In article ,
Chris J Dixon wrote:

You're missing the point. For a given leg separation, the distance
from the centre (at ground level) to the closest point outside the
triangle is much less than it is for the quadrilateral. Therefore,
the ladder will fall over for a much lower imbalance in the weight
or sideways force.

Isn't the whole point that the design under consideration doesn't
have the same leg separation as a conventional ladder. For
instance, the 3 m ladder is 1.45 m wide at the base.

https://www.niwaki.com/store/niwaki-tripod-ladder/

Ah. That would be enough, PROVIDED that the single leg is at a shallow
enough angle. Most step ladders have the non-step legs more vertical
than the other ones, which means the CoG is closer to them - and, if
there is a single one, that leads to instability. From the picture,
that looks the case.


Regards,
Nick Maclaren.