Proiect Diploma - Chapter 1

8/8/2019 Proiect Diploma - Chapter 1

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RICHEA OCTAVIAN - DIPLOMA PROJECT INTRODUCTION

1. CHAPTER 1 - INTRODUCTION, STATE OF ART.

1.1 A Quick History of Bicycles

In 1817 Baron von Drais invented the walking machinethat would help him get around the royal gardens faster: twosame-size in-line wheels, the front one steerable, mounted in aframe which you straddled. The device was propelled by pushingyour feet against the ground, thus rolling yourself and the deviceforward in a sort of gliding walk. The machine became known asthe Draisienne (fig. 1) or hobby horse. It was made entirely of wood.

The Velocipede or Boneshaker

The next appearance of a two-wheeled ridingmachine was in 1865, when pedals were applied directlyto the front wheel. This machine was known as thevelocipede (fig. 2). It was popularly known as the boneshaker, since it was also made entirely of wood, then later with metal tires, and the combination of these with thecobblestone roads of the day made for an extremelyuncomfortable ride. They also became a fad, and indoor riding academies, similar to roller rinks, could be found inlarge cities.

The High Wheel Bicycle

In 1870 the first all metal machine appeared. Previous to thismetallurgy was not advanced enough to provide metal which wasstrong enough to make small, light parts out of. The pedals were stillattached directly to the front wheel with no freewheeling mechanism.Solid rubber tires and the long spokes of the large front wheel

provided a much smoother ride than its predecessor. The front wheels became larger and larger as makers realized that the larger the wheel,the farther you could travel with one rotation of the pedals. Thismachine was the first one to be called a bicycle (fig.3). These

bicycles enjoyed a great popularity among young men of means.

Because the rider sat so high above the center of gravity, if

the front wheel was stopped by a stone or rut in the road, or thesudden emergence of a dog, the entire apparatus rotated forward onits front axle, and the rider, with his legs trapped under thehandlebars, was dropped unceremoniously on his head. Thus the term"taking a header" came into being.

Fig. 2

Fig. 1

Fig. 3


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The High Wheel Tricycle

While the men were assuming a risk on the high wheels,ladies, confined to their long skirts and corsets, could take aspin around the park on an adult tricycle (fig. 4). Thesemachines also afforded more dignity to gentlemen such as

doctors and clergymen. Many mechanical innovations nowassociated with the automobile were originally invented for tricycles: rack and pinion steering, the differential, and band

brakes, etc.

The High Wheel Safety

Improvements to the design began to be seen, manywith the small wheel in the front to eliminate the tipping-forward problem. One model was promoted by itsmanufacturer by being ridden down the front steps of thecapitol building in Washington. These designs became knownas high-wheel safety bicycles (fig.5). Since the older high-wheel designs had been known simply as bicycles, they werenow referred to as "ordinary bicycles" in comparison with thenew-fangled designs, and then simply as "ordinaries."

The Hard-Tired Safety

The further improvement of metallurgy sparked the next innovation, or rather return to previous design. With metal that was now strong enough to make a finechain and sprocket small and light enough for a human being to power. The nextdesign was a return to the original configuration of two same-size wheels as the

Draisine, only now, instead of just one wheel circumference for every pedal turn, youcould, through the gear ratios, have a speed the same as the huge high-wheel (fig.6).The bicycles still had the hard rubber tires, and in the absenceof the long, shock-absorbing spokes, the ride they providedwas much more uncomfortable than any of the high-wheeldesigns. Many of these bicycles of 100 years ago had frontand/or rear suspensions. These designs competed with eachother, your choice being the high-wheel's comfort or thesafety, but the next innovation tolled the death of the high-wheel design.

