Re: Centerstand Dynamics 101

[neil halbert <halbert@xxxxxxx>]

Tim,
It all depends upon the bike. My 1985 Honda Interceptor had a very tall side
stand with a small/narrow foot. It was leaned at most 90 degrees and the
slightest bump could send it over. As I said I had it tip over from the breeze
of a truck passing. The center stand was quite wide, so, I found it to be much
more reliable when I had to turn my back on the bike. Once it was on the
center it took a good shove to bring it back down where the side stand folded
easily. If it was bumped from behind it could roll and drop. Not to mention
those hot summer days where it impaled the tarmac.

The side stand is not symmetric in it's support. Once the bike is seated on it
will stay there and take quite a bit of effort to keep it going over onto to
it's side. The other direction takes significantly less effort to move it off
the stand and it to fall over do to the moment is about the tire patch on the
ground and the center of mass. Which is a long lever arm. This makes for
further travel but lower effort.

The center stand is symmetric in it's support. It takes the same amount of
effort to tip it either way. It is actually difficult to get it to tip
initially for you are lifting almost the entire weight of the bike through a
short lever that starts off parallel to the ground. The distance between the
out side of the foot and the center line of the bike. The amount of weight
decreases as the center of mass moves toward the out side of the foot. Once it
pass over the line of foot gravity kicks in and it's all over 'cept the
crying. The effort initially required is high but tapers off quickly since it
is a shorter arm. Ideally the center stand width should be such that the
center of gravity is over the foot when the arm is 45 degrees. Then the bike
would have to be tipped 45 degrees before it would drop.
I don't think this is the case.

Ascii graphics are left for extra credit. :) It's been a while since doing
mechanics so the math will have to be breezed over with a wave of the hand.

An empirical test would be to get a scale and connect it to the bike and
measure how much effort is required
over what distance to tip the bike. I believe you will find the effort to be
lower over a greater distance for the side stand over on to the right side.
The side stand would require a greater force but over a shorter distance.

My position is more one of track history, never had the bike go over on the
center stand. If you don't count the time that delivery van backed into the
front end pushed it over a foot backwards and knocked it over. Though it went
down on the side stand several times. You just got to hate that "Crunch" sound
body work makes. As with history "your mileage may vary".

Leatherbiker wrote:

> Neil.
>
> I'm kind of surprised at your theory.
> Accepted wisdom in the biking world is that the sidestand is
> much more stable, especially on ferries (I could write a whole
> book on that topic!), hills, unstable ground etc., as the bike
> is already leaning at maximum tilt in one direction and cannot
> go any further in that dimension. To topple the bike, you would
> then have to raise it to the vertical and push it over in the
> opposite direction, which takes considerably more doing.
> I hardly ever use my centre stand, except for filling the fuel
> tank, these days.
>
> Tim
>
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