Tankslapper Action

[CB ARGH]

Hey guys,

Whenever I have the packrack on the bike with no more than 5kg loaded onto it, when travelling at 50km/h with no hands the handlebars start the tankslapper action slightly, going left and right very very quickly. I can also feel it wanting to shake a little at 100km/h when I go along with one hand.

I expect it is something to do with the bearings?

Help!

[FJRider]

Hey guys,

Whenever I have the packrack on the bike with no more than 5kg loaded onto it, when travelling at 50km/h with no hands the handlebars start the tankslapper action slightly, going left and right very very quickly. I can also feel it wanting to shake a little at 100km/h when I go along with one hand.

I expect it is something to do with the bearings?

Help!

Perhaps if you keep your hands on the bars... it might not happen...

[Rockbuddy]

lose the packrack

[Del Fuego]

ride at 20kph?

[Usarka]

Anything at all without the rack? Ie. could it be amplifying a problem......?

[FJRider]

ride at 20kph?

or... dont ride ...no problems then...

[Jantar]

Check your front tyre. I suspect uneven wear.

[FJRider]

Check your front tyre. I suspect uneven wear.

Its a honda... unbalanced rider ???

[Mom]

+ 1 from Jantar. Check wear and pressure on the front tyre, surprisingly simply thing that can cause a head shake.

[piston broke]

wheel bearings,balance?

[T.W.R]

Front tyre pressure, head stock bearings, wheel bearings, & swing arm bearings; any one of these could be the cause of the issue. The packrack is just amplifying the problem

[CB ARGH]

Okay, going with the tyres... could the fact that it's running a BT45 on the rear and a Dunlop GPR100 on the front cause the problem? I believe they are two different types but the guy in the tyre shop said there would be bugger all difference.

[Jantar]

Okay, going with the tyres... could the fact that it's running a BT45 on the rear and a Dunlop GPR100 on the front cause the problem? I believe they are two different types but the guy in the tyre shop said there would be bugger all difference.
It wouldn't help, but probably not an actual cause. I would suspect that the front tyre is worn more on one side than on the other, but with plenty of tread still in the center.

[CB ARGH]

It wouldn't help, but probably not an actual cause. I would suspect that the front tyre is worn more on one side than on the other, but with plenty of tread still in the center.

I have just checked the tyre on the front, there seems to be small cracks in the rubber where it meets the road when upright. Tread wear seems even from side to side.


Thanks for the help guys.

[Number One]

Someone wise and experienced told me that you shouldn't mix radials with cross ply tyres.

Don't ask me anything else I can't tell ya but my old baby blade was solid and stable as no matter what I stuck on the back of it. Not nice and I would echo what others have said - keep your hands on the bars...if it's doing this you are much better off in control of it

[nodrog]

is it a tank slapper or a wobble? there is a difference, if its a wobble i would check tyre pressure, and if that is fine i would get it balanced before i went any further checking bearings etc.

[Brian d marge]

lose the packrack
x 2
horrible things

[Squid69]

Hey guys,

Whenever I have the packrack on the bike with no more than 5kg loaded onto it, when travelling at 50km/h with no hands the handlebars start the tankslapper action slightly, going left and right very very quickly. I can also feel it wanting to shake a little at 100km/h when I go along with one hand.

I expect it is something to do with the bearings?

Help!
What pressure are your tyres... When did you last check?
Has tyre got a flat spot just to the right of the centerline?
Any dings in the wheels?
Is the back wheel straight in the swingarm?
Check your wheel beerings.
Check your head beerings.



What about the back one?


is it a tank slapper or a wobble? there is a difference, if its a wobble i would check tyre pressure, and if that is fine i would get it balanced before i went any further checking bearings etc.
+1!
but...
He said it was a wobble.
If it were a "Proper tankslap" while he is riding with no hands then his frame probably resembles a bannana...

