Tankslapper, nearly got ejected !!
10-24-2007, 04:28 AM
#1
Senior Member
SuperSport
SuperSport
Thread Starter
Join Date: Dec 2006
Location: Victoriaville, Quebec, Canada
Posts: 880
Tankslapper, nearly got ejected !!
Well it was a great group ride last sunday, I was following that crazy 25 bikes group on a northern ride trough twisties, the man and machine were doing pretty well...until I hit a straight line, I was mildly accelerating and hit a few bumps at close to 200 km/h (120 MPH) and had a tankslapper of a lifetime 
The bike shaked so violently and widely that both legs went off the pegs and wide open, could not hold the handles and went lock to lock, I basically remember not to sit on the bike but kinda "float"on it, I did not really consider the possibility to save this one, it just stopped like it came since I lost enough speed. I still havent recovered from this one and lost confidence in my bike, I have been trough air pressure, SAG (max front preload and still 1/3 in, rear one notch before lesser preload), steering bearings, no death grip (but I may have pulled a bit since I had my tankbag and my upper body was exposed), the last culprit could be my tires, the wear pattern is a bit wierd on the front and the back is becoming flat. I hit 190 later and got a slight wobble, I guess it would hit the sweet spot at 200, I kept it under 180 for the rest of the ride and had no problems except my broken confidence.
Should I ditch my front or even both tires or get the front balanced ?? Change forks springs to raise the front some more ??
The bike shaked so violently and widely that both legs went off the pegs and wide open, could not hold the handles and went lock to lock, I basically remember not to sit on the bike but kinda "float"on it, I did not really consider the possibility to save this one, it just stopped like it came since I lost enough speed. I still havent recovered from this one and lost confidence in my bike, I have been trough air pressure, SAG (max front preload and still 1/3 in, rear one notch before lesser preload), steering bearings, no death grip (but I may have pulled a bit since I had my tankbag and my upper body was exposed), the last culprit could be my tires, the wear pattern is a bit wierd on the front and the back is becoming flat. I hit 190 later and got a slight wobble, I guess it would hit the sweet spot at 200, I kept it under 180 for the rest of the ride and had no problems except my broken confidence.
Should I ditch my front or even both tires or get the front balanced ?? Change forks springs to raise the front some more ??
10-24-2007, 08:31 AM
#3
Senior Member
MotoGP
Join Date: Apr 2005
Location: Montreal
Posts: 5,631
Not sure if this is relevant at all but I was warned by Roger Ditchfield of Revolution Racing in the UK that running a raised rear end (or dropped front) with stock forks can make the bike dagnerously unstable at high speed.
10-24-2007, 09:32 AM
#6
Senior Member
SuperBike
Join Date: Jul 2005
Location: MN
Posts: 1,548
I have raised the rear about 5mm and have the RC51 forks set to not more than 5mm lowered relative to stock height - have not had any problems with stability at all. But neither the forks nor the shock are stock and when I've backed off the rear damping have noticed that its more twitchy.
10-24-2007, 09:33 AM
#7
Senior Member
MotoGP
Join Date: Jan 2005
Location: Gainesville FLA.
Posts: 3,844
I've owned my SH for almost 7 years now and have several mods including a raised rear and shorter usd forks and have NEVER had a tank slapper or even become unstable. This after about 15 or more track days and hitting 140+mph several times, even before with stock suspension I've never even worried about it, so something is amiss.
10-24-2007, 09:35 AM
#8
Senior Member
SuperBike
Join Date: Feb 2007
Location: Portland, Oregon
Posts: 1,051
i also just mounted up a fork brace, i think that adds a lot more stability to the forks.
just keep riding ( slowing the pace ) till you feel more confident. it may have been the stars aligned for it to happen but i'd check everything out ...
tim
10-24-2007, 10:07 AM
#9
Banned
MotoGP
Join Date: Aug 2007
Location: Lake View Terrace, CA
Posts: 5,942
I would say it was the tires. You should get your suspension redone but the bike souldn't be that unstable in any case. I have revalved\resprung stock front forks and a revaled\resprung stock rear shock with the forks up 10mm and a little over 6mm up in the rear, no damper and have no problems with head shake of any kind.... but as always YMMV 
10-24-2007, 04:05 PM
#12
Senior Member
SuperSport
SuperSport
Thread Starter
Join Date: Dec 2006
Location: Victoriaville, Quebec, Canada
Posts: 880
both BT-20 stock size. I had the bike for 3 years and maybe had 2 wobbles at highway speed, I ran at least 30 200+ pulls and never had a hint of a problem, the bike was quite stable and I thought that an event like this would be impossible. The rear is at the second lowest preload setting, with my weight on it it drops from full extent to about 3/4 inch, the rear seem too stiff or I'm too light (155 lbs).
