Wat cause(s) tankslap?

[hitman]

any1?

[calyban]

multiple reasons I think, but essentially,

-being too heavy on the throttle, which lightens the front

-too light and sensitive front setup, which reacts strongly to load changes.

 

correct me if I am wrong pls.

[MC28]

Nearly encounter a tankslap while heading to Kulai last weekend..Small bump at the speed of 200+ and lucky my damper was there to correct the situation..

[hitman]

i encouter 1 last nite. 1st reaction was 2 close throttle. scary sia.

[apitBIOL]

i always slap my tank...or pat/stroke it..

[Strong Eagle]

multiple reasons I think, but essentially,

-being too heavy on the throttle, which lightens the front

-too light and sensitive front setup, which reacts strongly to load changes.

 

correct me if I am wrong pls.

 

You are on the right track. Imagine one of those spring loaded kitchen doors at a restaurant. Somebody pushes it open and walks through. The door doesn't just stop after it swings back, instead, it swings back and forth a few times, EACH TIME THE AMOUNT OF SWING BEING LESS THAN THE LAST.

 

This is an example of "diminishing/decreasing" harmonic motion.

 

Now imagine that you were to push open the door and instead of it slowing down and closing, it instead started to swing wider and wider until it finally ripped itself off the hinges. This is an example of increasing/amplified harmonic motion. For each change in direction, the amount of movement gets larger, not smaller.

 

The act of moving a door back and forth or handlenbars from one side to the other is called a harmonic oscillation.

 

This is what a tank slapper is... harmonic motion where inputs into the system result in wider and wider turns of the handlebars until the smack into the tank. Not good fun.

 

Tank slapping can be caused by a number of things. For example, a frame that is not very stiff (bends in the middle). You hit a bump with the front tire. It pushes the handlebars off center AND it causes the frame to bend slightly.

 

Then the frame straightens out and causes the handlebars to move the other way. The two movements re-inforce each other until you get a tank slapper. Older Harleys were famous for this. Their frames were quite flexible and at a certain speed, the harmonic oscillations would start and... BAM!!

 

Other things that can cause a tank slap: Loose steering head bearings, over inflated tires, top boxes, side boxes and other attachments that create a back and forth motion due to wind turbulence. Some brands of tires tend to be more susceptible to allowing harmonic motion. For example, with Avon tires on my Valk it began to demonstrate and back and forth motion of the handlebars at about 160 kph. Dunlop and Metzeler did not have this problem. Changing the rake and trail (by dropping the front or back end, or changing rake angle with new triple trees) can increase the tendency to tank slap.

 

Solutions for tank slap? You need to take the energy out of the harmonic motion so that the oscillations die down, not increase. Reducing throttle is one way, but be careful, shutting it down quickly could make it worse. Lightly using the rear brake to stop the oscillations is another thing to do.

 

Changing brands of tires and not overinflating can cure problems if a bike is prone to tank slap. Using a damper is a good idea for bikes with the problem. If you have a top box mounted try changing its front to back tilt to see if it makes a difference. And it all else fails, maybe it is just a bad design. Try another bike.

[hitman]

thx 4 the info.

[Jfor_Jimmy1986]

You are on the right track. Imagine one of those spring loaded kitchen doors at a restaurant. Somebody pushes it open and walks through. The door doesn't just stop after it swings back, instead, it swings back and forth a few times, EACH TIME THE AMOUNT OF SWING BEING LESS THAN THE LAST.

 

This is an example of "diminishing/decreasing" harmonic motion.

 

Now imagine that you were to push open the door and instead of it slowing down and closing, it instead started to swing wider and wider until it finally ripped itself off the hinges. This is an example of increasing/amplified harmonic motion. For each change in direction, the amount of movement gets larger, not smaller.

 

The act of moving a door back and forth or handlenbars from one side to the other is called a harmonic oscillation.

 

This is what a tank slapper is... harmonic motion where inputs into the system result in wider and wider turns of the handlebars until the smack into the tank. Not good fun.

 

Tank slapping can be caused by a number of things. For example, a frame that is not very stiff (bends in the middle). You hit a bump with the front tire. It pushes the handlebars off center AND it causes the frame to bend slightly.

 

Then the frame straightens out and causes the handlebars to move the other way. The two movements re-inforce each other until you get a tank slapper. Older Harleys were famous for this. Their frames were quite flexible and at a certain speed, the harmonic oscillations would start and... BAM!!

 

Other things that can cause a tank slap: Loose steering head bearings, over inflated tires, top boxes, side boxes and other attachments that create a back and forth motion due to wind turbulence. Some brands of tires tend to be more susceptible to allowing harmonic motion. For example, with Avon tires on my Valk it began to demonstrate and back and forth motion of the handlebars at about 160 kph. Dunlop and Metzeler did not have this problem. Changing the rake and trail (by dropping the front or back end, or changing rake angle with new triple trees) can increase the tendency to tank slap.

