CONTROLLING SLIDES AND TANK-SLAPPERS:
MIND OVER MATTER

Things are not always as they seem.
--Phaedrus

Occasionally, a rider may find himself deviating from the standard advice of the experts. Perhaps he is on a learning curve and is "pushing the edge of his riding envelope," or maybe an unusual hazard situation has presented itself. As they say about every type of motoring, riding is composed of hours of boredom punctuated with moments of sheer terror. There is not much that is more "exciting" than having one's motorcycle unexpectedly pointed sideways while traveling down a road at cruising speed. Especially when there is oncoming traffic and/or the edge of the road is rapidly approaching.

What do you do in such a situation? Panic and make the situation even worse? Accept your fate and "go into the light?" Follow the advice of government bureaucrats—bureaucrats who will profit from your crash by writing you a ticket or arresting you and throwing you in jail? The same bureaucrats who censored countersteering from you?

Or will you trust your brain's own genius for learning and billions of years of accumulated survival instinct? The human brain can process 12 trillion bits of information per second—millions of times faster than a Pentium computer chip. Trusting the government's (mis)information is like installing a computer virus—even the best computer will fail. Garbage in, garbage out. Feed your brain accurate knowledge, and it will reward you with accurate reactions if and when you ever need them.

The government advises riders to always obey its ridiculous (and usually illegal and dangerously low) speed limits, and predicts that this is the cure for all crashes. However, it is still possible to instantly lose control when driving under any government speed limit, especially when riding in rainy conditions. When a rider disobeys expert advice, and reverts back to novice bad habits when under pressure, he has placed himself in jeopardy of experiencing an unusual handling dynamic—or given himself an opportunity to discover the wonders of motorcycle physics, depending upon how one wants to look at it.

Once again, never use the rear brake when stopping in a straight line on dry pavement. This will give a rider maximum stopping performance with maximum stability. As the front tire approaches its traction limit, tire squeal ought to be easily heard (indicating maximum braking performance), with no loss of stability. If the front tire locks completely, the rear wheel's gyro force will hold the bike vertical long enough for the rider to release the front brake just enough to get the tire spinning again. This is how computerized ABS systems work, but an educated human can do it better and more accurately—that's why thoroughbred race vehicles don't use ABS.

On wet pavement, both brakes will need to be used if medium straight-line braking is required (heavy braking is impossible). If either tire locks up, just ease up pressure on that particular brake until the tire is spinning again.

When cornering, things can get very interesting when a tire locks up under braking. Perhaps a rider who usually avoids riding in the rain finds himself riding his favorite road on wet pavement. An entirely different riding style is required, and all cornering and braking speeds are lowered. Even his line is different, since the center oil strip offers little or no grip for sudden braking or cornering. Since the speed at which a particular tire begins to aquaplane on a wet road is directly related to the weight of the vehicle, motorcycles are at a slight disadvantage due to their lighter weight. Perhaps you have noticed how professional tractor trailer drivers appear to have more confidence in the rain than amateur four-wheeler drivers. This is not necessarily due to higher skill level, since a fully loaded trailer provides maximum squeegee action for its tires, and the forward tires sweep the water off the road for the rearward tires. At any rate, a motorcycle rider must be aware that his two-wheeled vehicle might not have as much traction reserve in the wet as do other vehicles on the highway—he is operating closer to his traction limit.

Locking a rear brake while cornering gives a rider the "thrill" of the rear tire trying to slide out from under him. Perhaps a rider decides he has miscalculated his speed entering a wet corner, and chooses to violate the rule requiring increasing throttle while cornering. The unloaded rear tire cannot maintain cornering traction while braking, too. No need to panic—release pressure on the brake slightly—regain traction—look forward to the next corner. Learn from it and go on.

Locking a front brake while cornering gives a rider even more of a "thrill." What happens next can scare an unwary rider into a brain-locking panic. The government calls this problem a "wobble" in its license test booklet, and blames it on mechanical defects, ignoring the fact that this phenomenon is a normal function of motorcycle physics. Experienced riders and racers refer to it as "head shake," or the more extreme version of "tank-slapper," since the handlebars (and front wheel) is rapidly turning back-and-forth at cruising speed. It's just like a castor wheel of a grocery store shopping cart that can't find its grip and oscillates in an annoying manner. Sooner or later a high-mileage rider may eventually get to experience head shake, even if he never exceeds a speed limit. Either he can learn from it or he can quit riding. The government does not allow for "wobble" while braking, advising riders it can only occur under accelleration.

If and when a tank-slapper happens, don't let go of the handlebars (good luck), release the front brake lever (maybe the bike is trying to tell you something), and try to keep your feet on the pegs (good luck)--or at least your butt on the seat. The spinning rear tire should keep the bike at a constant lean angle while all this is going on, and the shaking should stop almost immediately, returning you to peaceful motoring as if nothing had happened at all. Gather it up and get ready for the next curve. One more reason to give yourself extra distance when following another vehicle.