The Pneumatic-Tired Safety

The pneumatic tire was first applied to the bicycle by an Irish veterinarian whowas trying to give his young son a more comfortable ride on his tricycle. Thisinventive young doctor's name was Dunlop. Now that comfort and safety could behad in the same package, and that package was getting cheaper as manufacturingmethods improved, everyone clamored to ride the bicycle. This 1898 Yale uses a shaftdrive to dispense with the dirty chain (fig.7). ---------------------------------------------------------------------------------

Fig. 4

Fig. 5

Fig. 6


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The bicycle was a practical investment for theworking man as transportation, and gave him a muchgreater flexibility for leisure. Ladies heretoforeconsigned to riding the heavy adult size tricycles thatwere only practical for taking a turn around the park,now could ride a much more versatile machine and still

keep their legs covered with long skirts. The bicyclecraze killed the bustle and the corset, instituted"common-sense dressing" for women and increasedtheir mobility considerably. In 1896 Susan B. Anthony said that "the bicycle has donemore for the emancipation of women than anything else in the world." -------------------- Bicycling was so popular in the 1880s and 1890s that cyclists formed theLeague of American Wheelman (still in existence and now called the League of American Bicyclists). The League lobbied for better roads, literally paving the roadfor the automobile.

The Kid's Bike

Introduced just after the First World War byseveral manufacturers, such as Mead, Sears Roebuck,and Montgomery Ward, to revitalize the bikeindustry, these designs, now called "classic", featuredautomobile and motorcycle elements to appeal to kidswho, presumably, would rather have a motor. If ever a bike needed a motor, this was it. These bikesevolved into the most glamorous, fabulous,ostentatious, heavy designs ever (fig.8). It isunbelievable today that 14-year-old kid could do thetricks that we did, on these 30 kilograms machines.They were built into the middle '50s, by which time they had taken on designelements of jet aircraft and even rockets. By the '60s, they were becoming leaner andsimpler.

1.2 The Current Scene

Pedaling History has on display even the recent history of the bicycle inAmerica that we are more familiar with: the "English 3-speed" of the '50s through the'70s, the 10-speed derailleur bikes which were popular in the '70s (the derailleur had

been invented before the turn of the century and had been in more-or-less commonuse in Europe since), and of course the mountain bike of right now.

1.3 Uses for bicycles

Due to simple manufacturing, low cost, easy handling and high reliability, bicycles are used throughout the entire world as a mean of transportation.

Fig. 7

Fig. 8


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Bicycles uses:

Utility: bicycle commuting and utility cycling Work: mail delivery, paramedics, police, and general delivery. Recreation: bicycle touring, mountain biking, BMX and physical fitness. Racing: track racing, criterium, roller racing and time trial to multi-stage

events like the Tour of California, Giro d'Italia, the Tour de France, the Vueltaa Espaa, the Volta a Portugal, among others.

Military: scouting, troop movement, supply of provisions, and patrol. See bicycle infantry.

Show: entertainment and performance, e.g. circus clowns. Power: electricity for electronics can be generated by bicycle.

Examples:

Transporting milk churns in Kolkata, India (fig.9), Working bicycle inAmsterdam, Netherlands (fig.10).

1.4 Dynamics

A bicycle stays upright while moving forward by being steered so as to keepits center of gravity over the wheels. This steering is usually provided by the rider, butunder certain conditions may be provided by the bicycle itself.

A bicycle must lean in order to turn (fig. 11).This lean is induced by a method known as counter steering, which can be performed by the rider turningthe handlebars directly with the hands or indirectly

by leaning the bicycle.Short-wheelbase or tall bicycles, when

braking, can generate enough stopping force at thefront wheel in order to flip longitudinally. The act of

purposefully using this force to lift the rear wheel and balance on the front without tipping over is a trick known as a stoppie, endo or front wheelie. Fig. 11 - Bicycles leaning in a turn

Fig. 9 Fig. 10


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1.5 Performance

The bicycle is extraordinarily efficient in both biological and mechanicalterms. The bicycle is the most efficient self-powered means of transportation in termsof energy a person must expend to travel a given distance. From a mechanicalviewpoint, up to 99% of the energy delivered by the rider into the pedals istransmitted to the wheels, although the use of gearing mechanisms may reduce this by10-15%. In terms of the ratio of cargo weight a bicycle can carry to total weight, it isalso a most efficient means of cargo transportation.

