Abicycle frame is the main component of abicycle, onto whichwheels andother components are fitted. The modern and most common frame design for anupright bicycle is based on thesafety bicycle, and consists of twotriangles: a main triangle and a paired rear triangle. This is known as thediamond frame.[1] Frames are required to be strong, stiff and light, which they do by combining different materials and shapes.[2]
Aframeset consists of the frame andfork of a bicycle and sometimes includes theheadset andseat post.[3] Frame builders will often produce the frame and fork together as a paired set.
Besides the ubiquitous diamond frame,[1] many different frame types have been developed for the bicycle, several of which are still in common use today.
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 theheadset, the interface with thefork. The top tube connects the head tube to the seat tube at the top. The top tube may be positioned horizontally (parallel to the ground), or it may slope downwards towards the seat tube for additional stand-over clearance. The down tube connects the head tube to thebottom bracket shell.
The rear triangle connects to the rearfork 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 (often at or near the same point as the top tube) to the rear fork ends.
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 lowerstandover height. This was to allow the rider to dismount while wearing askirt ordress. 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.[4] Another style that accomplishes similar results is themixte.
In a cantilever bicycle frame the seat stays continue past the seat post and curve downwards to meet with the down tube.[5] Cantilever frames are popular on thecruiser bicycle, thelowrider bicycle, and thewheelie bike. In many cantilever frames the only straight tubes are the seat tube and the head tube.
Therecumbent 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,[6] manufacturing of recumbent bicycles remained depressed for another half century, but many models from a range of manufacturers were available by 2000.
The uncommonprone bike moves the cranks to the rear of the rider, resulting in a head-forward, chest-down riding position.
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.[7]
A truss frame uses additional tubes to form atruss.[8] Examples includeHumbers,Pedersens, and the one pictured.
Amonocoque frame consists only of a hollow shell with no internal structure.[9]
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Folding bicycle 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.[10][11]
Tandem andsociable frames support multiple riders.
There are many variations on the basic diamond frame design.
Thecycle types article describes additional variations.
It is also possible to addcouplers either during manufacturing or as a retrofit so that the frame can be disassembled into smaller pieces to facilitate packing and travel.
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.
Thehead tube contains the headset, the bearings for the fork via itssteerer 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 (in a cartridge or not) interface with "cups" pressed into the head tube.
Thetop tube,[18] orcross-bar,[19] 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 (parallel to the ground). In a compact-geometry frame, the top tube is normally sloped downward toward the seat tube for additional standover clearance. In amountain 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.[20][21][22] (SeeRoad and triathlon bicycles for more information on geometries.)
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 inmonocoque mainframe designs using a separated or hinged seat tube, and twin top tubes that continue to the rear fork ends as with themixte frame. These alternatives to the diamond frame provide greater versatility, though at the expense of added weight to achieve equivalent strength and rigidity.[20][21]
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 andhybrid 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.[23]
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.
Thedown 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, theshift 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.
Theseat tube contains theseatpost 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 aquick release lever. The seatpost must be inserted at least a certain length; this is marked with aminimum insertion mark.
The seat tube also may havebraze-on mounts for abottle cage or frontderailleur.
Thechain stays run parallel to the chain, connecting the bottom bracket shell (which holds the axis around which the pedals and cranks rotate) to the rearfork 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.[23]
When the rear derailleur cable is routed partially along the down tube, it is also routed along the chain stay. Occasionally (principally on frames made since the late 1990s) 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.
Theseat stays connect the top of the seat tube (often at or near the same point as the top 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 aHellenic stay after the British frame builder Fred Hellens, who introduced them in 1923.[24]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 byGT Bicycles (under the moniker "triple triangle"), who had incorporated the design element into their BMX frames, as it also made for a much stiffer rear triangle (an advantage in races); 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 byVolagi Cycles.[25] 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 thewishbone,single seat stay, ormono stay,[26] 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.[27] The wishbone design is most appropriate when used as part of a rear triangle subframe on a bicycle with independent rear suspension.
