BB drop - fact or fiction?

Discussion in 'Cycling Equipment' started by Clyde, Nov 14, 2003.

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  1. Clyde

    Clyde Guest

    Between 2 bikes, the same except for bottom bracket drop, one is 65mm, the other is 75mm, could you
    tell the difference when riding?

    Clyde
     
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  2. On Fri, 14 Nov 2003 20:02:35 +0000, Clyde wrote:

    > Between 2 bikes, the same except for bottom bracket drop, one is 65mm, the other is 75mm, could
    > you tell the difference when riding?

    In that your body would be higher up with the lower drop, yeah. The whole geometry is
    changed by that.

    --

    David L. Johnson

    __o | If all economists were laid end to end, they would not reach a _`\(,_ | conclusion. --
    George Bernard Shaw (_)/ (_) |
     
  3. daveornee

    daveornee New Member

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    If you are pedaling around corners or clearing obstacles you probably could. If all else is the same your seat will be 1 cm closer/further to the ground.
     
  4. What if the headtube is 1CM higher, same toptube length.. same stem and seatposts are both properly
    adjusted...

    Mike http://mikebeauchamp.com

    "David L. Johnson" <[email protected]> wrote in message
    news:[email protected]...
    > On Fri, 14 Nov 2003 20:02:35 +0000, Clyde wrote:
    >
    > > Between 2 bikes, the same except for bottom bracket drop, one is 65mm,
    the
    > > other is 75mm, could you tell the difference when riding?
    >
    > In that your body would be higher up with the lower drop, yeah. The whole geometry is changed
    > by that.
    >
    > --
    >
    > David L. Johnson
    >
    > __o | If all economists were laid end to end, they would not reach a _`\(,_ | conclusion. --
    > George Bernard Shaw (_)/ (_) |
     
  5. Mike S.

    Mike S. Guest

    "Mike Beauchamp" <[email protected]> wrote in message
    news:[email protected]...
    > What if the headtube is 1CM higher, same toptube length.. same stem and seatposts are both
    > properly adjusted...
    >
    > Mike

    Probably only if you're trying to pedal around corners...

    Mike

    > http://mikebeauchamp.com
    >
    > "David L. Johnson" <[email protected]> wrote in message
    > news:[email protected]...
    > > On Fri, 14 Nov 2003 20:02:35 +0000, Clyde wrote:
    > >
    > > > Between 2 bikes, the same except for bottom bracket drop, one is 65mm,
    > the
    > > > other is 75mm, could you tell the difference when riding?
    > >
    > > In that your body would be higher up with the lower drop, yeah. The
    whole
    > > geometry is changed by that.
    > >
    > > --
    > >
    > > David L. Johnson
    > >
    > > __o | If all economists were laid end to end, they would not reach
    a
    > > _`\(,_ | conclusion. -- George Bernard Shaw (_)/ (_) |
    > >
    >
     
  6. Bruce

    Bruce Guest

    I have two bikes with that difference - about one cm - in BB height. I notice the difference when
    mounting and dismounting. Since I use Speedplay pedals, even the low BB height of 26.3 cm (10 3/8" )
    doesn't scrap the pedals around corners. But while riding I can't quite tell the difference. I feel
    slightly lower compared to other riders, so I get a better draft and I can't see over them as
    easily. But that's a very small difference, so I might not actually notice it.

    -Bruce

    "Clyde" <[email protected]> wrote in message news:[email protected]...
    > Between 2 bikes, the same except for bottom bracket drop, one is 65mm, the other is 75mm, could
    > you tell the difference when riding?
    >
    > Clyde
     
  7. Paul Hays

    Paul Hays Guest

    On Fri, 14 Nov 2003 12:02:35 -0800, Clyde wrote (in message
    <[email protected]>):

    > Between 2 bikes, the same except for bottom bracket drop, one is 65mm, the other is 75mm, could
    > you tell the difference when riding?
    >
    > Clyde
    >
    >

    Here's a Rivendel Bicycles article about the relationship between bb height and handling:

    http://tinyurl.com/v2y0
     
  8. On Fri, 14 Nov 2003 20:02:35 GMT, "Clyde" <[email protected]> wrote:

    >Between 2 bikes, the same except for bottom bracket drop, one is 65mm, the other is 75mm, could you
    >tell the difference when riding?
    >
    >Clyde
    My mountain bike ( cannondale jekyll) has a rear shock adjustment that changes the BB height
    1+ inches .. and also changes the head tube angle.... so it is hard to tell which has the
    greater impact.

    in the cross country mode.. the BB is at it's highest point and the head tube angle is 70 degrees..
    good for navigating switchbacks, etc.

    in the freeride mode the BB is at it's lowest and the head tube angle is about 68 degrees... greater
    stability on rocky downhills.

