; Allen's Adventure: Bahan Frame Sepeda

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Selasa, 19 Juni 2012

Bahan Frame Sepeda

Frame adalah bagian yang sangat vital dari sepeda, jika pemilihan frame salah, maka berakibat fatal untuk kenyamanan si pengendara, jadi perhatikanlah sebelum anda membeli sepeda idaman (dibahas dan dikutip sebagian besar dengan bahasa Inggris)

Ada 4 faktor dalam pemilihan bahan frame sepeda, yaitu : Stiffness, Strength, Fatigue Strength and Weight, ini ada beberapa penjelasan mengenai 4 faktor ini :

1. Stiffness

Imagine fixing one end of a solid bar into a clamp so tightly that it will not budge. Now apply some force to the free end of the bar, for example, by hanging some weights from the free end. For small weights, the bar will bend slightly, but if you remove the weight the tube will spring back to being perfectly horizontal. This elastic property is the stiffness of the material. Under the same weight a stiff material will bend or flex less than an elastic one.

Testing the strength and stiffness of a material.
Illustration of bending of a solid bar under load.

The stiffness or elasticity of a bike frame will have an impact on the way a bike performs and feels during a ride. Elastic frames cushion bumps and knocks, much like a suspension, while a stiff frame will transmit more of the force of each bump directly to the rider. But elastic frames also flex more under load, absorbing some of the energy you're generating to move the bike forward. For this reason cyclists interested in maximizing their performance in sprints and time trials will often prefer a stiff frame.

While different frame materials have different levels of inherent elasticity, the stiffness of a tube is mostly determined by its diameter and length. A frame's geometry also has a significant impact on the overall stiffness of the bike.

2. Strength

Now imagine hanging more weight from the free end of that bar. At a heavy enough load the bar will no longer spring back to its original shape--it will permanently warp (or, if the material is brittle enough, crack or break entirely). The amount of force required to crack, break or permanently deform a material is its strength. The point at which the material permanently deforms is known as the "yield strength". The point at which it breaks is known as the "breaking strength". A relatively flexible material such as steel will bend before it breaks. Brittle materials such as concrete, common glass, and more relevantly, carbon fiber, will snap before they deform--their breaking strength is less than their theoretical yield strength.
The strength of the frame material doesn't influence the performance or feel of the ride under normal conditions, but it is a significant factor in the "crash worthiness" of the frame. A strong frame can withstand an impact that may destroy a weaker frame.

3. Fatigue Strength

Under normal riding conditions each pedal stroke, bump or hop places a small amount of stress on the frame. While well below the yield strength of the frame, over a long time (hundreds of thousands of cycles of loading and unloading) these small stresses can cause cracks to develop in some frame materials, eventually leading to failure from fatigue. A material's resistance to this type of failure is known at its fatigue strength. Failure from fatigue is a very complicated and dynamic process that depends not only on the amount of force applied in each cycle and the number of repetitions but also on microscopic defects and anomalies that may be present in the material.

If you plan to keep your bicycle for decades, are heavier than average, or ride your bike hard, you may want to consider fatigue strength as a factor.

4. Weight

The weight, or more accurately, density, of a material is simply a measure of how much mass the material has per unit volume.
While the frame is a large component of a bike, it is easy to overestimate the importance of weight. A typical frame weighs maybe 3 to 5 pounds and represents only about one quarter of the overall weight of a bicycle. More importantly, the entire bicycle will often weigh about one tenth as much as the fully accessorized rider. Most cyclists will not notice a small difference in the weight of the frame unless they do a lot of climbing or need to lift and carry their bike often.
Setelah membaca 4 faktor dari material frame, yuk..kenali jenis jenis bahan frame sepeda :

A. Bahan Steel Alloy (baja)

Harganya paling murah diantara bahan bahan frame sepeda lainnya, untuk jaman sekarang ini biasanya banyak digunakan untuk sepeda umum, banyak dipakai di sepeda kelas low end, di masa tahun 1949 bahan ini menjadi primadona sepeda race khusunya pabrikan sepeda dari Italia, seiring perjalanan waktu bahan Steel mulai ditinggalin produsen, bahannya kaku dan berat dan gampang karat. Apakah bahan Steel akan berakhir? Ternyata tidak...beberapa pabrikan memodifikasi campuran baja dengan bahan lain supaya lebih ringan dan kuat, tidak gampang berkarat. Begitu juga dengan trend sepeda Vintage mulai menjamur dan sepeda Vintage / Classic tetap memakai Steel sebagai bahan utama untuk frame, beberapa pabrikan Italia seperti Tommasini mengeluarkan tipe classic dengan bahan steel Neuron Columbus (Sintesi / Techno), penulis pernah mencoba test riding...wow sangat comfort...mantap dan nyaman sekali di jalan datar apalagi dipakai buat touring jauh...dengan teknologi steel sekarang selain empuk dan rigit juga stiff walaupun tidak se stiff karbon tetapi agak menyiksa di trek Tanjakan dikarenakan berat nya yang lumayan (+/- 8.9kg).

