Tankslappers!

[JohnR6]

I haven't experience one of these, touch wood that I won't and I really don't want one!

I've been reading about them and I was wondering if any of you guys have experienced one and how did you deal with it?

Here's a good read about them from joe250.com:

What is a tankslapper? It is an unwanted oscillation of the forks. You'll know you are experiencing one when the handlebars go back and forth uncontrollably, sometimes ripping themselves out of your hands. It is not pleasant. The name comes from the fact that tankslappers on certain bikes will actually smash the handlebars right into the sides of the fuel tank, denting them. The good news about tankslappers is that we have some ways to deal with them.

First, let's look at what causes them. When we turn a motorcycle, we are putting a fair amount of force into the tire laterally. This force is counteracted by the ground. We push the tire towards the ground and the ground pushes back.

What happens when the ground is no longer there? We have a lot of energy stored up in the front end, so if the ground no longer pushes back, that energy is suddenly released. You've been trying to rotate the bars and now with nothing pushing back, you can. The front end turns beyond your current direction of travel and when the front end comes back in contact with the road, the front wheel is not aligned with the bike's current direction of travel.

If the tire isn't perfectly aligned with your current direction of travel, the caster built into the front end's geometry will try and cause it to line up. Usually though, it will go too far in correcting things. Your handlebars will go to the right, then to the left, and so on. Eventually, the oscillation will die out on its own, unless we interfere.

Ok, but why would the ground not be there? Picture yourself exiting a turn on a powerful motorcycle like an R1. As you near the end of the turn, you are starting to stand the bike up and you are rolling on the throttle progressively harder. If you are accelerating hard enough, the front end will pick up and wheelie. If the bike was not perfectly upright, then you still would have had some turning input in the bars. Now with the front end off the ground, the ground can no longer push back. The bars are now turned further inward just as you pull in the clutch to perform an upshift. The front end sets back down on the road, immediately forcing the front tire to try and line back up with your actual direction of travel. A tankslapper ensues.

When tankslappers happen, it is hard not to interfere. The bars in our hands are going where we haven't pushed them. We naturally react by pushing and pulling the bars. However, we cannot react fast enough. The frequency of the oscillations is too high, so all we end up doing is adding energy into the mix, prolonging and even worsening the tankslapper. The best thing to do is not interfere. The tankslapper will work itself out if we let it. Relax your arms and accelerate. Relaxing will keep you from adding energy into the oscillation. Accelerating will take weight off the front end, letting the tankslapper die out quicker.

If you want tankslappers to die out even faster, install a steering damper. A steering damper works by making the front end more difficult to turn quickly. Tankslapper oscillations are at a relatively high frequency, so the damper eats up a lot of the energy. The speed at which you can turn your bike is low enough that the damper won't come into play.

On less powerful bikes, tankslappers are still possible. My RS250 won't wheelie out of turns, but I have experienced a tankslapper at Sears Point. Mine occurred while exiting a turn at the top of a hill. I was beginning to stand the bike up, was rolling on the throttle and crested the hill at the same time. The bars started shaking in my hands. Because I was now headed downhill towards the next sharp turn, I needed to slow down and quickly. I relaxed my grip on the bars and the oscillation died down. I was then able to brake hard for the turn and continue on my way.

The only other tankslapper I've experienced was also on the RS250, but this time on Mine's Road. I was headed South from Livermore and had just started the initial climb. Just a few turns into the ride, there is a medium-speed right-hander with a large hump in the center of the right lane. I had the bike cranked over in the turn, was accelerating hard uphill and I ran straight over the center of the bump, lifting the front end off the ground momentarily. This sent the bike into the most violent tankslapper I ever want to experience. The whole bike started to wobble. Again, I relaxed my arms and after a few anxious moments, the oscillation died out. I pulled over to clear my mind before continuing.

One other note. I have not experienced it, but I have heard from a number of people that violent tankslappers will actually force the front brake pads and brake pistons away from the rotors. When the tankslapper is done, the rider reaches for the front brake and finds out he has none. So if you ever experience a tankslapper, the first thing you should do after regaining control is to check your front brakes. If they feel soft, pump the lever repeatedly until pressure returns.

So to summarize:

Turning + Accelerating + Front end lifted & set back down = Tankslapper

Prevent tankslappers. Don't accelerate too hard with the bike leaned over if you are cresting a hill or there is a bump or object in the road (center reflector, etc.) in your path. This scenario has all the elements needed for a tankslapper, so watch for them and act accordingly.

Allow tankslapper oscillations to die out naturally by relaxing your arms. Trying to muscle the bike will increase the oscillations till you crash.

Negate tankslappers by accelerating. Lightening the front end or even wheelying will take pressure off the front end and allow the oscillations to die out.

Check your front brakes after a tankslapper. Pump them up again if necessary.

Invest in a steering damper, especially if your type of bike is more prone to tankslappers than other bikes (aggressive frame geometry, powerful engine, etc.).

I was just wondering, wouldn't applying the back brake help during a tankslap?

[YamaHead]

Depending on the circumstances....applying the rear brake could help some

A mate of mine Endurance raced an early Gixxer 1100 @ Road Atlanta once.....

I recall him telling me how scary it was when he experienced a tank-slapper going through the infamous Esses's section @ around 155mph!

[JohnR6]

I guess if you keep your fron't wheel on the ground all the time, then Tankslappers shouldn't really happen.....unless you hit a bump or a pot hole coming out a corner or something right?

[YamaHead]

My mate encountered that Tank-Slapper @ 155mph with front wheel down going through

the compression in the Esses's.....which actually effects the rake & trail dimensions causing the Tank-Slapper.

[mervin]

I had a couple of tank slapper,s on the old Rd years ago, one on a dead straight road just started wobbling for some reason shitty moments but managed to pull through, and the other one well she was a different story, wobble like hell when bent over the tank being given some from behind

merv

[Pete]

I was wondering if any of you guys have experienced one and how did you deal with it?

Feb 1978 I had a tankslapper at 110 on a GT750 Suzuki.

How did I deal with it? I fell off! Cos when you get a bad one you're going down....BIG STYLE! The bars rotate so violently you have no hope of saving it! Just say your prayers!

Very rare on modern bikes nowadays....so I wouldn't worry about it!

[Alex]

Fit a steering damper this should help reduce the chance of this happening.

[Boozehound]

Does anyone sell an aftermarket steering damper that works the same as the one on the new Fireblade? Genius bit of kit.