[Motor]

Can anybody explain to this simple redneck what the causes of a tank-slapper are? 

Are REs susceptible to this action by not having a steering dampener?

Have not experienced this on my Bullet and neither do I want to, but have on other bikes in the past.  Seems that tightening the steering damper eliminated the problem or was that just covering up for some other deficiency?

Thanks, Guys!

[The Garbone]

The only time I got that fun bit that is a tank slapper was when I was going down a dirt road and hit a spot of really soft sand at about 20mph...    I think in my case it was a weight distribution thing that caused it..   I have done the same spot since and it does not happen anymore..  My guess is that I am just more experienced and automatically shift my weight and modulate the throttle and clutch to compensate... 

I think if your front tire gets out of plane suddenly and acting as a gyroscope it tries to auto correct and that is the root cause..

[1Blackwolf1]

  increased rake angle and extended forks do most of the damage, unbalanced tires can also be the culprit.  Not enough weight on the front end/center of gravity over center.  Usually seen in choppers.  My wifes v65 Magna was the only bike that it was very noticeable on since someone had installed extended forks prior to my purchase of said bike.  It would become a tank slapper at about 85 mph under hard acceleraton.  I would say in its stock form a Bullet probably won't come loose on the driver, however anything is possible given the right circumstances.  I never used steering damper other than the stock one on my '75 Gold Wing.  So couldn't say if it masks the problem or not.  Will.

[c1skout]

  Go to http://w6rec.com/duane/bmw/safety.htm to read a bunch about tank slappers and such. The site deals with BMW's but has a lot of useful information for anyone.

[ace.cafe]

"Tank slappers" have many causes, and they are simply an unwanted oscillation of the steering assembly, which causes loss of control.

A properly set up Bullet, that isn't loaded up with a bunch of stuff all over it, should probably not exhibit that activity.
However, nearly any bike can have one under the "right" set of circumstances.

I don't consider a steering damper a necessity on a Bullet, and they are not easy to put on a classic Bullet, unless you remove the fork covers. Or you could change your front end to one that has the hollow steering stem from an old Bullet that has provision for a friction damper like the old ones had. But, if you want to put one on, it won't hurt anything. So, if it makes you feel better, then fine.

[single]

I once knew a fellow who induced a real tank slapper by hanging a full bucket of water onto each handle bar.Once the buckets started swinging there was no saving it.More embarassement than damage,luckily.He was riding a Duo Glide.I have stated on the forum before that I had this happen to me (no buckets)on a BMW,at 100 mph.There was a quiver and then a violent oscilation.I had just shifted into 4th.On quiver I should have tried to accelerate and then brake until I was slowed to the point of no wobble or quiver,so I have been told.This was a new 1971 750/5.I do not mean to say any thing detrimental about BMW motorcycles,have owned one since and it was great,perfect,also a 750/5.The only thing on the bike,accesory wise,was a set of saddlebags.A fellow I knew had previously ridden this same bike at the dealership with no wobble at 90 mph.Same guy that did the bucket thingy.Anyway,I didn't save it,wreck was scary,we both suffered.I say that if you feel a real quiver it is time to get back to where you were before the start of it,if possible.

[Chasfield]

I once had a motorbike that had previously been hitched to a side car and fitted with a front tyre of moderately square section. That machine pulled a tank slapper at 45 under modest acceleration and nearly put me into a hedge. I put a decent tyre on it pronto.

Early years learning curve!

[PhilJ]

The '71/5 had a short swing arm. They were known for high speed wobbles, or worse. It was solved in '72 when I bought my first of many Beemers.

That '72 was bored later to an 840 and .290 rear end, Habermann full cafe fairing and the equivalent of "Ace" bars. With a lot of tuning in would run an honest 130. What a ride. Only to be 30 again. 

[Jon]

My OIF Bonnieville would tank slap at 90 when ridden solo,with a pillion it didn't do it.
After checking wheel alignment,frame alignment,swinging arm bushes, head bearings
tyre pressures,wheel bearings etc I changed the rear tyre back to a TT100
from a Roadrunner and the problem went away.

[Motor]

Thanks, All for the replies!  This is the first bike I have had in a long time that did not have a friction dampener on the steering neck, so I was wondering if you guys had this issue come up on REs, and it seems that it has not. 

