A
bicycle frame is the main component of a
bicycleA bicycle, also known as a bike, push bike or cycle, is a pedal-driven, human-powered vehicle with two wheels attached to a frame, one behind the other. A person who rides a bicycle is called a cyclist or a bicyclist....
, onto which
wheelA bicycle wheel is a wheel, most commonly a wire wheel, designed for a bicycle. A pair is often called a wheelset, especially in the context of ready built "off the shelf" performance-oriented wheels....
s and
other components are fitted. The modern and most common frame design for an upright bicycle is based on the
safety bicycleA safety bicycle is a type of bicycle that became very popular beginning in the late 1880s as an alternative to the penny-farthing or ordinary and is now the most common type of bicycle. Early bikes of this style were known as safety bicycles because they were noted for, and marketed as, being...
, and consists of two
triangleA triangle is one of the basic shapes of geometry: a polygon with three corners or vertices and three sides or edges which are line segments. A triangle with vertices A, B, and C is denoted ....
s, a main triangle and a paired rear triangle. This is known as the
diamond frame.
In the diamond frame, 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. The head tube contains the
headsetThe headset is the set of components on a bicycle which provide a rotatable interface between the bicycle fork and the bicycle frame itself. The short tube through which the steerer of the fork passes is called the head tube. A typical headset consists of two cups which are pressed into the top and...
, the interface with the
forkA bicycle fork is the portion of a bicycle that holds the front wheel and allows the rider to steer and balance the bicycle. A fork consists of two dropouts which hold the front wheel axle, two blades which join at a fork crown, and a steerer or steering tube to which the handlebars attach ...
. The top tube connects the head tube to the seat tube at the top, and the down tube connects the head tube to the
bottom bracketThe bottom bracket on a bicycle connects the crankset to the bicycle and allows the crankset to rotate freely. It contains a spindle to which the crankset is attached and the bearings that allow the spindle and cranks to rotate. The chainrings and pedals are attached to the cranks...
shell. The rear triangle connects to the rear
dropoutA bicycle dropout , is a slot in a frame or fork where the axle of the wheel is attached.On bicycles that do not have a derailleur or other chain tensioning device, rear horizontal dropouts allow adjustment of chain tension, and can accommodate a range of chain lengths or cog sizes...
s, where the rear wheel is attached. It consists of the seat tube and paired chain stays and seat stays. The chain stays run parallel to the
chainA bicycle chain is a roller chain that transfers power from the pedals to the drive-wheel of a bicycle, thus propelling it. Most bicycle chains are made from plain carbon or alloy steel, but some are chrome-plated or stainless steel to prevent rust, or simply for aesthetics.-History:Obsolete chain...
, connecting the bottom bracket to the rear dropouts. The seat stays connect the top of the seat tube (often at or near the same point as the top tube) to the rear dropouts.
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 tubeA bicycle fork is the portion of a bicycle that holds the front wheel and allows the rider to steer and balance the bicycle. A fork consists of two dropouts which hold the front wheel axle, two blades which join at a fork crown, and a steerer or steering tube to which the handlebars attach ...
. 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.
Top tube
The
top tube connects the top of the head tube to the top of the seat tube. In a traditional-geometry
racing bicycleA racing bicycle, commonly known as a road bike, is a bicycle designed for road cycling according to the rules of the Union Cycliste Internationale . The UCI rules were altered in 1934 to exclude recumbent bicycles....
frame, the top tube is horizontal. In a compact-geometry frame, the top tube is sloped downward toward the seat tube. In a
mountain bikeA mountain bike or mountain bicycle is a bicycle designed for off-road cycling, including jumps, and traversing of rocks and washouts, and steep declines,...
frame, the top tube is almost always sloped downward toward the seat tube.
See Road and triathlon bicycles for more information on geometries. Step-through frameA step-through frame is a type of safety bicycle frame with a low top tube , in comparison to a diamond frame, or no top tube at all...
s 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 include leaving out the top tube out completely, and twin top tubes that continue to the rear dropouts as with the Mixte frame.
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 bicycleFor motorized-pedal hybrids, see motorized bicycleA hybrid bicycle is a bicycle designed for general-purpose utility or commuter cycling on paved and unpaved roads, paths, and trails...
s also route the front and rear derailleur cables along the top tube.
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 leversA bicycle shifter or gear control or gear levers is a component used to control the gearing mechanisms and select the desired gear ratio. Typically, they operate either a derailleur mechanism or an internal hub gear mechanism. In either case, the control is operated by moving a cable that connects...
were mounted on the down tube. On newer ones, they are mounted with the brake levers on the handlebars.
