Hard Braking Turned Into a Tank Slapper

[Navigator]

I have no idea how this happened as I was expecting the rear to come off the ground but instead the front did like 5 or 6 slaps before the tire slid. I have sport demons front and rear. A cager made a sudden U-turn right in front of me so I had to brake hard. Yes I crashed but stopped within a few inches of the car.

I will be into my 6th week of healing a broken collar bone from the above accident and would like to ride again soon. Any suggestions where I should be looking for problems? My steering head bearings are not loose and my brake pads are about 50% worn, same with the tires about 50% worn also.

This ninjette is my 10th motorcycle and I have been riding for more than 30 years. This is the first time it happened to me as all other hard braking I did always resulted in the rear coming off the ground.

Thanks for your inputs.

[Aggrotech]

Road condition when the tank slapper occurred?

[cuong-nutz]

My guess you had a lot of weight on the handle bars.

[alex.s]

^^^ +1


sounds like rider error to me

[Navigator]

Concrete road was dry, maybe a little dusty.

So there's nothing wrong with my bike? First time I ever had a tank slapper happen and it came as a complete surprise.

"Rider error" is too broad. Can you be more specific?

[250rr]

Originally Posted by Navigator

Concrete road was dry, maybe a little dusty.

So there's nothing wrong with my bike? First time I ever had a tank slapper happen and it came as a complete surprise.

"Rider error" is too broad. Can you be more specific?

+1

This is humbling. If a rider of 30 years experience can have this happen due to 'rider error', why is a noob like me not having my tank slapped silly on a monthly basis?

[cuong-nutz]

Originally Posted by Navigator

Concrete road was dry, maybe a little dusty.

So there's nothing wrong with my bike? First time I ever had a tank slapper happen and it came as a complete surprise.

"Rider error" is too broad. Can you be more specific?

Originally Posted by 250rr

+1

This is humbling. If a rider of 30 years experience can have this happen due to 'rider error', why is a noob like me not having my tank slapped silly on a monthly basis?

The stars did not align for you. 30 years experiences doesn't mean diddly squat unless you can ride any bike given to your and control it in any enviroment. street, track, dirt. I've seen many people boast about how many years they have ridden street but once they get on the track, all that experience gets thrown out the door.

The OP does not go into detail of the whole situation and how it went step by step. There are a lot of variables that can cause a tank slapper: unfamiliar with how the bike handles in different scenarios and how the rider reacts in those scenarios are the usual reasons why **** happens.

Speed has a great effect on the extent of the tank slapper as well as road condition, was the bike leaned over like as in a turn, rider weight distribution, etc.

From the picture I painted, car turns in front of rider, Rider grabs fistful of brake, front tires loses tractions, forks bottoms out and bounces up, brakes applied still, front tire out of alignment of bike, skids, bike still tank slaps and rider wrecks.

Putting weight on the handle bars under hard braking is adding excessive input to an already stressed situation. Basically the rider is fighting against what the bike is trying to do to "right" itself. Go hard into a turn at speed and putting too much input too fast and the bike will veer off from your line and you might instinctively(due to inexperience) try to overcorrect the steering input by putting more input into the bars.

The mind has to process multiple things going at once, and it's easy for one to think something did or did not happen in a split second when an oh sh!t moment happens.

! my explaination may suck as I'm a bit inebriated but sounds right in my head lol.

[Navigator]

Dunno how you can brake hard enuf to lift your rear tire off the ground without putting weight on the handlebars.

Point is, I have done the above on several bikes on several occasions but did not result on a tank slappper. Rider error, well, maybe. I do like my ninja but it needs to behave a lot better than this.

Thanks.

[Navigator]

I am seriously considering installing a steering damper now. I know these things are costly but don't want this slapper to happen again. Will a damper help? I have never ridden a bike with one before.

[Navigator]

Originally Posted by cuong-nutz

The stars did not align for you. 30 years experiences doesn't mean diddly squat unless you can ride any bike given to your and control it in any enviroment. street, track, dirt. I've seen many people boast about how many years they have ridden street but once they get on the track, all that experience gets thrown out the door.

The OP does not go into detail of the whole situation and how it went step by step. There are a lot of variables that can cause a tank slapper: unfamiliar with how the bike handles in different scenarios and how the rider reacts in those scenarios are the usual reasons why **** happens.

Speed has a great effect on the extent of the tank slapper as well as road condition, was the bike leaned over like as in a turn, rider weight distribution, etc.