A human being traveling on a bicycle at low to medium speeds of around 10-15 mph (15-25 km/h), using only the energy required to walk, is the most energy-efficient means of transport generally available. Air drag, which is proportional to thesquare of speed, requires dramatically higher power outputs as speeds increase. A

bicycle which places the rider in a seated position, supine position or, more rarely, prone position, and which may be covered in an aerodynamic fairing to achieve verylow air drag, is referred to as a recumbent bicycle or human powered vehicle. On anupright bicycle, the rider's body creates about 75% of the total drag of the

bicycle/rider combination.

In addition, the carbon dioxide generated in the production and transportationof the food required by the bicyclist, per mile traveled, is less than 1/10th thatgenerated by energy efficient cars.

1.6 Construction and parts

In its early years, bicycle construction drew on pre-existing technologies.More recently, bicycle technology has in turn contributed ideas in both old and newareas.

Fig. 12 - Diagram of a bicycle.


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The great majority of today's bicycles have a frame with upright seating whichlooks much like the first chain-driven bike. Such upright bicycles almost alwaysfeature the diamond frame, a truss consisting of two triangles: the front triangle andthe rear triangle. The front triangle consists of the head tube, top tube, down tube andseat tube. The head tube contains the headset, the set of bearings that allows the fork to turn smoothly for steering and balance. 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 bracket.The rear triangle consists of the seat tube and paired chain stays and seat stays. Thechain stays run parallel to the chain, connecting the bottom bracket to the rear dropouts. The seat stays connect the top of the seat tube (at or near the same point asthe top tube) to the rear dropouts.

1.6.1 Frames for women

Historically, women's bicycle frames had a toptube that connected in the middle of the seat tube insteadof the top, resulting in a lower standover height at theexpense of compromised structural integrity, since this

places a strong bending load in the seat tube, and bicycleframe members are typically weak in bending. Thisdesign, referred to as a step-through frame, allows therider to mount and dismount in a dignified way whilewearing a skirt or dress. While some women's bicyclescontinue to use this frame style, there is also a variation,the mixte, which splits the top tube into two small top tubes that bypass the seat tubeand connect to the rear dropouts. The ease of stepping through is also appreciated bythose with limited flexibility or other joint problems. Because of its persistent imageas a "women's" bicycle, step-through frames are not common for larger frames.

Another style is the recumbent bicycle. These are inherently more aerodynamic thanupright versions, as the rider may lean back onto a support and operate pedals that areon about the same level as the seat. The world's fastest bicycle is a recumbent bicycle

but this type was banned from competition in 1934 by the Union CyclisteInternationale.

1.6.2 Materials

Historically, materials used in bicycles havefollowed a similar pattern as in aircraft, the goal beinghigh strength and low weight. Since the late 1930salloy steels have been used for frame and fork tubes in

higher quality machines. Celluloid found application inmudguards, and aluminum alloys are increasingly usedin components such as handlebars, seat post, and brakelevers. In the 1980s aluminum alloy frames became

popular, and their affordability now makes themcommon. More expensive carbon fiber and titaniumframes are now also available, as well as advancedsteel alloys and even bamboo.

Fig. 13 - A triumph with the step-through frame

Fig. 14


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1.6.3 Drivetrain and gearing

Since cyclists' legs are most efficient over a narrowrange of pedaling speeds (cadence), a variable gear ratiohelps a cyclist to maintain an optimum pedaling speed whilecovering varied terrain. As a first approximation, utility

bicycles often use a hub gear with a small number (3 to 5) of widely-spaced gears, road bicycles and racing bicycles usederailleur gears with a moderate number (10 to 22) of closely-spaced gears, while mountain bicycles, hybrid

bicycles, and touring bicycles use drailleur gears with alarger number (15 to 30) of moderately-spaced gears, oftenincluding an extremely low gear for climbing steep hills.