    I set mine "in the middle".. because in the freeride mode, I hit the pedals on rocks, etc and in the
    cross country mode... I endo when going off steep drops,e tc.

    charlie
     
  9. Simon Brooke

    Simon Brooke Guest

    Charles Beristain <[email protected]> writes:

    > My mountain bike ( cannondale jekyll) has a rear shock adjustment that changes the BB height
    > 1+ inches .. and also changes the head tube angle.... so it is hard to tell which has the
    > greater impact.
    >
    > in the cross country mode.. the BB is at it's highest point and the head tube angle is 70
    > degrees.. good for navigating switchbacks, etc.
    >
    > in the freeride mode the BB is at it's lowest and the head tube angle is about 68 degrees...
    > greater stability on rocky downhills.
    >
    > I set mine "in the middle".. because in the freeride mode, I hit the pedals on rocks, etc and in
    > the cross country mode... I endo when going off steep drops,e tc.

    OK, my Jekyll is currently 'in the middle' as well. As a matter of interest, is there anyone out
    there with a Jekyll _not_ in the middle? I certainly would not want my BB any lower, because, as you
    say, you'd spend too much time bouncing pedals off rocks.

    --
    [email protected] (Simon Brooke) http://www.jasmine.org.uk/~simon/ ;; gif ye hes forget our auld
    plane Scottis quhilk your mother lerit you, ;; in tymes cuming I sall wryte to you my mind in Latin,
    for I am nocht ;; acquyntit with your Southeron ;; Letter frae Ninian Winyet tae John Knox datit 27t
    October 1563
     
  10. Clyde wrote:

    > Between 2 bikes, the same except for bottom bracket drop, one is 65mm, the other is 75mm, could
    > you tell the difference when riding?
    >
    > Clyde
    >
    >
    You could at traffic lights ;-)
     
  11. B

    B Guest

    >Between 2 bikes, the same except for bottom bracket
    >> drop, one is 65mm, the other is 75mm, could you tell the difference when riding?

    yes B

    (remove clothes to reply)
     
  12. Clyde

    Clyde Guest

    Remarkable!

    "B" <[email protected]> wrote in message news:[email protected]...
    > >Between 2 bikes, the same except for bottom bracket
    > >> drop, one is 65mm, the other is 75mm, could you tell the difference when riding?
    >
    > yes B
    >
    > (remove clothes to reply)
     
  13. On Sat, 15 Nov 2003 10:05:02 GMT, Simon Brooke <[email protected]> wrote:

    >OK, my Jekyll is currently 'in the middle' as well. As a matter of interest, is there anyone out
    >there with a Jekyll _not_ in the middle? I certainly would not want my BB any lower, because, as
    >you say, you'd spend too much time bouncing pedals off rocks.

    I had a bad experience with my jekyll's settings. One day I decided to try the full freeride
    position as we were heading out to a very technical area with lots of big rocks to climb up and
    down. The big ring took such a beating ( did not have a rock ring on).. that I stopped and took a
    minute to put it into full X/C position. The I rode down a very steep rock face and at the bottom,
    the front wheel just dug in and sent me flying. The head tube angle in the X/C position makes it so
    the front wheel does not want to ride over stuff that normally i would just float over. After that,
    I put it in the middle, took off the big ring and put a 32 bash ring on in it's place. I've been
    happy since.

    I'd like to go back to the full freeride position, but I think I would have to re-learn pedalling ..
    otherwise I'd hit every rock that i pass by <G>

    I have the "5 & 5" jekyll.. Max TPC+ shock in front and 5" travel in the rear - I love it. I have a
    scalpel for racing.

    charlie
     
  14. Jim Adney

    Jim Adney Guest

    On Fri, 14 Nov 2003 20:02:35 GMT "Clyde" <[email protected]> wrote:

    >Between 2 bikes, the same except for bottom bracket drop, one is 65mm, the other is 75mm, could you
    >tell the difference when riding?

    The main difference is the pedal clearance when cornering.

    -
    -----------------------------------------------
    Jim Adney [email protected] Madison, WI 53711 USA
    -----------------------------------------------
     
  15. Bvm

    Bvm Guest

    I could definitely tell the difference, but could live with either. Unless you're going off-road and
    hitting your pedals in corners, then lower is better--lower center of gravity.

    On Fri, 14 Nov 2003 20:02:35 GMT, "Clyde" <[email protected]> wrote:

    >Between 2 bikes, the same except for bottom bracket drop, one is 65mm, the other is 75mm, could you
    >tell the difference when riding?
    >
    >Clyde
     
  16. Ted Bennett

    Ted Bennett Guest

    BVM <[email protected]> wrote:

    > I could definitely tell the difference, but could live with either. Unless you're going off-road
    > and hitting your pedals in corners, then lower is better--lower center of gravity.

