What would cause 'speed wobble'?

jonnyc2420
jonnyc2420 Posts: 557
edited February 2011 in MTB general
Evening all,

This is a new one on me, and something i cant work out......

My current bike, Orange P7 is so damn unstable at any speed when riding no handed i'm starting to think its possesed....almost like the 'tank slappers' you see motorbikes get.

This is when on road (ok, quiet country lanes :roll: ), and at anything above a fast walking pace, the bars simply start to wobble to the point of stupidity .

ive never had a bike do this and cant figure out what the cause could be, tyres, road surface dont seem to make any difference - could it be the bike geometry? its as it came from orange with no changes to frame, fork or wheels.

i'm baffled - any thoughts?
Falcon Sierra - 80's
Muddy Fox Courier - 80's
GT Palomar 90's
GT Zaskar LE - 90's
Cannondale k v 900 90's
Santa Cruz Bullit - now
Orange Evo 8 STOLEN 26/09/10
Orange P7 Pro
Lots of kites.

Comments

  • Northwind
    Northwind Posts: 14,675
    Yeah, stop riding no-handed.
    Uncompromising extremist
  • ummm, thanks Northwind, but after 35 miles or so my backs killing me, and sitting up / no hands offers relief :)

    this is from a motorbike site......, ive had (and got) mtbs with more and less rake on the forks so cant be that. but the shopping trolley/wheel analogy just about sums up whats happening.

    Wobble is a steering oscillation that is basically the same as the wobble of a grocery cart wheel. Weave is a fish-tailing type motion involving roll and yaw. Every situation is different, of course, but wobbles are a slightly higher frequency than weave. Wobble is pretty much always caused by something in the front end, and weave is always caused by something in the rear. Sportbikes are much more prone to wobble because of the very small amount of rake. Steering head dampers can help with this, but they exacerbate the weave.

    In my years of repairing motorcycles, the vast number of wobbles was caused by faulty steering head bearing, or incorrect adjustment of steering bearings, while weave was almost always caused by loose swingarm bearings.


    they also go on to say accelarating past 80mph may help :shock: or fitting a steering damper :?

    no still no idea...
    Falcon Sierra - 80's
    Muddy Fox Courier - 80's
    GT Palomar 90's
    GT Zaskar LE - 90's
    Cannondale k v 900 90's
    Santa Cruz Bullit - now
    Orange Evo 8 STOLEN 26/09/10
    Orange P7 Pro
    Lots of kites.
  • Northwind
    Northwind Posts: 14,675
    Well then:

    http://www.intobikes.co.uk/products/001347/Ohlins_Steering_Damper?src=fro&highlight=027350

    Just kidding ;) I would ignore that motorbike site, it's not all that well conceived even for motorbikes, most tankslappers kick off from the rear end not the front (which is why TLs and 636s are famous for it while GSXRs with essentially the same forks don't) but the geometry and use is so different it's not likely to apply. Do you get it while coasting? Or just when pedalling?
    Uncompromising extremist
  • Michael J Fox riding the bike?
  • I get it with both, if it was just pedalling i could put it down to bad spinning technique, but its while coasting too, if anything slightly worse coasting than under power. :?

    ive got a few rangerover dampers lying about, but they dont match the colour of the bike...... :)
    Falcon Sierra - 80's
    Muddy Fox Courier - 80's
    GT Palomar 90's
    GT Zaskar LE - 90's
    Cannondale k v 900 90's
    Santa Cruz Bullit - now
    Orange Evo 8 STOLEN 26/09/10
    Orange P7 Pro
    Lots of kites.
  • Andy!
    Andy! Posts: 433
    cone lose on a hub?

    wheel distorted?

    Not in the drop outs right?
  • Anonymous
    Anonymous Posts: 79,667
    Hub bearings, headset bearings, fork bushes, bent wheel. In that order of likeliness would be my guess.
  • cooldad
    cooldad Posts: 32,599
    Or drunk.
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

    London Calling on Facebook

    Parktools
  • Stuy-b
    Stuy-b Posts: 248
    iv had this happen a few times when riding sat up hands off the bars, i think it has something to do with un weighting the front end as as soon as i lean forward to the bars again it stops.
  • nicklouse
    nicklouse Posts: 50,675
    Stuy-b
    you are on it. as bikes get slacker angles you sit further back. then you sit up. this un weighting of the front wheel by rider mass being further back is the biggest change over the years.

    you then have the change in trail, the difference. between the contact point and the steering axis.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • Stuy-b
    Stuy-b Posts: 248
    its hard being right all the time hahaha
  • dennisn
    dennisn Posts: 10,601
    I would think that fast speeds would cause speed wobble. I've never heard of it at slow speeds. Or is "slow speed" sort of an oxymoron? :? :?
  • Anonymous
    Anonymous Posts: 79,667
    Slow fast would be an oxymoron, slow speed, or low speed isn't.
  • timpop
    timpop Posts: 394
    Agreed. But I had issues once with my bike excessively wondering off when going no-handed. It was just the headset so once that was sorted it was much better. Ok but still not amazing though but that's because of the weight transfer thingy that goes on as stated above.
    But I don't have to worry about that now as it was removed from my possession last week by some thieving b'tards. Grr. (thought I'd pop that in, still quite sad) :(
    Many happy trails!