Different gears and ranges of gears are appropriatefor different people and styles of cycling. Multi-speed

bicycles allow gear selection to suit the circumstances, e.g. itmay be comfortable to use a high gear when cycling downhill, a medium gear whencycling on a flat road, and a low gear when cycling uphill. In a lower gear every turnof the pedals leads to fewer rotations of the rear wheel. This allows the energyrequired to move the same distance to be distributed over more pedal turns, reducingfatigue when riding uphill, with a heavy load, or against strong winds. A higher gear allows a cyclist to make fewer pedal cycles to maintain a given speed, but with moreeffort per turn of the pedals.

The drivetrain begins with pedals which rotate the cranks, which are held inaxis by the bottom bracket. Most bicycles use a chain to transmit power to the rear wheel. A relatively small number of bicycles use a shaft drive to transmit power. Avery small number of bicycles (mainly single-speed bicycles intended for short-distance commuting) use a belt drive as an oil-free way of transmitting power.

With a chain drive transmission, a chainring attachedto a crank drives the chain, which in turn rotates the rear wheel via the rear sprocket(s) (cassette or freewheel). Thereare four gearing options: two-speed hub gear integrated withchain ring, up to 3 chain rings, up to 10 sprockets, hub gear

built in to rear wheel (3-speed to 14-speed). The mostcommon options are either a rear hub or multiple chain ringscombined with multiple sprockets (other combinations of options are possible but less common).

With a shaft drive transmission (fig. 16), a gear set at the bottom bracket turnsthe shaft, which then turns the rear wheel via a gear set connected to the wheel's hub.There is some small loss of efficiency due to the two gear sets needed. The onlygearing option with a shaft drive is to use a hub gear.

Fig. 15 - a set of rear sprocketsand a derailleur

Fig. 16 - a bicycle with shaftdrive instead of a chain


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1.6.4 Steering and seating

The handlebars turn the fork and the front wheel via thestem, which rotates within the headset. Three styles of handlebar are common. Upright handlebars, the norm inEurope and elsewhere until the 1970s, curve gently back

toward the rider, offering a natural grip and comfortableupright position. Drop handlebars are "dropped", offering thecyclist either an aerodynamic "crouched" position or a moreupright posture in which the hands grip the brake lever mounts.Mountain bikes feature a straight handlebar which can provide

better low-speed handling due to the wider nature of the bars.

Saddles also vary with rider preference, from the cushioned ones favored byshort-distance riders to narrower saddles which allow more room for leg swings.Comfort depends on riding position. With comfort bikes andhybrids the cyclist sits high over the seat, their weight directeddown onto the saddle, such that a wider and more cushionedsaddle is preferable. For racing bikes where the rider is bentover, weight is more evenly distributed between the handlebarsand saddle, the hips are flexed, and a narrower and harder saddleis more efficient. Differing saddle designs exist for male andfemale cyclists (fig. 18), accommodating the genders' differinganatomies, although bikes typically are sold with saddles mostappropriate for men.

A recumbent bicycle (fig. 19 )has a reclined chair-likeseat that some riders find more comfortable than a saddle,especially riders who suffer from certain types of seat, back,neck, shoulder, or wrist pain. Recumbent bicycles may haveeither under-seat or over-seat steering.

1.6.5 Brakes

Modern bicycle brakes are either rim brakes (fig. 20), in which friction padsare compressed against the wheel rims, internal hub brakes, in which the friction padsare contained within the wheel hubs, or disc brakes. Disc

brakes are common on off-road bicycles, tandems andrecumbent bicycles.

With hand-operated brakes, force is applied to brakelevers mounted on the handlebars and transmitted via Bowden

cables or hydraulic lines to the friction pads. A rear hub brakemay be either hand-operated or pedal-actuated, as in the back pedal coaster brakes which were popular in North Americauntil the 1960s, and are still common in children's bicycles.

