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  • speed wobble
  • birdy
    Free Member

    Have recently bought a road bike and am just getting used to using the drops. Coming down a long fast descent this afternoon (about 40mph the bike develops crazy speed wobble. Tried to bring it back under control but ended up picking a nice soft leafy patch at the side of the road to bail out in. Bloody petrifying!

    Never experienced anything like this on an MTB though.

    Anyone else experienced this?

    druidh
    Free Member

    PIO??

    birdy
    Free Member

    Say what?

    coffeeking
    Free Member

    pilot induced oscillation. Dumb ass at the controls. Garbage in, garbage out etc ūüôā

    stuartlangwilson
    Free Member

    Apparently pressing your knees against the top tube helps, must be true as I read it on the internet somewhere…

    birdy
    Free Member

    Hey ive seen plenty of talented moto gp riders do something similar. If they do it then I think i can be excused.

    thomthumb
    Free Member

    40 mph sounds slow for it to develop.

    list of things to check in no particular order:

    tyre seated
    tyre pressures
    headset
    quick releases
    hub bearings
    wheels true, round etc

    thisisnotaspoon
    Full Member

    sound’s a bit hairy, try dragging the rear brake a little to see if it helps. Quite likey to be you doing it subcociously (i.e. the oscilation is just out of sync with your reaction time, so you end up making it worse). Stay lose and unlock your elbows, you should be holding onto the bottom of the bends, not the flat sectons, theyr just for sprinting.

    birdy
    Free Member

    Ive put a new stem on recently and i think my headset might have been slightly loose. Not sure if my brakes were centred correctly as well (ie one block hitting the rim before the other)

    aP
    Free Member

    Probably loose headset ‚Äď but check for true wheels, loose skewers, mis-shaped tyres. Are you hanging on for grim death? Try not to as if you clench up the bike moves you rather than when you take a lightly looser grip you move as well as the bike.

    Pickers
    Full Member

    I bought a TT frame from a chap who’d had this problem, had no confidence in the bike at all.
    It had an older type threaded headset which needed 3 whole turns of the adjusting nuts to set right!
    I saw 48mph on it down the hill at Glynneath without problem. I’d look at the headset first.

    birdy
    Free Member

    As I said im new to using drops, so I might be a little on the tense side.

    deuchars
    Free Member

    Def check for loose h.set/front hub qr etc as posted above but as I understand it any bike can shimmy in right/wrong circumstances-basically just structure hits it’s resonant frequency.Had this happen on a road-bike yrs ago + scared the crap out of me.
    It’s impossible to react fast enough to damp the vibration-if you try you’ll just feed it,all you can do is press thigh(s) around top tube to damp it…assuming presence of mind-I hit the back brake + must’ve got out of the dangerous speed range but OMG scary,lorry up the back of me too.
    Never had anything like it on a mountainbike-stiffer frames + steering geometry more stable probably.

    speaker2animals
    Full Member

    It’s easy to say but it can be rider tension. Try to relax. Maybe get used to descending on the hoods before going for drops.

    Having said that check mechanicals. As noted tyres seated ok, headset. Too tight can be worse than loose. As you ride you’re constantly making subconscious corrections. If the headset is too tight or even brinelled your micro adjustments have to become bigger especially at speed where gyroscopic effect adds to force needed for corrections. Once this starts then you get speed wobble/tank slapper. On motorbikes they recooend that you let go of bars. Oh yeah.

    Do your wheels need balancing? Try spinning them with your brakes loosened so they aren’t effecting the spin. If they always stop at same place, typically valve at bottom. Try adding some lead foil on opposite side spokes and spin till stopping point is random.

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