What causes a........ - SV650.org

30-01-05, 06:31 PM

Can someone explain what causes a tank slapper? Ive had quite a major one before with a pillion on board and although I learnt from that particular incident, generally im not entirely sure what causes it?

30-01-05, 06:54 PM

Head bearings, unstable geometry, landing a crossed up wheelie, hitting a manhole cover on the apex. Shutting off the throttle mid bend can do it too.
Some bikes are very prone to this, my 1985 GSXR750 did it frequently.

30-01-05, 07:20 PM

A pilion will make you more susceptable also. With the centre of gravity further back, it'll be easier to lift the front under acceleration. With little weight on the front wheel, a bump in the road can get the bars to slap.

Loose head barings as burner said can contribute to this problem - I know Jonboy had problems because of this.

northwind · 30-01-05, 07:43 PM

Badly setup rear suspension too.

embee · 30-01-05, 08:03 PM

If you go right back to basics, the front end of a bike is just like a castor on a supermarket trolley

Whether it's stable or not depends on stiffnesses of the tyre, forks, and frame, castor angle, mass (inertia) of the forks+wheel relative to the frame+rider etc, and to some extent any damping (such as a steering damper or tight/loose head bearings).

You'll know that supermarket trolleys are OK up to a certain speed and then go resonant, and it's the same with a bike. Most "resonant" systems can be forced through the critical frequency (speed in bike terms), but getting it through can be hazardous!

Carrying a pillion tends to make it worse because it tends to make the front end lighter relative to the rest. It usually helps if you both lean forwards to get more weight on the front.

Make absolutely sure the tyre pressures are right.

30-01-05, 08:20 PM

I've never had one. How do you control them?

30-01-05, 08:36 PM

From what I have been told you need to keep a constant throttle and stay relaxed. Easy said than done. I have only had a tank slapper happen once on my old FZ400 and it scared the life out of me. Luckly the bike corrected it self and I stayed rubber side down.

30-01-05, 09:10 PM

bit of a noob, but whats a tank slapper anyway? the fuel in the tank going slapping against the sides or somthing?

Iain

carelesschucca · 30-01-05, 09:22 PM

Quote:

Originally Posted by Sythree

I've never had one. How do you control them?

You don't ever seen the Video of the guy at the TT on the Black Fireblade scary stuff...

http://www.StupidVideos.com/?VideoID=390

Fingers crossed this works and this is worst case Tank slapper, as far as I know the rider was ok (relatively speaking)

30-01-05, 09:23 PM

Tank slappers are when the handle bars rapidly swing from side so side. They can range from a slight shudder to an extremely violent lock to lock motion. I assume they're called tank slappers from back in the day when there was nothing to stop the handle bars slapping into the tank

30-01-05, 06:31 PM	#1
caines Guest Posts: n/a	What causes a........ Can someone explain what causes a tank slapper? Ive had quite a major one before with a pillion on board and although I learnt from that particular incident, generally im not entirely sure what causes it?

30-01-05, 07:43 PM	#4
northwind Moderator Mega Poster Join Date: Jan 2004 Location: In the garage where I belong Posts: 17,083	Badly setup rear suspension too. __________________ "We are the angry mob, we read the papers every day We like what we like, we hate what we hate But we're oh so easily swayed"

30-01-05, 06:54 PM	#2
BURNER Guest Posts: n/a	Head bearings, unstable geometry, landing a crossed up wheelie, hitting a manhole cover on the apex. Shutting off the throttle mid bend can do it too. Some bikes are very prone to this, my 1985 GSXR750 did it frequently.

30-01-05, 07:20 PM	#3
Flamin_Squirrel Guest Posts: n/a	A pilion will make you more susceptable also. With the centre of gravity further back, it'll be easier to lift the front under acceleration. With little weight on the front wheel, a bump in the road can get the bars to slap. Loose head barings as burner said can contribute to this problem - I know Jonboy had problems because of this.

30-01-05, 08:03 PM	#5
embee Member Mega Poster Join Date: Jul 2003 Location: Warwickshire Posts: 2,804	If you go right back to basics, the front end of a bike is just like a castor on a supermarket trolley Whether it's stable or not depends on stiffnesses of the tyre, forks, and frame, castor angle, mass (inertia) of the forks+wheel relative to the frame+rider etc, and to some extent any damping (such as a steering damper or tight/loose head bearings). You'll know that supermarket trolleys are OK up to a certain speed and then go resonant, and it's the same with a bike. Most "resonant" systems can be forced through the critical frequency (speed in bike terms), but getting it through can be hazardous! Carrying a pillion tends to make it worse because it tends to make the front end lighter relative to the rest. It usually helps if you both lean forwards to get more weight on the front. Make absolutely sure the tyre pressures are right.

30-01-05, 08:20 PM	#6
Ed Guest Posts: n/a	I've never had one. How do you control them?

30-01-05, 08:36 PM	#7
chris SVK3 Guest Posts: n/a	From what I have been told you need to keep a constant throttle and stay relaxed. Easy said than done. I have only had a tank slapper happen once on my old FZ400 and it scared the life out of me. Luckly the bike corrected it self and I stayed rubber side down.

30-01-05, 09:10 PM	#8
Balsca Guest Posts: n/a	bit of a noob, but whats a tank slapper anyway? the fuel in the tank going slapping against the sides or somthing? Iain

30-01-05, 09:23 PM	#10
Flamin_Squirrel Guest Posts: n/a	Tank slappers are when the handle bars rapidly swing from side so side. They can range from a slight shudder to an extremely violent lock to lock motion. I assume they're called tank slappers from back in the day when there was nothing to stop the handle bars slapping into the tank