 

Solutions for tank slap? You need to take the energy out of the harmonic motion so that the oscillations die down, not increase. Reducing throttle is one way, but be careful, shutting it down quickly could make it worse. Lightly using the rear brake to stop the oscillations is another thing to do.

 

Changing brands of tires and not overinflating can cure problems if a bike is prone to tank slap. Using a damper is a good idea for bikes with the problem. If you have a top box mounted try changing its front to back tilt to see if it makes a difference. And it all else fails, maybe it is just a bad design. Try another bike.

 

 

still very chim lehh... got a more simplified version anot??

 

what is a tankslap arhh ??

[redbeacon]

Nearly encounter a tankslap while heading to Kulai last weekend..Small bump at the speed of 200+ and lucky my damper was there to correct the situation..

I wasn't so lucky

Time to invest in dampers liao.

 

 

 

Tankslapper:

[xiaowen]

what is a tankslap?

[hitman]

click on the youtube link fm the post b4 urs.

[Mengz_Zai]

Tank slap, an example of harmonics, is a dangerous and scary situation condition for motorcycle riders.

A Tank Slap can occur at any speed and is characterized by rapid and wild swings of the handlebars from hard-stop right to hard-stop left and back again. Tank slap happens when harmonic feedback is generated following the front tire hitting an imperfection on the road surface such as the slight bump at the end of your driveway.

 

With motorcycles being light, it is very easy for the front end of the motorcycle to lose contact with the road surface. When the front end makes contact again with the road surface and is not in line with the back tire, the front end reacts violently transferring the energy into oscillations of the handle bars.

 

The condition, in the hands of inexperienced riders, lead to a high-side crash.

 

 

It is recommended to maintain throttle position and let the oscillations diminish. The reason for this is it allows the motorcyle weight to reach equilibrium. Applying the front brakes or chopping the throttle, puts a forward bias of the front end which combined with oscillations, leads to a break in traction causing an accident.

 

 

 

From Wikipedia

[Mengz_Zai]

more videos

 

Recover from tank slap

 

Do this if u can but i dun wan to try

 

[Refugee]

tank slap occurs when a rider thinks his bike is a b-i-t-c-h that day... and decides to slap the tank hard... then whilst doing that loses balance and buang.

[MonoWorld]

omg so scary

[asmi]

oh ok.. so this is what they called it.. i kanna before, and self-skidded.. cost me a bomb

[MC28]

I wasn't so lucky

Time to invest in dampers liao.

 

 

 

Tankslapper:

 

Definitely an investment worth the money spend..

[5687]

Heard that TL1000 is common with this problem... dunno which version S or R.. Can this be corrected with damper?

[redbeacon]

Do this if u can but i dun wan to try

 

 

 

This one looks more like a (recovered) highside than a tankslapper.

[kmax]

how about installing damper? does it reduce the chance of tankslapping ?

[redbeacon]

how about installing damper? does it reduce the chance of tankslapping ?

Yep, that's the purpose of the steering damper: To reduce the effects of tankslapping should it happen.

[hitman]

Tank slap, an example of harmonics, is a dangerous and scary situation condition for motorcycle riders.

A Tank Slap can occur at any speed and is characterized by rapid and wild swings of the handlebars from hard-stop right to hard-stop left and back again. Tank slap happens when harmonic feedback is generated following the front tire hitting an imperfection on the road surface such as the slight bump at the end of your driveway.

 

With motorcycles being light, it is very easy for the front end of the motorcycle to lose contact with the road surface. When the front end makes contact again with the road surface and is not in line with the back tire, the front end reacts violently transferring the energy into oscillations of the handle bars.

 

The condition, in the hands of inexperienced riders, lead to a high-side crash.

 

 

It is recommended to maintain throttle position and let the oscillations diminish. The reason for this is it allows the motorcyle weight to reach equilibrium. Applying the front brakes or chopping the throttle, puts a forward bias of the front end which combined with oscillations, leads to a break in traction causing an accident.

 

 

 

From Wikipedia

 

thx 4 the info.

[driftbaker]

Yep, that's the purpose of the steering damper: To reduce the effects of tankslapping should it happen.

 

last time see ple install steering damper on s4.. tot it was dumb.. aft reading this thread.. think it's not so dumb after all.. OMG!!!!

[JbAtRaCeR]

Now i know this called tankslap.Encounter it before at 2nd link. Was going down the bridge,open up throttle cleared my meter while chasing my fren on St11..Then suddenly it happens. Close throttle and start praying.Thank God...

[xiaowen]

scary encounter.