Step-through frame

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A step-through frame in Amsterdam

Woman with a step-through frame bicycle in the 1890s

A step-through frame (aka low-step frame) is a type of bicycle frame with a low top tube (crossbar), in comparison to a diamond frame, or no top tube at all.

It is most commonly found on utility bicycles. In some cultures, it is thought of as a 'girls' bike.

1 Advantages
2 Disadvantages
3 Mixte
4 See also

[edit] Advantages

there is less risk of stretching or ripping clothes when mounting the saddle.
the rider can wear a skirt (also requires a skirt guard and possibly a chain guard).
very quick to mount and dismount, so is suitable for delivery bicycles, or any journey with a lot of stops.
suitable for elders, or anyone with restricted agility.
potentially safer than a high crossbar, for several reasons
- if the rider loses balance, he can step through the bicycle without becoming tangled in it;
- if the rider is sideswiped or blown sideways, both legs will sweep through the frame and the rider is more likely to land safely.^{[citation needed]}

[edit] Disadvantages

potentially heavier, and therefore slower. The lowered top tube must be longer, and so simply has more material. The frame may also be substantially thickened and strengthened to compensate for the loss of the primary triangle in the frame geometry.
potentially less stiff, and therefore less efficient. If the thickening and strengthening is insufficient to compensate for the loss of the primary triangle in the frame geometry, the frame becomes too flexible and therefore slightly less efficient.
fewer places for accessories, eg. a pump or water bottle.

Motobécane Nomade with a mixte frame mounted on bike rack of a bus.

[edit] Mixte

One particular type of step-through frame is called a mixte. In A mixte frame, the top tube of the traditional diamond frame is replaced with a pair of smaller tubes running from the top of the head tube all the way back to the rear axle, connecting at the seat tube on the way. The normal seat stays and chain stays are retained. This provides the greater stand-over height of a step-through frame bicycle while avoiding the additional stresses the step-through frame bicycle places on the seat tube.