[mogiman]

had the same prob on gsxr 87
firstly my tyre was going down very slowly causing same prob fixed that and it still happened but not as bad,next i found that one of my fork seals was leaking causing unbalanced forks fixed that seemed to mellow it more ,but still had a prob ,found that because when i put the power on front wheel went light got the tank slap back but no where near as bad so dropped my forks in the trees by 20mm putting more weight forward on the front wheel seemed to fix the problem ,another cause you could have a slight warp in you rotor which the brake pads catch causing the slap check for uneven wear on your pads and disc ,and another thing you should adjust your rear shock when putting a load or 2 up as , if you dont your front end will be very light Im pretty sure all the pros on here will agree with me
hope this helps

[Mishy]

,and another thing you should adjust your rear shock when putting a load or 2 up as , if you dont your front end will be very light

I agree with you. The extra weight on the back would seem to be causing the problem. Check REAR tyre pressure, and consider using a little more when carrying a load. typically we would expect to use an extra 2psi when carrying pillion or luggage, as well as an extra 2psi if you are spending a lot of time at high speed :) Also, a little extra preload on the rear spring could help if it's doing what I think it is.

[HenryDorsetCase]

I saw the worst tankslapper I had ever seen on Saturday that someone rode out of. It was at the track day, and I was following a guy on a big road bike.

coming out the sweeper on to the main straight, head down and I realise the guy in front is shaking wildly, heading for the wall..... at one point I thought he had let go and was kind of lying on the seat.... went on for half the length of the main straight it looked like, but he managed to ride it out. Mad skills!. I did notice he wasnt on any of the other sessions...... might have got a bit of a scare.

[bsasuper]

Sounds like your 250 is on steroids, last bike that did that to me was a fireblade in the first 3 gears.

[Mishy]

I saw the worst tankslapper I had ever seen on Saturday that someone rode out of. It was at the track day, and I was following a guy on a big road bike.

coming out the sweeper on to the main straight, head down and I realise the guy in front is shaking wildly, heading for the wall..... at one point I thought he had let go and was kind of lying on the seat.... went on for half the length of the main straight it looked like, but he managed to ride it out. Mad skills!. I did notice he wasnt on any of the other sessions...... might have got a bit of a scare.


WOOOOOOOHOOOOOOO ! ! ! !
time for fresh undies :)

[Robert Taylor]

What others have said about accessories such as packracks amplifying the problem is 100% true. It can be a number of things lurking beneath the surface and placing weight ( and aerodynamic drag ) in that area is the absolute worst possible place to put weight on a motorcycle. For moderate loads tankbags make a whole load more sense as you are placing the weight much closer to the centre of gravity.
Back in the 70s when I was working on motorcycles there were a number of traffic police XS650s with rear panniers and radios in a low rear topbox. We had one that was using all the road at 140kmh plus. All it took to 'tip the balance' was a front disc with 8/100th millimetres runout. A new disc fixed it. Put weight in a silly place and you will run into such problems.
Notwithstanding a number of possible issues suggested by others you could try altering the dynamic geometry of the motorcycle to try and compensate. Increase rear spring preload ( which you should do with a load anyway ) and / or lower the front of the bike by raising the front forks in the clamps by say 5mm.

[Sully60]

Okay, going with the tyres... could the fact that it's running a BT45 on the rear and a Dunlop GPR100 on the front cause the problem? I believe they are two different types but the guy in the tyre shop said there would be bugger all difference.

As the above posters said, load distribution.

As for the above don't go back to that bikeshop, that is shit advice. The guy in the bikeshop probably ordered that tyre in error and just told you that to offload it.

[Squid69]

As the above posters said, load distribution.

As for the above don't go back to that bikeshop, that is shit advice. The guy in the bikeshop probably ordered that tyre in error and just told you that to offload it.

I thought that running a Bias ply and a radial together was a big no no! in fact, i would go as far as saying that its probably got quite a lot to do with the weave.
get the gpra 100 rear, unless your into trackdays you should be fine on it!
Bt45s are good, and you can make them squeal when pushed hard, but the fronts chew out quickly.

