bike down to maximum lean, the rear tire starts to work. It's not until you apply power though that it really matters.
Someone like Kenny Roberts can feel intuitively how the rear tire is interacting with the road. Knowledge of all those difference circumferences, that one small point of traction, tire flex and grip are what give the confidence to apply power and even initiate and hold a slide. Most people can't just hop on a bike and feel that though. This is where APRC comes in.
APRC understands the rear tire. It knows about the changing circumferences and it knows that there's really only one very tiny point that's matching speed with the road. It knows how far the throttle is open and how much power is being produced. And it knows (because you told it when you selected a setting from 1-8) how aggressive you are and just how comfortable you are handling a sliding motorcycle.
Best of all, it can make very fine changes and do it very smoothly. When it works, it feels like you're controlling the interaction between the tire and the road surface with your thoughts. You see the corner exit, smoothly open the throttle all the way and adjust your steering as you feel the tire start to slip as APRC moves accelerates the tire and moves it's point of traction out to the very edge. It's good enough that if you want, you can even take it past the edge and spin the whole tire, just a bit. You still have to be good enough to know what you want, but APRC makes it easy. APRC allows you to learn about traction with significantly less risk and at an accelerated pace
The answer to the age old question of how to apply maximum power with maximum control is one that motorcycle manufactures will always be asking, but for the time being, APRC is the best answer we have.