Adual 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.[28]
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.
Thebottom bracket shell is a short and large diameter tube, relative to the other tubes in the frame, that runs side to side and holds thebottom bracket. It is usually threaded, often left-hand threaded on the right (drive) side of the bike to prevent loosening byfretting induced precession, and right-hand threaded on the left (non-drive) side. There are many variations, such as aneccentric bottom bracket, which allows for adjustment in tension of the bicycle's chain. It is typically larger, unthreaded, and sometimes split. The chain stays, seat tube, and down tube all typically connect to the bottom bracket shell.
There are a few traditional standard shell widths (68, 70 or 73 mm).[29] Road bikes usually use 68 mm; Italian road bikes use 70 mm; Early model mountain bikes use 73 mm; later models (1995 and newer) use 68 mm more commonly. Some modern bicycles have shell widths of 83 or 100 mm and these are for specialiseddownhill mountain biking orsnowbiking applications. The shell width influences theQ factor or tread of the bike. There are a few standard shell diameters (34.798 – 36 mm) with associated thread pitches (24 - 28 tpi).
On somegearbox bicycles, the bottom bracket shell may be replaced by an integrated gearbox or a mounting location for a detachable gearbox.
The length of the tubes, and the angles at which they are attached define aframe geometry. In comparing different frame geometries, designers often compare the seat tube angle, head tube angle, (virtual) top tube length, and seat tube length. To complete the specification of a bicycle for use, the rider adjusts the relative positions of the saddle, pedals and handlebars:
The geometry of the frame depends on the intended use. For instance, aroad bicycle will place the handlebars in a lower and further position relative to the saddle giving a more crouched riding position; whereas autility bicycle emphasizes comfort and has higher handlebars resulting in an upright riding position.
Frame geometry also affects handling characteristics. For more information, see the articles onbicycle and motorcycle geometry andbicycle and motorcycle dynamics.
Frame size was traditionally measured along the seat tube from the center of the bottom bracket to the center of the top tube. Typical "medium" sizes are 54 or 56 cm (approximately 21.2 or 22 inches) for a European men's racing bicycle or 46 cm (about 18.5 inches) for a men'smountain bike. The wider range of frame geometries that now exist has also led to other methods of measuring frame size.[39] Touring frames tend to be longer, while racing frames are more compact.
A road racing bicycle is designed for efficient power transfer at minimum weight and drag. Broadly speaking, the road bicycle geometry is categorized as either atraditional geometry with a horizontal top tube, or acompact geometry with a sloping top tube.
Traditional geometry road frames are often associated with more comfort and greater stability, and tend to have a longer wheelbase which contributes to these two aspects. Compact geometry allows the top of the head tube to be above the top of the seat tube, decreasing standover height, and thus increasing standover clearance and lowering the center of gravity. Opinion is divided on the riding merits of the compact frame, but several manufacturers claim that a reduced range of sizes can fit most riders, and that it is easier to build a frame without a perfectly level top tube.
Road bicycles for racing tend to have a steeperseat tube angle, measured from the horizontal plane. This positions the rider aerodynamically and arguably in a stronger stroking position. The trade-off is comfort. Touring and comfort bicycles tend to have more slack (less vertical) seat tube angle traditionally. This positions the rider more on the sit bones and takes weight off the wrists, arms and neck, and, for men, improves circulation to the urinary and reproductive areas. With a slacker angle, designers lengthen the chain stay so that the center of gravity (that would otherwise be farther to the back over the wheel) is more ideally repositioned over the middle of the bike frame. The longer wheelbase contributes to effective shock absorption. In modern mass-manufactured touring and comfort bikes, the seat-tube angle is negligibly slacker, perhaps in order to reduce manufacturing costs by avoiding the need to reset welding jigs in automated processes, and thus do not provide the comfort of traditionally made or custom-made frames which do have noticeably slacker seat-tube angles.
Road racing bicycles that are used in UCI-sanctioned races are governed byUCI regulations, which state among other things that the frame must consist of two triangles. Hence designs that lack a seat tube or top tube are not allowed.
