F650GS Massive Tank Slapper!

[Picklehoffer]

Very very nearly had a nasty off yesterday

I've had the 650 single for about 2 weeks now and I have noticed a couple of handling niggles, but just put that down to my previous bike being a 1150GS which handles brilliantly with awesome suspension.

Yesterday, whilst overtaking a line of slow moving traffic on a wet road, I rode over some white chevron lines on the road (the type that you can drive on if clear). Well, it was clear in the opposite direction so I was accelerating gently when the whole bike started to wobble like an angry bull. Within a second I was having a world class tank slapper and thought I was going to have a personal introduction to the tarmac very soon. However, backing off the throttle and leaning my weight forward did the trick and she smoothed out enough to stay upright. I got away with that one!

So now my thoughts have turned to why that happened, I've performed similar manoeuvres on all sorts of other bikes without any issues at all, so why did the little GS want to spit me off? The previous owner has replaced the rear shock with a non-adjustable Hagon shock (which feels quite stiff), could that be the root of the problem? I don't want another "moment" like that, my gusset can't handle any more "fear"!

[Richard Simpson]

It should not be doing that.

Check your front tyre isn't worn: the centre band may be standing proud of a worn area to each side, this can set off a tank slapper when the centre band 'falls off' the white line.

Check tyre pressure: low rear tyre pressure can set off tank slapper.

Check wheels aren't out of round, and tyres are installed correctly.

Check the front wheel has been installed correctly, sometimes people don't centre it in the forks correctly, so it's worth undoing everything and doing it all in the correct order.

Check for lateral play in the swinging arm and wheel bearings.

Check fork bearings are set correctly

Check wheel alignment: and don't just go by the markings.

[bull]

you were lucky, you wont always get away so easy from a bad tank slapper. had a few myself over the years mostly from speed and acting the maggot. its a bit like riding a bull at a rodeo. i didnt walk away from couple of them.

[johnnyboxer]

21" front wheel?

They can all do that, especially on a bike with a short wheelbase

On my XR250, if you sit well back in the seat, flat out @ 70mph on a dual carriageway - you can move the handlebars from lock to lock, without changing direction, good fun when you try it :laugh:

[Rederic]

Is you rear tyre squared off and maybe a bit low in pressure ?
I think your front wheel is a 19" I have the 21" on my 800 and it gets a bit of stick, but handles great
If you can not see anything obvious, I would get the bike checked out preferably by some one who can check suspension and geometry
Was you giving it some stick ?

[Nigel]

My 800 can white line a bit when the tyres are worn but no problem, certainly no tank slappers, not unknown for head bearing to go on 800 (mine replaced under warranty)don`t know about the 650?

[adrian650]

The head bearings are well known to fail rapidly on these machines - the grease runs out as the oil heats up. That makes them loose and then notchy if you try to tighten them up. Having said that I abused and overloaded, used unmatched tyres and a Hagon rear shock on my 19" F650 and never had anything close to a tank slapper.

With respect to 21" wheels and short wheelbase, ican certianly agree that my Alp can start to develop a weave and the bars go wobbly as speed approaches 70mph, especially with a bag on the back. Luckily at that speed it accelerates so slowly I've never gone into danger territory. A F650 isn't so tardy.

Hope you find a cause.

[Simon_100]

With respect to 21" wheels and short wheelbase, ican certianly agree that my Alp can start to develop a weave and the bars go wobbly as speed approaches 70mph, especially with a bag on the back. Luckily at that speed it accelerates so slowly I've never gone into danger territory. A F650 isn't so tardy.

Hope you find a cause.

Is that Beta Alp? If so i'm having similar problems with mine, just can't get it to run smoothly over any kind of speed.

Regs

Simon

[Picklehoffer]

Is you rear tyre squared off and maybe a bit low in pressure ?
I think your front wheel is a 19" I have the 21" on my 800 and it gets a bit of stick, but handles great
If you can not see anything obvious, I would get the bike checked out preferably by some one who can check suspension and geometry
Was you giving it some stick ?

Mine has the 19" front wheel...and yes, I was giving it some stick!

Thanks for the replies, having given it some thought, I was just riding it like I rode the 1150 and I got caught out. :silly: The bike is alot lighter and it doesn't handle as well at what I'd got used to. Put it down to pilot error on this occasion I think! :whistle:

[Wilso122]

What tyres have you got on it? knobblies and heavy bikes = interesting moments especially when crossing white lines...

Usual, check fork oil, wheel in line, tyre pressures, wheel balance etc...