Motorcycle riding comes with many situations that can scare you worse than a Halloween prank and even result in a crash and causing injury or worse. An event of this nature is the dreaded tank slapper that can catch you unaware and kick your adrenalin into overdrive, especially if you manage to hold it. So, what is a tank slapper, can it be controlled, and can you avoid the experience altogether?
A tank slapper is when a motorcycle’s front wheel rotates in an unbalanced way, causing instability in the front region of the motorcycle. This causes the handlebars to twitch violently from one side to the other, slapping the side of the tank on one side and then the other.
Riding a bike is an adventure every time you get in the saddle, and you had better be prepared and ready for anything if you want to stay upright. A tank slapper is an experience you will never forget, and one that you will never want to experience again should you have previously endured one. Don’t let a tank slapper catch you by surprise without knowing the best course of action to take.
What Is A Tank Slapper On A Motorcycle?
In bike riding circles, the tank slapper is known by many names, but the same event is being referenced. A tank slapper is sometimes called a wobble, speed wobble, head wobble, death wobble, or even a shimmy. However, the delicate term “shimmy” seldom adequately describes the often violent nature of the experience.
A tank slapper is when a motorcycle’s front wheel becomes unbalanced and rotates erratically. The oscillation of the unbalanced rotation is translated directly up the forks of the bike to the handlebars. The oscillation causes the handlebars to flick hard to one side and then the other at an ever-increasing intensity.
A tank slapper can result in a high-side accident where the entire bike oscillates and the back-end fishtails, throwing the rider off the bike, sometimes over the bike’s handlebars.
Experiencing a tank slapper on a motorcycle, especially at speed, is a hair-raising terrifying experience, especially the first time it happens.
The oscillation is often so violent that there is no way you can muscle through it and forcibly control the bike with the strength of your arms alone.
What Causes A Tank Slapper?
If you ride motorcycles, you will know that many things happen out on the road that defies explanation, and sometimes this is the case with a tank slapper. Let’s take a look at the mechanics of what happens to cause a tank slapper and some things that can trigger this event on your bike.
There is a natural, slight oscillation of the bike’s front wheel due to imperfections in tires or wheel balancing, or the road surface, but these are normally imperceptible to the rider. This natural oscillation is usually dampened by other physical forces associated with forward motion.
A tank slapper is initiated when some irregularity forces the front wheel to accelerate to one side. When this happens, a restoring torque tries to pull the front wheel back in the opposite direction. This force over-corrects from the initial pull and forces the wheel to turn in the opposite direction.
The same restoring torque attempts to pull the wheel in the original to the opposite side again. It becomes a self-perpetuating cycle, often becoming more violent with each over-correction.
If there are enough dampening forces, the wobble or tank slap can correct itself, bringing the front wheel back into a straight line. If the oscillation becomes too violent, it overpowers the dampening forces, and the entire bike begins to be affected, ultimately high-siding the rider off the bike.
What Initiates A Tank Slapper?
The event that initiates the violent oscillation in a tank slapper can be from numerous causes, including the following.
- An incorrectly balanced front wheel. An incorrectly balanced front wheel will have an over-exaggerated natural wobble which can become progressively worse as the speed of the motorcycle increases.
- Bumps in the road. Bumps and inconsistencies in the road surface can kick the front wheel to one side, even slightly, which could cause a tank slap to begin.
- Painted lines on the road. Turning the front tire at the wrong angle when crossing a painted line on the road can accelerate the front wheel to one side, starting the reaction.
- Potholes in the road. Potholes or uneven areas where the tarmac has subsided, creating a small divot in the road can start the oscillation.
- The poor condition of the tires. Tires in poor condition can initiate tank slap.
- Incorrect tire pressure. Tires inflated to incorrect pressures can result in instability, causing tank slap, particularly at speed.
- Landing a wheelie incorrectly. Putting the front wheel down at the incorrect angle after a wheelie is a surefire way to start a tank slapper!
All these tank slapper causes are accentuated when traveling at high speed on your motorcycle and serve to get the tank slap to the point of no return much faster.
How Do You Control A Tank Slapper?
Now that we understand the mechanics of a tank slap, we can investigate ways to control and avoid this event out on the road.
Most modern superbikes come standard with steering dampers to help control the front wheel at high speed and prevent the wobble from starting. Steering dampers increase the dampening force that makes the front wheel “want” to self-correct much faster to come out of the wobble.
If your bike does not have a steering damper, you can have one fitted, which will help to limit the occurrence of a tank slapper.
There are other ways to increase the dampening forces that will help correct the wobble.
- Lean forward on the bike. Shifting your weight forward towards the oscillating handlebars while keeping the speed constant. Moving the center of gravity forward on the bike increases the dampening effect on the front wheel.
- Increase or decrease speed. Slowly increasing or decreasing speed changes the frequency of the oscillation increases the dampening, and brings the bike out of the wobble. The speed change, either way, must be gradual. Slowing the bike down too quickly can push down hard on the front wheel, worsening the wobble. Likewise, accelerating too quickly can reduce traction, allowing the oscillation to increase.
- Change your lean-angle. Changing the lean-angle of the bike to one side can help dampen the oscillation on that side, which breaks the oscillation cycle.
In some instances, riders have had success recovering from a tank slapper by taking their hands off the handlebars. This works because they have let go of the throttle, and the bike decelerates slowly, effectively dampening the wobble.
It is probably not advisable to let go of the grips completely, but releasing the throttle and holding the bars lightly can help break the slap cycle.
Conclusion
A tank slapper is a frightening experience that can result in a dangerous crash that can cause injuries or even fatalities to motorcycle riders.
Even if you have never experienced one before, it is probably only a matter of time before you do. Now that you know what causes this problem, you can take steps to minimize the event happening at all.
At the very least, you will know what to do when you get your tank slapper to get the bike safely back under control!