The front is another story, with the adjuster cranked all the way in it's sitting almost 2 inch , I have to use all my strength to pull the forks all out. I may have a broken front springs, anyway these springs have to go. They are the stockers yes.
If I come across a cheap damper, I'll buy it, definitely.
The front is another story, with the adjuster cranked all the way in it's sitting almost 2 inch , I have to use all my strength to pull the forks all out. I may have a broken front springs, anyway these springs have to go. They are the stockers yes.
If I come across a cheap damper, I'll buy it, definitely.
Last edited by gboezio; 10-24-2007 at 04:17 PM.
10-24-2007, 05:15 PM
#13
Administrator
World Champion
Join Date: Dec 2004
Location: Fulton, MO
Posts: 105,287
Sounds like you have quite a few miles on these tires. I'd try replacing them first, then check steering head bearings next. Question: If you roll to 60mph (100? kph) and let go of the bars, do they shake while decelerating down to about 20mph?
10-24-2007, 05:15 PM
#14
Senior Member
Back Marker
Join Date: Oct 2007
Posts: 130
well i am at ease with the tank slapping.. i had someone tell me that they did it alot.. and this was a suzuki gsxr guy that told me this, he has a 1000 turbo, and his did it to him a few times, and he said it is scary as hell..
well to ask a question about the rear preload setting.. can the rear be lowered by adjusting it?
well to ask a question about the rear preload setting.. can the rear be lowered by adjusting it?
10-24-2007, 05:51 PM
#15
Senior Member
SuperSport
SuperSport
Thread Starter
Join Date: Dec 2006
Location: Victoriaville, Quebec, Canada
Posts: 880
I read on this topic and the closest thing I read that could do this is worn rear tire, it says that the rear act as a pendulum and the outer edges make abnormal thrust angles ?!? I'll re-check the air pressure with a better pressure gauge than the one of the mini compressor that I have here. I think that the front of the bike dived under the intense slapper.
Last edited by gboezio; 10-24-2007 at 05:53 PM.
10-24-2007, 05:55 PM
#16
Senior Member
SuperSport
SuperSport
Thread Starter
Join Date: Dec 2006
Location: Victoriaville, Quebec, Canada
Posts: 880
well i am at ease with the tank slapping.. i had someone tell me that they did it alot.. and this was a suzuki gsxr guy that told me this, he has a 1000 turbo, and his did it to him a few times, and he said it is scary as hell..
well to ask a question about the rear preload setting.. can the rear be lowered by adjusting it?
well to ask a question about the rear preload setting.. can the rear be lowered by adjusting it?
10-24-2007, 06:47 PM
#17
Senior Member
SuperSport
SuperSport
Thread Starter
Join Date: Dec 2006
Location: Victoriaville, Quebec, Canada
Posts: 880
Someone else had it, same speed, lock to lock
http://www.fireblades.org/forums/gen...er-occurs.html
4th post from top
http://www.fireblades.org/forums/gen...er-occurs.html
4th post from top
Last edited by gboezio; 10-24-2007 at 07:14 PM.
10-24-2007, 10:34 PM
#18
Senior Member
Back Marker
Join Date: Dec 2006
Posts: 113
+1 on replacing tires - my last tank slapper was due to worn front tire - I run Michelin Pilot powers front and back - best tires out there - I have a rear shock shim with 5 MM and a dropped the from forks about 2-3MM but I sit low in the bike - about 1" removed from the seat foam for lower center of gravity. Stable as hell.
10-25-2007, 05:22 AM
#19
Senior Member
SuperSport
Join Date: Aug 2004
Location: MICHIGAN
Posts: 731
I've owned my SH for almost 7 years now and have several mods including a raised rear and shorter usd forks and have NEVER had a tank slapper or even become unstable. This after about 15 or more track days and hitting 140+mph several times, even before with stock suspension I've never even worried about it, so something is amiss.