Bottle cageA bottle cage is device used to affix a water bottle to a bicycle. Composed of plastic, aluminum, stainless steel, titanium or carbon fiber, it is attached to the main frame of a bicycle, the handlebars, or behind the saddle...
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
seatpostA bicycle seatpost or seatpinis a tube that extends upwards from the bicycle frame to the saddle. The amount that it extends out of the frame can usually be adjusted, and there is usually a mark that indicates the minimum insertion...
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-onA braze-on is name for any number of parts of a bicycle which have been permanently attached to the frame. The term "braze-on" comes from when these parts would have been brazed on to steel frame bicycles...
mounts for a
bottle cageA bottle cage is device used to affix a water bottle to a bicycle. Composed of plastic, aluminum, stainless steel, titanium or carbon fiber, it is attached to the main frame of a bicycle, the handlebars, or behind the saddle...
or front derailleur.
Chain stays
The
chain stays run parallel to the chain, connecting the bottom bracket shell to the rear
dropoutA bicycle dropout , is a slot in a frame or fork where the axle of the wheel is attached.On bicycles that do not have a derailleur or other chain tensioning device, rear horizontal dropouts allow adjustment of chain tension, and can accommodate a range of chain lengths or cog sizes...
s. 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.
Chain stays can be straight or tapered tubes. Sometimes, on higher-end bikes, they are sculpted to allow clearance for the rear wheel and cranks.
Seat stays
The
seat stays connect the top of the seat tube (often at or near the same point as the top tube) to the rear dropouts. 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
Hellenic after the British frame builder Fred Hellens who introduced them in 1923.
The expressions
single seat stay,
mono stay or
wishbone all refer to seat stays which merge onto one section before joining the front triangle of the bicycle, thus meeting at a single point. A
dual seat stay refers to seat stays which meet the front triangle of the bicycle at two separate points, usually side-by-side. A single stay can provide stiffer mounting points for cantilever brakes.
Fastback seat stays meet the seat tube in the back instead of the sides.
There may be a bridge or brace that connects the stays above the rear wheel and below the connection with the seat tube. Besides additional bracing, this provides a mounting point for rear brakes, fenders, and racks.
The seat stays themselves may also provide a mounting point for rear rim or disc brakes. Usually, no rear mount is provided on a fixed gear or track frame.
When the rear derailleur cable is routed partially along the top tube, it is also usually routed along the seat stay. One combination aluminum/carbon fiber racing frame design uses carbon fiber for the seat stays and aluminum for all other tubes. This takes advantage of the better vibration absorption of carbon fiber compared to aluminum.
Bottom bracket shell
The
bottom bracket shell is a short and wide tube, relative to the other tubes in the frame, that runs side to side and holds the
bottom bracketThe bottom bracket on a bicycle connects the crankset to the bicycle and allows the crankset to rotate freely. It contains a spindle to which the crankset is attached and the bearings that allow the spindle and cranks to rotate. The chainrings and pedals are attached to the cranks...
. It is usually threaded, often left-hand threaded on the right (drive) side of the bike to prevent loosening by
fretting induced precessionPrecession is the name given to the process of one part rotating with respect to another due to fretting between the two. It is described as "precession, in which a round object rolling in a circular ring in one direction will itself turn in the opposite direction." "In machinery, fretting is the...
, and right-hand threaded on the left (non-drive) side. It will be over-sized, unthreaded, and possibly split in the case of an
eccentricIn mechanical engineering, an eccentric is a circular disk solidly fixed to a rotating axle with its centre offset from that of the axle ....
bottom bracket. The chain stays, seat tube, and down tube all connect to the bottom bracket shell.
There are a few standard shell widths (68, 70 or 73 mm). 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. The shell width influences the
Q factorThe Q factor of a bicycle is the distance between the pedal attachment points on the crank arms. It may also be referred to as the "tread" of the crankset....
or tread of the bike. There are a few standard shell diameters (34.798 - 36 mm) with associated thread pitches (24 - 28 tpi).
Frame geometry
The length of the tubes, and the angles at which they are attached define a
frame 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:
- saddle height, the distance from the center of the bottom bracket to the point of reference on top of the middle of the saddle.
- reach, the distance from the saddle to the handlebar.
- drop, the vertical distance between the reference at the top of the saddle to the handlebar.
- setback, the horizontal distance between the front of the saddle and the center of the bottom bracket.
- standover height, the height of the top tube above the ground.
- toe overlap, the amount that the feet can interfere with steering the front wheel.
