I experienced my first tank slapper on 2007-06-20. That’s when a harmonic instability causes the handlebars to swap from side-to-side as far as they can go (AKA full lock). I purchased a Suzuki SV650SA7 one month earlier (2007-05-19), and I already have over 1200 miles on it. Anyway, I was coming out of the parking lot on the NE corner of Iowa and 23rd in Lawrence, KS after lunch. These cars were coming at me pretty fast so I wanted to accelerate out-of-there. I gunned it while I was leaned over. First the rear wheel starts spinning, or I hit a false neutral, or who knows what (VROOOOOOM), and then the handlebars are doing a high speed dance (JIGGY-JIGGY-JIGGY), and left foot comes of the peg. Afraid? HAH! Danger is my middle name! Embarrassed? You bet.
Here is a video of a tank slapper that looked like mine:
(Originally posted on 2008-03-04 as /archives/160)
This simulator could have been awesome, but the steering works backwards! BACKWARDS!
Someone asked me, “Are you using countersteering?” at my last track day, and I didn’t know how to answer that question. I thought, “Is there any way that I could not be countersteering at these speeds?” Countersteering occurs when the rider of a single-track vehicle (bicycle or motorcycle) pushes on the right side of the handlebar to turn right, and pushes on the left side of the handlebar to turn left. By pushing on the same side, the rider is “turning” the handlebars the opposite way. With cars you steer right to go right, but with bikes you steer left to go right.
OK, so you might be thinking, “I don’t do that! I lean!”, but you are doing that. Imagine this: a bicycle rider holds her arms out straight. She needs to turn right, so she leans to the right. What’s happening here? As she moves her weight to the right her right arm begins to push the right side of the handlebars out farther than the left: she is now countersteering. Countersteering has more to do with initiating the turn than the leaning itself does. You might have to sit on a bike and actually try this out to be able to picture it. Do it in an exaggerated fashion, lock your arms, and watch the handlebars as you lean.
Motorcycle instruction usually includes discussion on countersteering because the locking-of-the-arms-thing greatly slows down steering. Sometimes the effect on steering is so bad that riders ride right off the road when they tense up. If the rider can learn to loosen her arms, and consciously push on the opposite side of the handlebar, then she will turn much quicker.
I literally practice holding the bars loosely when I ride my wife’s cruiser. I take each hand off the handlebars one at a time (it has a throttle lock). I practice bending my arms. Etc. This can actually help in all kinds of conditions. That instability that occurs next to a truck? It’s less troublesome if you hold the bars lightly. When you push back against the shaking of the bars, your pushes lag behind the bars movement slightly. Your periodic pushing summates with the periodic movement of the bars increasing the shaking. Really.
So, how does this all work? Countersteering initiates the lean by using the bike’s momentum to pull it over. Imagine the momentum that you feel when a car turns. When you turn to the left the momentum makes you feel like you are being pushed slightly to the right in your seat: correct? This is the same with a two wheeled vehicle. Turning left simultaneously causes momentum to push your vehicle to lean to the right (like an upside-down pendulum). The bike then turns in the direction that it is leaning. It’s that simple. Really. I didn’t understand this for a long time, because I was told that the affect was caused by gyroscopic precession, and for sure, that occurs, but it doesn’t cause bikes to turn. Anyway I am sitting there watching a Kieth Code video, and he explains it. He only spent a few seconds on the subject, but it made the whole thing clear.
Here is the Wikipedia entry for countersteering. The very top says “For the similar technique used in automobiles, see opposite lock.” Please ignore that first statement. The technique described there is about pointing your car’s wheels in the direction that you want the car to move, even if your car’s body is stepped-out. This automotive technique is not remotely like the motorcycle technique, even though Doc Hudson says otherwise.
Before I tell you about this next part I want to make something very clear: I very much appreciate MSF instruction. Without the MSF I wouldn’t be riding. I would have no idea how to get started.
I took the MSF Basic RiderCourse twice. In 2007 I took it near Topeka Kansas (where I earned 100% on both tests), and in 2003 I took it in Plano Texas. While in Plano one of the RiderCoaches told us some things about countersteering that weren’t exactly correct. I don’t know if any of those things are part of the official curriculum, but I want to quickly cover them, just in case you are told something similar.
She had us sit on motorcycles that were standing still and told us to turn our bars and feel the motorcycle fall in the other direction, while using our legs to not let it fall all the way. About 50% of the time my motorcycle fell in the same direction. Of course it did. Countersteering doesn’t work while standing still: gyroscopic, momentum, or otherwise. A motorcycle should never be used as a Ouija board! To be sure the RiderCoach in Kansas had us do the same exercise, but he made it clear that we were to make the bike lean ourselves by using our legs and imagine that the handlebar turning caused it.
She told us to watch the other RiderCoach’s front wheel, and to see how it was facing the opposite way while he was riding around. I couldn’t see this, and I said so, and the reason that I couldn’t see it is that it just wasn’t so. The front wheel doesn’t go the opposite way once you are leaned over. (The speedway/flat track thing is something slightly different. It works more like the automobile-reverse-lock technique once the bike is leaned over.)
She told us that countersteering doesn’t work under 13 MPH. This is not true. What is true is that there is another, much-safer, turning-technique that involves turning the handlebars in the direction of the turn, weighting the outside peg, and using your own body to lean the bike. That doesn’t mean that countersteering won’t work. It just means that you are capable of exerting enough-force to overcome-it at those slower-speeds. Here is a video that proves that countersteering works at-all-speeds, and on-all single-track-vehicles (motorcycles, scooters, bicycles, etc.)