Tank Slapper anyone?

Has anyone experienced a tendency for the VFR to go into a tank slapper? If I'm riding down a hill, under deceleration, and take my hands off the controls at about 45 mph, she starts shaking her head....scary. It doesn't do it all the time - about 50% of the attempts. I'm hoping it is only the front tire or some other easy fix. I believe I have a Continental BT014 on the front with lots of tread - wearing evenly. On the rear I have a Dunlop 616, near new. The bike is a 2003 with 5600 miles, non-ABS. I haven't played with tire pressures yet, but keep it at around 38 psi. I weigh 240 lbs. Any suggestions?

Thanks,

Hillbilly.

 

Yeah... don't take your hands off the bars under hard deceleration downhill. ;-))

Seriously, it can happen due to many different variables: tire cupping, tire load, street surface, head bearings, unequal fork tube oil/air.

Basically, something has upset the front suspension so the tire is unloading and loading the front tire pogo-like in an attempt to equalize the load on the the front forks. Similar to a trailer fishtailing on the back of a vehicle - except with the forks, it's really fast. The tire may never actually leave the ground.

Typically, acceleration usually fixes this as it reduces the load on the front suspension and allows the front forks time to equalize the load.

That being said, too much unloading of the tire can lead to a tank slapper also - but only in specific circumstances. 4 years ago, I had a bike accelerate past me doing 80-100. Speed limit was 45. He was on a Suzuki TL1000 racer-replica. He hit a good-sized pothole and went into a nasty tankslapper. After six revolutions he went over the handlebars. I was first on the scene and it was not a pretty site...

Unloading from the high acceleration, short fork angle, and the pothole upsetting his front suspension led to the tankslapper.

check out this website for more info: http://www.motorcycleproject.com/motorcycle/text/shucking.html

 

Thanks for the info and the article. I may wait until the front tire needs to be replaced then have the dealer perform the wiring harness recall and check the steering head bearing all at the same time.

 

i would check the front tire real closely my 06 did the same thing , and the front tire was what caused it. front was cupped just a little.

 

Not to sound stupid, but what is a tankslapper?? I'm new to cycles and just starting out.

 

on a car it's called death wobble. it's when the front wheel starts to shake uncontrollably and lots of times ends up in a crash.

 

That is just deceleration wobble, not a tank slapper.

The VFR's steering geometry makes it almost immune from tank slappers, unlike the notorious TLR. When you have a tank slapper, the bars will oscillate so fast they are a blur and you wouldn't be able to grab them without breaking things in your hands. You are along for the ride at that point and they often don't end well.

Try some different tires, if that doesn't fix it, steering head bearings.

 

Tires are about $120 before mount and balance, but a set of steering bearings is about $40-60. Easiest way to check the bearings is put something heavy on the pillon seat while it's on the the center stand. once the front tire is airborne, slowly move the handle bars and feel for any notches that the bars want to stop at (usually right at center). if there are no notches found then move onto the pull check. sit on the floor stradling the front tire. gently, but firmly, pull the forks towards you and see if there is any play (might want someone to hold the back of the bike to keep it from coming off the center stand). play is bad.
replacing the bearings is something anyone can do, but you will probably need a shop to remove and install the new races on the steering stem. The manual will give you some great tips, and keep you pointed in the right direction.

 

At 5600 miles on low grade Dunlops, I would bet $100 the problem is the tire over the steering bearings, and steering bearings would be more than $120 for the labor if you paid someone to do it.

And you don't need a shop to remove the races, there are notches cut in the steering head so you can pound out the races (relatively) easily.

 

I would be willing to bet a used regulator that your steering head bearings need to be tightened. Period. Do that first before spending money on something el$e.

 

mmmmm..... I've commented on this before , having gone through the same sort of situation with mine .I swing Left turn into right , an s , and in the middle of the transition I found the bike shaking it's head like a bull . The bike has 2000 miles on it , so I'm doubting Head bearing . Tyres are the stockers , in our case they are Metzelers , and I am happy with em . Was a bit unnerving at first , but I havent really minced the bike since then to repeat the occurrence . I now head into an s expecting it to do this , and even though It's only a mild flutter , but I don't particulalry enjoy being ridden, instead of me riding the BIke ...
I see various answers bandied around , I'm hoping to cancel out most of them by the fact of having a relatively newish bike .

 

I agree with Porshe Bob. The steering head bearing torque spec tightens them to a set pre-load. so just because they don't wiggle when you try to move them in the shop...they might not be torqued up to the pre-load spec. I chased a front end decel wobble all around the barn with balancing tires, new tires, etc. Turned out to be the steering head bearing pre-load torque.

"tank slappers" have the bars going lock-to-lock. If you look at the pavement afterward there are hash marks where the tire jumped from skipping one way, then the other. The 16" front wheel models were famous for it. Best way out is to gas it (if you're still hanging on to the bars).

 

I ad the same problem with my 06 and i had a badly cupped stock Dunlop (they are crap)with 6000 miles on it. I replaced it and the decel wobble went away. It wasn't really a tank slapper it would just wobble. hard to imagine a head bearing being too loose on a new bike

 

Hillbilly - My '02 does the shimmy-shake. 4500miles. Bike is solid when riding, but when i let go of the bars the front wobbles (bar ends travel about 1-2" or so?). It doesn't seem to grow worse...i can kinda just sit there an watch it. But its rather unnerving - never had other bikes do that before. Definitely needs a look at the steering stem torque / stem bearings. Think I have original tires too...those seem to be OK though.

Don't knock the tiller! Ha ha...nevermind, its deserved. I've got a TL too...its a beast. Motor is top notch, but the chassis makes you work for it. Never had any wobble issues. But its unforgiving if you get in over your head (which is easy w/ that v-twin). And now that I'm here, I might as well whore it off... :biggrin:


I digress...back to VFRs...

 

About the steering head bearings, I think the inherent problem is this...

When the new motorcycle is assembled the "stem bearing adjusting nut" is usually tightened the first time to 18 foot pounds, then the front end is rotated lock-to-lock at least 5 times to seat the bearings.

Then it is loosened and retightened again to 18 foot pounds (on my '98 VFR800), making sure that the steering stem moves smoothly without play or binding.

That's fine as a starter, however after some break-in miles, maybe 2,000 miles, I like to do the following:

1. Put the bike on the centerstand.

2. Have somebody heavy enough sit on the passenger seat so that the front tire is off the ground.

3. Then rotate the handlebars lock-to-lock and see if there is any drag.

4. On my bikes I want a small amount of drag. (unlike the service manual). Then I tighten the steering stem nut until I can feel just a tiny bit of drag.

5. Then I take the bike for a test ride by going up to 60mph, then decelerate with both hands off the grips (but very close) to see if there is any "tank slapper" tendency. I do this test on every bike I buy.

NOTE: If you are a new rider don't attempt do this.

When I was racing 250 gp bikes we use to do the same thing.

Okay, all experts flame away . . .

 

Just a question...

Why would you even do that in the first place? I don't think it would be a problem if you just kept your hands on the bars. That would be the cheapest fix. :biggrin:

 

Sometimes it is nice to lean back and stretch, take a break. I have a throttle lock and ride with no hands for long periods of time

 

Most mfr's recommend replacing tires if they are over 5-6 yrs. old.

Seems they tend to get hard and loose their resiliency.

 

i do too but not on steep downhills unless its a nice straight road where i can see everything ahead of me! i dont know maybe it just sounded like he was haulin ass when he let off the bars... :tongue:

 

Amen to that.