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Triathlon- ortime-trial-specific frames rotate the rider forward around the axis of the bottom bracket of the bicycle as compared to the standard road bicycle frame. This is in order to put the rider in an even lower, more aerodynamic position. While handling and stability is reduced, these bicycles are designed to be ridden in environments with less group riding aspects. These frames tend to have steep seat-tube angles and low head tubes, and shorter wheelbase for the correct reach from the saddle to the handlebar. Additionally, since they are not governed by the UCI, some triathlon bicycles, such as theZipp 2001, Cheetah and Softride, have non-traditional frame layouts, which can produce better aerodynamics.
Track frames have much in common with road and time trial frames, but come with horizontal, rear-facing, rear fork ends,[40] rather than dropouts,[41] to allow one to adjust the position of the rear wheel horizontally to set the proper chain tension. Rear hub spacing is 120 millimetres (4.7 in) rather than 130 millimetres (5.1 in) or more for road frames. Bottom bracket drop is smaller, typically 50–60 millimetres (2.0–2.4 in). Also the seat tube angle is steeper than on road racing bikes.
For ride comfort and better handling,shock absorbers are often used; there are a number of variants, includingfull suspension models, which provide shock absorption for the front and rear wheels; andfront suspension only models (hardtails) which deal only with shocks arising from the front wheel. The development of sophisticated suspension systems in the 1990s quickly resulted in many modifications to the classic diamond frame.
Recent[when?] mountain bicycles with rearsuspension systems have a pivoting rear triangle to actuate the rear shock absorber. There is much manufacturer variation in the frame design of full-suspension mountain bicycles, and different designs for different riding purposes.
Roadster bicycles traditionally have a fairly slack seat-tube and head-tube angle of about 66 or 67 degrees, which produces a very comfortable and upright "sit-up-and-beg" riding position. Other characteristics include a long wheelbase, upwards of 40 inches (often between 43 and 47 inches, or 57 inches for alongbike), and a long fork rake, often of about 3 inches (76mm compared to 40mm for most road bicycles). This style of frame has had a resurgence in popularity in recent years due to its greater comfort compared to Mountain bicycles or Road bicycles. A variation on this type of bicycle is the "sports roadster" (also known as the "light roadster"), which typically has a lighter frame, and a slightly steeper seat-tube and head-tube angle of about 70 to 72 degrees.
Historically, the most common material for the tubes of a bicycle frame has beensteel. Steel frames can be made of varying grades of steel, from very inexpensive carbon steel to more costly and higher quality chromium molybdenum steelalloys. Frames can also be made fromaluminum alloys,titanium,carbon fiber, and evenbamboo andcardboard. Occasionally, diamond (shaped) frames have been formed from sections other than tubes. These includeI-beams andmonocoque. Materials that have been used in these frames includewood (solid orlaminate),magnesium (cast I-beams), andthermoplastic. Several properties of a material help decide whether it is appropriate in the construction of a bicycle frame:
Tube engineering and frame geometry can overcome much of the perceived shortcomings of these particular materials.
Frame materials are listed by commonality of usage.
