I spent half an hour typing this out for the sake of my track going kakis. I myself have experienced this tankslapping phenomenom before on my sportsbikes… to say the least, it is most unnerving when you feel 2 lumps in your throat. Hope this article will help you guys too.
Ride hard and ride safe on the tracks!!! - Raptor
The following article is an extract from the Roadracing World magazine.
This article was written by Misti Hurst, an instructress at the California Superbike School for Roadracing World magazine.
What’s a tankslapper?
A tankslapper is a rapid, high intensity and unwanted motion of the handlebars back and forth. Literally it is slapping of the bars from side to side that can get violent enough that it seems like they will actually hit the tank of the motorcycle, hence the name ‘tankslapper’. The bad news is they are scary as hell and can cause some pretty nasty crashes. The good news is that there are some very effective techniques you can use to handle them.
What causes tankslappers? The suspension on a motorcycle is designed to make the ride more comfortable for the rider and primarily to keep the tires in good contact with the road surface which can include bumps, cracks, potholes and all manner of other imperfections. This system must work while the motorcycle is straight up and down and also during turning when the motorcycle is leaned over, sometimes at very extreme lean angles.
In his book, A Twist of the Wrist II, Keith Code explains, “The process of head shake (which can be the beginnings of a tankslapper) begins when the tire hits a ripple and along with the suspension, compresses. This throws the wheel slightly off centre. When the suspension and tire release, the wheel is light and flicks back toward a centred position, but again slightly off centred. Still off centred when it loads again, from the next ripple, again it is flicked past its centred position. The cycle of flicking back and forth repeats as the front end seeks to stabilize through this automatic and necessary self-correcting process. Any bike will do it, and what most riders fail to realize is that this shake is a necessary part of the bike’s suspension system.
The little wiggle in the front of the bike is how the motorcycle self-corrects and gets itself back on track. Ever see a motorcycle race where something, either a tankslapper or a big slide, causes the rider to be ejected or fall off the bike? As soon as the rider is no longer on the bike, it wiggles a bit, straightens out, keeps on going perfectly straight until it runs out of momentum and falls over. This is a classic example of how a bike, when left to its own devices will sort itself out. Code mentions that “Based on the amount of wiggling, squirming and overuse of controls most riders exhibit, the bike would, if it could, surely ask them to leave. Riders create instability on their mounts.”
Headshake can be caused by hitting a bump or a ripple in the pavement or it can occur when accelerating hard out of a corner. Hard acceleration can cause the front to get light or wheelie, which means that the tire is not following the road very well and when it touches back down, it can skip or bounce or be off centre, starting the headshake. Code explains that “the good news is that if your bike is basically tight (steering head bearings not excessively worn, forks and shocks not sticking etc) the head shake always stays up front and does not transfer to the rest of the bike.”
Eventually, the oscillation will die out on its own, unless we interfere.
How riders make the situation worse.
A normal reaction when the handlebars start to slightly shake is to stiffen up on the bars. Keith Code calls this part of our “survival reactions,” noting that we do not usually choose to get stiff and tight on our bars, our bodies just do it. When we stiffen up the headshake is transferred though our bodies to the whole bike and that is when the shaking can get more violent. Code says that “too tight on the bars, is the most common source of motorcycle handling problems.”
How to prevent a tankslapper.
Knowing that gripping the bars to tight is what transfers head shake through the bike and makes it feel like a ferocious tiger ripping a piece of meat into shreds, we can work to prevent a tankslapper from ever occurring by maintaining a relaxed position on the bike at all times. Practice sitting on your bike with your knees gripping the tank for more stability. Sit back a little further in your seat so that your arms have a nice bend in them with your elbows pointed to the ground and then flap them like you’re doing the Funky Chicken. That’s relaxed, and from that position you can easily use your legs to lift your weight off the seat a little bit, like a jockey on a horse, so that your butt is not banging down hard on the seat. Think light as a feather, one with the bike. Zen and the art of motorcycle riding.
Installing a steering damper is another way to help prevent tankslappers. A steering damper works to limit the travel and intensity of any head shake the bike is experiencing by damping or soaking up the excess energy. They are necessary on some of the more modern bikes that have aggressive frame geometry, relatively short wheelbases and powerful engines. Dampers are mounted up front so that there is insufficient leverage to transfer shake through the bike. Keep in mind that a motorcycle with a damper will still shake if you are tight on the handlebars, so relax.
What to do if you experience a tankslapper.
If you do find yourself in the unfortunate situation of experiencing a tankslapper first hand, don’t try to muscle the bike or force it to stop as it will only make it worse. Try to relax your grip on the bars, pinch the tank with your knees and lift your butt off the seat a little bit. Also, don’t chop the throttle as that will put more weight onto the front and make the situation potentially more worse. Ideally you would want to continue to accelerate to get the weight further to the back of the bike, or at least maintain a steady and smooth throttle. Popping a wheelie would immediately eliminate a tankslapper because there would no front wheel bouncing back and forth in an effort to straighten itself out., but I don’t know of many people who could pull off a stunt like that in the middle of a panic situation.
If all else fails, let go. The bike will try to fix itself.
Another important thing to remember is that occasionally very violent tankslappers can knock the front brake pads and brake pistons away from the rotors, causing the brakes to go soft or fade completely. So once you regain control of the motorcycle, check the front brakes and if they feel soft then pump the lever a few times until the pressure returns.
Finding yourself in a situation where the motorcycle you are on is suddenly out of control is no doubt a scary predicament. The more knowledge you are able to arm yourself with, the better you are equipped to handle emergency situations and the more you are able to practice certain techniques (such as being nice and relaxed on the bike at all times) the more likely you will be to actually do it when it is absolutely necessary. It’s a pretty cool feeling to able to consciously decide to do something that makes a bad situation better.