10-25-2007, 06:44 AM
#21
Senior Member
Superstock
Join Date: Jul 2007
Posts: 387
Sounds like YOU need......
https://www.superhawkforum.com/forum...ad.php?t=13039
https://www.superhawkforum.com/forum...ad.php?t=13039
10-25-2007, 09:33 AM
#23
Senior Member
Back Marker
Join Date: Feb 2005
Location: New York City
Posts: 146
Did you go back and check the road surface? The only tank slappers I've had were when the bumps in the road were at the perfect distance apart creating a resonance or vibrating frequency that destabilizes until you pull through it.
10-25-2007, 03:44 PM
#24
Senior Member
SuperSport
SuperSport
Thread Starter
Join Date: Dec 2006
Location: Victoriaville, Quebec, Canada
Posts: 880
I remember to hit some bumps, more like a crack, but that was very samll, there is no doubt that it induced the slapper, but after a few seconds, I tried to catch up the others, and had a wobble at 190, again some small bumps triggered it, so I kept it under to 180 for the rest of the ride.
I suspect my whole bike setup, I guess it's an uncalculable resonnance of many components, I guess that the steering damper is not an option for spirited rides.
I suspect my whole bike setup, I guess it's an uncalculable resonnance of many components, I guess that the steering damper is not an option for spirited rides.
10-29-2007, 01:18 PM
#26
Member
Squid
Join Date: Apr 2007
Location: Connecticut
Posts: 46
Had a minor tank slapper experience on my cbr after a tire change. Rode home carefully, raised front tire off ground using a sling around upper triple, loosen all axle / pinch bolts / nuts / etc that secure front axle, spin wheel by hand as fast as possible, then grab front brake. Repeat a few times and this seems to align front axle or something. If too much brake drag to get the wheel spinning to your satisfaction, push the calipers in a bit but only a bit, you still need the brake to really bite when you pull the lever.
Good luck.
Go Sox.
Good luck.
Go Sox.
10-29-2007, 07:22 PM
#27
Senior Member
Superstock
Join Date: Jul 2007
Posts: 387
I'd like to see someone "muscle" their way outta THIS.....
http://www.youtube.com/watch?v=rMwDmN-s8Cc
http://www.youtube.com/watch?v=rMwDmN-s8Cc
10-29-2007, 07:27 PM
#28
Banned
MotoGP
Join Date: Aug 2007
Location: Lake View Terrace, CA
Posts: 5,942
I'd like to see someone "muscle" their way outta THIS.....
http://www.youtube.com/watch?v=rMwDmN-s8Cc
http://www.youtube.com/watch?v=rMwDmN-s8Cc
11-01-2007, 11:36 AM
#29
Senior Member
Back Marker
Join Date: Oct 2006
Location: Fresno, Ca
Posts: 224
This has me a little concerned. I may be wrong, but a cycle in proper running order should not pull in any direction without input. If it is pulling to the left; is it possible that your rear wheel is out of alignment? Forks bent?
If the tires need it, certainly replace them and have them balanced. Then when remounting, make sure all alignments are correct and and everything is torqued properly.
I have gotten the front light out of turns and all shaking works itself out very quickly. No slappers for me.
Let us know if you find anything out of spec.
11-02-2007, 09:27 AM
#30
Senior Member
SuperSport
SuperSport
Thread Starter
Join Date: Dec 2006
Location: Victoriaville, Quebec, Canada
Posts: 880
The complete bike investigation is over, bike pulls straight, no wobble at any speed even hands off, the front suspension feels like a 2x4 it transmit incredible shocks but is not bottoming out, it happened before and I easily hear it., head bearing is healthy, front fork should be dead straight since I bought the bike new off the crate and never hit anything, the front tire pressure was on the low side, 27 psi, but should not have caused such a wild rodeo. The worst thing on my bike is the front fork that seem to have only an inch of travel, a spring or even better fork upgrade don't seem to be an option, otherwise I'll definitely kill myself. The front SAG sits at 2 inches from full extent and I barely could push the forks down at all more than one inch, probably 1 1/2 while braking.
I don't know how normal it could be, that the adjustment is maxed out and I can't even come close to and ideal setup. The fork sits at 1 1/2 inch while on the sidestand and IMO should be fully extended or damn close.
This Showa forks looks like modded trunk cylinders...
I don't know how normal it could be, that the adjustment is maxed out and I can't even come close to and ideal setup. The fork sits at 1 1/2 inch while on the sidestand and IMO should be fully extended or damn close.
This Showa forks looks like modded trunk cylinders...