The geometry of the frame depends on the intended use. For instance, a
road bicycleA road bicycle is a synonym for the term racing bicycle. As such, road bicycles have drop handlebars and multiple gears, although there are single and fixed gear varieties...
will place the handlebars in a lower and further position relative to the saddle giving a more crouched riding position; whereas a
utility bicycleA utility bicycle is a bicycle designed for practical transportation, as opposed to bicycles which are primarily designed for recreation and competition, such as touring bicycles, racing bicycles, sport/training bicycles, and mountain bicycles. The vast majority of bicycles can be found in the...
emphasizes comfort and has higher handlebars resulting in an upright riding position.
Frame geometry also affects handling characteristics. For more information, see the
Bicycle and motorcycle geometryBicycle and motorcycle geometry is the collection of key measurements that define a particular bike configuration. Primary among these are wheelbase, steering axis angle, fork offset, and trail...
and the
Bicycle and motorcycle dynamicsBicycle and motorcycle dynamics is the science of the motion of bicycles and motorcycles and their components, due to the forces acting on them. Dynamics is a branch of classical mechanics, which in turn is a branch of physics. Bike motions of interest include balancing, steering, braking,...
articles.
Frame size
Frame size was traditionally measured 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's mountain bicycle. The wider range of frame geometries that are now made have given rise to different ways of measuring frame size; see the
discussion by
Sheldon BrownSheldon Brown was an American bicycle mechanic and technical authority. He maintained a website containing articles relating to bicycle mechanics and maintenance, as well as a of bicycling terminology...
. Touring frames tend to be longer, while racing frames are more compact.
Road and triathlon bicycles
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 a
traditional geometry with a horizontal top tube, or a
compact 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 contribute to these two aspects. Compact geometry road frames have a lower center of gravity and tend to have a shorter wheelbase and smaller rear triangle, which give the bike quicker handling. Compact geometry also 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 steeper
seat 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 seat tube angle traditionally. This positions the rider more on the sit bones and takes weight off of the wrists, arms, neck and, for men, improves circulation to the urinary and reproductive areas. With slacker angle, designers lengthen the chainstay 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 because of the need to otherwise reset welding jigs in automated processes and thus increase manufacturing costs, and thus do not provide the comfort of traditionally made or custom made frames which do have noticeably slacker seat tube angles.
Road racing bicyclesA racing bicycle, commonly known as a road bike, is a bicycle designed for road cycling according to the rules of the Union Cycliste Internationale . The UCI rules were altered in 1934 to exclude recumbent bicycles....
that are used in UCI sanctioned races are governed by
UCIUnion Cycliste Internationale is a cycling association that oversees competitive cycling events internationally. It is the world governing body for jurisdiction in the sport of cycling. The UCI is based in Aigle, Switzerland...
regulations, which state among other things that the frame must consist of two triangles. Hence the designs that lack a seat tube or top tube are not allowed.
TriathlonA triathlon is a multi-sport endurance event consisting of swimming, cycling, and running in immediate succession over various distances. Triathletes compete for fastest overall course completion time, including timed "transitions" between the individual swim, bike, and run components.Triathlon...
or
time trialIn many racing sports an athlete will compete in a time trial against the clock to secure the fastest time. In cycling, for example, a time trial can be a single track cycling event, or an individual or team time trial on the road, and either or both of the latter may form components of...
specific frames rotate the rider forward around the axis of the bottom bracket of the bicycle as compared to the standard road bicycle frame. The reason for this is 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 goverened by the UCI, some triathlon bicycles, such as the
Zipp 2001Zipp 2001 and 3001 were a line of bicycle frames, now discontinued, made by the Zipp company. While they have been out of production for 7 years, they are still considered one of the fastest time trial frames ever made, and still have a cult following within triathlon, where they remain...
, Cheetah and Softride have non traditional frame layouts, which can produce better aerodynamics.
Track bicycles
Track framesA track bicycle or track bike is a bicycle optimized for racing at a velodrome or outdoor track. Unlike road bicycles, the track bike is a fixed-gear bicycle and so has a single gear and neither freewheel nor brakes. Tires are narrow and inflated to high pressure to reduce rolling resistance....
have much in common with road and time trial frames, but come with rear-facing, horizontal fork ends, rather than dropouts, to allow one to adjust the position of the rear wheel horizontally to set the proper chain tension. Also the seat tube angle is steeper than road racing bikes.
Mountain bicycles
For ride comfort and better handling,
shock absorberA shock absorber in common parlance is a mechanical device designed to smooth out or damp shock impulse, and dissipate kinetic energy.- Explanation :...
s are often used; there are a number of variants, including
full suspension models, which provide shock absorption for the front and rear wheels; and
front 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 mountain bicycles with rear
suspensionSuspension is the term given to the system of springs, shock absorbers and linkages that connects a vehicle to its wheels. Suspension systems serve a dual purpose – contributing to the car's roadholding/handling and braking for good active safety and driving pleasure, and keeping vehicle occupants...
