Bicycle frame
A bicycle frame is the main component of a bicycle, onto which wheels and other components are fitted. The modern and most common frame design for an upright bicycle is based on the safety bicycle, and consists of two triangles: a main triangle and a paired rear triangle. This is known as the diamond frame. Frames are required to be strong, stiff and light, which they do by combining different materials and shapes.
Variations
Besides the ubiquitous diamond frame, many different frame types have been developed for the bicycle, several of which are still in common use today.Diamond
In the diamond frame, the main "triangle" is not actually a triangle because it consists of four tubes: the head tube, top tube, down tube and seat tube. The rear triangle consists of the seat tube joined by paired chain stays and seat stays.The head tube contains the headset, the interface with the fork. The top tube connects the head tube to the seat tube at the top. The top tube may be positioned horizontally, or it may slope downwards towards the seat tube for additional stand-over clearance. The down tube connects the head tube to the bottom bracket shell.
The rear triangle connects to the rear fork ends, where the rear wheel is attached. It consists of the seat tube and paired chain stays and seat stays. The chain stays run connecting the bottom bracket to the rear fork ends. The seat stays connect the top of the seat tube to the rear fork ends.
Step-through
Historically, bicycle frames designed for women had a top tube that connected in the middle of the seat tube instead of the top, resulting in a lower [|standover height]. This was to allow the rider to dismount while wearing a skirt or dress. The design has since been used in unisex utility bikes to facilitate easy mounting and dismounting, and is also known as a step-through frame or an open frame. Another style that accomplishes similar results is the mixte.Cantilever
In a cantilever bicycle frame the seat stays continue past the seat post and curve downwards to meet with the down tube. Cantilever frames are popular on the cruiser bicycle, the lowrider bicycle, and the wheelie bike. In many cantilever frames the only straight tubes are the seat tube and the head tube.Recumbent
The recumbent bicycle moves the cranks to a position forward of the rider instead of underneath, generally improving the slipstream around the rider without the characteristic sharp bend at the waist used by racers of diamond-frame bicycles. Banned from bicycle racing in France in 1934 to avoid rendering diamond-frame bicycles obsolete in racing, manufacturing of recumbent bicycles remained depressed for another half century, but by 2000 many models were available from a range of manufacturers.Prone
The uncommon prone bike moves the cranks to the rear of the rider, resulting in a head-forward, chest-down riding position.Cross or girder
A 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.Truss
A truss frame uses additional tubes to form a truss. Examples include Humbers, Pedersens, and the one pictured.Monocoque
A monocoque frame consists only of a hollow shell with no internal structure.Folding
frames are characterized by the ability to fold into a compact shape for transportation or storage.Penny-farthing
frames are characterized by a large front wheel and a small rear wheel.Tandem and sociable
and sociable frames support multiple riders.Others
There are many variations on the basic diamond frame design.- Frames without [|seat tubes], such as the Trek Y-Foil, the Zipp 2001, the Kestrel Airfoil, and most frames by Softride.
- Frames without top tubes such as "Old Faithful" by Graeme Obree.
- Frames that use cables for members that are only under tension, such as the Dursley Pedersen bicycle pictured, the Pocket Bicycle, the 2009 Viva Wire, the Wire Bike from designer Ionut Predescu, or the Slingshot Bicycles fold-tech series.
- Frames with hoops replacing the seat tube, chain stays and seat stays: called "roundtail"s.
- The elevated chain stay bicycle was popular in the early 90s. It featured a rear triangle with elevated bottom frame stays, negating the need for the chain to be drawn through the rear frame. This allowed for a shorter wheelbase and improved handling during technical ascents, at the cost of compromised integrity and resultant increased bottom bracket flex compared to a frame with traditional chain stays.
It is also possible to add couplers either during manufacturing or as a retrofit so that the frame can be disassembled into smaller pieces to facilitate packing and travel.
Frameset
A frameset consists of the frame and fork of a bicycle and sometimes includes the headset and seat post. Frame builders will often produce the frame and fork together as a paired set.Frame tubes
The diamond frame consists of two triangles, a main triangle and a paired rear triangle. The main triangle consists of the head tube, top tube, down tube and seat tube. The rear triangle consists of the seat tube, and paired chain stays and seat stays.Head tube
The head tube contains the headset, the bearings for the fork via its steerer tube. In an integrated headset, cartridge bearings interface directly with the surface on the inside of the head tube, on non-integrated headsets the bearings interface with "cups" pressed into the head tube.Top tube
The top tube, or cross-bar, connects the top of the head tube to the top of the seat tube.In a traditional-geometry diamond frame, the top tube is horizontal. In a compact-geometry frame, the top tube is normally sloped downward toward the seat tube for additional standover clearance. In a mountain bike frame, the top tube is almost always sloped downward toward the seat tube. Radically sloped top tubes that compromise the integrity of the traditional diamond frame may require additional gusseting tubes, alternative frame construction, or different materials for equivalent strength.