Beberapa pabrikan sepeda mengembangkan beberapa teknik pembentukan frame steel supaya lebih ringan antara lain :

1. Straight Gauge

2. Single Butted

3. Double Butted

4. Triple Butted

Campuran baja dengan beberapa bahan lainnya menghasilkan :

1. High-Tensile (Hi-Ten) Steel,
High-tensile or carbon steel is a common and inexpensive alloy comprised of iron mixed with 0.2% to 2.0% carbon. (Of note, when iron is mixed with more than 2.1% carbon it is no longer "steel", it goes by the name "cast iron".)
High-tensile steel is an inexpensive but relatively weak alloy. Although it has essentially the same density as other steels, manufacturers working with hi-ten steel are forced to use thick walled tubes to ensure adequate strength, and rarely use butting. For this reason, high-tensile frames are much heavier than their chromoly counterparts.
Today, high-tensile steel frames are primarily used for children's bikes and are sometimes found on inexpensive adult bikes

                                         Sepeda BMX banyak memakai bahan Hi-Ten

2. ChroMoly (CRMO) Steel

ChroMoly is a steel alloy composed of iron combined with chromium (roughly 1% by weight), molybdenum (roughly 0.2%), carbon (roughly 0.3%), silicon (roughly 0.2%), manganese (roughly 0.04%) and sulphur (roughly 0.04%). 4130 is actually just one of a family of chromoly alloys, but it is the one used for bicycle frames. ChroMoly steel is also used in the construction of airplanes, and is sometimes known as "aircraft tubing".
Chromium is the component that makes stainless steel rust proof, but the chromium level of chromoly steel is not high enough to provide corrosion resistance. (Stainless steel is 10% to 11% chromium.)
Chromoly is frequently used to build mid-to-high-range steel framed bikes. A well made butted chromoly frame is typically only marginally heavier than an aluminum frame, and quite strong and durable.

3. Reynolds Steel

In 1953 the Reynolds Cycle Company began manufacturing a steel tube composed of proprietary manganese-molybdenum steel alloy they branded Reynolds 531. This alloy was strong and for its time, relatively light. It was once the preferred tubing for steel racing bikes (as well as British aircraft).
Over the years, Reynolds has introduced a number of branded steel tubes, the brand name indicating both the specific alloy and heat treatment but also the wall thickness and butting of the tubes. These include Reyolds 453 (a single-butted tube made of a manganese-titanium alloy), Reynolds 501, 520, 525 and 725 tubes (using 4130 chromoly steel), Reynolds 753 (high-end tubes made of a manganese-molybdenum alloy, essentially a better Reynolds 531), Reynolds 853 (4130 chromoly made stiffer by air hardening) and Reynolds 953 (a lightweight rust-proof maraging stainless steel introduced in 2006).
Reynolds steel is less common in bike frames today than it once was, but some of these alloys are still in use. The Reynolds 520 family is a well made class of 4130 chromoly tubes. You'll pay a bit more for the brand name, but you'll know you're getting a well manufactured tube. Reynolds 853 is a higher quality chromoly, made stiffer than usual by the way it is manufactured. Reynolds 953 is perhaps the best steel available for bikes today: Reynolds 953 frames are stronger than titanium, no heavier than high end aluminum and rust proof

Reynolds 953 tubing

B. Alloy (Alumunium)
Bahan ini terbilang agak murah dan umum digunakan untuk sepeda sport dan profesional. Kualitas framenya juga lebih ringan dibanding dengan steel dan chromoly. Bahan frame ini dikategorikan di level menengah. Kekurangan bahan Alloy tidak se stiff steel tetapi memiliki strength-to-weight ratio lebih baik tentunya juga bahan ini tidak berkarat.

Aluminum Alloys

Aluminum is typically combined with (alloyed with) other elements to improve upon its material properties. The alloying elements make up a small fraction of the material by weight (typically less than 10%) but they can have a significant impact on the strength, weldablity, corrosion resistance and expense of the material.

6061 Aluminum Alloy (AA 6061)

6061 aluminum is a family of aluminum alloys combining aluminum with magnesium (roughly 1.0% by weight) and silicon (roughly 0.5% by weight), sometimes mixed with a variety of other materials including iron, copper, chromium, zinc, manganese and titanium. 6061 is a strong an easily welded alloy frequently used for bike frames (as well as aircraft, boats and more).
All 6061 aluminum alloys have the same weight (density) and stiffness, but the strength of the alloy varies slightly with the specific alloying elements and the "temper" or heat treatment used to produce the material.