Steel frames are often built using various types of steel alloys includingchromoly. They are strong, easy to work, and relatively inexpensive. However, they are denser (and thus generally heavier) than many other structural materials. It is common (as of 2018, in hybrid commuter bikes) to use steel for the fork blades even when the rest of the frame is made of a different material, because steel offers better vibrationdampening.[23]
A classic type of construction for both road bicycles and mountain bicycles uses standard cylindrical steel tubes which are connected withlugs. Lugs are fittings made of thicker pieces of steel. The tubes are fitted into the lugs, which encircle the end of the tube, and are thenbrazed to the lug. Historically, the lower temperatures associated with brazing (silver brazing in particular) had less of a negative impact on the tubing strength than high temperature welding, allowing relatively light tube to be used without loss of strength. Recent advances inmetallurgy ("Air-hardening steel") have created tubing that is not adversely affected, or whose properties are even improved by high temperature welding temperatures, which has allowed bothTIG &MIG welding to sideline lugged construction in all but a few high end bicycles. More expensive lugged frame bicycles have lugs which are filed by hand into fancy shapes - both for weight savings and as a sign of craftsmanship. Unlike MIG or TIG welded frames, a lugged frame can be more easily repaired in the field due to its simple construction. Also, since steel tubing can rust (although in practice paint and anti-corrosion sprays can effectively prevent rust), the lugged frame allows a fast tube replacement with virtually no physical damage to the neighbouring tubes.[42][43]
A more economical method of bicycle frame construction uses cylindrical steel tubing connected by TIGwelding, which does not require lugs to hold the tubes together. Instead, frame tubes are precisely aligned into a jig and fixed in place until the welding is complete.Fillet brazing is another method of joining frame tubes without lugs. It is more labor-intensive, and consequently is less likely to be used for production frames. As with TIG welding, Fillet frame tubes are preciselynotched ormitered[44][45] and then a fillet of brass is brazed onto the joint, similar to the lugged construction process. A fillet braze frame can achieve more aesthetic unity (smooth curved appearance) than a welded frame.
Among steel frames, usingbutted tubing reduces weight and increases cost.Butting means that the wall thickness of the tubing changes from thick at the ends (for strength) to thinner in the middle (for lighter weight).
Cheaper steel bicycle frames are made of mild steel, also calledhigh tensile steel, such as might be used to manufacture automobiles or other common items. However, higher-quality bicycle frames are made of high strength steel alloys (generallychromium-molybdenum, or "chromoly" steel alloys) which can be made into lightweight tubing with very thin wall gauges. One of the most successful older steels wasReynolds"531", amanganese-molybdenum alloy steel. More common now is 4130 ChroMoly or similar alloys. Reynolds andColumbus are two of the most famous manufacturers of bicycle tubing. A few medium-quality bicycles used these steel alloys for only some of the frame tubes. An example was theSchwinnLe tour (at least certain models), which used chromoly steel for the top and bottom tubes but used lower-quality steel for the rest of the frame.
A high-quality steel frame is generally lighter than a regular steel frame. All else being equal, this loss of weight can improve the acceleration and climbing performance of the bicycle.
If the tubing label has been lost, a high-quality (chromoly or manganese) steel frame can be recognized by tapping it sharply with a flick of the fingernail. A high-quality frame will produce a bell-like ring where a regular-quality steel frame will produce a dull thunk. They can also be recognized by their weight (around 2.5 kg for frame and forks) and the type of lugs and fork ends used.
Aluminum alloys have a lower density and lowerstrength compared with steel alloys; however, they possess a better strength-to-weight ratio, giving them notable weight advantages over steel.Early aluminum structures have shown to be more vulnerable tofatigue, either due to ineffective alloys, or imperfect welding technique being used. This contrasts with some steel and titanium alloys, which have clearfatigue limits and are easier to weld or braze together. However, some of these disadvantages have since been mitigated with more skilled labor capable of producing better quality welds, automation, and the greater accessibility to modern aluminum alloys. Aluminum's attractive strength to weight ratio as compared to steel, and certain mechanical properties, assure it a place among the favored frame-building materials.
Popular alloys for bicycle frames are6061 aluminum and7005 aluminum.
The most popular type of construction today uses aluminum alloy tubes that are connected together byTungsten Inert Gas (TIG) welding. Welded aluminum bicycle frames started to appear in the marketplace only after this type of welding became economical in the 1970s.
