Tankslapper : What to do if you face one?

Ever faced a situation where your motorcycle’s handlebars start wobbling without any seeming provocation?? That, my dear rider, could be a dreaded tankslapper. Few riders escape unscathed from such a situation, and live to tell the tale.

It was the morning of 23rd June, 2014. The sun had hidden itself behind puffy clouds, occasionally peeking out of its cover, as if to keep a tab on the activities of us earthlings. It was one of those days when the cloud cover provides a pleasant ambient temperature, yet somehow magically the heavens don’t open up. In short, it was the perfect riding weather. I embarked on a journey from Bhubaneswar to Cuttack along the NH-5, a notable stretch of the Golden Quadrilateral that links the four Indian metros.

But was the ride going to be a perfect one? Read on.

I mentioned notable because the NH-5 witnesses heavy traffic. Freight trucks from Andhra Pradesh, and long-haul buses are just a few among those present in the list. And the NH-5 is undergoing upgradation. In addition to widening, flyovers are being built at major intersections to allow traffic movement without hindrance. The construction activity also involves laying down of new road surfaces.

As I was cruising down the highway at a healthy speed of 80 kmph @ 6,000 revs ( Guess which bike? 😉 ) , I encountered a wide curve. Instinctively, I shifted slightly on my saddle. Simultaneously, I also began weighting down the foot peg nearer to the center of the imaginary arc traced by the curve. My hands followed suit, and as if in a practised ritual, the palm closer to the curve’s arc started pushing the handlebar grip it was clinging onto. As the moves laid themselves out in copybook fashion, I started imagining a clean conquer of the corner.

But, it wasn’t to be so.

Without any provocation, the front forks seemed to rise up viciously towards me. Moments later, the handlebars began their horrific trance, left to right to left again. I say, it was a hair-raising situation. I didn’t want to kiss the tarmac. The bike was bent over in a dive to attack the corner, and all I was thinking was : Will it tip over and spit myself out from the saddle?

Again, by instinct, I jabbed at the front brakes. As the slotted disc was bit upon by the caliper, the front end dipped. Employing a fail-safe method of applying brakes using only the index and middle fingers, I managed to roll off the throttle at the same time. My thumb, and the other two fingers had enveloped the throttle grip, ready to close the throttle by moving forward as the brakes were jabbed upon. Fortunately, the clip-on handlebars stopped their deadly dance. And I escaped a tankslapper, virtually shaken and stirred.

As I returned home, I realized that I had almost no idea about a tankslapper. I had escaped due to sheer luck. For the benefit of fellow riders, I decided to delve into deeper depths, and pen down my thoughts.

WHAT CAUSES A TANKSLAPPER?

A motorcycle is basically a huge gyroscope. Often, it has an inherent tendency for stability. If acted upon by external forces and disturbed from its state, it will try to return to that state it was present in. The rider-motorcycle pair forms a system, i.e. a joint entity. This entity faces various external forces like wind resistance and feedback from undulations on the road. In addition, it also faces internal forces like the ones leading to a change in the motorcycle geometry. These can be cornering forces which can bring stress on a bike’s frame, or they can be something as mundane as a front end dip brought about by pressing the front brake lever.

The point is : the rider and the motorcycle together vibrate at a certain natural frequency.

And as the entity of rider-motorcycle faces external forces, it witnesses different kinds of external frequencies. In certain cases, the external frequency corresponds to the natural frequency of the rider-motorcycle entity. It could be anything; a specific size of the undulations on the road that bring about a up-and-down vibrating motion at a certain frequency. And then, here comes the effect of Resonance, something which we have studied in our school textbooks. As the driving frequency matches the natural frequency, the vibrations become amplified to a deadly level.

Throw in some more factors into the mix. For example, the bike is leaning into a corner. It is also travelling at a healthy cruising speed. And the road surface is being laid out, thereby throwing up imperfections. Why do you think I glossed over the fact that NH-5 is witness to teeming construction activities? 😀

WHAT TO DO??

1. Do not panic. That is important.
2. Start rolling off the throttle, and apply the brakes “gently”. Mind you, the bike is leaning and hence the tire’s adhesion with tarmac is pushed to the limits.
3. Even if you fall at this point, you will have won half the battle. Falling at a lower speed reduces your risks.
4. Try changing the bike’s geometry by leaning forward or backward. You can also use your brakes judiciously to do so. Doing so will change the bike-motorcycle entity’s natural frequency, and avoid the phenomenon of resonance.
5. Avoid, I repeat AVOID accelerating further. You will risk losing traction and ending up in a dangerous skid.
6. A novel method of avoiding tankslappers is by the use of steering dampers. But then, these are found on expensive sportbikes. The inherent nature of sportbikes to attack corners at great angles makes them more vulnerable to tankslappers. 

Have you ever faced a tankslapper? What did you do to get your motorcycle under control?