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/Utility Bicycles
Roadster bicyclesA roadster, aka English roadster, is a type of utility bicycle once common in Britain and still very common in Asia, Africa, Denmark and the Netherlands.-Design and variants:...
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), 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.
Variations
There are many variations on the basic diamond frame design, most notably for the purpose of achieving a reclining rider position on a
recumbentRecumbent may refer to:* Recumbent bicycle, a bicycle which places the rider in a seated or supine position* Recumbent stone circles, a variation on the more familiar standard stone circles found throughout the UK...
bicycle. Historically, women's bicycle frames 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
skirtA skirt is a tube- or cone-shaped garment that hangs from the waist and covers all or part of the legs.In European culture, skirts are usually considered women's clothing. However, there are exceptions...
or
dressA dress is a garment consisting of a skirt with an attached bodice or with a matching bodice giving the effect of a one-piece garment.Dress may also refer to:*Clothing in general*Costume, fancy dress...
. This is also known as a
step-through frameA step-through frame is a type of safety bicycle frame with a low top tube , in comparison to a diamond frame, or no top tube at all...
. Another style that accomplishes similar results is the mixte.
The cycle types article describes additional variations.
It is also possible to add
couplersAn S and S Coupling also known as a Bicycle Torque Coupling or BTC is a coupling which enables bicycle frames to be separated into smaller pieces, usually to facilitate packing and transporting. They can be built into the frame by the frame manufacturer when the frame is originally assembled or...
either during manufacturing or as a retrofit so that the frame can be disassembled into smaller pieces to facilitate packing and travel.
Frame materials
Generally, the tubes of the frame are made of steel. Steel frames can be very inexpensive carbon steel to highly specialised using high performance
alloyAn alloy is a partial or complete solid solution of one or more elements in a metallic matrix. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may be homogeneous in distribution depending on thermal history...
s. Frames can also be made from aluminum alloys, titanium, carbon fiber, and even
bambooThe bamboos are a group of woody perennial evergreen plants in the true grass family Poaceae, subfamily Bambusoideae, tribe Bambuseae. Some are giant bamboos, the largest members of the grass family. Bamboos are the fastest growing woody plants in the world...
. Occasionally, diamond (shaped) frames have been formed from sections other than tubes. These include
I-beamI-beams are beams with an
I- or H-shaped cross-section. The horizontal elements are flanges, while the vertical element is the web...
s and
monocoqueMonocoque, from Greek for single and French for shell , is a construction technique that supports structural load by using an object's external skin as opposed to using an internal frame or truss that is then covered with a non-load-bearing skin. Monocoque construction was first widely used in...
. Materials that have been used in these frames include
woodWood is an organic material; in the strict sense wood is produced as secondary xylem in the stems of trees . In a living tree it transfers water and nutrients to the leaves and other growing tissues, and has a support function, enabling woody plants to reach large sizes or to stand up for themselves...
(solid or
laminateA laminate is a material constructed by uniting two or more layers of material together. The process of creating a laminate is lamination, which in common parlance refers to the placing of something between layers of plastic and sealing them with heat and/or pressure, usually with an adhesive...
),
magnesiumMagnesium is a chemical element with the symbol Mg, atomic number 12 and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the earth's crust by mass, although ninth in the Universe as a whole...
(cast I-beams), and
thermoplasticA thermoplastic is a polymer that turns to a liquid when heated and freezes to a very glassy state when cooled sufficiently. Most thermoplastics are high-molecular-weight polymers whose chains associate through weak Van der Waals forces ; stronger dipole-dipole interactions and hydrogen bonding ;...
. Several properties of a material help decide whether it is appropriate in the construction of a bicycle frame:
- Density
The density of a material is defined as its mass per unit volume. The symbol of density is ρ .- Formula :Mathematically:where: is the density, is the mass, is the volume....
(or specific gravity) is a measure of how light or heavy the material per unit volume.
- Stiffness
Stiffness is the resistance of an elastic body to deformation by an applied force. It is an extensive material property.-Definition:The stiffness, k, of a body is a measure of the resistance offered by an elastic body to deformation .whereIn the International System of Units, stiffness is typically...
(or elastic modulusAn elastic modulus, or modulus of elasticity, is the mathematical description of an object or substance's tendency to be deformed elastically when a force is applied to it...