Braking-while-cornering is more likely to produce a violent tank-slapper, since the forks are more compressed and cannot handle any large bumps without overloading the tire, while acceleration-while-cornering produces a milder version of head shake, due to underloading of the tire. Either keep an eye on it and continue to accellerate (it will stop when the corner is over) or back out of the throttle a little if you want to. Aggressive countersteering mid-turn to increase lean angle suddenly (a violation of The Rules) can contribute to head shake. Holding tight on the handlebars (attempting to, anyway) and stiff-arming them will surely shake a rider off the bike and/or cause a crash. Just like in normal cornering, it is necessary to hold on loosely in order to remain in control. Wet conditions can produce head shake at relatively low speeds.

In a hypothetical example, imagine a rider in typical wet-weather conditions, cruising along with traffic flow, well below the posted speed limit. He is following a tractor-trailer rig, maintaining an overly conservative distance just to be extra safe. While traveling downhill around a gentle curve, approaching a busy Interstate intersection, he observes the truck's rear brakes lock up. The rider is amazed that tires could smoke that much on a wet road surface. He also notices that the rapidly approaching rear bumper of the trailer looks even less user friendly to motorcycles than to automobiles (500 drivers are decapitated annually in such "underride" collisions). The concerned rider decides to slow down, just in case the truck decides to stop completely. FORK COMPRESSED OVERLOAD FROM BUMP However, he is understandably distracted by the truck's smoking tires, and he accidentally allows his front brake to lock. This locked front tire creates a violent tank-slapper, since the lockup occurred while negotiating a curve. Due to self-countersteering and gyroscopic precession, the bike is also leaning rapidly left-right-left as the handlebars are whipping back and forth. The bucking bike is trying to throw him off into the path of oncoming traffic. An instant dose of adrenaline kicks his heart and brain into overdrive. Time slows down as his thinking speeds up.

Fortunately, this rider has studied his motorcycle riding fundamentals, preventing deadly panic. He knows he has to release the front brake pressure and get that front tire spinning again, even while the gap to the next vehicle is closing rapidly. This strategy achieves instant success, and the motorcycle stabilizes perfectly. Since the rider had been generous with his following distance, there is no collision, and he continues to his destination.

Thanks to education, the rider is not hospitalized (or mortuaryized). Since the rider understands motorcycle physics, he is not tempted to give up his love of riding after this one heart-racing incident. He does revue his riding textbooks, to see if he can learn anything from this lesson. He looks up the chapters on head shake and braking to gain more understanding of his experience. When he returns to the scene of his fright, he discovers a dip in the pavement that allowed the front tire to lock-up as he target-fixated on the truck's smoking tires. The author—I mean the hypothetical rider—gained more insight of motorcycles and more confidence in his riding abilities after his brush with a real-life tank-slapper. Going to the edge and knowing how to return in one piece is the fundamental premise of wreckless riding (and driving).

Riding in the rain can be just as much fun as riding in sunshine, provided the rider is prepared both with rain-proof clothing (and fog-proof helmet) and educated on recovery from slides and shakes. Steering stabilizers can be installed to dampen head shake (Dennis Kirk, $150), but cannot eliminate it completely in all situations. The steeper a bike's front fork angle, the more likely it will experience head shake (although any bike can do it in the "right" circumstances)NOT??? . This is a normal trade-off for sport bikes that are designed for quick steering and good cornering performance. Be ready for it by programming your brain with emergency instructions. One does not have to speed or compete on a racetrack to experience sudden head shake.

Motorcycles can slide just like cars. Whether the slide is under the rider's control or not is entirely up to the rider. In racing, The Zone refers to controlled riding the tires at the edge of their performance envelope. This means that the tires are usually sliding in every turn. On asphalt, the front tire is usually allowed to slide while entering the corner, when the tire is slightly overloaded from braking forces. In the middle of the corner, both tires are allowed to slide together since both have equal cornering forces. At the exit of the corner, the rear wheel is allowed to slide under accelleration. The point of this information is to let a rider know that a small slide is nothing to panic over. No drastic steering, braking or throttle actions are required or wanted. In fact, because of the reverse action of countersteering, trying to steer a sliding bike like a sliding car can backfire on the unwary rider. The bike will try to correct itself, thanks to its self-steering caster effect, as long as the rider does not interfere. At these small levels of sliding, the tires actually stick to the road even better, allowing quicker braking, sharper cornering and stronger accelleration.

This is where "knee-dragging" becomes useful. Any bumps or ripples in the road's pavement can start a slide. As a safety precaution, keeping a knee close to the pavement in readiness for a bump can help a rider catch a slide before it turns into a crash. Like training wheels on a child's first bicycle, a rider's knees can ensure that a motorcycle won't be able to tip over when it slides a little bit. Since the rear wheel is spinning and producing gyroscopic stability, a slide won't make the bike instantly fall over. The bike will also slow down when sliding, allowing the tires to grip again. Obviously, "knee sliders" are required to perform this safety action without grinding one's knee into a bloody pulp. Disposable sliders can either be part of a leather suit or can be purchased to fit over any pair of pants. Even if the bike never slides, keeping a knee down just-in-case can give a rider a useful margin of safety.