Track bicycles do not have brakes. Brakes are notrequired for riding on a track because all riders ride in thesame direction around a track which does not necessitate sharpdeceleration.

Fig. 17 - conventional dropdownhandlebars with added aerobars

Fig. 18 - a Selle San Marcosaddle designed for women

Fig. 19

Fig. 20 - linear-pull brake on rear wheel of a mountain bike


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Track riders are still able to slow down because all track bicycles are fixed-gear, meaning that there is no freewheel. Without a freewheel, coasting is impossible,so when the rear wheel is moving, the crank is moving. To slow down one may applyresistance to the pedals.

1.6.6 Suspension

This mountain bicycle features oversizedtires, a full-suspension frame, two disc brakesand handlebars oriented perpendicular to the

bike's axis (fig. 21).Bicycle suspension refers to the system

or systems used to suspend the rider and allor part of the bicycle. This serves two

purposes:

y To keep the wheels in continuouscontact with rough surfaces in order to improve control.

y To isolate the rider and luggage from jarring due to rough surfaces.

Bicycle suspensions are used primarily on mountain bicycles, but are alsocommon on hybrid bicycles, and can even be found on some road bicycles, as theycan help deal with problematic vibration. Suspension is especially important onrecumbent bicycles, since while an upright bicycle rider can stand on the pedals toachieve some of the benefits of suspension, a recumbent rider cannot.

1.6.7 Wheels

The wheel axle fits into dropouts in the frame and forks. A pair of wheels may be called a wheelset, especially in the context of ready-built "off the shelf", performance-oriented wheels.Tires vary enormously. Skinny, road-racing tires may becompletely smooth, or (slick). On the opposite extreme, off-road tires are much wider and thicker, and usually have a deep tread for gripping in muddy conditions.

1.7 Accessories, repairs, and tools

Touring bicycle equipped with head lamp, pump, rear rack, fenders/mud-guards, water bottlesand cages, and numerous saddle-bags. Puncture repair kit with tire levers, sandpaper to clean off an area of

the inner tube around the puncture, a tube of rubber solution (vulcanizing fluid), round and oval patches, ametal grater and piece of chalk to make chalk powder (fig. 22). Kits often also include a wax crayon to mark the puncture location. Some components, which areoften optional accessories on sports bicycles, are standard features on utility bicyclesto enhance their usefulness and comfort. Mudguards, or fenders, protect the cyclistand moving parts from spray when riding through wet areas and chainguards protectclothes from oil on the chain while preventing clothing from being caught between

Fig. 21 full-suspension frame

Fig. 22


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the chain and crank set teeth. Kick stands keep a bicycle upright when parked. Front-mounted baskets for carrying goods are often used. Luggage carriers and panniersmounted above the rear tire can be used to carry equipment or cargo. Parentssometimes add rear-mounted child seats and/or an auxiliary saddle fitted to thecrossbar to transport children.

Toe-clips and toe-straps and clipless pedals help keep the foot locked in the

proper position on the pedals, and enable the cyclist to pull as well as push the pedalsalthough not without their hazards, eg. may lock foot in when needed to prevent a fall. Technical accessories include cyclocomputers for measuring speed,distance, etc. Other accessories include lights, reflectors, security locks, mirror, water

bottles and cages, and bell.Bicycle helmets may help reduce injury in the event of a collision or accident,

and a certified helmet is legally required for some riders in some jurisdictions.Helmets are classified as an accessory or an item of clothing by others.

1.8 Standards

A number of formal and industry standards exist for bicycle components tohelp make spare parts exchangeable and to maintain a minimum product safety.

The International Organization for Standardization, ISO, has a specialtechnical committee for cycles, TC149, that has the following scope: "Standardizationin the field of cycles, their components and accessories with particular reference toterminology, testing methods and requirements for performance and safety, andinterchangeability."

