Worrying tankslappers on the blade

[supZ]

I'm well under way trying to sort this out but I thought I'd post it here to see if any of you guys have any ideas I haven't thought of.

The back story is the other week I suddenly got a major tankslap on as I was overtaking a couple of cars. Not hard on the throttle, probably around 50-60mph.

I chalked it down to dodgy road surface (looks pretty err undulating) and didn't think much of it.

3 days later on the same road but a few miles further down it I have the same experience.

I then had it again the following day and this one shook me up. I've had front and rear tyres slip out on track, and the odd headshake hitting catseyes with the front as it comes back down after some hard throttle but this was completely different. I wasn't pushing it, I wasn't doing anything out of the ordinary but yet I was currently in the middle of the road, handlebars swinging wildly, with cars around me convinced I was about to hit the floor.

Thankfully I got control back but at that point I thought something has to be wrong.

Bike's a 03 954 which I've had for around 4-5 years.

# Headrace bearings were replaced 2 services ago and were re-checked and are fine
# Wheel bearings seem fine, freely spins
# Tyre pressure/balance was fine (around 34psi)
# Suspension serviced - forks and shock by MCT, new oil, springs, setup all done

Even after the suspenders gone re-done the bike still doesn't feel right. Feels like there's not enough weight on the front so any bump appears to unsettle it. Even with next to no throttle at low speed the slightest bumps seem to give it a problem. Should point out that just a normal bump in the road is fine but many bumps seem to magnify the issue, it's almost like it can't recover in time and it gets worse every time (like when you're crossing painted lines)

Had another headshake again after re-fitting the forks and that so at this point I've lost all confidence in the bike.

The only thing that could be a factor is a few days before I started getting this I got a new front tyre. I've mainly used BT023s on the blade but the shop didn't have one so I got a T30 instead which is just meant to be bridgestones newer version of their sport touring tyre.

I began wondering if there was something wrong with the tyre.

To that end, to try to eliminate any possibility I've bought another 23 and had that fitted yesterday. I haven't ridden today to see if that's made any difference so that's still to be determined.

Now the road where I've mainly these issues (A30 - between bagshot/sunningdale) has a middle turning lane with hatchings on. It's almost like the front wheel is bumping over these hatchings and getting all out of alignment. The only issue is, I've been riding this road virtually every time I've been out on the bike for the last 6+ years and never had any issues overtaking.

It's happened in 5 different places now, and other than the 1st time, there's been no road works where they'd repaint the lines thick or something (clutching at straws here)

I don't think it's JUST this road, it's just I use this road to go to and from work and due to the issue I've not ridden it anywhere else

The worst thing is, it's killed my confidence on the bike. I can't overtake any more as I'm scared to death the moment I do the bike will spit me off!

Any thoughts?

TL;DR: Bike's trying to throw me off! Why?!
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CBR954RR - Daily toy
CBR600RR - Trackbike

[baldy]

Have you checked the rear shock components? There could be a problem or the geometry could have changed.
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[UrbanRacer]

Have you had this bike for a while and its now suddenly started doing it? any changes to suspension setup? Does the bike have a steering damper? Try dropping the front tyre pressure a little and see if the headshakes settle down any, if its only started since the front tyre change then i think its safe to say that probably the cause.

[JoeDougieDoug...]

So it's just happening on this stretch of road? It doesn't appear to happen anywhere else on any of your journeys?
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CBT Passed - 22 / 10 / 11 >> Theory Passed - 16 / 02 / 2012 >> Mod 1 Passed - 07 / 03 / 2012 >> Mod 2 Passed - 18 / 05 / 2012.

[robertw95]

Are the forks sitting flush with top yoke?
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07 Dt125r, sv650s k8, zx6rr 04

[samv]

did anything on the suspension change?

i very much doubt that the fron tyre is capable of causing this problem. i have had bikes with a different rear and front tyre and never had any issues.

my thought would be that the geometry changes somehow. maybe after servicing the suspension

[-]

My TDR used to weave quite badly on long sweeping corners due to worn swing arm bushings. It was noticeable on that just by tipping it on the side stand and checking for up/down play in the swing arm.