While hanging off will give a rider an improved margin of safety in ground clearance, knee dragging is the only way to control a mid-corner slide. These techniques are useful even at speeds below the government's speed limits, whether the road is wet or dry. It is intelligent for a rider to learn how far his bike can safely lean, in preparation for the day when he might require that experience in an emergency situation. It is amazing how far a modern bike can lean over, and there is no way to learn this without gradually sneaking up on it. Learning a bike's lean-angle limit in a controlled environment can reduce a rider's panic should he accidentally find himself in need of a tighter cornering radius. Note that hanging off does not have any effect on increasing the tires' grip (which is limited to about 1.0g, since there is no aerodynamic downforce). Hanging off only increases the available ground clearance at a given speed for a given corner.

Photos 35 mph in 40 zone: (1) sit up, (2) hang off, (3) knee slide.
Lean angle is also affected by bike weight and rider weight. The heavier a bike and rider are, the more lean angle is required to go through a given corner at a given speed. Center of gravity height also affects lean angle: the higher the center of gravity ("C.G"), the more lean angle required (a heavy rider will raise the C.G.). That's why 125cc race bikes are faster through a corner than a 500cc race bike that has wider tires and three times the horsepower (and why racers learn on the smaller, faster-cornering bikes before moving to bikes with higher straightaway speeds). That's why 600cc street bikes can lap a racetrack in less time ("faster") than a 1,000cc street bike that costs thousands of dollars more. That's also why factory race teams only employ featherweight riders. Weight reduction is the same as adding horsepower, widening the tires and strengthening the front brake, all at the same time. Bigger is definitely not better when trying to cut corners. This quirk can catch a rider off guard if he is not aware of it, especially if he is on a big-cc (heavy) bike and is trying to follow a smaller (lighter) bike, or try to follow one that is a newer version that has weighs less. If a rider is tries to follow an identical bike but the leading rider weighs significantly less (such as a female), the heavier rider ought to recognize and respect his lean-angle limitations.

Although there is no law against leaning a bike over in a curve, police routinely arrest riders for dragging a knee or hanging off. This is about as unintelligent as profiling riders for being intelligent enough to wear safety pads and leathers. "Reckless driving" (one rider) or "drag racing" (two or more riders) is the alleged crime. Any rider faced with such an arrest situation would do well to gently explain the facts of life to the driving-instructor wanna-be. Of course, to speak to a cop makes a citizen "guilty" of "contempt of cop" and faces the threat of "resisting arrest". (ALL traffic citations are technically an arrest, which the citation only prevents going to jail while awaiting arraignment in court.) So maybe it's best you allow the cop to remain stupid and ignorant.

Wheelies are another accidental phenomenon that can catch a rider unawares. Many modern bikes have such excellent power-to-weight ratios that wheelies can literally occur at any time and at any speed. The downward dip of the front forks between gear changes or throttle changes can bounce the front end upward. A sudden twist of throttle at the same moment can catapult the front wheel skyward. Accidentally popping the clutch from a standing start can also create a more violent style of wheelie. Fortunately, rear-wheel gyroscopic stability keeps everything going in a straight line, so long as the rider doesn't panic and hold a death-grip on the throttle at max-power, flipping the bike on its back. Reducing the throttle when only sky is visible should keep things under control, bringing the errant tire back to earth without too much shock. A rider stopped by police for wheeliing might solicit sympathy for being forced to travel on such a monstrous machine. Performance Bikes magazine published a reader's letter to the editor (June 1999) which declared it was actually possible to avoid a ticket or arrest for a 120-mph wheelie. Being deselected for selective enforcement would depend on a rider remaining cool under pressure, which a rider is obviously capable of if he can ride a wheelie at 120 mph. (Wheelies are the motorcycle equivalent to playing a with a music-making machine--both can result in criminal citation or arrest when done without a government permit anywhere near "government" roadways.)

Burn outs can also be accidental or intentional, due to many bikes' strong power-to-weight ratio. Grabbing the front brake while standing off the seat and dumping the clutch at full throttle is useful for drag racers at the track (to heat the tire and make it grip better), or for street riders who enjoy buying overpriced new tires. Accidental wheel-spin is not uncommon in the rain, and is best handled by reducing the throttle slightly. Chopping the throttle is rarely a wise move on a motorbike.

Good luck.

Return to Home Page

Chapter 1. Let's Look at Some Data

Chapter 2. Risk Management

Chapter 3. Two Wheeled Physics

Chapter 4. Countersteering: Cornering Techniques

Chapter 5. Gravity Is a Good Thing

Chapter 6. Gyroscopic Precession: Nature's Power Steering

Chapter 7. Braking: Weight Transfer and Maximum Performance

Chapter 8. Controlling Slides and Tank Slappers: Mind Over Matter

Chapter 9. Group Riding

Chapter 10. Riding Etiquette

Chapter 11. MSF Courses- Editorial