CEN, European Committee for Standardisation, also has a specific TechnicalCommittee, TC333, that defines European standards for cycles. Their mandate statesthat EN cycle standards shall harmonise with ISO standards. Some CEN cyclestandards were developed before ISO published their standards, leading to strongEuropean influences in this area. European cycle standards tend to describeminimumsafety requirements, while ISO standards have historically harmonized partsgeometry.

1.9 In daily life Around the turn of the 20th century, bicycles reduced

crowding in inner-city tenements by allowing workers tocommute from more spacious dwellings in the suburbs. Theyalso reduced dependence on horses. Bicycles allowed peopleto travel for leisure into the country, since bicycles were threetimes as energy efficient as walking and three to four times asfast. Recently, several European cities have implementedsuccessful schemes known as community bicycle programs or

bike-sharing (fig. 23). These initiatives complement a city's public transport system and offer an alternative to motorizedtraffic to help reduce congestion and pollution.Users take a

bicycle at a parking station, use it for a limited amount of time, and then return it tothe same or different station. Examples include Biking in Barcelona (fig. 24), Vlo'vin Lyon and Vlib' in Paris.

Fig. 23 - a commuting bike inAmsterdam


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Bicycles offer an important mode of transport in manydeveloping countries. Until recently, bicycles have been astaple of everyday life throughout Asian countries. They arethe most frequently used method of transport for commuting towork, school, shopping, and life in general. As a result,

bicycles there are almost always equipped with baskets.

1.10 Legal requirements

Early in its development, like in the caseof automobiles, there were restrictions on theoperation of bicycles. The1968 Vienna Convention on Road Traffic of theUnited Nations considers a bicycle to be avehicle, and a person controlling a bicycle(whether actually riding or not) is considered anoperator. The traffic codes of many countriesreflect these definitions and demand that a bicyclesatisfy certain legal requirements, sometimeseven including licensing, before it can be used on

public roads. In many jurisdictions, it is anoffence to use a bicycle that is not in roadworthycondition.

In most jurisdictions, bicycles must havefunctioning front and rear lights when ridden after dark (fig. 25). As some generator or dynamo-driven lamps only operate whilemoving, rear reflectors are frequently also mandatory. Since a moving bicycle makeslittle noise, some countries insist that bicycles have a warning bell for use whenapproaching pedestrians, equestrians, and other cyclists.

1.11 Bicycles in Romania

In Romania we have two names that defines theinternal bicycle production: Tohan and Pegas (fig. 26). In1938 the Tohan ammunition factory was launched atZarnesti-Brasov. To hide the real goal of the production, a

bicycle production and assembly line is installed and thus,the Tohan bicycles takes birth, along with the Pegas thatwere addressed to kids. The most popular model was Ideal

Tohan, launched in the second half of the 19thcentury. Thismodel is still in production. Before 1990, the factory produced around 17.000 pieces per month. Today, it onlyreaches 1500 pieces per year. The decade of the productionwas determined partially by the entrance on the market of very cheap chinesse bicycles. Beside the classic models andthe well known brand Pegas, the factory producesergonomics bicycles for fitness classes, tricycles andmountain-bikes.

Fig. 24 - a bike-sharing station inBarcelona

Fig. 25 - Reflectors for riding after dark

Fig.26 Pegas poster Fig.26 Pegas poster


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1.12 Technical aspects

The bicycle has undergone continual adaptation and improvement since itsinception. These innovations have continued with the advent of modern materials andcomputer-aided design, allowing for a proliferation of specialized bicycle types.Themost common materials used today are Aluminium alloys, fibers and steel for bolts

and hub axes.

1.13 Types of bicycles

Bicycles can be categorized in different ways: e.g. by function, by number of riders, by general construction, by gearing or by means of propulsion.