When I lived in Brazil I had a Zundapp 250 of approximately 1930 vintage that threw me off on a dirt road at approximately 40-45 mph.  I believe I hit a soft spot in the sand which caused the tank-slapper.  The soft spot also eased my landing somewhat I am inclined to believe.  Talk about a double edged sword! 

I have religiously applied the steering dampener ever since, especially on a Duo-Glide that had an issue with the front tire.  It was assembled from parts and the front wheel had come from a Servi-Car that had never leaned in its' previous life, and was worn down square.  Tire replacement cured that one.

Again, thanks a bunch!

Motor

[sqf]

As Ace mentioned a "tank slapper" is an oscillation, it isn't the same as a "high side" or "low side" that result from loss of traction, or in the case of a high side loss of traction followed by regaining traction that causes the bike to vault, losing its rider.  A low side is what happens when people try to "lay it down" in an accident, the bike tips to the low side and slides on the low side.  A high side happens when the rear tire slides out, then catches, this causes the bike to "stand up" often times launching the rider off the "high side".  In accidents we often see high sides in slick weather or when you get a high speed turn and the rear tire hits the painted line in the road.  Believe it or not the coefficient of friction on the painted lines is about half that of the roadway, when you've got something as small as the contact patch of a motorcycle it is definitely something to keep in mind!

If you ever feel the oscillation starting all you have to do to get out of it (before it gets too bad) is lay down on the gastank, that will shift your center of gravity and resolve the issue).   Tankslap is actually something we look for during accident investigations, especially for smaller stature riders as it tends to happen more with lighter folks.

[LotusSevenMan]

My Classic Army has a tendancy to shake its head. Not a nice feeling. Not sure if it's an out of balance front tyre or head bearing yet as need to investigate said problem.
LSM

[pknopp]

 There is one section of the town I ride in generally that will cause this. Ride 40 mph and I'll get a vibration. Ride elsewhere and nothing.
 
 My only conclusion is that the surface was laid down overtop the original brick pavers. Much of the rest of downtown is still brick.

[500KsGerry]

RE is a light bike with a short wheelbase and high rider seat so the center of gravity more suited to low speed B roads or even off road trails where manhandling is needed. So the rider should be mindfull of  the center of gravity in regards to ride postion and weight distribution.  Thankfully the bike is very simplistic and mods to the rear suspension cured my particular riding quirks/Re center of gravity. would also add that the very 1st mod Made was getting rid of that godawful Speedmaster rear tyre with the profile of a pancake.   Gerry

[Blltrdr]

would also add that the very 1st mod Made was getting rid of that godawful Speedmaster rear tyre with the profile of a pancake.   Gerry

What did you replace it with?

Blltrdr

[500KsGerry]

Blltrdr....Replaced rear tyre with a 110/90 19  Chengshien . Changed  front out to match also.    Gerry

[RBHoge]

Years ago When my Honda CB-450 and I were first getting acquainted, I experienced my first "High Speed Wobble"  I was following my friend and motorcycling mentor Mike, onto I-40 in Nashville. I passed over a rain grating and nearly bought the farm. The bike was without windshield or fairing at that time.

It really scared the s#-t out of me.  Mike advised me to avoid rain gratings and should I ever experience such a wobble again, to either let the throttle close,  lightly touch the rear brake, or lean into the handlebars,give ti more throttle and "punch through it.

Some weeks later, when I had added a Wixom Ranger fairing to the bike, I noticed that at thirty-two M.P.H. the bike would wobble gently if I took my hadns off of the handlebar. Otherwise the wobble was completely unnoticeable.  I did notice at seventy-four M.P.H. the bike would give a marked "shrug" as I accelerated through that speed. (There was nothing noticeable if I decelerated back through)  At eighty the bike hummed along like a champion. (I rode from Nashville to Atlanta a dozen or so times on that bike and only noticed a "wobble" passing through 74 or when I found myself "dancing in the @#$%! "Rain Grooves" Georgia put on every bridge.   

[Geirskogul]

Only ever experienced speedmans wobble at the same type of area as RBHoge. 

Stupid cattle grooves!

[RBHoge]

After several bridges, I noticed that there was usually a gap in the rain groves where the grooving machine was not quite the width of the lane. this most often left a gap near the center of one lane or the other about a foot wide. I just aimed for that smooth strip. No problems from there on.