    I keep hearing this, but I am skeptical.

    A higher center of gravity makes a bike more stable, not less. The natural frequency is slower and
    therefore requires slower inputs.

    You can think of a bike as an inverted pendulum, pivoted at the ground. Try balancing a short stick
    and a long one on the palm of your hand and you will see what I mean.

    This can also be demonstrated by how much of a learning curve is required for a low racer and a
    tall bike.

    --
    Ted Bennett Portland OR
     
  17. Jay Hill

    Jay Hill Guest

    Ted Bennett wrote:
    > BVM <[email protected]> wrote:
    >
    >
    >>I could definitely tell the difference, but could live with either. Unless you're going off-road
    >>and hitting your pedals in corners, then lower is better--lower center of gravity.
    >
    > I keep hearing this, but I am skeptical.
    >
    > A higher center of gravity makes a bike more stable, not less. The natural frequency is slower and
    > therefore requires slower inputs.
    >
    So a bike whose rider is 10 feet off the ground can make a, say, 45 degree turn faster than a
    bicycle whose rider is at normal height?
     
  18. Ted Bennett

    Ted Bennett Guest

    Jay Hill <[email protected]> wrote:

    > Ted Bennett wrote:
    > > BVM <[email protected]> wrote:
    > >
    > >
    > >>I could definitely tell the difference, but could live with either. Unless you're going off-road
    > >>and hitting your pedals in corners, then lower is better--lower center of gravity.
    > >
    > > I keep hearing this, but I am skeptical.
    > >
    > > A higher center of gravity makes a bike more stable, not less. The natural frequency is slower
    > > and therefore requires slower inputs.
    > >
    > So a bike whose rider is 10 feet off the ground can make a, say, 45 degree turn faster than a
    > bicycle whose rider is at normal height?

    I doubt it. When I wrote about stability I was thinking about riding in a straight line, where each
    lean of the bike must be corrected in order to not turn. The shorter the height of the mass, the
    higher the frequency of the excursions which must be corrected.

    This thread began with a question about stability effects of a higher or lower BB. Within the range
    found on virtually all "normal" bikes, the stability effect is very small. Pedal strikes are another
    matter entirely and is a good reason for higher BBs on, for example, a criterium bike.

    On most bikes, the centroid is at a similar height to that of a pedestrian and that is a factor in
    learning to balance a bike. For a much lower centroid, such as on this:
    http://www.wisil.recumbents.com/wisil/gritters/20-20-lowracer-side.jpg which requires smaller,
    higher-speed steering inputs. Not easy at all at first, but luckily humans readily train and adapt.

    For a tall bike, the higher centroid needs slower inputs which are easier to learn, once you get up
    there, that is.

    Any single track vehicle doesn't really go straight. Careful observation will show that both wheels
    follow a sinusoidal path, the frequency inversely related to the centroid height and directly
    related to the mass.

    --
    Ted Bennett Portland OR
     
  19. Bvm

    Bvm Guest

    On Sun, 16 Nov 2003 17:57:59 GMT, Ted Bennett <[email protected]> wrote:

    >BVM <[email protected]> wrote:
    >
    >> I could definitely tell the difference, but could live with either. Unless you're going off-road
    >> and hitting your pedals in corners, then lower is better--lower center of gravity.
    >
    >
    >I keep hearing this, but I am skeptical.

    Well, you can test it fairly easily on the same bike. Let's say you usually use 175 cranks. Get some
    170's or shorter. If the difference is 5mm, then that is close to raising your BB by 5mm for
    cornering. Try cornering and you will have more stability and can carve a tighter line, though only
    a little bit. I used to race BMX bikes over 20 years ago, and this was a fairly big issue. On road
    bikes, I usually ride in a straight line for long periods of time and the tires are relatively
    skinny, so the benefit, while real, is probably not going to cut much time off your trip.
     
  20. Peter Cole

    Peter Cole Guest

    "Ted Bennett" <[email protected]> wrote in message
    news:[email protected]...
    > BVM <[email protected]> wrote:
    >
    > > I could definitely tell the difference, but could live with either. Unless you're going off-road
    > > and hitting your pedals in corners, then lower is better--lower center of gravity.
    >
    >
    > I keep hearing this, but I am skeptical.
    >
    > A higher center of gravity makes a bike more stable, not less. The natural frequency is slower and
    > therefore requires slower inputs.

    Low bottom brackets are common on touring bikes because it makes it easier to put a foot down while
    in the saddle. The trade off is more pedal strike risk when cornering. The effects on handling are
    negligible.
     
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