General categories:

1. By terrain type on which the bicycle rides:

City bikes - used for urban transportation Cruisers - used for long runs on tarmac Cross-country - used for runs on both tarmac and gravel Trial - used for crossing very technical obstacle tracks Four-cross - used on steep slopes with small jumps Freeride - used on steep slopes with medium jumps Downhill - used on very steep slopes with high jumps and drops

2. By suspension:

Hard (no suspension) Hard tail (front suspension) Full suspension (both front and rear suspension)

3. By wheel radius:

24 size 26 size 28 size

The more common types include utility bicycles,mountain bicycles, racing bicycles, touring bicycles, hybrid

bicycles, lowcruiser bicycles, and BMX bicycles. Lesscommon are tandems, tall bikes, fixed gear (fixed-wheel),

folding models and recumbents. _

Unicycles, tricycles, quadracycles and half wheelers(fig. 27) are not strictly bicycles, as they have respectivelyone, three and four wheels, but are often referred to informallyas "bikes". Fig.27 - a Half Wheeler trailer bike


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On the following development, we will study the downhill category, in order to develop a suspension frame for the toughest terrain.

1.13.1 Downhill bicycles and frames

Downhill biking (DH) is a gravity-assisted time trialmountain biking event (fig. 28). Riders race against the clock,usually starting at intervals of 30 seconds (seeded from slowestto fastest), on courses which typically take two to fiveminutesto complete. Riders are timed with equipment similar tothat used in Downhill skiing. The placing is determined by thefastest times to complete the course; races are often won bymargins of under a second. As the name of this disciplineimplies, downhill races are held on steep, downhill terrain withno extended climbing sections, resulting in high speed descentswith extended air time off jumps and other obstacles.

The 1st downhill time-trial race took place in Fairfax, California on October 22, 1976 on a fireroad now referred to as Repack Road, due to the need to repack hub

bearings after a descent (the hub brakes used at the time would overheat, causingthegrease within the hub to break down). Ten riders descended 1300 feet of Repack inabout 5 minutes; the winner, Alan Bonds, was also the only one to make it to thefinish line. The first bikes used for descending were known as "clunkers" or "paperboy bikes": coaster brake cruisers using balloon tires first imported to America

by Ignatz Schwinn. By 1979, two organizers and competitors of the Repack downhill,Charlie Kelley and Gary Fisher founded the company which named the sport,MountainBikes. As mountain biking grew enormously during the 80's, downhill riderscontinued to use either rigid or limited suspension travel (under 2 inches) bicycles,and purpose made downhill bikes were not made until the 90's. Some of theseinnovations included dual crown suspension forks and disc brakes, as well as veryelaborate frame suspension designs.

A downhill bike tends to weigh between 17 to25 kg, most commonly 16-20 kg, and usually feature afull-suspension design, and frame geometry that leans

back further than other mountain bikes (fig. 29). As of 2006, 203 mm (8-inch) is the 'norm' for suspension travelhowever some commercially available bikes can have asmuch as 300 mm (12-inch). Large-diameter 203-5 mm(8-inch) hydraulic disc brakes moderate the riders' speed,

just like in motorcycles or cars. Downhill bikes and

freeride bikes are very similar but there are some slight differences. Downhill race bikes typically are much lower and have slacker head angles than freeride bikes, sothat the bike is more stable at speed and in corners. Freeride bikes have a moreupright geometry and a higher bottom bracket height, so that they are better for

jumping and stunts, however Freeride bikes sometimes usesingle crown forks, whichare smaller and lighter than the dual crown forks often used by downhill riders, dualcrown forks usually have around 200mm (8-inch) of travel, and single crown forksare usually around 180 mm maximum. The price of downhill bikes ranges from 2000US dollars or 1500 British pounds for an entry level bike, all the way to 9000 US

Fig. 28

Fig. 29


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dollars or 6000 British pounds for a top of the line world cup race bike. The pricedifferences have to do with the components that are on the bikes, also the moreexpensive bikes are usually made with higher quality materials and more time andcare is put into quality frame production. Choosing components on a downhill bike, aswith most performance orientated bicycles, involves a trade off between weight andstrength. Recent advances in technology have allowed companies to improve the

strength and weight of components.