) can in theory affect the ride comfort and power transmission efficiency. In practice, because even a very flexible frame is much more stiff than the tires and saddle, ride comfort is in the end more a factor of saddle choice, frame geometry, tire choice, and bicycle fit. Lateral stiffness is far more difficult to achieve because of the narrow profile of a frame, and too much flexibility can affect power transmission, primarily through tire scrub on the road due to rear triangle distortion, brakes rubbing on the rims and the chain rubbing on gear mechanisms. In extreme cases gears can change themselves when the rider applies high torque out of the saddle.
- Yield strength
Tensile strength is indicated by the maxima of a stress-strain curve and, in general, indicates when necking will occur. As it is an intensive property, its value does not depend on the size of the test specimen...
determines how much force is needed to permanently deform the material (for crash-worthiness).
- Elongation determines how much deformity the material allows before cracking (for crash-worthiness).
- Fatigue limit and Endurance limit
'In materials science, fatigue is the progressive and localized structural damage that occurs when a material is subjected to cyclic loading...
determines the durability of the frame when subjected to cyclical stress from pedaling or ride bumps.
Tube engineering and frame geometry can overcome much of the perceived shortcomings of these particular materials.
Steel
SteelSteel is an alloy consisting mostly of iron, with a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most cost-effective alloying material for iron, but various other alloying elements are used such as manganese, chromium, vanadium, and tungsten...
frames are often built using various types of steel alloys including chromoly. They are strong, easy to work, and relatively inexpensive, but denser (heavier) than many other structural materials. Steel tubing in traditional standard diameters is often less rigid than oversized tubing in other materials (due more to diameter than material); this flex allows for some shock absorption giving the rider a slightly less jarring ride compared to other more rigid tubings such as oversized aluminum. cf.
www.sheldonbrown.com/frame-materials.html
A classic type of construction for both road bicycles and mountain bicycles uses standard cylindrical steel tubes which are connected with
lugs. 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 then
brazedBrazing is a metal-joining process whereby a filler metal or alloy is heated to melting temperature above and distributed between two or more close-fitting parts by capillary action. The filler metal is brought slightly above its melting temperature while protected by a suitable atmosphere or flux...
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 in
metallurgyMetallurgy is a domain of materials science that studies the physical and chemical behavior of metallic elements, their intermetallic compounds, and their mixtures, which are called alloys. It is also the technology of metals: the way in which science is applied to their practical use...
("air hardening") have created tubing that is not adversely affected, or whose properties are even improved by high temperature welding temperatures, which has allowed both
TIGTig may refer to:*TIG Welding, a metal welding process.*Tig Notaro, an American stand-up comic** TIG, abbreviation of Triennial Inter-varsity Games, held by the University of Hong Kong, the National University of Singapore, the University of Malaya and the University of Indonesia every three years...
&
MIGGas metal arc welding , sometimes referred to by its subtypes metal inert gas welding or metal active gas welding, is a semi-automatic or automatic arc welding process in which a continuous and consumable wire electrode and a shielding gas are fed through a welding gun...
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.
A more economical method of bicycle frame construction uses cylindrical steel tubing connected by TIG
weldingWelding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material that cools to become a strong joint, with pressure sometimes...
, 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.
FilletIn mechanical engineering, a fillet is a concave easing of an interior corner of a part design. A rounding of an exterior corner is called a "round".-Applications:...
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 precisely
notchedNotching is a metal-cutting process used on sheetmetal or thin barstock, sometimes on angle sections or tube. A shearing or punching process is used in a press, so as to cut vertically down and perpendicular to the surface, working from the edge of a workpiece...
or
miteredA mitre or miter joint is a joint made by bevelling each of two parts to be joined, usually at a 45° angle, to form a corner, usually a 90° angle. It is often used in making picture frames....
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, using
butted tubingOn a bicycle frame, stress concentrates where the material is joined. There are three types of stress; joint, corner, and heat. These stress converges at the joints. Butted Tubing increase the thickness at the joints but thin everywhere else. It decreases weight while maintaining the strength at...
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, such as might be used to manufacture automobiles or other common items. However, higher-quality bicycle frames are made of high strength steel alloys (generally
chromiumChromium is a chemical element which has the symbol Cr and atomic number 24, first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odourless, tasteless, and malleable...
-
molybdenumMolybdenum , is a Group 6 chemical element with the symbol Mo and atomic number 42. The free element, which is a silvery metal, has the sixth-highest melting point of any element. It readily forms hard, stable carbides, and for this reason it is often used in high-strength steel alloys...