There are three common tempers of 6061 aluminum:
6061-O is a soft annealed alloy and is the weakest of the three common tempers. It is too weak to be of use for bike frame tubes.
6061-T4 is a heat treated, naturally aged alloy that is roughly twice as strong as 6061-O.
6061-T6 is a heat treated, artificially aged alloy that is roughly 2.5 times stronger than 6061-O. 6061-T6 aluminum alloy is probably the single most popular material used in modern bike frames, and is also used extensively in the manufacture of other components such as derailleurs, stems, cranks and handlebars.

7005 Aluminum Alloy (AA 7005)

7005 aluminum is a family of aluminum alloys combining aluminum with zinc (roughly 4.5% by weight), sometimes mixed with a variety of other materials including silicon, magnesium, iron, copper, chromium, manganese and titanium. 7005 is 10% stronger and a little more brittle than 6061 aluminum.
7005 occupies a curious market position relative to 6061 frames. Unlike 6061, 7005 does not require expensive heat treatment to be strong enough to use within a bike frame. However, a non-heat-treated 7005 frame requires more material to provide its strength. This means you can find cheap but relatively heavy frames made of non-heat-treated 7005 alloy. One can also create a very strong and light frame out of heat-treated 7005 aluminum, but this adds cost to the manufacturing process. This means you can find more expensive, but very light and strong 7005 frames as well. Hence depending on the heat treatment, 6061 aluminum is comparable to 7005 at both high and low price points, but 6061 occupies the middle part of the market in addition to competing well at the high and low end. 7005 aluminum is primarily found in low-end bikes (when not heat treated) or high-end bikes (when heat treated) but rarely in the middle.

Proprietary Aluminum Alloys

Some major manufacturers use custom aluminum alloys or apply custom treatment to stock aluminum alloys in order to improve their material properties. This is as much a marketing exercise as a materials science one, but these custom treatments can produce higher quality frames.

Giant's Proprietary Aluminum Alloys

Giant is a major manufacturer of bikes with aluminum frames. (In fact, Giant sells the most bikes of any manufacturer in the world.) They have created a proprietary frame building process that they have branded "AluxX" aluminum. Giant's AluxX comes in two forms:
Giant AluxX Aluminum

Regular "AluxX" is simply 6061 aluminum, but Giant applies a custom tube construction and heat treating process to the manufacture of their AluxX aluminum frames. The result is a butted, shaped and heat treated 6061 frame. Giant cites the weight reduction benefits of this process, but doesn't tout significant improvements to stiffness or strength. At the very least, the word "AluxX" implies a well made, butted and shaped 6061 aluminum frame.
Giant AluxX SL Aluminum

Unlike plain AluxX aluminum, AluxX SL starts with a 6061 alloy but mixes in a trace amount of copper to form a stiffer alloy. This premium alloy is then butted, shaped and heat treated much like AluxX tubes. Giant claims that the resulting alloy is 18% stiffer than pain AluxX aluminum and can be used to create "the lightest and stiffest aluminum frames current available".

Trek's Proprietary Aluminum Alloys
Trek is another major manufacturer of bikes with aluminum frames. Like Giant, they have created a proprietary aluminum frame building process that they brand as "Trek Alpha". Trek's Alpha aluminum comes in three forms:
Trek Alpha White Aluminum
Alpha White is the lowest end of Trek's aluminum frame building materials. It is simply straight gauge 6061 aluminum tubing, Trek branded.

  Trek Alpha Black Aluminum

Alpha Black is Trek's mid-range aluminum alloy. It is 6061 aluminum that has been shaped and butted to reduce weight and increase strength. Frames built with Alpha Black aluminum are likely on par with Giant AluxX and any other well made shaped and butted 6061 aluminum frames.
Trek Alpha Red Aluminum
Alpha Red is Trek's premium aluminum alloy. It is heat-treated 7075 aluminum that has been shaped and butted to reduce weight and increase strength

C. Carbon Fiber

Harga dari bahan ini termasuk mahal, karena melalui proses pembuatan yang cukup rumit. Bahan frame ini dikategorikan sebagai top level karena frame ini dibuat dengan teliti untuk setiap sambungan antara main tube, side tube dan top tube yang nyaris tidak terlihat. Frame ini sangat ringan dan kuat dan tidak akan berkarat (carbon bukan bahan metal) , namun mudah tergores dan patah.  Stiffness dan Rigit udah pasti mantap...

