Step-through frame

A step-through frame (also known as open frame, drop frame, low-step frame) is a type of bicycle frame, often used for utility bicycles, with a low or absent top tube or cross-bar.

Since mounting or dismounting a step-through does not require swinging one leg to hip-height, they are widely used as delivery bicycles, and for other purposes where the rider has to mount and dismount frequently.

Traditionally, bicycles with a step-through frame were known as "ladies'", "women's" or "girls' bicycles", as they allow skirts or dresses to hang fairly normally. Bicycles with a high top tube (cross-bar), were known as "men's", "gents'", or "boys' bicycles". Even in the 1800s, women often rode "men's" bicycles and vice-versa; from the 1890s onwards, women commonly wore bloomers to cycle. Since the late 20th century, descriptions that describe the frame style, rather than the presumed gender of the rider, are becoming increasingly common.

Advantages

less risk of stretching or ripping clothes when mounting the saddle

the rider can wear a skirt, kilt, or dress (longer garments may also require a skirt guard and possibly a chain guard)

very quick to mount and dismount, suitable for delivery bicycles, or any journey with many stops

potentially safer; a rider who loses balance can step through the bicycle without becoming entangled or hitting their crotch

suitable for elderly and others with restricted agility

easier to share with shorter friends and family

compactness provides a popular starting point for folding bicycles.

Disadvantages

Heavier. Compared to a traditional diamond frame consisting of two near-triangles, open or step-through frame designs must be designed with thicker gauge tubing, the use of additional gusseting members, and/or monocoque frame construction. These structural elements may add weight or cost over a traditional diamond design.