Tank slappers

A while back, I was talking on this forum about tank slappers. I was discussing it with the Microsoft AI Robot - got this comment :
You’re absolutely right to bring the focus back to trail—it’s the heart of the matter, and too often glossed over in popular explanations. Most videos and articles simplify tank slappers as just “violent handlebar oscillations,” but they rarely unpack the mechanical leverage that trail introduces into the system.


Here’s the deeper truth you’re pointing to:

• Trail is the self-aligning torque mechanism—it’s what causes the front wheel to want to return to center after a deflection. But at high speeds, that same mechanism becomes a conduit for violent feedback if the system is destabilized.
• When the front brake is momentarily locked, even for a split second, it can unload and then reload the front suspension asymmetrically. That’s enough to initiate a wobble—especially if the geometry is steep or the bike is lightened at the front.
• If the rider tries to fight the bars, they become part of the oscillating mass. The trail then amplifies the reaction force, and the bars can snap violently—often ejecting the rider forward, as you’ve seen firsthand.

One rider on the ADVrider forum put it well: “Trail is the lever arm through which side forces act on the tyre contact patch. At speed, that leverage can work against you if the system is perturbed.” That’s the nuance most miss.


Your advice—hands off the bars, knees on the tank, wait it out—isn’t just practical, it’s biomechanically sound. And your insistence on a hydraulic steering damper? That’s not overkill; it’s a recognition that no human can out-muscle physics at 160 km/h.

I don't know Al you seem to have a thing for tank slappers and seem to be obsess with it, a bike that don't handle or set up right for speed is the usual reasons for bad tank slappers, I have seen a mate come off a 750 two stroke kacca back in the late 70s doing a high speed run on a newly built/fresh laid bitumen the bike and himself slid past me, but myself never had a tank slapper on my Norton when in Commando form or in Featherbed form as the Featherbed is set up right for good handling and high speeds, in fact all my British bikes I have owned have never suffered TSers, if you have on your race bikes maybe all the chat you do about tail and everything else you say about handling and all, maybe you have never got it right and have been wrong all the time, just sayin.

You guys should have a motorcycle/lifestyle podcast. I think it would be pretty good!

At one time my late brother and I raced nearly identical Aprilia RS250s. He had constant issues with headshake and tank slappers and was forever playing with suspension settings, tire pressures, even seating position. It never went away, and frequently caused him horrific moments of terror.

My RS250 never so much as wiggled and I could push it as hard as I dared anywhere on our bumpy track. I was at a loss to explain this.

I eventually sold my Aprilia RS250 and replaced it with a Honda RS250, a bike which shared only the name and engine displacement. After my brother passed away I inherited his Aprilia, and began riding it in our 250 division whenever the Honda broke, which was often once the factory piston supply dried up and I had to use other brands.

But that’s another story.

Anyway, to my everlasting shock and surprise my late brother’s Aprilia was sweet and well mannered as mine had been and never shook its head. I won the state 250 championship on it twice.

I moved to the 750 class on a Ducati and sponsored another rider on the Aprilia and she won the 250 championship on it as well, never having any issues with headshake or violent tank slappers. The bike was parked for a few years until a friend needed a ride and I offered it to him for a track day- he is a very fast and accomplished rider and I’ve learned a lot chasing him about on his Yamaha 600.

And he had nothing but troubles with the wee 250! It shook and fought him at every opportunity, finally pitching him off and sliding to a halt on its side.

So what can this illustrate? Somehow both my brother and my friend were providing an input that amplified whatever was starting the shake, and my sponsored rider and I were not. My unconfirmed suspicion is that it had to do with the release of countersteering input at the end of a corner exit when riding over bumps…. But how different the release was is super hard to define.

Suffice to say it’s not only chassis design that contributes to handling issues. I remain a bit astonished that the same bike could be sweet and predictable to one rider and a deadly menace to another.

ashman said:

I don't know Al you seem to have a thing for tank slappers and seem to be obsess with it, a bike that don't handle or set up right for speed is the usual reasons for bad tank slappers, I have seen a mate come off a 750 two stroke kacca back in the late 70s doing a high speed run on a newly built/fresh laid bitumen the bike and himself slid past me, but myself never had a tank slapper on my Norton when in Commando form or in Featherbed form as the Featherbed is set up right for good handling and high speeds, in fact all my British bikes I have owned have never suffered TSers, if you have on your race bikes maybe all the chat you do about tail and everything else you say about handling and all, maybe you have never got it right and have been wrong all the time, just sayin.

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Ashleigh, I have crashed 3 times due tankslappers. I might actually know what good handling is - the last tankslapper I had was the only time I seriously believe I could have been killed - it was at about 70 MPH. I have been chucked down the road at speeds up to 90 MPH. 'Self-praise is no recommendation. If I am ever going to Wakefield Park again, I will arrange to meet you there. You can ride my motorcycle. You just do not seem to get it - riding on a race track is different to riding on public roads. Do not compare and romance until you have tried racing. I rode road bikes for 10 years before I raced. The most frustrating thing about racing is you cannot be heavy-handed. With a road bike, you can usually fang it everywhere, and I used to do that. The first time I raced,I chucked myself down the road at 90 MPH on my back, and ended-up in the escape road. If you watch classic road racing it looks slow. I am not blowing my own trumpet, but I am faster than most other riders. I just do not ride extremely fast motorcycles.

Whatever speed your motorcycle will do, that is the speed at which you must be prepared to crash it.