From the picture I painted, car turns in front of rider, Rider grabs fistful of brake, front tires loses tractions, forks bottoms out and bounces up, brakes applied still, front tire out of alignment of bike, skids, bike still tank slaps and rider wrecks.

Putting weight on the handle bars under hard braking is adding excessive input to an already stressed situation. Basically the rider is fighting against what the bike is trying to do to "right" itself. Go hard into a turn at speed and putting too much input too fast and the bike will veer off from your line and you might instinctively(due to inexperience) try to overcorrect the steering input by putting more input into the bars.

The mind has to process multiple things going at once, and it's easy for one to think something did or did not happen in a split second when an oh sh!t moment happens.

! my explaination may suck as I'm a bit inebriated but sounds right in my head lol.

Thanks Cuong. I am not bragging in any way. My only point was that I am not a noob when it comes to bikes. I just need to understand what can be done about this since I do want to keep my ninja but right now I'm scared to ride it again. After this accident the 30 years of experience is out the door.

[250rr]

Originally Posted by cuong-nutz

The stars did not align for you. 30 years experiences doesn't mean diddly squat unless you can ride any bike given to your and control it in any enviroment. street, track, dirt. I've seen many people boast about how many years they have ridden street but once they get on the track, all that experience gets thrown out the door.

The OP does not go into detail of the whole situation and how it went step by step. There are a lot of variables that can cause a tank slapper: unfamiliar with how the bike handles in different scenarios and how the rider reacts in those scenarios are the usual reasons why **** happens.

Speed has a great effect on the extent of the tank slapper as well as road condition, was the bike leaned over like as in a turn, rider weight distribution, etc.

From the picture I painted, car turns in front of rider, Rider grabs fistful of brake, front tires loses tractions, forks bottoms out and bounces up, brakes applied still, front tire out of alignment of bike, skids, bike still tank slaps and rider wrecks.

Putting weight on the handle bars under hard braking is adding excessive input to an already stressed situation. Basically the rider is fighting against what the bike is trying to do to "right" itself. Go hard into a turn at speed and putting too much input too fast and the bike will veer off from your line and you might instinctively(due to inexperience) try to overcorrect the steering input by putting more input into the bars.

The mind has to process multiple things going at once, and it's easy for one to think something did or did not happen in a split second when an oh sh!t moment happens.

! my explaination may suck as I'm a bit inebriated but sounds right in my head lol.

Impressive for posting while taned!

[Motofool]

Originally Posted by Navigator

I have no idea how this happened as I was expecting the rear to come off the ground but instead the front did like 5 or 6 slaps before the tire slid..........

Do you remember if you released the front brake, and if so, at what point during the 5 or 6 oscillations?

I ask because a front tire in a cycle of gripping and skidding off-center could do that.

Slappers happen when the contact patch suffers a sudden lateral force which repeats at the exact time during the natural oscillation of the steering (both have the same oscillation frequency), magnifying it to an extreme.

Things that change the geometry of the steering (head angle and trial) are bad for that, and that happens each time that you brake hard, the trail (distance between the steering axis and contact patch) is reduced very much.
Lowering the front and rising the rear suspensions do basically the same.

http://en.wikipedia.org/wiki/Bicycle...cycle_geometry

As explained above, any deficiency in the front suspension (including the tire pressure and condition) is also bad (too hard or too soft).

Any changes to the inertial moment (resistance to rotation) of the whole steering may induce tank slappers, being reducing the weight of the ends of the handlebars the most common.

Please see this:
http://www.ninjette.org/forums/showthread.php?t=133351

Yes, absorbers will help, but may not eliminate the oscillations completely if they are caused by other problems.
They should allow you to turn the steering bar normally and resist any sudden movement.

[csmith12]

There are 2 schools of thought on tank slappers.

1. Don't fight it, be light on the bars and ride it out
2. Be light on the bars and change speeds ASAP

I have had 3 or 4 slappers on my R6 at the track (no damper) and a ton of head shake. Most happen when the front wheel has lifted off the ground or hitting a bump at pace. I am normally light on the bars and roll off the throttle (change speed) as best I can and let the bike figure it out on it's own. All my friends tell me I am a fool for not having a damper but meh. I know they are right and it will bite me one day but adding a damper is still NO guarantee that you will never get a slapper.

To the 2 schools of thought I would add the following;
Lean forward slightly to balance the weight to more 50/50.
An ounce of prevention is worth a pound of cure. Have you had your ninja's suspension set up to your fully geared weight? Do you check your tire pressure before every ride? Tires in good shape? Rear tire aligned well?