Aluminum has a different optimal wall thickness to tubing diameter from steel. It is at its strongest at around 200:1 (diameter:wall thickness), whereas steel is a small fraction of that. However, at this ratio, the wall thickness would be comparable to that of a beverage can, far too fragile against impacts. Thus, aluminum bicycle tubing is a compromise, offering a wall thickness to diameter ratio that is not of utmost efficiency, but gives usoversized tubing of more reasonable aerodynamically acceptable proportions and good resistance to impact. This results in a frame that is significantly stiffer than steel. While many riders claim that steel frames give a smoother ride than aluminum because aluminum frames are designed to be stiffer, that claim is of questionable validity: the bicycle frame itself is extremely stiff vertically because it is made of triangles. Conversely, this very argument calls the claim of aluminum frames having greater vertical stiffness into question.[46] On the other hand, lateral and twisting (torsional) stiffness improves acceleration and handling in some circumstances.
Aluminum frames are generally recognized as having a lower weight than steel, although this is not always the case. A low quality aluminum frame may be heavier than a high quality steel frame. Butted aluminum tubes—where the wall thickness of the middle sections are made to be thinner than the end sections—are used by some manufacturers for weight savings. Non-round tubes are used for a variety of reasons, including stiffness, aerodynamics, and marketing. Various shapes focus on one or another of these goals, and seldom accomplish all.
Titanium is a relatively specialised material for bicycle frames. It has many desirable characteristics including a highspecific strength, highfatigue limit, and excellent corrosion resistance.[47] While not as light as carbon fiber, titanium bicycles can provide a more pleasant ride quality, making the material popular among cyclists seeking comfort over performance.[48][49] However, titanium has a high material cost and is more difficult to machine than steel or aluminum, which translates to relatively expensive frames compared to steel, aluminum, and carbon fiber.[48][49]
Titanium frames typically usetitanium alloys and tubes that were originally developed for theaerospace industry. The most commonly used alloy on titanium bicycle frames are 3AL-2.5V (3.5% aluminum and 2.5%vanadium), followed by6AL-4V (6% aluminum and 4% vanadium). Some manufacturers are experimenting with other alloys designed specifically for cycling.[47][49] Tubes can becold-drawn andhydroformed into various shapes and allow for internal cabling.[50] Welding is typically done ininert conditions to protect the welds from oxidation.[48][50]
Carbon fiber composite is a popular non-metallic material commonly used for bicycle frames.[51][52][53][54] Although expensive, it is light-weight, corrosion-resistant and strong, and can be formed into almost any shape desired. The result is a frame that can be fine-tuned forspecific strength where it is needed (to withstand pedaling forces), while allowing flexibility in other frame sections (for comfort). Custom carbon fiber bicycle frames may even be designed with individual tubes that are strong in one direction (such as laterally), while compliant in another direction (such as vertically). The ability to design an individual composite tube with properties that vary by orientation cannot be accomplished with any metal frame construction commonly in production.[55] Some carbon fiber frames use cylindrical tubes that are joined with adhesives and lugs, in a method somewhat analogous to a lugged steel frame. Another type of carbon fiber frames are manufactured in a single piece, calledmonocoque construction.
In one series of tests conducted bySanta Cruz Bicycles, it was shown that for a frame design with identical shape and nearly similar weight, the carbon frame is considerably stronger than aluminum, when subjected to an overall force load (subjecting the frame to both tension and compression), and impact strength.[56] While carbon frames can be lightweight and strong, they may have lower impact resistance compared to other materials, and can be prone to damage if crashed or mishandled. Cracking and failure can result from a collision, but also from over tightening or improperly installing components.[57] It has been suggested that these materials may be vulnerable to fatigue failure, a process which occurs with use over a long period of time,[58] though this is often limited to interlaminar cracks or cracks in adhesive at joints, where stresses can be well controlled with good design practices. It is possible for broken carbon frames to be repaired, but because of safety concerns it should be done only by professional firms to the highest possible standards.[59]
Many racing bicycles built forindividual time trial races andtriathlons employ composite construction because the frame can be shaped with anaerodynamic profile not possible with cylindrical tubes, or would be excessively heavy in other materials. While this type of frame may in fact be heavier than others, its aerodynamic efficiency may help the cyclist to attain a higher overall speed.
