Another challenge in downshifting is that it's typically combined with braking and often while hung-off in preparation for a corner. Stay smooth and relaxed on the controls and use your inner thigh, back and abdominal muscles to hold your body in position while allowing your arms to stay somewhat relaxed and your hands light on the bars.
Sliding your right hand to the far inside of the handgrip puts your first two fingers on the least sensitive portion of the brake lever and, with a bit of inward pressure, allows the web of the hand some twistgrip traction as well. Leave your two outer fingers on the grip to control the throttle; all it takes is a slight blip to bring the revs up.
Reviewing video, it's surprising how many riders unintentionally lift their foot off the peg and stomp down on the shifter like they're crushing cockroaches.
Proper technique leaves the foot on the peg, rotating at the ankle and toeing the shift lever smoothly into gear. Obviously, the shift-lever height should be adjusted to allow this with the least amount of thought and effort.
Presumably, we've all been downshifting since the time we learned to ride, and when performed at the most basic level, it isn't too difficult. But proper downshifting—matching engine rpm to the lower gear in order to avoid rear wheelhop caused by the wheel being forced to work against the disparity in engine and transmission ratio/road speeds—is one of the more difficult riding skills to master. Matching revs becomes important when you're braking hard enough to transfer a significant portion of the bike and rider's combined mass to the front tire, leaving the rear-tire contact patch lightly loaded or perhaps just skimming the ground. At this point, a conventional click-the-next-lower-gear-and-release-the-clutch downshift will likely add enough engine braking (using the engine's compression to slow wheel speed) to cause the rear tire to skip, chatter or slew side-to-side. Compromised control is the last thing you want to experience under heavy braking, and that's when matching revs becomes a priority.
I know what some of you are thinking: “Doesn't my bike's slipper clutch do that for me?” True, the slipper clutch does significantly reduce the amount of engine braking that reaches the rear wheel, but it doesn't eliminate it entirely. In fact, I've been surprised at the variation found in the amount of back-torque (the force of the engine braking) allowed by the slipper clutches in most of the latest sportbikes. And not every bike comes equipped with a slipper clutch; Honda's SR-comparo-winning CBR600RR, for instance, doesn't have one. Matching revs on downshifts is definitely something you should learn, regardless of the type of clutch your bike has. It allows you to get your downshifting done as early in the braking zone as your gear ratios allow, to take advantage of engine braking and permit more time to prepare for the corner and accurately judge your entrance speed.
The trick is that several critical control inputs must be synchronized in overlapping sequence, with the right hand performing double duty maintaining constant front brake pressure while increasing engine rpm by “blipping” (momentarily opening) the throttle to match the higher rpm required in the lower gear. It's challenging, but thankfully the skills can be broken down and learned in digestible bites then later combined.
There are two philosophical camps on how to match revs: the “blippers” and the “slippers.” I'm firmly in the first camp, but we'll discuss both. Both techniques have strong proponents, and I've taught alongside notable racers who use either one: The blipper is former World 500 Grand Prix Champion Kevin Schwantz, and the slipper is two-time AMA Champ Jason Pridmore. There isn't so much a right or wrong here; it's more a matter of choosing which works best for you.
When you're learning either technique, it's best to learn it in a controlled environment, at moderate speed and without the brakes to free you of distractions. This can be a parking lot or a straight section of lightly traveled road. Get accustomed to the technique of throttle blipping on downshifts, then gradually add braking and corners to the equation.
The main challenge of the throttle-blipping technique is maintaining consistent brake-lever pressure. The amount of throttle rotation required is very small and quick, which allows you to slide the center segment of your fingers smoothly over the lever without affecting brake-lever pressure. Schwantz suggests lifting your wrist slightly while closing the throttle, then pushing downward with your now-vertical thumb to blip. Another method is to try flicking your wrist downward slightly. Either way, the increase in rpm you need to match revs varies from as much as 2000 rpm to perhaps less than 1000, depending on your bike's transmission ratios and the gear change you're making (more in the lower gears and less in the upper range), so again, the amount of actual throttle movement is relatively small.
Don't be too easily discouraged; you might miss it the first 10 attempts, but vary the technique each time and you'll hit it right eventually. Soon you'll be getting it right more than wrong, and it will quickly become second nature. I find it's better to add a few hundred rpm more than needed rather than risk too few, and as I steadily press down on the shifter it literally slips into gear as the revs fall into the proper rpm range, matching the speed of the transmission shafts. On the clutch side, I try to use only my first two fingers as a reminder that the lever need only travel less than an inch (if you were to measure the movement at the end of the clutch lever) to engage and disengage the clutch. The movement itself is best done smoothly yet quickly, perhaps half of a “one-one thousand” count.
If you hesitate too long with the clutch in, the revs can drop too low before the clutch is released, negating the effect of the throttle blip. The whole purpose of the blip is to maximize the amount of time the clutch is out and take advantage of engine braking. Let the clutch out between each shift so that, in the event of hitting a false neutral between gears, you become aware of it as soon as it happens.
After learning the throttle-blip technique, it will eventually become so natural that you'll be performing it on a subconscious level. The beauty of the technique is that it allows you to devote your full concentration to the front brake and sensing front-tire traction, crucial components of a controlled corner entry.
The slip-downshift technique does away with the throttle blip, and instead depends on slowly releasing the clutch to introduce the engine braking to the rear wheel as gradually and smoothly as possible. This technique requires even more physical dexterity and concentration, though, because you must be very careful in how you release the clutch while simultaneously dealing with braking forces (the lack of engine braking increases the amount of braking force required) and performing steering inputs; you must release it slowly enough to avoid upsetting rear-tire traction, yet you must do it quickly enough to avoid trailing the clutch to the point that it intrudes upon your corner entry. Actually, slip-downshift proponents such as Aaron Yates often release the clutch late enough to intentionally slide the back end out entering corners, in effect getting the bike turned earlier by “backin' 'er in.” While sliding the rear tire into the corner may look cool and spectacular, it takes a lot of skill to make the transition between sliding the rear tire to slow/steer the bike and using it to propel the motorcycle while leaned over on pavement. Regardless, nearly all pro racers agree that in the majority of cornering situations, sliding the back end into the corner actually compromises entry speed, because that transition takes too much effort and time.
To decide for yourself which technique to use, I suggest trying each one, giving yourself enough time to adjust and even have a friend watch (or perhaps videotape you) and offer a critique. Better yet, attend schools that offer each technique. My advice is to apply yourself and learn whatever technique is being taught at the school, and then decide later which version of matching revs works best for you.