Tank slappers seem to be the combination of many factors, a la "The perfect storm".

[rojoracing53]

Originally Posted by Navigator

I am seriously considering installing a steering damper now. I know these things are costly but don't want this slapper to happen again. Will a damper help? I have never ridden a bike with one before.

A steering dampener help a little but I find in order for them to save you from this they have to be very tight and you may not like the ride the other 99.9% of the time.

If this was a surprise incident then its possible you slammed on the brakes bottoming the forks quite hard instead of applying the brakes quickly and progressively and as they reached the bottom of the stroke you were then at 110% braking power. We're splitting hairs here when you look at the difference between the two methods when in relation to time but both methods will have very different effects on the chassis response. For simplicity we'll slamming on the front brake in a panic method #1 and applying maximum braking power method #2

Method #1 becuase the ninja's front suspension is so soft and the chassis isn't as ridged as some the bikes it will respond differently to this method. When you slam on the brakes the forks with dive and immediatly bottom out cuasing the rear wheel to lighten up and try to lift off the ground. But while this is happening the torque in the chassis is still trying to catch up in a hurry a d if the rider is slightly heavier on one handlebar then the other or the road surface isn't perfect it can cause the chassis to flex in a horizontal direction instead of just purly lateral.

First road conditions could be anything for sand/debris to surface undulations and they only need to be minor in order to effect the bike when its being applied maximum effort.

Second handlebar input like road conditions only need to be slightly off to cause an influence and its nearly impossible to avoid this entirly for any rider so I would worrie about it to much. When your hard on the brakes you hand position of your left vs right are totally different because your right hand is holding a brake lever. This will cause the pressure being applied to the bars to differ slightly and when you rear wheel is nearly off the ground you no long have to points of stabilization to help compensate. Rear brake if used is also another variable but I'd say more so in relation to road conditions.

When your chassis flexes under load it acts like a spring and like any spring it will need to rebound eventually and this is where your tank slapper starts from. After the first slap it only gets worse because your still compressing the spring(bike chassis) by applying continuing to apply the front brake so the chassis continues to compress and rebound from left to right down the road.

A steering dampener like most rider aids act as a bandaid to act as dampener for rider or road impurities. In a perfect world you wouldn't need them but its not perfect so they are needed from time to time. Please to argue with me about how all racers use steering dampeners on thier bikes so they must be needed. First most pros have them because they are sponsored so it looks good to have it on the bike for said sponsoring company. Second even if we have it at the very lightest setting doing nothing 90% of the time it convenient to have it there just incase an imbalance in chassis setup occurres that can't be solved so we just give it a few clicks to help until we can solve the problem. Something's the problem is never solve so the dampener is always at a mid setting to keep things from getting out of hand. So a steering dampener may have saved you but at this point we will never know for sure and if you had responded just a little different you may also have saved it but at this point we will never know.

Method 2 has all the same effects as method 1 but the effects are reduced greatly because they were eased into instead of impacted. Method 2 is what you have to use going into every corner when racing fast on stock suspension. basically you apply the brakes in a progressive fashion so you ease the forks into the bottom bumper without shocking the chassis then you continue to apply most braking force loading the chassis progressively so the overall maximum load applied to the chassis is much less then when you impacted it from slamming the brakes in method 1. With less overall less load and no impacting force being applied to the chassis it won't have excess energy stored in it so it won't need to rebound while still applying brakes. So no horizontal defection and no head shaking.

Now onto why other bike are less prone to this outcome but not in any way immuned. Most other bikes with equally soft front suspension as the Ninjette typically have more rake in the front end(like a chopper) so the chassis dynamics are totally different and much more forgiving. As for other sportbike with similar chassis dementions, well they will normally have stiffer valving and springs. With stiffer suspension even when slamming on the brakes the impact when reaching the bottom of the forks is reduced because you had to first get through the suspension first. Also if we're talking a more modern sport bike then it will have a much stiffer chassis that's less prone the flexing so it won't have a rebounding effect. Now I will say that if you manage to flex a current generation chassis then the volatility of the energy stored is much greater then on the Ninjette and when released it can be very violent. For this reason most sportbikes come equipped with steering dampeners.

I know that was a long explanation and honestly I made all of it up as I typed based on theorems I thought of as I went but it all seems to make sense in the end so I hope to could find it useful.

If you want to help prevent this in the future
1. use method 2 by practicing it all the time by doing a trackday on the Ninjette, this is by far the hardest of the three options I'm going to give you.

