Alterning steering behaviour

Discussion in 'UK and Europe' started by Nc, Sep 13, 2003.

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  1. Nc

    Nc Guest

    Not sure if this one needs to go to rec.bicycles.tech, but I'll try the UK first....

    My partner rides an Orbit Mercury with flat bars (a tiny road bike with 26in MTB wheels). The
    steering is somewhat twitchy, and she would prefer it to be a bit slower steering and thus
    more stable.

    The Mercury has a traditional steering stem with locknuts and expander bolt. Her bike has a very
    short reach stem, originally intended for drop-bars. The handlebars are straight (MTB), with the
    grips/brakes/shifters set well inward of the original bar width.

    So, what changes will give an improvement in steering and how to fit it ?

    I can think of the following: Different tyres - does this make any difference ? Currently using
    Specialized Fat-Boy slicks. Different stem, taller and longer reach, possibly combined with
    different bars - might make a slight change to the feel of the steering, but doesn't alter the
    geometry. Would it make much difference ? Replacement forks, either longer (decreases the steering
    angle, which should increase trail) or with a different trail. Altering the existing forks to
    increase the trail, either by bending the forks or moving the drop out position. Stacking the head
    bearings to increase the effective fork length. Probably not enough fork steerer to reach the
    top-nut to do this.

    I guess this will need a trip up to Madgetts in Diss, but advice in advance would be useful.

    Nigel
     
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  2. Pete Biggs

    Pete Biggs Guest

    NC wrote:
    > Not sure if this one needs to go to rec.bicycles.tech

    It's a good one for them so you should post there as well.

    > My partner rides an Orbit Mercury with flat bars (a tiny road bike with 26in MTB wheels). The
    > steering is somewhat twitchy, and she would prefer it to be a bit slower steering and thus
    > more stable.

    How long has she had it and how many miles done?

    > The Mercury has a traditional steering stem with locknuts and expander bolt. Her bike has a very
    > short reach stem, originally intended for drop-bars. The handlebars are straight (MTB), with the
    > grips/brakes/shifters set well inward of the original bar width.
    >
    > So, what changes will give an improvement in steering and how to fit it ?
    >
    > I can think of the following: Different tyres - does this make any difference ?

    Not much at all, in the way required.

    > Different stem, taller and longer reach

    Longer reach will make the steering slower but that's not worth doing if it would make the riding
    position uncomfortable. It would need to be more than 15mm longer to make a significant difference
    to steering, possibly a lot more.

    > , possibly combined with different bars - might make a slight change to the feel of the steering

    Different bars may help stability and feeling of stability quite a bit, but first, try different
    heights and tilts.

    > Replacement forks, either longer (decreases the steering angle, which should increase trail) or
    > with a different trail.

    Different forks could make a big difference. LESS offset or rake will make the bike more stable.
    See: http://www.phred.org/~josh/bike/trail.html
    . But there's a danger of the steering feeling very weird with a different rake (plus or minus).

    Longer? No!

    > Altering the existing forks to increase the trail

    No.

    > , either by bending the forks or moving the drop out position.

    No no!!!! Will mess up steering and will be dangerous if you got that even slightly wrong,

    > Stacking the head bearings to increase the effective fork length. Probably not enough fork steerer
    > to reach the top-nut to do this.

    No.

    I think it's all either a case of more practice and setting required or bike is wrong size & shape
    for your partner. The steering of the bike is likely to be ok for a rider of the right size - but
    perhaps not everyone will happen to like the "feel" of this particular bike.

    ~PB
     
  3. NC wrote:

    > Not sure if this one needs to go to rec.bicycles.tech, but I'll try the UK first....
    >
    > My partner rides an Orbit Mercury with flat bars (a tiny road bike with 26in MTB wheels). The
    > steering is somewhat twitchy, and she would prefer it to be a bit slower steering and thus
    > more stable.
    >
    > The Mercury has a traditional steering stem with locknuts and expander bolt. Her bike has a very
    > short reach stem, originally intended for drop-bars. The handlebars are straight (MTB), with the
    > grips/brakes/shifters set well inward of the original bar width.
    >
    > So, what changes will give an improvement in steering and how to fit it ?
    >
    > I can think of the following: Different tyres - does this make any difference ? Currently using
    > Specialized Fat-Boy slicks. Different stem, taller and longer reach, possibly combined with
    > different bars - might make a slight change to the feel of the steering, but doesn't alter the
    > geometry. Would it make much difference ? Replacement forks, either longer (decreases the steering
    > angle, which should increase trail) or with a different trail. Altering the existing forks to
    > increase the trail, either by bending the forks or moving the drop out position. Stacking the head
    > bearings to increase the effective fork length. Probably not enough fork steerer to reach the
    > top-nut to do this.

    New (straight) forks might help, but you then have to watch for toes fouling the front wheel or
    mudguard. 26" wheels are a good way to design a small frame, but if it's really "tiny" then there
    could still be compromises in the design.
     
