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 :shock:
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 ??

sounds scary, glad it turned out well. do you have stock suspension otherwise? have you altered front or rear ride height much from stock?

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.

good thing you are ok.. i have heard that these bikes are bad about tank slapping.. kinda got me worried..

Not sure where you came across that rumour as the VTR is generally reputed to be quite stable. For added insurance I run a steering damper but that is really only because I got a good deal on one.

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.

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.

i run one too. i have the front end dropped a little and run take-off ( race DOT ) which have a taller rear profile. i also have it regeared -1+2. on bumby roads when i get a little ham fisted at the apex i could tell the front end was getting VERY light. a recipe for disaster. so i got a steering damper.
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

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 :)

What kind/brand/model of tires?

By reading his post I got , Front:funky wear
Rear:Flat spot so I kind of assumed from there.......:rolleyes:

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.

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?

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?

Good point, no not at all the bike will just decel may go a tad to the left, but no biggie, no shakes, the bike have a solid feel, I checked the head bearings and they are as good as new.
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.

The preload is more to adjust the ride height to account for the rider weight and spring wear.

Someone else had it, same speed, lock to lock
http://www.fireblades.org/forums/gen...er-occurs.html
4th post from top

+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.

Same here.

i have approx. 15,000 mi. on mine.
running with busa and gixxer 1000.
never had a prob even running flat out as fast as bike would go.

Sounds like YOU need......
https://www.superhawkforum.com/forum...ad.php?t=13039

so whats going on your bike?

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.

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.

after 2 years on this bike I never had a tank slapper.

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.

I'd like to see someone "muscle" their way outta THIS.....
http://www.youtube.com/watch?v=rMwDmN-s8Cc

All kinds of fun happens at the IOM........

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.

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.

Attachment 31295

This Showa forks looks like modded trunk cylinders...

Even if your sag and other numbers are off, at 155 lbs you should NOT have the front adjusters all in that could most definetly cause adverse effects... The springs are to soft for your weight and that means you have to live with the numbers being off...
The adjustment on pre-load isn't enough for anything above 45 Kg or 100 Lbs... and it really shouldn't be used to force sag like that... then you get really harsh bouncing like you describe...

Back it of a bit and it might help, increase rebound dampening a bit instead perhaps... (depending on what it's set at now)... and by everything Holy, get a pair of new front springs...

Even if you don't get springs now... I'd recommend swapping that fork oil... For some reason Honda hasn't really included that in the service intervalls but 3 years (04 model) and X miles is most definetly way overdue... I swap mine roughly every year as it comes out of winter storage... probably a bit overkill but the cost is negligable...

I started this after I first got the bike 3 years ago (bike is a 97) and found that the PO newer ever swapped the oil in 7 years... The oil was 1 part foam, 1 part water and the rest black goop and it smelled like rotten eggs...:(

Yeah, I definitely need to raise them to 1 ", stiffer springs seem to be the next best thing, as oil it seems that the valves don't flow enough oil, I thought to use thiner oil to help this.
But as you say oil is overdue or at least I need to have a look in there, I keep an eye open for a set of better forks, never know.

I'm not so sure thinner oil is a good idea...

I'd recommend correct springs for your weight, Race Tech main valves, don't bother with the rebound valves as the stock should be sufficient with the "taper mod"... and stock oil weight... then get the sag dialed in and start trying out settings...

Mayby Greg and the other experts can chime in... I'm like a fish in water with electronics and got loads of experience with tires, both bikes and cars... but in suspension my only experience specific on bikes are my own VTR... Cars are a whole other ball game...;)

But my general knowledge of suspension say's that oil ages... And forcing it through that stock valve X times ages it even faster... and adjusting for ride height and sag with the settings for suspension character is a bad idea as you overload a soft spring... that should be done with spring stiffness and a spacer...

I am 95kg and my vtr has stock suspension. I have never experience it tank slap. I always squeeze the tank(under power) hard with my legs to prevent it. Something I only learned riding dirt bikes.

You are fairly light so Id imagine the springs will be OK. Back your compression off a little more . To much will make it unsettled. Increase rebound in the rear will settle the ass end down. It will be like a pogo stick only weighing only 155pound causing the rear shock to rebound to fast.

These bikes are fairly neutral and turn slow unlike a race bike(gsxr or R6 etc) so it is highly unlikely you will need to firm up the suspension for road use

Cheers

Joel

With a few tweeks (like pulling the forks up 10mm and raising the rear ride height 5-6mm) and good suspension the SH turns very quick and firming up the suspension is one of the best things you can do to the bike. YMMV

I have to disagree. In the end it's all about the skill of the rider. Even when my suspension was stock I had very little trouble keeping up with the 600cc "race bikes" on the track or twisties.

I love it when young guys make fun of my bike. I just smile and invite them to come on a ride with me.;)

I'd say it's more unlikely that you will get a decent setup with stock front springs at 95kg... Since the stock springs are estimated to be the right stiffness for about 45kg (~100 Lbs) And that combined with a rear spring hard enough to load a passenger and you have a seriously mismatched setup...:(

I'm about your weight (93 kg) And I found it slightly unnerving to take a corner fast with stock setup as it was on the edge of bottoming out even with a flat road... That was fully stock with it cranked as hard as possible, and still waaay to soft...

And yeah... slip the forks up a few mm and then slow isn't really the right word...:)

I think of a broken coil spring, has anyone has his fork travel sitting less than half the full travel ?? That seem odd to me, but still the bike turns like a semi truck, I would drop the forks for a track day, it will help for sure.

My preloads, yes they are equal.
Attachment 31294

Um... you are aware that they are set to the absolute maximum preload? ie past the normal setting? That could definetly make them behave odd...

With that setup I would be scared to ride the bike...

If I where in your shoes I'd back it off until the full diameter of the top is visible and see what happens... It can't really make matters worse can it?

I'd say you are overloading your poor springs to the point where they go rigid...