Bicycle frame

A bicycle frame is the main component of a bicycle where wheels and other parts attach. The most common frame design is the diamond frame, made of two triangles, a main triangle and a rear triangle.^[1] Frames must be strong, stiff, and light, achieved through various materials and shapes.^[2] A frameset includes the frame, fork, and sometimes the headset and seat post, often built as a paired set.^[3]

A steel hardtail mountain bike frame by Rocky Mountain Bicycles.

Variants

In addition to the diamond frame,^[1] many other bicycle frame types are still in use today.

The 'diamond' frame's top bar forces the rider to swing a leg over the seat.

Diamond

In the diamond frame, the "triangle" isn't a triangle but four tubes, head tube, top tube, down tube, and seat tube. The rear triangle includes the seat tube with chain stays and seat stays.

The head tube houses the headset and connects to the fork. The top tube links the head tube and seat tube, positioned either horizontally or sloping for clearance. The down tube connects the head tube to the bottom bracket.

The rear triangle connects to the rear fork ends for the rear wheel, comprising the seat tube, chain stays, and seat stays, which link the bottom bracket to the rear fork ends.

Step-through

A Triumph step-through, ladies', or open frame.

Historically, women's bicycle frames had a mid-top tube for a lower standover height, enabling easy dismounting in a skirt. This design is now used in unisex utility bikes, known as step-through or open frames.^[4] Another similar style is the mixte.

Cantilever

In a cantilever bicycle frame, the seat stays curve down to meet the down tube.^[5] These frames are popular on cruisers, lowriders, and wheelie bikes, with only the seat tube and head tube being straight.

Recumbent

The recumbent bicycle positions the cranks forward of the rider, enhancing the slipstream without the sharp bend at the waist seen in diamond-frame bikes. Banned in France in 1934 to protect diamond-frame bikes, recumbent bicycle manufacturing remained low for decades, but by 2000, many models became available from various manufacturers.

Prone

The uncommon prone bike places the cranks behind the rider, creating a head-forward, chest-down position.

A modern truss frame.

Cross

A cross frame mainly has two tubes forming a cross, a seat tube from the bottom bracket to the saddle and a backbone from the head tube to the rear hub.^[6]

Truss

A truss frame uses extra tubes to form a truss,^[7] like Humbers, Pedersens, and the one pictured.

Monocoque

A penny-farthing in the Škoda Auto Museum, Czech Republic.

A monocoque frame is a hollow shell without internal structure.^[8]

Folding

Folding bicycle frames can compactly fold for transport or storage.

Penny-farthing

Penny-farthing frames have a large front wheel and a small rear wheel.^[9][10]

Tandem and sociable

Tandem and sociable frames support multiple riders.