Other materials besides carbon fiber, such as metallicboron, can be added to the matrix to enhance stiffness further.[citation needed] Some newer high end frames are incorporating Kevlar fibers into the carbon weaves to improve vibration damping and impact strength, particularly in downtubes, seat stays, and chain stays.
Thermoplastics are a category of polymers that can be reheated and reshaped, and there are several ways that they can be used to create a bicycle frame. One implementation of thermoplastic bicycle frames are essentially carbon fiber frames with the fibers embedded in a thermoplastic material rather than the more common thermosettingepoxy materials.GT Bicycles was one of the first major manufacturers to produce a thermoplastic frame with their STS System frames in the mid 1990s. The carbon fibers were loosely woven into a tube along with fibers of thermoplastic. This tube was placed into amould with a bladder inside which was then inflated to force the carbon and plastic tube against the inside of the mould. The mould was then heated to melt the thermoplastic. Once the thermoplastic cooled it was removed from the mould in its final form.
A handful of bicycle frames are made frommagnesium, which has around 64% the density of aluminum. In the 1980s, an engineer, Frank Kirk, devised a novel form of frame that wasdie cast in one piece and composed ofI beams rather than tubes. A company, Kirk Precision Ltd, was established in Britain to manufacture both road bike and mountain bike frames with this technology. However, despite some early commercial success, there were problems with reliability and manufacture stopped in 1992.[60]The small number of modern magnesium frames in production are constructed conventionally using tubes.[61]
Some manufacturers of bikes make frames out of aluminum alloys containingscandium, usually referred to simply as scandium for marketing purposes although the Sc content is less than 0.5%. Scandium improves the welding characteristics of some aluminum alloys with superior fatigue resistance permitting the use of smaller diameter tubing, allowing for more frame design flexibility.
American Bicycle Manufacturing of St. Cloud, Minnesota, briefly offered a frameset made ofberyllium tubes (bonded to aluminum lugs), priced at $26,000. Reports were that the ride was very harsh, but the frame was also very laterally flexible.[62]
Several bicycle frames have been made of bamboo tubes connected with metal or composite joinery. Aesthetic appeal has often been as much of a motivator as mechanical characteristics.[63][64]
Several bicycle frames have been made of wood, either solid or laminate. Although one survived 265 grueling kilometers of theParis–Roubaix race, aesthetic appeal has often been as much of a motivator as ride characteristics.[65] Wood is used to fashion bicycles in East Africa.[66]Cardboard has also been used for bicycle frames.[67]
Combining different materials can provide the desired stiffness, compliance, or damping in different areas better than can be accomplished with a single material. The combined materials are usually carbon fiber and a metal, either steel, aluminum, or titanium. One implementation of this approach includes a metal down tube and chain stays with carbon top tube, seat tube, and seat stays.[68] Another is a metal main triangle and chain stays with just carbon seat stays.[69]Carbon forks have become very common on racing bicycles of all frame materials.[70]
Thebicycle types article describes additional variations.
Butted tubing has increased thickness near the joints for strength while keeping weight low with thinner material elsewhere. For example, triple butted means the tube, usually of an aluminum alloy, has three different thicknesses, with the thicker sections at the end where they are welded. The same material can be used in handlebars.
A variety of small features—bottle cage mounting holes,shifter bosses,cable stops,pump pegs,cable guides, etc.—are described asbraze-ons because they were originally, and sometimes still are,brazed on.[71]
Many bicycles, especially mountain bikes, have suspension.
Their range of seventeen models includes a woman's open frame bicycle.
Other names for bicycles with an extra reinforcing tube were girder frame or truss frame.
The RoundTail bicycle is featured on the front of the January issue of Road Bike Action Magazine — one of the largest international bike publications with a global circulation of 90,000.[permanent dead link]
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
Used on a bicycle with unsuspended rear wheel, the wishbone seat stay actually adds rigidity in the wrong direction - vertical rather than lateral stiffness.
| Frame |  | |
|---|---|---|
| Wheels | ||
| Drivetrain | ||
| Cabling | ||
| Peripherals | ||