Understanding Tank Slappers

The Speedman's Wobble (AKA Tank Slapper) is something I've heard about, but I've never known anyone who has actually experienced one.

I found this article which seems to indicate that the odds are so dependent on specific conditions colliding that I'm not surprised I don't hear about them so often. However, this article was written in 2002.

I'm wondering if anyone here has experienced a Tank Slapper in the past? How do you get out of them? Can you? Have motorcycle engineers mitigated the odds of Tank Slappers?

I'm scared poop-less of these things. :22yikes:

I have, and I have watched friends have them. One guy (when we were young hooligans) came down off a 3rd gear wheelie with me about a foot behind him. His bike went in to a slapper and spit all 6'7" of him off. He was rolling down the road like a 225 lb tumbleweed, breaking all kinds of bones. I was hard on the brakes to keep from joining him.
Last year I hit a pothole leaned over on my R100RS. Major tank slapper in mid curve. I accelerated out of it. Thought for sure I was toast. That bike would ONLY come out of a slapper by accelerating. Well all twice anyway. The RS bars are SO close together they are actually easier to hang on to, but with less leverage.
On old BMW's for one, you do NOT take your hands off the bars while coasting in to town. That is when they are at their slap happiest. Some do, some don't.
I would guess that MOST tank slappers are caused by poor setup, or damage, or hooliganism, or people just not knowing they exist. Many bikes will start by nudging one side of the bars. One or two hands on the bars to settle/dampen them is usually all it takes to stop it before it gets "out of hand", so to speak.
Also worth noting, is if you do get out of a tank slapper, be sure to pump up the front brake BEFORE you need it. My R100RS front pads get pushed back into the calipers. That almost cost me at the traffic light a few hundred feet ahead.
My ST has never shown any tendency towards this behavior so far. At all. Not the slightest hint, though I admit I have never tried to initiate it.
I was reading somewhere that a guy hit some tar snakes going straight and his bike went into a bad wobble and spit him off. Just riding down the road behaving himself. I think.. Might have been an ST. Dunno.

A monotrack vehicle is designed to self-correct any deviation from normal steering operation through what is called 'trail'. While riding along hitting a small object in the road or a collision with a small animal can knock the front wheel hard enough to one side that the self-correction action of trail is violent and results in the bars whipping violently back and forth. Left to it's own devices the front wheel acts like a castor and wants to return to straight ahead. A motorcycle stays upright when moving because it describes a slight weave from side to side and this oscillation is damped by the designed-in steering geometry of fork rake and head stock angle that creates trail. Tank slappers are this self-correction action on steriods but fortunately do not happen out of the blue to bikes with head bearings, wheel bearings, swing arm bearings and tires in design specification. Of course there are outliers and onery bikes, airhead BMWs for one are not very tolerant of minutely loose/worn head stock bearings, but as a rule if the bike is kept it good condition and both hands are kept on the bars the rider will never experience one. If it does happen a gradual slowing of the bike without the use brakes and a loose grip on the bars can often ride it out.

I recently posted this elsewhere about experiencing a tank slapper on my ST: "In the "dumb but I did it anyway column" right after I got my ST1300 I was practicing launching the bike as quickly as I could. I was doing this in a large brand new parking lot surfaced with concrete, bright virgin white. I was trying to hook up the tire without wheel spin or lofting the front. In one attempt the front wheel came slightly off the ground and I guess I cocked the bars a little so when the front tire weighted again the forks started slapping. I got off the gas gradually and slowed without brakes and the bike stabilized. When I went back and looked on the ground you could see these long slightly s-shaped skid marks where the front tire was skipping along alternately side-to-side on either side of the straight path the bike had taken. The trail of the forks self-corrects itself if given time to do so. The bike is usually smarter than the rider and given it's head will stabilize.

I always go back to Murray Walker's oldie-but-goodie video whenever I need to refresh my memory.

Linky

That's a pretty interesting video!

