Interesting experience, the tank slapper.
I take my hands off the bars (any speed it seems) and the bars start oscillating and build up to quite a violent shake. Why? Any ideas? Back tyre is pretty much worn out, but that shouldn't cause this surely?

Hi,

It could be a slight imbalance of your front wheel. Not enaugh to feel it when you hold it but enaugh to build into a heavy shake when loose. (When you let go of the bar's you dramaticaly reduce the mass of it and thus make way for the vib's)

Ofcourse this is only a guess.
You could try handle-bar weight's.

Maarten

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- www.maartensworld.tmfweb.nl -

This isn't all that unusual - many bikes will do it at a particular speed, even when all is well.

But yours shouldn't do it at all speeds.

The way I look at it is thus:

It's a miracle the bike doesn't wobble and wiggle it's way off the road even with your hands on the bars...

So, everything has to be just so - and a worn out tire - very square - could easily cause the problem.

A list of what could cause the problem:

the steering head bearings,
swing arm bearings,
wheel bearings,
swing arm side to side positioning,
rim straightness,
wheel balance,
condition of BOTH tires,
fork leg straightness,
fork yokes alignment,
frame alignment (minor crash can tweak the frame easily),
excess weight at the rear,
loose saddlebag mounts,
loose rear subframe mount bolts,
incorrectly adjusted swing arm bearings,
fork oil type, age, and weight,
fork damping components,
rear shock, same things as for fork,
fairing mounting,
large tankbag,
fat passenger,

and I'm sure I've missed a few.

Have a thorough check, and if you're not an experienced mechanic have your dealer check the bearings out - they can be difficult to discern a problem unless you really know what you're doing.

Oh yeah, and change the tire.


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Grant Johnson

Seek, and ye shall find.
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One world, Two wheels.
www.HorizonsUnlimited.com

hi
try getting your front wheel balanced

Thanks for your responses. I fitted new tyres which it needed anyway and the tank slapper has virtually vanished.

Just as an additional - possibly - life saving tip.
My old R80/7 would 'tank-slap' at low speed in higher gears if tyres worn, carbs out of balance etc.
I found the easiest way to stop it dead was whip the clutch in - stops it pretty damn immediately.
My R100GS got a serious tank slapper exiting a wide bend at 85 mph (worn tyres). For a moment I went down the ****, panic, grab bars as tight as possible (obviously no way you'll stop a tank slapper that way !) before I remembered to whip the clutch in. From being at the 'I'm off, and still travelling 80 odd' to under control baring required change of trousers was a matter of split seconds.
Don't sue me if it doesn't work for you - but it's worked for me at both ends of the scale !
Of course the best thing is prevention.....

Apparently this is perfectly normal for a GS. The big front wheel is mainly to blame. Honda Pan Euro's often do it too. Nothing to worry about, and certainly not a sign of worn head races/bearings or unbalanced tyres. Some people claim that stiffening up the front forks helps.

Interesting, my 1986 R80 G/S started doing this at low speeds after I had a new tyre fitted and balanced where as it wouldn't before, probably down to fitting a Shinto tyre in Riga Lithuania as that was all I could find, before with Avon Gripsters front and back even bald ones it was fine. Cheers Chris, 11,400 miles done and lot's more to go.

ahoi!
i know its a bit late but: check the tire pressure (at least all 1000km or 14 days). low pressure causes wild slabbering (nice word, in germany we say 'schlabbern'). another problem are bad (new!) tires. last year i had one in the front wheel which was about 5mm off center. the dealer changed it (of course!) and told me it was the sixth damaged tire in that year (its a big garage, but it was only may).
may long you run
gerd