A step-through frame (aka open frame or low-step frame) is a type of bicycle frame, often used for utility bicycles, with a low or absent top tube or cross-bar.
Traditionally, bicycles with a step-through frame were known as “Ladies'”, “Women’s”, or “Girls'”, mainly for their advantage to riders wearing skirts or dresses.
Bicycles with a high top tube (cross-bar), known as a diamond frame, were known as “Men’s”, “Gents'”, or “Boys'”.
As a result of changing clothing styles since the late 20th century, descriptions that describe the frame style, rather than the presumed sex of the rider, are becoming increasingly common.
- 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 many stops
- suitable for elderly and others with restricted agility
- potentially safer than a high top tube; a rider who loses balance can step through the bicycle without becoming entangled
- compactness provides a popular starting point for folding bicycles.
- 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. Inattention to structural design can lead to excessive flexing, resulting in lower pedaling efficiency and reduced frame life.
- Fewer places to mount accessories, e.g. an air pump or water-bottle.