, or "chromoly" steel alloys) which can be made into lightweight tubing with very thin wall gauges. One of the most successful older steels was
ReynoldsReynolds Cycle Technology is a manufacturer of tubing for bicycle frames and other bicycle components based in Birmingham, England established in 1898.-History:...
"531"Reynolds 531 is a brand name, registered to Reynolds Cycle Technology of Birmingham in the United Kingdom, for a manganese-molybdenum, medium carbon steel bicycle tubing....
, a
manganeseManganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature , and in many minerals...
-molybdenum alloy steel. More common now is 4130 ChroMoly or similar alloys. Reynolds and
ColumbusColumbus is a manufacturer of steel tubing used in bicycle frames, located in Settala, in the Province of Milan. The company was founded in 1919 by A.L. Columbo and was taken over by Columbo's youngest son, Antonio, in 1977...
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 the Schwinn
Le 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 lighter than a regular steel frame. This lightness makes it easier to ride uphill, and to accelerate on the flat. Also many riders feel thin-walled lightweight steel frames have a "liveliness" or "springiness" quality to their ride.
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 dropouts used.
Aluminum alloys
Aluminum alloyAluminium alloys are mixtures of aluminium with other metals , often with copper, zinc, manganese, silicon, or magnesium. They are much lighter and more corrosion resistant than plain carbon steel, but not as corrosion resistant as pure aluminium...
s have a lower density and lower
strengthIn materials science, the strength of a material is its ability to withstand an applied stress without failure. Yield strength refers to the point on the engineering stress-strain curve beyond which the material begins deformation that cannot be reversed upon removal of the loading...
compared with steel alloys, however, possess a better strength-to-weight ratio, giving them notable weight advantages over steel.
Early aluminum structures have shown to be more vulnerable to
fatigue'In materials science, fatigue is the progressive and localized structural damage that occurs when a material is subjected to cyclic loading...
, either due to ineffective alloys, or imperfect welding technique being used. This contrasts with some steel and titanium alloys, which have clear
fatigue limitFatigue limit, endurance limit, and fatigue strength are all expressions used to describe a property of materials: the amplitude of cyclic stress that can be applied to the material without causing fatigue failure. Ferrous alloys and titanium alloys have a distinct limit, an amplitude below which...
s and are easier to weld or braze together. However, some of these disadvantages have since been partly negated, with more skilled labor capable of producing better quality welds, automation, and the greater accessibility of the same modern aluminum alloys as used in commercial airliners' structures, assuring strength and reliability comparable to steel frames. Aluminum's attractive strength to weight ratio as compared with steel, and certain mechanical properties, assure it a place among the favored frame-building materials (for example, a very strong rider, who does lots of hill-climbing, may prefer the stiffness of aluminum). Some disadvantages are that an aluminum frame doesn't have the same "feel" to an experienced cyclist as a steel frame, excessive ride harshness in lower quality frames, and decreased ease of repairability.
Popular alloys for bicycle frames are
6061 aluminum6061 is a precipitation hardening aluminium alloy, containing magnesium and silicon as its major alloying elements. It has good mechanical properties and exhibits good weldability...
and
7075 aluminum7075 is an aluminium alloy, with zinc as the alloying element. It is strong, with good fatigue strength and average machinability, but has less resistance to corrosion than many other alloys...
.
The most popular type of construction today uses aluminum alloy tubes that are connected together by Tungsten 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 than 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 us
oversized 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, the sides of which do not change in length under stress. Conversely, this very argument calls the claim of aluminium frames having greater vertical stiffness into question. 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. An inexpensive aluminum frame may be heavier than an expensive 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
TitaniumTitanium is a chemical element with the symbol Ti and atomic number 22. Sometimes called the “space age metal”, it has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color.Titanium can be alloyed with iron, aluminium, vanadium, molybdenum, among other...
is perhaps the most exotic and expensive metal commonly used for bicycle frame tubes. It combines many desirable characteristics, including a high strength to weight ratio and excellent corrosion resistance. Reasonable stiffness (roughly half that of steel) allow for many titanium frames to be constructed with "standard" tube sizes comparable to a traditional steel frame, although larger diameter tubing is becoming more common for more stiffness. As many titanium frames can be much more expensive than similar steel alloy frames, cost can put them out of reach for many cyclists. Many common
titanium alloyTitanium alloys are metallic materials which contain a mixture of titanium and other chemical elements. Such alloys have very high tensile strength and toughness , light weight, extraordinary corrosion resistance, and ability to withstand extreme temperatures...
s and even specific tubes were originally developed for the
aerospaceAerospace engineering is the branch of engineering behind the design, construction and science of aircraft and spacecraft. It is broken into two major and overlapping branches: aeronautical engineering and astronautical engineering...
industry.