Worth a check if the front end has all been checked and the tyres are not different to normal.
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[chris-red]

Give MCT a call, I've always found Darren more than willing to have a chat about stuff like that.
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[MarJay]

I had a 954, I sold it for this kind of reason.
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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F; Cheap project: CBR900RR FireBlade
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.

[stinkwheel]

Stop looking at the front end.

Tankslappers propogate from the rear of the bike not the front. The slapping is just the result of the back-end squirming about.

So check all the sort of stuff you've already checked but at the back end of the bike.
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I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Bikeless]

I had 2 bad slappers on my 16 inch front wheeled blade but it was something they were known for, fitting a damper set low completely cured it. Both incidents were provoked to some extent, one overtaking hitting a white line about 50mph the other in a straight line about 40mph over lots of little bumps and a small crest which felt like my thumbs had been broken.
Maybe your suspension is on its limit of stability and the new tyre pushed it over with a steeper profile or stiffer carcass, i would check your rebound/compression settings front and rear and fit a damper.
My bike later had a KAIS fork rebuild to TT road spec with 90nm linear srings and rear shock setup which made it feel much better on the road.

[supZ]

Thanks for the replies all.. I'll try to answer all the questions.

[supZ]

I've just remembered there's a bike garage in taplow called PDQ. They worked wonders dynojetting my old 600F. Spent ages setting it up and afterwards it was perfect.

They do suspension too so maybe they're worth talking to.. 13 miles vs 130 does sound more appealing
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CBR954RR - Daily toy
CBR600RR - Trackbike

[evoboy]

Does the bike feel like it 'understeers' or runs wide when in a corner?

I would try backing off the compression adjusters in the forks a few clicks or quarter of a turn. See if this improves how the suspension reacts to bumps.

How much fork travel is it using under heavy braking? Put a cable tie on the fork slider and see how far it travels.

The rebound may also be set too slow so the forks dont have the time to return after hitting a bump.

All speculation without having the bike to play with unfortunately.
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[Pigeon]

[struan80]

Could it also be that since your first scare you have been inadvertently holding the bars tighter thus amplifying the issue from then on due to not being confident in the bike anymore?

Had two very small tank slappers on my non damped R6, they make me poop myself and it is difficult to determine when it's going to happen. For me solution has been softer squeeky bum roll on of throttle and yes I am slower than need be sometimes because of this fear. Was going to fit a damper but am just going to grow to know the bike better as is. My R1 has a damper and it makes the steering feel quite heavy. I've got no where near seeing if R1 will head shake.

[Pol Anorl]

you sure the frames straight?
motoliner can check and straighten it.
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[sickpup]

[supZ]

Slight update (and lol at frame straight.. surprised 'subframe twisted' hadn't come up sooner).

Rode into work today on my new front tyre and it did feel a bit better. Still got no confidence to throttle past people as I would normally but I did sit in the middle of the road on the hatchings at around 45 to see how it feels. Bumpy, moreso than I think it should be, but did seem more stable.

I don't think that's the cure, but it's a step in the right direction I feel. Need to get geometry checked out and check a few other things... will get to the bottom of this.

[sickpup]

[mfactor]

Its not done this before , you fitted different front tyre , it started playing up ,, dunno but all the clues are there.


But to be serious I used to fit tyres and you would be amazed at some weird shit mismatched/faulty tyres can cause.....


My thoughts are that the tyre caused the problem , you have now changed that but your confidence is shot, just take it easy and see how it goes...............

[Acemastr]

I had the exact same thing on the R6, open throttle, bumpy road, tank slapped so hard the pistons went back in the calipers...

Verdict: I was holding on too tightly.

Now I've relaxed my grip on the bars I've not had a single wiggle since, and the R6 is known for being a wiggler. I called up multiple places about suspension, checked tire pressures, even contemplated a damper... nope. In the end it was simply my grip on the bars.

*Edit* I run 35psi front and rear
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2017 KTM 350 XC-F - 2014 Yamaha R6 - 2005 Yamaha YZ125
2016 Toyota Tacoma Limited

[chris-red]

[orac]

I am just going to put this out there seeing as it hasn't been mentioned as yet. rear suspension linkage bearings. I have only ever had 2 set go completely and on lower powered bikes, don't know what they would do on something with the poke of a blade.

also:
https://www.youtube.com/watch?v=LmHU-gtlOKo
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[supZ]