I've only experienced a tankslapper once. It was my first road bike (85 Nighthawk 650) and I was 20-21 years old. Riding way too fast for where I was and I went into slight right hand leaner when in the middle of the lean I went over a bridge where the road was slightly lower than the bridge. It started wobbling and turned into a slapper very quickly. I don't really remember the actions I took other than letting off of the throttle and saying "Oh Sh**! So now after watching that video I'll say speed, road condition and the fact that I was a bit lighter than today contributed to the experience.

Age and experience have slowed down my speeds unless in a controlled environment and my decisions today are much, much better.

Skip

I had what I would consider the opposite of a tank slapper once. 1981 Maxim 550 doing about 90 coming out of a corner and the back end started hopping back and forth. And by back and forth I mean the front wheel stayed straight but the tank was still reaching the my hands on each end. Turns out a loose chain can cause problems at high speed. I used my dirt bike experience and transferred my weight to the tire that was still on the ground. With my weight on the front I was able to ride it out as I slowed down. My buddy was right behind me. He told me I died 5 times by his count.

Well that's a new one on me. Holy smokes!

schlep1967 said:

I had what I would consider the opposite of a tank slapper once. 1981 Maxim 550 doing about 90 coming out of a corner and the back end started hopping back and forth. And by back and forth I mean the front wheel stayed straight but the tank was still reaching the my hands on each end. Turns out a loose chain can cause problems at high speed. I used my dirt bike experience and transferred my weight to the tire that was still on the ground. With my weight on the front I was able to ride it out as I slowed down. My buddy was right behind me. He told me I died 5 times by his count.

Click to expand...

I lived through the 16" front wheel era in my formative motorcycling years, and in spite of owning plenty of potential slappers (VF400, VF500, VF750, CBX750) only had a scare on one of the 400's. Going much too fast over a hump-back bridge, probably got a little air over the top, and landed in a tank slapper. The bike sorted itself out (can't claim any heroic reactions on my part, except for buttock-clenching) without exiting the road, and the only lasting damage was some severely wrenched thumbs from trying to resist the movement.

In spite of plenty of provocation, all of my 17 or 18" wheel bikes will twitch occasionally, but I've never had that same increasing amplitude scare of a proper tank slapper with them. I do pay very close attention to suspension set-up, tyre wear and pressures.

I'm seeing a common issue with that front tire leaving the ground momentarily as a causation based on everyone's experiences so far.

I'm also seeing that most people managed to conduct some correction that prevented a disaster. Maybe my biggest fear is that they can come out of nowhere, and I'm convinced I'll panic versus thinking my way through a correction.

I am glad I watched that, as I'd never have had a clue what to do in a weave. On the other hand, as the presenter pointed out several times, weave is a high-speed issue and I'm not planning to go that fast, ever.

Working in my favor is that I tip the scales at an .... ahem, *generous* number, which he showed to be a minimizing factor. Now I also know (will I remember? that's a separate issue) to lean into it.

I've experienced weave (or at least speed shimmy) on a bicycle several times. The trick there is to loosen your grip, stand up so all of your weight is applied at the pedals (lowers the effective c/g of the bike), and rest a leg against the top tube of the frame as a dampener. Wonder whether that would also work on a moto?

I do not plan to put it to the test.

... and this Murray Walker is not to be trusted!!! He's driving the wrong way all the time! Same with his motorcycle club! That's gonna get someone hurt!

Also, I tried to look at his chart, but could not determine the proper tire and pressure combination for a 9 stone fellow riding a BSA.


Seriously: It was a great video, and actually reassuring to see.

You just need to take that new bike over to DTCT for a track day

EASt said:

I'm seeing a common issue with that front tire leaving the ground momentarily as a causation based on everyone's experiences so far.

I'm also seeing that most people managed to conduct some correction that prevented a disaster. Maybe my biggest fear is that they can come out of nowhere, and I'm convinced I'll panic versus thinking my way through a correction.

Click to expand...

Rich R said:

You just need to take that new bike over to DTCT for a track day

Click to expand...

