Headset & Stem Tightness

Discussion in 'Cycling Equipment' started by noonievut, Apr 30, 2006.

  1. noonievut

    noonievut New Member

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    Twice while riding fast downhill into a cross wind I've had my friend end shake (I thought I had a flat). It's only when I'm going 50km+ and downhill into a cross wind. It usually happens when I'm sheltered from the wind by trees then there is an opening and the wind hits. It takes a lot of strenth to keep the front end straight.

    When I inspected how tight the bolts were on the step (the ones that attach to the fork/headset and the headset (bolt on top of fork...sorry if I don't have part names right) I was able to turn them with the allen key easily. So I tightened them to the point where with good pressure they were tight (not crazy pressury, but I put some weight behind it).

    To the question...how tight should these bolts be? The headset bolt on top and the 2 that attach the stem to the fork?
     
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  2. serenaslu

    serenaslu New Member

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    The single bolt on top of the headset is used only for adjustment or pre-tensioning of the steerer. It's tighteness, after adjustment, becomes inconsequential (aside from rattling) as the steerer is held into the headset by the stem's clamping bolts when properly installed.

    see:
    http://www.parktool.com/repair/readhowto.asp?id=65

    Manufacturers' specs will vary as to the exact torque which should be applied to the stem mounting bolts. As an example, Ritchey typically recomemends a maximum torque of 5Nm.

    I would be suspicious that your front end wobbles are caused by headset adjustment unless it is way-way out of whack.
     
  3. noonievut

    noonievut New Member

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    Thanks...I was looking for that section on the park tool site and couldn't find it. I understand what you're saying about the headset adjustment. However, when I was checking tightness I did notice that the bottom bolt on the stem was pretty loose, can this be the reason?

    I plan to take the bike to the shop (only after getting the bike back from the shop for a tune-up did I notice this though...), but in case I ride around now I want to make sure any adjustments I make won't cause much problem.
     
  4. HowardSteele

    HowardSteele New Member

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    I've had the bearings collapse in my headset from time to time; this always starts to happen on downhill fast runs.

    The sealed bearings seam to be hardier so if you dismantle the headset before just tightening it consider the sealed type if they are available for your specific bike.

    I wash my bike after every ride and it took me a while, and replacing bearings to figure out how much water collects in the headset. Now i always turn the bike on end after a wash to drain the headset. The water defiantly shortened the bearing lifespan.
     
  5. noonievut

    noonievut New Member

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    How can you tell specifically if the it's the bearings? Did you notice a wobble on fast decents? In general I find steering to be 'loose', not a problem per say, but even when I'm not pedalling with my hands off the bars, the front end doesn't want to stay straight.
     
  6. artmichalek

    artmichalek New Member

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    It had nothing to do with the headset/stem. If it did the front wheel would be shaking independently of the bars, and you probably would have crashed. Front end shimmy is a resonant vibration phenomenon, which often happens at high speeds. It's usually excited by hard pedalling or cross winds. You can usually get it under control by putting your knees up against the top tube or pushing hard forward on the bars and back against the saddle.

    This sounds like an unrelated wheel dish/frame alignment problem.
     
  7. noonievut

    noonievut New Member

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    Thanks again...so to get my mind straight on this, the vibration is something that will happen from time to time given the fast speeds and strong cross winds, so I'm best to take it easy going downhill with cross winds...and that's it? I assume there isn't anything wrong with the bike or anything I can do to avoid it?

    In the 2 times it happened the winds were strong and cutting right across the road (from cover to no cover so it was like a strong gust of wind). I've been down hills faster since this happened, but I was downwind or into the wind, so I attribute it to the cross wind specifically (just surprised it hadn't before, which made me think it's a mechanical thing).
     
  8. artmichalek

    artmichalek New Member

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    I've noticed the same thing with cross winds. When you get hit with a sudden gust of side wind it's going to cause all kinds of off-axis vortex shedding around your front wheel, which may excite resonance vibration. There's not too much you can do to avoid it. Just pay attention, and if it happens again don't hit the brakes too hard.
     
  9. noonievut

    noonievut New Member

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    It's hard to avoid white knuckle braking, especially when you're going fast and your hit by this vibration. Do you think it would help if I have my weight more towards the front-end (I'm usually weight back when descending), also, when it hits to you go soft on the brakes, or pump them (while doing the other things you suggested)?

    Thanks.
     
  10. dhk

    dhk New Member

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    Yes, would say weight on the bars helps. I had the dreaded speed wobble for the first time last weekend when I took my hands off the bars at 55 kph to sit up and stretch (it was a long descent). Just putting weight back on the bars damped it out quickly. Since it's never happened before at any speed up to 88 kph, assume taking weight off the bars was the cause. Down low on the drops is faster anyway, and IMO feels best for stability and grip when cranking through a twisty descent.
     
  11. noonievut

    noonievut New Member

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    I've never went 'no hands' on a decent at that speed, but when the wobble happened, both times I shifted my weight way back (moutain biking thing) for fear I may go over the bars. Next time, hopefully there won't be one, I'll stay in the drops, weight even, light squeeze on brakes, knees pushing against the top tube...and we'll see what happens. I need to have this happen once and be able to control it to get the confidence up.
     
  12. noonievut

    noonievut New Member

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    Well it happened the other day, going downhill with a cross wind gusting at about 50km an hour. I wasn't going too fast but when it hit I pushed my knees against the tob tube and pressed out against the handlebars, gentle on the brakes and it went away instantly. I'm still not comfortable going too fast downhill with a cross wind, but at least I know this works.
     
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