More recently (2007-present), most world cupdownhill bikes have showed a trend towards lighter weight,air-sprung suspension forks and rear shocks(fig. 30). This isto reduce weight and improve responsiveness. manyDownhill bikes also have lesser travel these days, with 6-7inches (150-180 mm) instead of the older standard of 200 mm or 8 inches. This is for the same reasons as theswitch to air-sprung suspension. This has led to blurred

boundaries between freeride and downhill bikes. WhereFreeride bikes used to be lighter and made up of steeper angles, Downhill bikes now occupy this description, withfreeride bikes now heavier and comprising slacker angles.

This is for two reasons:1. Many world cup downhill tracks are more technical than before, requiring

steeper head angles to facilitate faster changes in bike direction2. Newer Freeride-lite bikes offer lighter weight than either downhill OR 'full-

on' freeride cycles, meaning that freeride bikes can focus on being tougher, anddownhill bikes can focus on being lighter, while freeride-lite bikes can offer a little of

both. Freeride-lite bikes argenerally for those who like to be able pedal up hills as well as down them, and areslightly heavier and tougher than trail bikes (fig. 31).

Downhill gear features body armor and full-face motocross-type helmets.

Fig. 30

Fig. 31 - Dunedin, NZ


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1.14 Existing downhill frames. Description and comparison

Figure 32

1.14.1 Krutor Zam Pro

Krutor Zam Pro (fig. 32) is full-carbon downhill frame of single-pivotconstruction, with rear frame above the chain. The frame is based on a thick-wallcarbon tube of elliptical shape, which holds the bottom bracketand the main pivot.The front half of the tube is hided in shaped carbon monocoque, fluently joining thehead and seat tube. The rear frame is laminated as on piece including the bridge and isequipped with massive aluminium endings for main pivot and rear wheel axle. Thedumper goes from aproximately 1/3 of the rear frame to the seat-part. The fixed pivotof the damper is joined to the main pivot with a pair of linear carbon fibre links whichsignificantly decreases the tensions in the main frame.

. Equipment

y rear thru-axle 12 mmy 160 mm rear brake disc mounting standardy saddle tube sleevey flexible mechanical stops for double-crown fork y bowdens (rear brake + shifter) guided inside main and rear frame


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1.14.2 Intense SPS-666DH2

Intense SPS-666DH2 (fig. 33) is a 26 size downhill suspension frame. Itfeatures an aluminum monocoque construction and rear triangles.

Equipement:

y Dual crown fork y Rear coil shock y Dual ply or UST DH tires in a tubeless setupy 8 front / 7 rear brakey No carbon bar or seatpost

1.14.3 Formula 1 Jedi

The biggest frame in therange, the Jedi (fig. 34) is a 7.75travel machine made fromAluminum alloy. With 2.5 of rear travel this is a beast. The chainstaysare extra short at 16.25 whichmaintains a quick, sharp, livelyfeel. Weighing in just under 8 kg

the MSRP is 1699.99 with a DHX5.0 rear shock.

Riding High UK have just been appointed the Europeandistributors of Canfield Brothers2008 range of downhill frames. TheUS company have been designing and building full suspension bikes for eight yearsand now, for the first time, their frames are available to European riders.

Figure 33.

Figure 34


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R C OC - DIPLO M PR OJE C INTR ODU CTION

1.15 Ma i d i advantages

Ana l ing t curren t downh ill frames, we can def ine the ma jor d isadvan tages :

H igh cen ter of grav it due to c lass ic d iamond frame shape H igh cen ter of grav it due to shock absorber pos itioning Inex istence of frame tuning accord ing to the track t pe R educe re liab ilit due to h igh number of ba ll bear ing used and sys tem

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Proiect Diploma - Chapter 1