Rich is alive!

And... no. Track day for this cat would be the surest way to effect that will I had drawn up.

The closest I ever came was while accelerating through a long, high speed (60-ish mph) sweeping curve on hot pavement (two lane rural), and I hit a tar snake. The rear wheel momentarily lost traction and the bike jerked hard, which will get your attention in a hurry at any time but especially so when you're leaning over in a sweeper. It was one of those moments on a bike when the voice in my head said "Ok, this could get ugly". My heart jumped into my throat but I stayed with it and resisted the temptation to overreact, or react at all. After a couple of wobbles she settled down and stayed right in the bank. It was probably more of a testament to the inherent stability of the bike itself than my "mad skillz" on a scooter.

'98PanAm said:

The closest I ever came was while accelerating through a long, high speed (60-ish mph) sweeping curve on hot pavement (two lane rural), and I hit a tar snake. The rear wheel momentarily lost traction and the bike jerked hard, which will get your attention in a hurry at any time but especially so when you're leaning over in a sweeper. It was one of those moments on a bike when the voice in my head said "Ok, this could get ugly". My heart jumped into my throat but I stayed with it and resisted the temptation to overreact, or react at all. After a couple of wobbles she settled down and stayed right in the bank. It was probably more of a testament to the inherent stability of the bike itself than my "mad skillz" on a scooter.

Click to expand...

As long as you make it through... doesn't matter how!

I had a buddy low-side on a tarsnake. To this day, I do everything I can to go around them, but some states use the stuff so liberally, that there's no option but to slow down and keep the bike more upright.

Had a couple, one was a result of lifting the front end coming out of a corner hard. The bike settled on it's own after a few heart stopping seconds. The second, same bike, resulted slowing down following a high speed run, rolling back hard on the throttle stabilized it, slowing down started it up again, I actually ran out of road trying to deal with it, and ended up on some brand new pavement of the yet unopened part of the highway. If I remember correctly I eventually got it through the wobble zone by getting hard on the front brake and planting the front wheel. I believe I replaced the front tire right after that, and that seemed to fix the issue.
Subsequent reading led me to believe that if this happens, relax your grip on the bars, the bike will right itself, if it doesn't throw you off first. Tank slappers are scary, and not something I want to experience again.

EASt said:

Maybe my biggest fear is that they can come out of nowhere

Click to expand...

Though that may seem to be the case at the time ultimately they come from somewhere somehow.

Mine happened while riding through a wide sweeping freeway curve at maybe 70+ on my 305 scrambler. The bars shook so violently that I was actually losing my grip. As it turn out that may have been what let the bike recover. There was nothing I consciously did to help.

I think the problem was caused by 'slugs' that I used to extend the front fork 6". The normal way to install them is to screw them into the top of the fork tubes and tack weld them at every 90º. Then weld all the way around them.

That seemed time consuming to me and expensive to get done. So the smart thing to do was just screw them in myself and be done with it. This put the joint of the two between the triple clamps.

Maybe tire wear added something. I have no idea. But I never rode that fast on that bike again.

I went through a phase of trying to get radial tires to fit my Honda Nighthawk, CB650SC. I couldn't get the exact size, so I went a little smaller on the rear. On the way home from the tire installer, I accelerated up to 75 or so, then when I let off the throttle it started. I just let off the gas and waited for it to stop. The bike had hard panniers and a fairing. I'm sure that didn't help. I put the stock tires back on, sold the offending tires on ebay, and sold the bike. I never rode it more than a quarter mile again. The new buyer called to tell me that the head bearings were too tight, so that may have contributed. I bought my ST1100 right after.

Here's a tank slapper video that shows how fast it will throw you down.

https://www.youtube.com/watch?v=uNwQK_HIHRU&feature=youtu.be

BTDT! It hurts!

Back in 1987 I had a tankslapper, I hit the ground at 65MPH. Back then ATGATT wasn't considered. Gear back then consisted of a helmet, gloves and boots. Leather jackets were around but too expensive.