Carbon is not a metal--it is composite of strands of carbon pressed together in layers with an epoxy glue, much like a high-tech version of particle board. Carbon can be shaped into interesting and aerodynamic forms, and it is common to see carbon bike frames composed of teardrop, flat or wing shaped tubes rather than the perfect cylinders used in steel bike frames.
Carbon is very lightweight and can be made very stiff. Due to the alignment of the individual fibers, carbon frames have a more distinctive "grain". This allows carbon bike frames to have different amounts of stiffness directions and to stiffen "non-linerally". That is, while a steel frame will flex twice as much under 40 pounds of pressure as it did at 10 pounds, a carbon frame tends to get "tighter" as it flexes. It will give a little bit under slight pressure, but resist more stiffly as pressure increases. Manufacturers often exploit this property to give carbon frames the stiffness of aluminum for sprinting but the springiness of steel when rolling over bumps.
Carbon-fiber-reinforced polymer has found a lot of use in high-end sports equipment such as racing bicycles. For the same strength, a carbon fiber frame weighs less than a bicycle tubing of aluminum or steel. The choice of weave can be carefully selected to maximize stiffness. The variety of shapes it can be built into has further increased stiffness and also allowed aerodynamic considerations into tube profiles. Carbon-fiber-reinforced polymer frames, forks, handlebars, seatposts, and crank arms are becoming more common on medium- and higher-priced bicycles. Carbon-fiber-reinforced polymer forks are used on most new racing bicycles

D. Titanium

Ditemukan pada tahun 1791 oleh William Gregor dari Inggris, untuk soal harga, frame berbahan Titanium termasuk yang paling mahal karena bahannya ringan, kuat seperti baja, tahan terhadap karat dan langka.

Sifat dari Titanium :

• Terlihat berkilauan, metalik.

• 3 kali lebih kuat dari baja

• 42% lebih ringan dari baja

• Tahan terhadap segala kondisi dan temperatur cuaca

• Mampu direndam dalam air untuk periode lama tanpa terjadi kerusakan

• Sekuat baja namun seringan aluminum

Sejak tahun 1950 an digunakan pada industri alat-alat perang Setelah PD II, Militer Amerika mengembangkan system misil mutahir & pesawat yang bisa terbang lebih cepat dari kecepatan suara. Titanium dipilih karena bisa mengatasi temperatur tinggi dan gesekan yang lebih kecil pada kecepatan tinggi. Dapat terbang lebih dari 2,200 mph (lebih dari tiga kali kecepatan suara).

Akhirnya dipakai dalam produksi misil, kapal selam, senjata ringan, satelit, pesawat pengintai. Pesawat Concord yang termashyur juga ber bahan dasar Titanium. NASA juga menggunakannya untuk membuat pesawat ulang-alik yang menjelajahi ruang angkasa. Memiliki respon yang kecil terhadap listrik, magnit dan panas. Membuatnya sempurna digunakan sebagai bahan gelang magnetis Untuk kulit sensitif, titanium barangkali satu-satunya perhiasan logam yang menjadi pilihan anda.
Titanium terbukti cocok bagi tubuh manusia, dan telah dipergunakan secara luas dalam operasi penggantian tulang. 
Nigata Industri Teknologi, Jepang menyatakan bahwa titanium dapat meningkatkan sirkulasi darah. Ini adalah berita baik bagi umat manusia

A metallic element, titanium is recognized for its high strength-to-weight ratio. It is a strong metal with low density that is quite ductile (especially in an oxygen-free environment),lustrous, and metallic-white in color. The relatively high melting point (more than 1,650 °C or 3,000 °F) makes it useful as a refractory metal. It is paramagnetic and has fairly low electrical and thermal conductivity.

Commercial (99.2% pure) grades of titanium have ultimate tensile strength of about 63,000 psi (434 MPa), equal to that of common, low-grade steel alloys, but are 45% lighter. Titanium is 60% more dense than aluminium, but more than twice as strong as the most commonly used 6061-T6 aluminium alloy. Certain titanium alloys (e.g., Beta C) achieve tensile strengths of over 200,000 psi (1,400 MPa). However, titanium loses strength when heated above 430 °C (806 °F).

It is fairly hard (although not as hard as some grades of heat-treated steel), non-magnetic and a poor conductor of heat and electricity. Machining requires precautions, as the material will soften and gall if sharp tools and proper cooling methods are not used. Like those made from steel, titanium structures have a fatigue limit which guarantees longevity in some applications. Titanium alloys specific stiffnesses are also usually not as good as other materials such as aluminium alloys and carbon fiber, so it is used less for structures which require high rigidity


Common frame materials have very different strength, stiffness and weight profiles. For the same volume of material...
  • ...steel is roughly twice as strong, and nearly three times heavier and stiffer than aluminum.
  • ...titanium is only half as heavy or stiff as steel, but just as strong.
  • ...titanium is about 50% heavier and stiffer than aluminum, but roughly twice as strong.
  • ...carbon fiber is more than seven times stronger than steel (when the force is applied in the right direction), but only one fourth as heavy.
  • ...carbon fiber is more than 15 times stronger than aluminum (when the force is applied in the right direction), but only half as heavy.