Titanium frame tubes are almost always joined by Tungsten inert gas (TIG) welding , although vacuum
brazingBrazing is a metal-joining process whereby a filler metal or alloy is heated to melting temperature above and distributed between two or more close-fitting parts by capillary action. The filler metal is brought slightly above its melting temperature while protected by a suitable atmosphere or flux...
has been used on early frames. It is more difficult to machine than steel or aluminum, which sometimes limits its uses and also raises the effort (and cost) associated with this type of construction.
Carbon fiber
Carbon fiberCarbon fiber is a material consisting of extremely thin fibers about 0.005–0.010 mm in diameter and composed mostly of carbon atoms. The carbon atoms are bonded together in microscopic crystals that are more or less aligned parallel to the long axis of the fiber...
, a
composite materialComposite materials are engineered materials made from two or more constituent materials with significantly different physical or chemical properties which remain separate and distinct on a macroscopic level within the finished structure.- History :The most primitive composite materials were straw...
, is an increasingly popular non-metallic material commonly used for bicycle frames. 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 for
specific strengthThe specific strength is a material's strength divided by its density. It is also known as the strength-to-weight ratio or strength/weight ratio. Materials with high specific strengths are widely used in aerospace applications where weight savings are worth the higher material cost...
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.
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, called monocoque construction. While these composite materials provide light weight as well as high strength, they have much lower impact resistance and consequently are prone to damage if crashed or mishandled. It has also been suggested that these materials are vulnerable to fatigue failure, a process which occurs with use over a long period of time.
Many racing bicycles built for
individual time trialAn individual time trial is a road bicycle race in which cyclists race alone against the clock . There are also track-based time trials where riders compete in velodromes, and team time trials...
races and
triathlonA triathlon is a multi-sport endurance event consisting of swimming, cycling, and running in immediate succession over various distances. Triathletes compete for fastest overall course completion time, including timed "transitions" between the individual swim, bike, and run components.Triathlon...
s employ composite construction because the frame can be shaped with an aerodynamic 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 speed and consequently outweigh other considerations in such events.
Other materials besides carbon fiber, such as metallic
boronBoron is the chemical element with atomic number 5 and the chemical symbol B. Boron is a trivalent metalloid element which occurs abundantly in the evaporite ores borax and ulexite....
, can be added to the matrix to enhance stiffness further.
Thermoplastic
ThermoplasticA thermoplastic is a polymer that turns to a liquid when heated and freezes to a very glassy state when cooled sufficiently. Most thermoplastics are high-molecular-weight polymers whose chains associate through weak Van der Waals forces ; stronger dipole-dipole interactions and hydrogen bonding ;...
s, according to a study from 2001 done by the Advanced Technology Project (ATP), is a new material that is still within testing.
http://statusreports-atp.nist.gov/reports/91-01-0178PDF.pdf It was originally developed by "
Ford Motor CompanyThe Ford Motor Company is an American multinational corporation based in Dearborn, Michigan, a suburb of Detroit. The automaker was founded by Henry Ford and incorporated on June 16, 1903. In addition to the Ford, Lincoln, and Mercury brands, Ford also owns Volvo Cars of Sweden, and a small stake...
Scientific Research Laboratory" and "
General ElectricThe General Electric Company, or GE , is a multinational American technology and services conglomerate incorporated in the State of New York. In 2009, Forbes ranked GE as the world's largest company...
Research and DevelopmentThe phrase research and development , according to the Organization for Economic Co-operation and Development, refers to "creative work undertaken on a systematic basis in order to increase the stock of knowledge, including knowledge of man, culture and society, and the use of this stock of...
" within a
joint ventureA joint venture is an entity formed between two or more parties to undertake economic activity together. The parties agree to create a new entity by both contributing equity, and they then share in the revenues, expenses, and control of the enterprise...
. The ATP pioneered the use of cyclic thermoplastics in automotive components. Such parts are used in Ford's
Aston MartinAston Martin Lagonda Limited is a British manufacturer of luxury sports cars, based in Gaydon, Warwickshire. The company name is derived from the name of one of the company's founders, Lionel Martin, and from the Aston Hill speed hillclimb near Aston Clinton in BuckinghamshireFrom 1994 until 2007...
model automobile. Intellectual proprietary rights were sold to Cyclics Corporation which is using the process to produce such items as recyclable bicycle frames.
