Got a bit of a tank slapper going on a few days ago going downhill at 40+ mph and wondered if it was down to the long valve inner tube I had fitted in an emergency. The wheel is true to within a mm or so and is it has never happened before. Changed the inner tube now and will find out tomorrow for myself but wondered in anyone else has had similar tank slapping issues at high speeds and what it was down to.

Not a pleasant feeling I can assure you. 😯

I doubt it…I was almost asking if you were having a laugh.

When you say tankslapper, you mean speed wobble?

When you say tankslapper, you mean speed wobble?

Probably a very vigorous wobble but at the time felt like I had a puncture and the world was going to end.

What are you talking about?

What are you talking about?

Really.?

I’m not a physicist, but I’d have thought a couple of grams difference in weight distribution on your wheels will have a negligible effect on the stability of a rider and bike at 40mph compared to all the other variables (wind, road surface, frame & wheel flex, rider position, alignment of the planets etc).

But yes, whatever the reason, speed wobbles are definitely rather brown-chamois inducing when they happen 😯

http://www.hewittbikefitting.co.uk/wheels/wheel-balancing/

As a road rider with a long sucessful raceing career i can tell u that ur barking up the wrong tree.your wobble was 100% not caused by long valves. im not saying this was the problem but when going downhill at high speed you have to be relaxed and at one with your bike, the bike has to be part of your body and flow you have to be confident and relaxed

What the hell is a tank slapper? and airbus387 are you serious?

most probably, it’s all testament to the underlying issues of Presta Valves, you need some nice short schraders in there

HEXHAMSTU i have came down mountains in excess of 60mph and im telling you if your body gets all tense and not withone with your bike your can have your worse nightmare i have seen the aftermath of riders getting it wrong bigtime

Ahh….”tank-slapper” reminds me of a girl I once dated who hailed from Bovington.

Tony Foale and Vic Willoughby wrote a book about motorbike design that has probably the best insight into why a single track two-wheeled vehicle (bike) wobbles.

Firstly as the handlebars/forks etc turn (wobble) from side to side the front end of the frame will rise and fall. This can be seen when stationary if kneeling at the side of the bike facing the bike (looking at the head tube top tube) and turning the bars slightly to-and-fro. You should be able to see that the headtube toptube fall slightly 3 or 4 millimetres when the bars are turned left or right and rise as the bars are returned to the centre/staightahead position. In a speedwobble this includes the rider and frame rocking up and down slightly, pivoting about the rear hub.

Ironically it is the stability of the bike that causes the wobble of the bike created at speed by the two wheels spinning as gyroscopes create a restorative force that brings the front wheel back to the straightahead position. Unfortunately this restorative force is so great (too much) that it overshoots (over compensates) and takes the handle bars too far to the opposite side. This cyclical (almost pendulum) effect then increases in intensity to produce the speedwobble.

http://www.tonyfoale.com/Articles/Balance/BALANCE.htm

Brilliant answer there Macavity.

No experience with speed wobbles on push bikes but quite a bit with motorbikes – I raced early Kawasaki triples 🙂

Anyway, the fault or characteristic that caused the issue was 95% of the time nothing to do with the front end as such, usually something daft like rear tyre pressure or seating position.

My first road bike was a no-brand carbon frame from china. It was cheap but light, but very flexy. Got a bad case of speed wobbles above 45-50.
Eventually replaced it with a cervelo R3, very stiff, never happened again (although I use deep rims with long values).
So could be a flexy frame…

there was a good article and series of letters in the ctc magazine a while back – they called the effect “shimmy” from memory it seemed to be related to resonance. The way to prevent crashing, again from memory was to close knees on the top tube to damp the vibration or maybe that just reduced the risk of sh*tting yourself 🙂

Buy yourself an early Honda Fireblade, with the 16″ front wheel if you want to try a tank slapper… 🙂

There’s an old YouTube clip of one at the Isle of Man.

Buy yourself an early Honda Fireblade, with the 16″ front wheel if you want to try a tank slapper…

Or one of the original TL1000R – think they all had to be recalled to be fitted with steering dampers IIRC.

Maybe that’s the solution – stick a steering damper on it? 😉

imo a road bike getting a speed wobble is mainly down to resonance between the steering trail and frame stiffness. the frame flex is enough to allow the spring of the frame to interact with the steering and it can resonate. I’ve ridden some bikes (old steel ones) where it can be induced briefly at will with a near-hands-off light tough on the steering. A mid-to-long trail frame with a skinny steel tubeset is the potential worst offender (older MTBs can do it badly on tarmac too), a neutral, short trail frame in stiff al or carbon will rarely if ever get a wobbble on.

The valves ‘could’ be the start if they really upset the wheel balance and you initiate a minor turn along the descent (long-stem brass valves on a light wheel and bike at 40mph, possibly), but the steeering and frame flex is most likley to be what turns the minor wobble of an off-centre-weighted wheel into genuine speed-wobble.

Foale’s writings on this and every other area of motorbike handling are very good reading, but imo don’t always relate to MTBs / esp not road bikes. Road bikes have much less trail (<60mm normally) so the front-end rise and fall under steering is minimal (you steer by leaning a road bike mainly anyway) and the weight isn’t a significant factor. (edit to add, your weight on the bike is more sig, but only if you’re practically motionless on the bike)

i have experienced this, but usually at much lower speeds/when riding no hands.
shimmy was indeed the term used at that time (early 90s)
general opinion seemed to be that it would afflict really light steel frames the worst.
i seriously doubt that wheel balance would have any effect unless the wheel was so far out of true that it would be uncomfortable to ride anyway.
any time it has happened to me its been in the 15-20mph region.
EDIT: ive never had it on a mtb, always a road bike.

just ask Sheldon, he may be dead but he has the answers
http://www.sheldonbrown.com/brandt/shimmy.html

Think you’ll find out that it will be your wheel bearings that need changing rather than the wheel build itself.

Could it be that the tube that has the valve is the problem or that you perhaps didn’t get a nice uniform re-installation of the tyre on the rim.

It’s all very well talking about being tense/relaxed but from the OPs post I assumed he has done this before and not had this problem. I know tension can have an effect, one of the classic solutions for tankslappers on motorbikes is to actually let go of the bars momentarily.

I’d take the tyre off and reinstall personally. My understanding is that something has changed that has effected the harmonics of the bike and introduced an escalating wobble at this speed.

Is the wheel sitting exactly back in the dropout too. Late thought.

[video]http://www.youtube.com/watch?v=9jSYiU-JdRw[/video]

Tank slap on a pushbike is often caused by a loose headset…

Edit: JUst read Sheldon’s dismissal of this as an old wives’ tale; he’s wrong.
Again.

loose headset or slight out of alignment either forks or rear end wheel can be true but if your alignment is out can cause this

http://www.tonyfoale.com/Articles/RakeEx/RakeEx.htm

http://www.tonyfoale.com/book/Turning.PDF

http://www.tonyfoale.com/Articles/Tyres/TYRES.htm

speed wobble will be caused by a resoance effect. You will have to check everything and change on thing at time and retest.

Fitting a valve stem or moving a speed sensor amy balance the wheel better. Your tyre may not be seated proeprely.

Oh by the way the gyroscopic effect of the wheels on bicycle stability is longer considered important as several studies using bike with a counter rotating wheel have shown stability remains. There have been a couple of recent papers by the guy at Cornell on this.