Head shake/tank slapper causes?

[CBR42]

At the drags on Thursday night at about 230 clicks I had a butt clenching massive tank slapping moment and have no real idea why.Had it happen again on another run later after a normal run through so it wasn't consistent.My initial though,after thinking I'm about to make a goose of myself and dump the bike in a straight line was it seemed to be at the point where the track surface changes at the end of 1/4(I was still hard on the gas at that point) or a front wheel balance issue ,but I have no educated idea.Anyone know any probable causes?

[Phat3R]

What is the bike ??? Dampener? Some diarrhea's from Dave ... :


http://www.youtube.com/watch?v=LmHU-gtlOKo

http://en.wikipedia.org/wiki/Speed_wobble

[Marty]

Did you drop your forks through to lower it for the drags? If so headshake is a bad side effect of doing this.

At Sydney drag way in the left lane there's a drop off after you cross the line, this hasn't always been there but i noticed it when I went earlier this year.

you could be hanging on too tight it's very common at the drags, I've had hip craps before from squeezing the tank so hard when I first started going.

[CBR42]

My bikes a 2010 CBR1000.I haven't altered the forks.
Your probably right Marty about holding on too tight as on the first run i was racing a mate and probably was more tense than usual where usually i zone out whoever is riding in the other lane.More concerned about my own time rather than the result.I lost BTW but it was my quickest run of the night 10.2,mate ran 10.04.
I try to always run in the right lane.Both lanes look like the surface changes from the coated part to the normal stuff and that was the only thing that i could think of at first that may have been why it got unsettled.The odd time i've run in the left they have been crappy runs so i avoid it.
That video also offers up a quite few possibles but most are more centred around if you'd made a recent suspension adjustment or not setup properly to start with.Mines been at its current settings for the last 6 months.

[Marty]

My bikes a 2010 CBR1000.I haven't altered the forks.
Your probably right Marty about holding on too tight as on the first run i was racing a mate and probably was more tense than usual where usually i zone out whoever is riding in the other lane.More concerned about my own time rather than the result.I lost BTW but it was my quickest run of the night 10.2,mate ran 10.04.
I try to always run in the right lane.Both lanes look like the surface changes from the coated part to the normal stuff and that was the only thing that i could think of at first that may have been why it got unsettled.The odd time i've run in the left they have been crappy runs so i avoid it.
That video also offers up a quite few possibles but most are more centred around if you'd made a recent suspension adjustment or not setup properly to start with.Mines been at its current settings for the last 6 months.

Yeh with the surface change it wasn't always rough, it's in the spot where the big cars hit the anchors or pull the chutes so I think it's rutting up. I never noticed it in the past so I think it's getting worse. Last time I only went in the left since I find I prefer it usually. If your holding on tight across that bump it could easily get a tank slapper happening.