Step-through frames usually have a top tube that slopes down steeply to allow the rider to mount and dismount the bicycle more easily. Alternative step-through designs may include leaving out the top tube out completely, as in monocoque mainframe designs using a separated or hinged seat tube, and twin top tubes that continue to the rear fork ends as with the mixte frame. These alternatives to the diamond frame provide greater versatility, though at the expense of added weight to achieve equivalent strength and rigidity.
Control cables are routed along mounts on the top tube, or sometimes inside the top tube. Most commonly, this includes the cable for the rear brake, but some mountain bikes and hybrid bicycles also route the front and rear derailleur cables along the top tube. Inside routing, once only present in the highest price ranges, protects the cables from damage and dirt, which can e.g. make gear shifting unreliable.
The space between the top tube and the rider's groin while straddling the bike and standing on the ground is called clearance. The total height from the ground to this point is called the height lever.
Down tube
The down tube connects the head tube to the bottom bracket shell. On racing bicycles and some mountain and hybrid bikes, the derailleur cables run along the down tube, or inside the down tube. On older racing bicycles, the shift levers were mounted on the down tube. On newer ones, they are mounted with the brake levers on the handlebars.Bottle cage mounts are also on the down tube, usually on the top side, sometimes also on the bottom side. In addition to bottle cages, small air pumps may be fitted to these mounts as well.
Seat tube
The seat tube contains the seatpost of the bike, which connects to the saddle. The saddle height is adjustable by changing how far the seatpost is inserted into the seat tube. On some bikes, this is achieved using a quick release lever. The seatpost must be inserted at least a certain length; this is marked with a minimum insertion mark.The seat tube also may have braze-on mounts for a bottle cage or front derailleur.
Chain stays
The chain stays run parallel to the chain, connecting the bottom bracket shell to the rear fork ends or dropouts. A shorter chain stay generally means that the bike will accelerate faster and be easier to ride uphill, at least while the rider can avoid the front wheel losing contact with the ground.When the rear derailleur cable is routed partially along the down tube, it is also routed along the chain stay. Occasionally mountings for disc brakes will be attached to the chain stays. There may be a small brace that connects the chain stays in front of the rear wheel and behind the bottom bracket shell, called a "chainstay bridge".
Chain stays may be designed using tapered or untapered tubing. They may be relieved, ovalized, crimped, S-shaped, or elevated to allow additional clearance for the rear wheel, chain, crankarms, or the heel of the foot.
Seat stays
The seat stays connect the top of the seat tube to the rear fork dropouts. A traditional frame uses a simple set of paralleled tubes connected by a bridge above the rear wheel. When the rear derailleur cable is routed partially along the top tube, it is also usually routed along the seat stay.Many alternatives to the traditional seat stay design have been introduced over the years. A style of seat stay that extends forward of the seat tube, below the rear end of the top tube and connects to the top tube in front of the seat tube, creating a small triangle, is called a Hellenic stay after the British frame builder Fred Hellens, who introduced them in 1923. Hellenic seat stays add aesthetic appeal at the expense of added weight. This style of seat stay was popularized again in the late 20th century by GT Bicycles, who had incorporated the design element into their BMX frames, as it also made for a much stiffer rear triangle ; this design element has also been used on their mountain bike frames for similar reasons.
In 2012, a variation of the traditional seat stay that bypasses the seat tube and connects further into the top tube was patented by Volagi Cycles. This frame element added length to the traditional design of seat stays, making a softer ride at the sacrifice of frame stiffness.
Another common seat stay variant is the wishbone, single seat stay, or mono stay, which joins the stays together just above the rear wheel into a monotube that is joined to the seat tube. A wishbone design adds vertical rigidity without increasing lateral stiffness, generally an undesirable trait for bicycles with unsuspended rear wheels. The wishbone design is most appropriate when used as part of a rear triangle subframe on a bicycle with independent rear suspension.
A dual seat stay refers to seat stays which meet the front triangle of the bicycle at two separate points, usually side-by-side.
Fastback seat stays meet the seat tube at the back instead of the sides of the tube.
On most seat stays, a bridge or brace is typically used to connect the stays above the rear wheel and below the connection with the seat tube. Besides providing lateral rigidity, this bridge provides a mounting point for rear brakes, fenders, and racks. The seat stays themselves may also be fitted with brake mounts. Brake mounts are often absent from fixed-gear or track bike seat stays.