2. Equip a steering dampener and hope it works, I can't say I'm fond of this solution but to each his own I guess.

3. Fix your front suspension to handle the extra load applied in an emergency and when paired with method 1 it works even better. As to fixing the suspension I have a thread in the works currently that reviews the changes I've made to mine last week that fixed every issue including the one you experience and many more. So keep an eye out for it over the next few days.

Best of luck with your full recovery.

Ps. I didn't proof rear this and did type it on my phone so.....well you get the idea

[Panda]

Originally Posted by csmith12

I have had 3 or 4 slappers on my R6 at the track (no damper) and a ton of head shake.

You are a braver man than I.

[alex.s]

I don't think I've gotten a tank slapper on the 250. But a few on my ****** 600... It's an eye opener and butthole closing moment for sure.

[Navigator]

Thank you everyone for your replies!

It's gonna take a while to digest and make sense out of all this but I do have the time.......

I do rapid on/off braking all the time but that got quickly thrown out the door in this panic situation. I didn't have enough braking distance (at least that's what I thought) so my panic reaction was to slam on the front brake.

Speaking from experience, I did off road bikes some time ago and owned an RMX-250 at one time. That bike had about 12" suspension travel and it's a lot softer compared to the ninja's. Still, I can do hard braking on the RMX without experiencing any tank slapper. Perhaps its relative lightness compared to the ninja helped in that aspect, and possibly the frame is a lot stiffer too. Regardless, this leaves me scratching my head on the steering geometry theory because surely the RMX's rake & trail varies a lot more compared to the ninja what with the 12" travel on the forks.

Looking forward to reading your thread rojoracing!

Thanks again everyone.

[csmith12]

Originally Posted by Panda

You are a braver man than I.

I can say I am fully trained on being super light on the bars. If you ever pay close attention to my pics, my hands don't even wrap the grips all the way. Don't get much more relaxed than that.

[alex.s]

27d rake... thats not going to tank slap without trying.

also, quite the novel to type up on a phone, jason.

[250rr]

Originally Posted by 250rr

Impressive for posting while taned!

I meant tanked. Apparently the condition when I posted this!

[Tigerpaw]

I RARELY hear about tank slappers on this frame. I think you had the worst possible luck ever, and will never see one again on a ninjette. If it was me, I would invest any possible "damper money" on protective gear. There are so many more types of wrecks to worry about, outside of tank slappers.

Heal up soon!

[rojoracing53]

Here's the link to my suspension setup that will give the bike much better feel on the brakes.
http://www.ninjette.org/forums/showt...200#post695200

[SLOWn60]

Originally Posted by Navigator

I am seriously considering installing a steering damper now. I know these things are costly but don't want this slapper to happen again. Will a damper help? I have never ridden a bike with one before.

^^ This. Yes it can help reduce or eliminate them. But don't crank it up to maximum! On a scale of 0-10; a 3 is about right for "set it and forget it" which is probably what most riders will do.

I will never own a bike without a steering damper. It doesn't make you bullet proof but it will reduce the severity of the vast majority of "tank slappers".

As to why it happened? Too many variables to know the true cause from reading an internet post but most times they are exacerbated by rider inputs. Lots of videos show violent tank slappers but once the rider falls off; the bike straightens up and smoothly rolls along until something gets in its way!

[Kurgan]

Originally Posted by 250rr

+1

This is humbling. If a rider of 30 years experience can have this happen due to 'rider error', why is a noob like me not having my tank slapped silly on a monthly basis?

Mostly because most "noobs" don't push as hard as someone with 30 years of riding experience, and a tank slapper generally requires the rider to be at or beyond their own handling skills and the handling limits of the bike itself.

[SLOWn60]

Oops! I see I dug up a 2 year old thread! Sorry! Just following the related post recommendations! I'll check the stale dated stamps a little more diligently! Lol!
However; as I'm new here: it's all new to me and there are some excellent question & answer exchanges here and without the flaming so often found in other forums! Well done all!
And so despite this being an old thread; I found an interesting video from Dave Moss discussing causes of tank slippers and how to avoid them!
http://www.youtube.com/watch?v=LmHU-gtlOKo&sns=em

[250rr]

Originally Posted by Kurgan

Mostly because most "noobs" don't push as hard as someone with 30 years of riding experience, and a tank slapper generally requires the rider to be at or beyond their own handling skills and the handling limits of the bike itself.

Fair point.