Step-through frame

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

A step-through frame (aka open frame[1] 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.[2][3]

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.

Advantages[edit]

  • 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 crossbar; a rider who loses balance can step through the bicycle without becoming entangled
  • compactness provides a popular starting point for folding bicycles.

Disadvantages[edit]

  • Heavier. Compared to a traditional diamond frame consisting of two near-triangles, alternative open or step-through frame designs of equivalent construction have been shown to be demonstrably less strong using finite element structural analysis.[4][5][6] Consequently step-through frames must be made of substantially stronger sections to achieve similar overall strength, accomplished by thicker gauge tubing, the use of additional gusseting members, and/or monocoque frame construction, all of which add weight over a traditional diamond design.
  • Reduced rigidity and frame life, unless reinforced. While a certain amount of vertical frame flexibility is desirable for a compliant ride on a bicycle with an unsuspended rear wheel, any lateral flexing or excessive vertical flex due to loss of the primary triangle can result in reduced frame life and a loss in pedaling efficiency.[7][8]
  • Fewer places to mount accessories, e.g. an air pump or water-bottle.

Mixte[edit]

A Peugeot mixte frame bicycle

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 (lateral tubes, or lats) 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 lower standover height of a step-through frame bicycle while avoiding some of the additional stresses the step-through frame bicycle places on the seat tube.

A variant on the mixte uses a single, full sized top tube running from the upper head tube to the seat tube, but retains the middle set of stays.[9]

"Mixte" (pronounced [mikst]) is a direct appropriation of the French word meaning "mixed" or "unisex". The usual North American bicycle industry pronunciation of this loan word is /ˈmɪkst/.[10]

A Dahon folding bicycle with a cross frame

Cross[edit]

Another type of step-through frame is called a cross. The cross frame consists mainly of two tubes that form a cross: a seat tube from the bottom bracket to the saddle, and a backbone from the head tube to the rear hub.[11] [12]

Gallery[edit]

See also[edit]

References[edit]

  1. ^ "Nimrod road tests the Jack Taylor touring bicycle". Cycling. March 16, 1960. Retrieved 2013-04-02. "their range of seventeen models includes a woman's open frame bicycle" 
  2. ^ "Top Tube". Sheldon Brown. Retrieved 2010-02-07. 
  3. ^ Oxford English Dictionary (2nd ed.). Oxford University Press. 1989. "cross-bar, n. 1. a. A transverse bar; a bar placed or fixed across another bar or part of a structure. spec. The horizontal bar of a bicycle frame" 
  4. ^ Van Der Plas, Rob, Bicycle Technology, San Francisco: Bicycle Books (3rd ed.), ISBN 0-933201-30-3, ISBN 978-0-933201-30-9 (1995), pp. 60-2
  5. ^ Peterson, Leisha A. and Londry, Kelly J., Finite-Element Structural Analysis: A New Tool for Bicycle Frame Design: The Strain Energy Design Method, Bike Tech, Bicycling Magazine, Vol. 5 No. 2 (1986)
  6. ^ Wingerter, R., and Lebossiere, P., ME 354, Mechanics of Materials Laboratory: Structures, University of Washington (February 2004), p.1
  7. ^ Van Der Plas, Rob, Bicycle Technology, San Francisco: Bicycle Books (3rd ed.), ISBN 0-933201-30-3, ISBN 978-0-933201-30-9 (1995), pp. 60-2
  8. ^ Peterson, Leisha A. and Londry, Kelly J., Finite-Element Structural Analysis: A New Tool for Bicycle Frame Design: The Strain Energy Design Method, Bike Tech, Bicycling Magazine, Vol. 5 No. 2 (1986)
  9. ^ http://www.sheldonbrown.com/gloss_m.html#mixte
  10. ^ Brown, Sheldon (Revised April 19, 2010 by John Allen). "Sheldon Brown's Bicycle Glossary". Harris Cyclery. Retrieved April 4, 2011. 
  11. ^ Sheldon Brown. "Glossary: Cross Frame". Retrieved 2011-05-04. 
  12. ^ Cross Frames at rijwiel.net http://www.rijwiel.net/kruisfre.htm