One implementation of thermoplastic bicycle frames are essentially carbon fiber frames with the fibers embedded in a thermoplastic material rather than the more common
epoxyEpoxy or polyepoxide is a thermosetting polymer formed from reaction of an epoxide "resin" with polyamine "hardener". Epoxy has a wide range of applications, including fiber-reinforced plastic materials and general purpose adhesives.- Chemistry :...
materials.
GT BicyclesGT Bicycles is a large American manufacturer of road, mountain, and bmxbicycles. The company was founded in 1979 by Gary Turner, a welding engineer and Richard Long, a bike shop owner. The company merged with Schwinn in 1998, but the conglomerate went bankrupt in 2001, and was acquired by Pacific...
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 a
mouldMolding or moulding is the process of manufacturing by shaping pliable raw material using a rigid frame or model called a pattern....
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.
Magnesium
A handful of bicycle frames are made from
magnesiumMagnesium is a chemical element with the symbol Mg, atomic number 12 and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the earth's crust by mass, although ninth in the Universe as a whole...
which has around 64% the density of aluminum. In the 1980s, an engineer, Frank Kirk, devised a novel form of frame that was die cast in one piece and composed of I 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.
The small number of modern magnesium frames in production are constructed conventionally using tubes.
Reportedly, a major problem with these frames is corrosion caused by the chemical reactivity of magnesium. Unless care is taken during assembly of the bicycle, there is likely to be galvanic corrosion at points where steel or aluminum components attach to the frame.
Scandium
Some manufacturers of bikes make frames out of
scandiumScandium is a chemical element with symbol Sc and atomic number 21. A silvery-white metallic transition metal, it has historically been sometimes classified as a rare earth element, together with yttrium and the lanthanides...
-aluminum alloy, usually referred to simply as scandium.
Bamboo
Several bicycle frames have been made of bamboo tubes connected with steel or carbon fiber lugs. Aesthetic appeal has often been as much of a motivator as ride characteristics.
Wood
Several bicycle frames have been made of wood, either solid or laminate. Although one survived 265 grueling kilometers of the
Paris-RoubaixParis–Roubaix is a one-day professional bicycle road race in northern France near the Belgian frontier. Since its beginning in 1896 until 1967 it started in Paris and ended in Roubaix ; since 1968 the start city is Compiègne , whilst the finish is still in Roubaix...
race, aesthetic appeal has often been as much of a motivator as ride characteristics. Wood is used to fashion bicycles in East Africa.
Combinations
A recent innovation is the construction of frames out of tubes of different materials. This is intended to 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. Another is a metal main triangle and chain stays with just carbon seat stays.
Braze-ons
A variety of small features -- bottle cage mounting holes,
shifterA bicycle shifter or gear control or gear levers is a component used to control the gearing mechanisms and select the desired gear ratio. Typically, they operate either a derailleur mechanism or an internal hub gear mechanism. In either case, the control is operated by moving a cable that connects...
bosses,
cableA bowden cable is a type of flexible cable used to transmit mechanical force or energy by the movement of an inner cable relative to a hollow outer cable housing...
stops,
pumpA bicycle pump is a type of positive-displacement pump specifically designed for inflating bicycle tires. It has a connection or adapter for use with one or both of the two most common types of valves used on bicycles, Schrader or Presta...
pegs,
cable guideA cable guide is a fitting or part of a bicycle frame which guides a piece of bare inner bowden cable around a corner. Most multi-speed bicycles have cable guides to get the derailleur cables past the bottom bracket....
s, etc. -- are described as
braze-ons because they were originally, and sometimes still are, brazed on.
Suspension
Many bicycles, especially mountain bikes, have suspension built into the frame.
History
See also
- Bicycle
A bicycle, also known as a bike, push bike or cycle, is a pedal-driven, human-powered vehicle with two wheels attached to a frame, one behind the other. A person who rides a bicycle is called a cyclist or a bicyclist....
- Bicycle chain
A bicycle chain is a roller chain that transfers power from the pedals to the drive-wheel of a bicycle, thus propelling it. Most bicycle chains are made from plain carbon or alloy steel, but some are chrome-plated or stainless steel to prevent rust, or simply for aesthetics.-History:Obsolete chain...
- Bicycle fork
A bicycle fork is the portion of a bicycle that holds the front wheel and allows the rider to steer and balance the bicycle. A fork consists of two dropouts which hold the front wheel axle, two blades which join at a fork crown, and a steerer or steering tube to which the handlebars attach ...
- Bicycle suspension
Bicycle suspension refers to the system or systems used to suspend the rider and all or part of the bicycle in order to protect them from the roughness of the terrain over which they travel...
- Step-through frame
A step-through frame is a type of safety bicycle frame with a low top tube , in comparison to a diamond frame, or no top tube at all...
External links