  4. Tony Raven

    Tony Raven Guest

    NC wrote:
    > Not sure if this one needs to go to rec.bicycles.tech, but I'll try the UK first....
    >
    > My partner rides an Orbit Mercury with flat bars (a tiny road bike with 26in MTB wheels). The
    > steering is somewhat twitchy, and she would prefer it to be a bit slower steering and thus
    > more stable.
    >

    Go for a longer stem providing it doesn't make her feel too stretched to reach the bars. Longer
    stems = slower steering, shorter stems = faster twitchier steering. Most of the other changes will
    make no difference other than new forks to increase trail or longer to slacken the head tube angle.
    However that is more expensive and more difficult to do

    Tony

    --
    "If you tell the truth you don't have to remember anything." Mark Twain
     
  5. Pete Biggs

    Pete Biggs Guest

    Zog The Undeniable wrote:

    > New (straight) forks might help, but you then have to watch for toes fouling the front wheel or
    > mudguard.

    That's not right. Straight fork blades are offset at an angle from the crown, so the offset (aka
    rake) can be (and usually is) the same as that with curved forks. In other words the front wheel
    and mudguard end up in exactly the same place and steering is exactly the same when the offset
    is the same.

    Straight forks are usually chosen for their modern looks, really. Curved forks are chosen for their
    traditional looks and supposed better damping qualities.

    ~PB
     
  6. Nc

    Nc Guest

    "Pete Biggs" <pLime{remove_fruit}@biggs.tc> wrote in message
    news:[email protected]...
    > NC wrote:
    > > Not sure if this one needs to go to rec.bicycles.tech
    >
    > It's a good one for them so you should post there as well.
    >
    > > My partner rides an Orbit Mercury with flat bars (a tiny road bike with 26in MTB wheels). The
    > > steering is somewhat twitchy, and she would prefer it to be a bit slower steering and thus more
    > > stable.
    >
    > How long has she had it and how many miles done?

    Several years and at least 1000 miles. 45 mile ride on Friday last week.

    > > So, what changes will give an improvement in steering and how to fit it ?

    > > Different stem, taller and longer reach
    >
    > Longer reach will make the steering slower but that's not worth doing if it would make the riding
    > position uncomfortable. It would need to be more than 15mm longer to make a significant difference
    > to steering, possibly a lot more.

    Could work if the stem was higher as well. I'll look at this option. I'll need to replace cables
    (not enough length to move them much further at the moment).

    > > Replacement forks, either longer (decreases the steering angle, which should increase trail) or
    > > with a different trail.
    >
    > Different forks could make a big difference. LESS offset or rake will make the bike more stable.
    > See: http://www.phred.org/~josh/bike/trail.html

    I've read that before. Perhaps I should go and calculate the trail for the bikes in the shed and
    make some comparisons.

    > . But there's a danger of the steering feeling very weird with a different rake (plus or minus).
    >
    > Longer? No!
    >
    > > Altering the existing forks to increase the trail

    > > , either by bending the forks or moving the drop out position.
    >
    > No no!!!! Will mess up steering and will be dangerous if you got that even slightly wrong,

    Sorry, not clear. I had in mind re-building the existing forks by a frame maker, not hitting them
    with my own hammer ! To my mind, that's very similar to new forks.

    > I think it's all either a case of more practice and setting required or bike is wrong size & shape
    > for your partner. The steering of the bike is likely to be ok for a rider of the right size - but
    > perhaps not everyone will happen to like the "feel" of this particular bike.

    Size is an issue; at the time we bought it, there were not many bikes suited to 5ft riders, this has
    a 42cm frame and took more than a year to find. The number of small bikes around has improved a bit,
    but we're loathed to spend another £500+ on another bike. The steering is quick and a bit twitchy -
    I can feel it (though I look comical riding it) - slightly slower might be better.

    Nigel.
     
  7. Ivor Cave

    Ivor Cave Guest

    NC wrote:

    >
    > Size is an issue; at the time we bought it, there were not many bikes suited to 5ft riders, this
    > has a 42cm frame and took more than a year to find. The number of small bikes around has improved
    > a bit, but we're loathed to spend another £500+ on another bike. The steering is quick and a bit
    > twitchy - I can feel it (though I look comical riding it) - slightly slower might be better.
    >

    I thought the steering on the giant ocr was a bit twitchy after an older claude butler but after two
    days of commute it felt normal to me.

    Ivor Cave
     
  8. Pete Biggs

    Pete Biggs Guest

    NC wrote:
    >>> Different stem, taller and longer reach
    >>
    >> Longer reach will make the steering slower but that's not worth doing if it would make the riding
    >> position uncomfortable. It would need to be more than 15mm longer to make a significant
    >> difference to steering, possibly a lot more.
    >
    > Could work if the stem was higher as well.

    Generally longer stems need to be lower. It's the short stubby ones that are usually put up high.

    >>> Altering the existing forks to increase the trail
    >
    >>> , either by bending the forks or moving the drop out position.
    >>
    >> No no!!!! Will mess up steering and will be dangerous if you got that even slightly wrong,
    >
    > Sorry, not clear. I had in mind re-building the existing forks by a frame maker, not hitting them
    > with my own hammer ! To my mind, that's very similar to new forks.

    Ok, but there's still a risk of them ending up asymetrical and new forks are likely to be cheaper
    than getting the work done. See St John Street Cycles for examples.

    ~PB
     
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