Only two back legs should be provided with rollers.
Each castor may be half hidden in the each back legs of the chair.
In normal position (see the left picture) the chair stands on the floor on all four legs firmly.
The rollers do not touch the floor because there is a small gap between the floor and the rollers in this position.
If the chair is tilted back slightly (as it shown at the right picture — center of gravity of the chair passes through the rollers), the rollers touch the floor (the legs do not touch). So you can roll the chair easily. It is especially convenient for old persons.
The top of the back of the chair may be provided with a special slit for fingers.
Proposed chair is safer for children than regular chair or chairs for four or five rolls.
The chair does not slide along the floor when the child is climbing on it.
That is why it is not necessary to provide the chair with any locking devices.
Such chair do not damage or scratch the surface of the floor because the rollers touch the floor only when you move it. Nobody sits on the chair in this time.
When somebody sits on the chair, it rests on the floor with all squares (areas) of the legs. So the floor is left dents.
The proposed chairs may be used in offices, cafes, clinics and so on because they are easier and more convenient to move, for example during cleaning floor.
If you use chairs rolling them on the floor (not moving the portage), they will serve you longer.
If two legs of ordinary wardrobes, bookcases, tables, chest of drawers etc. are provided with rollers according to this proposal, any man will be able to move such furniture in his flat alone easily and without scratching the floor.
All already produced (already used) furniture may be provided with such rollers too.
By analogy, we are not comparing bicycle with motorcycle.
And we do not ask — what is better. We understand that they are goods of different categories and different market niches.
Just like this, we should not compare ordinary chair with five rollers with the proposed chair.
They are also goods of different categories (different market niches).
The niche of two-rollers-chair is completely empty now.
If things are qualitatively differ from each other, these items have different names in any language.
Therefore, we have two similar, but different individual words for bicycle and a motorcycle. Just like this two-rollers-chair should have own individual name too, for example «rollchair» (by analogy with «armchair»).