[CB ARGH]

Thanks for the help guys,

I have inspected the front tyre in the sunlight and it is time for a new one. One of the forks is leaking fluid so I'll get some new fork seals too. I am sure this should fix the problem.

It's good to see the corners of the tyre wearing more than the centre! :headbang:

[mikeey01]

I saw the worst tankslapper I had ever seen on Saturday that someone rode out of. It was at the track day, and I was following a guy on a big road bike.

coming out the sweeper on to the main straight, head down and I realise the guy in front is shaking wildly, heading for the wall..... at one point I thought he had let go and was kind of lying on the seat.... went on for half the length of the main straight it looked like, but he managed to ride it out. Mad skills!. I did notice he wasnt on any of the other sessions...... might have got a bit of a scare.

Yeah I saw this as well, it was sooooo close.. it looked as though it was that violent it threw his hands off the bars, nothing to hold onto and speed so he caught the wind blast and it just about ejected him off the back.. this some how managed to settle it down enough so he could re-gain control, by this time wall was close..
If ya know Rua-huna it started about 200 mtrs before the start finish line and ended up about 200 mtrs after.. the most violent and closest I've ever seen to nearly binning it!

Rider completed said lap Very slowly and never saw him out on track for the rest of the day!

[CB ARGH]

I've got the bike apart now, sadly no riding time for a while.

After taking off both of the front forks to change the seals over, I wiggled around at the steering column to see how the bearings were going, they're dry as crap and 'clicked' into the centre position, this could have been the cause. I took it all apart and found no damage so re applied the grease and put it back together, doesn't do it anymore.

Should be on the road in no time.

[86GSXR]

Here's something I posted elsewhere after a very nasty one 9 days ago. Writing this with one hand :pinch:


I've had a couple of scary ones years ago on first generation Gixxers. But last Sunday I had the most close up encounter with one of these bitches to make me never want to encounter one again. Put me in hospital for two days and I'm now recovering from four broken ribs, a cracked shoulder blade, a badly broken hand, plus various scrapes and abrasions.

I was going up the Pahiatua track, one of my favourite roads and one I've done hundereds of times.

I was following a mate on a Sprint ST and I was on my (now wrecked) 08 Tiger.

All was normal, we were travelling at a reasonable, legal pace and just coming out of an uphill right hander onto a short straight. It was a beautiful sunny day, no wind and a completely dry road in good condition. In short, a perfect biking day.

My tyres (Pilot Roads) were warm and in decent condition. The front and rear suspension were set up pretty well for my weight and riding style.

As we rounded the bend my front suddenly let go and slid a few inches to the left. I have no idea why it slipped, maybe there was a small stone, diesel patch, slippery patch, whatever.

When it regained traction the bike started to highside me off to the left. I reacted pretty quickly and hoisted it back but by then the front and rear had become completely uncoordinated and I was in the midst of the most violent and powerful tankslapper I could ever have imagined.

I tried applying power and tried to even it out but I was helpless to do anything in a controlled manner as the oscillations were just too powerful.

The only thing I could do was to just bail off before I was thrown off. I did that and landed hard on my back on the right side doing the aforementioned damage to myself.

It's a bit of a blur after that, but apparantly my bike kept on shaking itself up the road before falling over and sliding up the road and down a bank.

Later on in hospital my friend told me that he'd seen most of it in his mirrors and I'd looked like a rag doll with my legs going everywhere. I don't remember that bit as I must have been too busy trying to control it, unsuccessfully.

I was saved by my fully armoured and well fitting leathers, which held up pretty well. My helmet was really crunched in at the front and I thank god I always wear my gear and had made a point of making sure my helmet strap was tight before setting off.

I'm in for a few weeks of pain yet though, broken bones, especially ribs are NOT fun!

Always wear armoured, snug fitting gear and do your helmet up securely PLEASE! I wouldn't wish this shit on anyone :done: