What different frame materials have been used?

Question

In response to yet another frame materials question, I thought it might be useful to start with a more answerable question. One answer per material please, with an example of a bicycle frame using that material.

Please use the format I've used in my answer(s) to make it easy to compare materials.

I see no harm in having all 400+ steel alloys listed if someone wants to do that, but "steel" must specifically be low-grade mild steel rather than a specific alloy. Likewise for aluminium, titanium, magnesium and other metals.

For composites, including metal composites, I would again prefer specific examples with details (there's a big difference between steel reinforced concrete and kevlar/polyester composites). I would also love to see weird and wonderful bikes included.

Materials

(ie index to answers. Please update links as you add an answer):

Metals

• Aluminum Bikes
  • Aluminum
  • Scandium - Aluminium alloy
• Steel Bikes
  • Columbus Steel (not written yet)
  • ChromeMoly Steel (not written yet)
  • Gaspipe Steel
  • Ishiwata Steel (not written yet)
  • Kaisei Steel (not written yet)
  • Mild Steel
  • Reynolds Steel (needs extension)
  • Tange Steel (not written yet)
  • Vitus/Super Vitus Steel (not written yet)
• Titanium
• Beryllium
• Gold (pure) (theoretical)
• Magnesium (not written yet)

Organic

• Bamboo
• Bones
• Wood Bikes
  • Carved Wood
  • Plywood (composite)
  • Wood (complete frame and bicycle)
• Cardboard (not yet written) (https://bicycles.stackexchange.com/a/44582/20060)**

Composites and Polymers

• Carbon Fibre
• Flax fiber (90% flax, 10% carbon)
• Plastic

Layout Specific

• Cables aka Tensegrity or Tensional Integrity
• 3D Printed (not yet written)

Answer 1

Bones

Density average 1.84 g/cm³ for dry bone.

This would be a pretty bad material for a bike frame, and its quite likely that any bone bike really has a metal core in the middle.

Advantage

• Shock factor, or as part of a costume ("Death rides a Pale Horse")

Disadvantage

• Bones aren't particularly structural by themselves. A skeleton is made from tendons and cartilage and soft tissues as well.

• Durability - bones that dry out get brittle and will snap easily.

• Intolerant - A crack could go from a minor hairline to a full break very quickly.

Answer 2

Titanium

Density 4.506 g/cm³

Advantages

• Titanium has many positive characteristics that make it ideal for bicycle frame building. Titanium has excellent elongation, tensile strength and fatigue strength. Titanium frames can generally be built as light as a aluminum frame, but with a much longer life span similar to (or longer than) a steel frame.
• Titanium has extraordinary corrosion resistance, even in an aggressive environment such as sea water, and doesn't require painting or coating. This also translates to easier maintenance, as minor scratches and blemishes won't cause any problems without re-coating.
• It's possible to make a "high end" light and strong frame with titanium that will have a long life. Titanium is currently the material of choice for custom and one-off frames. It's cost effective (relatively speaking) to design and build a single titanium frame, whereas other "high end" materials (like carbon) are prohibitively expensive to design and build a single frame.

Disadvantages

• Titanium is an expensive material. Raw material prices are most often higher than other metal options. (Apart from pure gold, perhaps).
• Titanium can be difficult to work with. Titanium requires different procedures to machine and weld. Failure to follow these procedures can lead to contaminated welds that will fail.
• Titanium is a poor conductor of electricity, so the frame can't be used as one leg of a lighting circuit.

Answer 3

Mild Steel

Density ranges from 7.75 to 8.05 g/cm3

Many BSO's are made of mild steel, or recycled steel with so little care for its make-up that it is effectively mild steel. Examples include this KMart bike. This question on BSO Identification has more.

Advantages

• cheap to buy
• easy to work with - the technology is common and machinery is affordable
• easy to repair - if your bike is made of steel you can fix it with a forge if you have to, so it's more repairable than any other frame material.

Disadvantages

• weak/heavy - for a given strength, you need more mild steel than other common frame materials.
• rusts - chips in the paint or immersion in water will cause the frame to corrode.

Answer 4

Wood-only Bicycle

This is more an example of what's technically possible, rather than a particularly practical material.

Advantanges

• rarity/shock value

Disadvantages

• difficult to make bearings from wood
• many compromises to performance required because of limitations of the material

Pure wooden bicycle by Slawomir Weremkowicz (via BuzzHunt)

Answer 5

Plywood

Density

• 0.46-0.52 g/cm^3 for conifer plywood
• 0.62 g/cm^3 mixed plywood
• 0.68 g/cm^3 for birch plywood

Technically a composite material, plywood has been used in several different ways to make bike frames. The two most obvious are as a sheet material, and as a linear material.

Advantages

• wood is easy to work (tools are cheap and readily available)
• plywood is easy to find

Disadvantages

• even weaker than mild steel, making design difficult and frames heavy
• epoxy composite, so the expoxies (glue and sealant) need to be chosen carefully and may be toxic
• key parts of the frame will still be metal, or great effort must be put into making them from wood.
• durability is not great (years rather than decades)

Sawyer bike by Jurgen Kuipers via CityLab

BONOBO PLYWOOD BICYCLE via CycleExif

_{(source: coocan.jp)}

SANOMAGIC Mahogany bikes by Sueshiro Sano

Answer 6

Carbon Fibre Reinforced Polymer

Density ranges from 1.75–2.0 g/cm3 and varies with type and layup.

Carbon fibre (CF) frames are made out of sheets of carbon fibres set in a polymer resin, usually epoxy.

In 1975 the first CF tubed bike appears, the Exxon Graftek, It had steel lugs and was prone to breaking. This was followed in 1986 by Kestrel and Trek releasing full CF-framed bikes.

A modern, top end example of a carbon fibre bike is a Pinarello Dogma F8 which is riden by Team Sky and also therefore by Team Bradley Wiggins.

Although Sheldon Brown and others are not very enthusiastic about CF, there's a large body of opinion that CF is the best material for racing and riding fast.

Advantages

• Very high stiffness to weight ratio can lead to frames that are stiff but very light.
• CF has directional strength meaning that depending on the alignment of fibres it can be used to make frames that are stiff when transferring power but compliant when absorbing road vibrations.
• CF is able to form a wide range of shapes meaning aero profile tubes can be created more easily than with metals.
• CF doesn't wear in the same way that metals do, meaning that it can theoretically have an indefinite lifespan because it does not wear under regular forces. CF is not prone to corrosion even without coating/paint.
• Although the lay-up process takes a lot of time, it does not require high levels of skill. This means that less-skilled workers are able to produce CF frames.
• Perhaps some people like the look and status of a CF bike. I remember when I first got a CF bike how my non-cyclist friends would think it's some sort of spaceship and wanted to lift it up just to feel its weight.

Disadvantages

• CF frames are expensive due the long time it takes to hand lay all the individual strips of CF.
• CF frames (or any parts) require more careful and qualified assembly. A special lubricant must be used to prevent parts from bonding together, and CF will not tolerate overtightening as well as metal.
• CF frames tend to become damaged easily. Because CF has directional strength it means that it is less resistant to forces that it is not designed to be exposed to, i.e. crashes. When forces are applied in a way that the CF fibres are not taking the strain themselves, then it is the polymer matrix that takes all the force and so is more easily broken.
• At the same time, the damage is often unnoticeable. Where a metal frame will have a visible dent or bend, a CF frame may look undamaged, but may in fact delaminate internally, leading to a sudden unexpected failure later.
• CF is not easily repairable; in fact many people would say it can't be repaired. In any case, if an expensive CF frame is broken you're probably not going to want to race on it again in case there is a risk of sudden failure of the repair job.
• CF bikes quickly lose their value. If you buy a CF bike it's probably because you want to race on it or at least ride fast, therefore you buy something that is at the forefront of technology for your price point. however because CF bike technology has been improving very quickly over the last two decades and is still improving now, it means your purchase will quickly be outdated by newer bikes.
• Many people who buy CF bikes will end up with a bike that far surpasses their ability. A learner driver won't go much faster in a Porsche 911 than in a Nissan Micra. People fall for the marketing claim of CF bikes as the only option for buying a good bike, or that it is the best way to get faster rather than training more and losing a few kilograms.

Answer 7

Beryllium (alloy)

Ridiculously rare and impressively high performance metal. It has a density of 1.85 g/mL (comparable to carbon fiber), tensile strength of 270 MPa, and Young's modulus (stiffness) of 300 GPa (better than steel). Beryllium and its alloys are used extensively in aerospace and defense applications.

Unfortunately, there are some drawbacks. First, because its stiffness is disproportionate to its strength, it fails at low elongation. This means it's brittle. This also makes it hard to work, and very labor intensive manufacturing processes are needed to form it properly. Due to its extreme rarity, the stuff costs about $8,000/kg just for bulk metal. Also, the metal is very toxic, and its dust or vapor can kill you.

I only know of one example of a Beryllium framed bike. Bush Wellman (a Be company) made a frame for an American Bicycle Manufacturing M-16 mountain bike in 1990 for $25,000 (in 1990 dollars). I believe the frame weighed around 900g.

Answer 8

Pure Gold

note: this picture is not a pure gold bike - its just plated.

This answer has not been done in real life, but it did achieve a lot of discussion under Could you make a bike frame out of 24kt gold?

Advantage

• Bling factor - it looks "WOW" A boorish display of wealth aimed at impressing other boors.

Disadvantages

• Material strengths and hardening - gold doesn't harden when heated and quenched, like steel

• Deformation - dropouts would have a very limited life because they would squash under pressure. Your dropouts would have to be made of something better than gold.

For the above two reasons, wheels and spokes, axles, cranks chain cassette, bearings, brake parts, bowden cables, rims, nipples and nuts could not be made of gold.

• Abrasion - Pure gold is not very resistant to wear. That is why everyday jewellery is often made of 9 or 18 karat gold, not 24 karat pure gold. Your gold bike would start rubbing off on anything it brushed against. And any sort of accident could leave a shower of gold dust down the asphalt. More on that below.

• Weight - gold is 19.32 grams per cubic centimeter. Steel varies from 7.75 to 8.05 g/cm^3 and aluminium is is 2.7 g/cm^3 Carbon fibre is harder to pin down, but the fibre itself is 1.6 to 2.2 g/cm^3 A bike made from the same volume of pure lead would be lighter than a gold one, because lead is only 13.55 g/cm^3

• Cost As of 2016-11-15, gold is $39,600 USD/kilo. A super lightweight carbon bike frame at 780g would cost you over $30,000 USD for the material alone, assuming the material strengths could cope. A more likely 5 kilo frame will cost you $200,000 USD. Even crashing your bike and rubbing 5g of gold off would leave $200 worth of the metal on the roadside.

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In reality, this is more likely to be a gold electro-plated steel bike, or an anodised aluminium frame underneath a very thin layer of 9 karat gold.

Answer 9

Bamboo & Bamboo Carbon-Fibre Composite

Bamboo bikes have been about far longer than most people assume. First patents for bamboo bikes were issued in England and the US in 1894 and 1896, respectively.

With the advent of Green Thinking bamboo bikes are slowly edging back into fashion.

Bamboo Carbon-fibre composite frame. Courtesy of Biotic Bikes:

Bamboo-tubed frames with metal/composite joints can be home built more easily than many other frame materials

Advantages

• High strength-to-weight ratio, higher tensile strength than steel!
• Natural vibration control which makes for a more comfortable ride
• Sustainable
• Lightweight, bamboo has a density of 0.35 g/qcm
• In a lot of developing parts of the world bamboo bicycles stimulate the local industry

Disadvantages

• If no proper QC procedures are in place, raw materials may naturally be compromised
• Since bamboo is a natural material no consistent look can be guaranteed (this may be regarded as an advantage by some)

Answer 10

Steel Cables aka Tensegrity or Tensional Integrity

This is not a unique frame build material because wires or cables only work under tension. So this bike requires at least two beams of some other non-compressible material, in the form of a main beam and a seat post.

Earlier:

More modern construction with only one wire:

Advantages

• Less frontal area, lower wind resistance and therefore more aero.

• Theoretically lighter than tubes.

Disadvantages

• Not actually lighter than tubes, because the main beam has to be beefier, and steel cable is not light in the first place.

• Cheesecutter - In the event of an accident, the topwire/toptube would do significantly more focused damage based on its smaller size. Like those taunt wires used to cut fancy cheese. cringe

• Flex - these bikes were excessively compliant in the horizontal direction.

Future

Some development has been done with kevlar cables and carbon fibre main beams.

Answer 11

Flax Fibre/Fiber

Schwinn Vestige was (is?) made of flax fiber (90 percent flax, 10 percent carbon).

http://bicycletimesmag.com/review-schwinn-vestige-made-from-flax-fiber/

Advantages

• Green - it looks ecologically conscietious.

Disadvantages

• Greenwashing - it's not as ecologically conscietious as it looks.

Answer 12

Plastic

Density

~0.91 g/cm³ for Polypropylene (triangle #5)
~0.92 g/cm³ for low density Polyethylene (triangle #4)
~0.95 g/cm³ for high density Polyethylene (triangle #2)
1.03-1.06 g/cm³ for polystychrene (triangle #6)
1.35-1.38 g/cm³ for PETE like water bottles (triangle #1)
1.32-1.42 g/cm³ for PVC polyvinyl Chloride (triangle #3)

There have been a few attempts to build plastic bicycles since the 70's. Construction materials include Lexan and HDPE (high-density polyethelyne) but I can't find any evidence of commercial success in adult's bicycles. Plastic children's bikes are popular but they are usually in the form of balance bikes without pedals (still technically a bicycle?).

https://www.designboom.com/cms/images/user_submit/2011/07/frii5.jpg

Advantages (For children's bikes)

• Light-weight
• Cheap
• No sharp edges

Disadvantages

• Heavy
• Overly flexible
• Deteriorates when subjected to UV light
• Embarrassing

Answer 13

Scandium

Density 2.985 g/cm³

"Scandium frames" actually refer to specific aluminum alloy frames with some small amount of scandium (often less than 1%).

Advantages

• Similar advantages to aluminum, light and stiff.
• Stronger and more durable than other aluminum alloys. The Russians built missile parts from scandium for missiles that were designed to be fired through polar ice. Parts of the MiG lines of fighters were also built from scandium alloys.
• Scandium also increases durability for welding aluminum, meaning welds are less prone to failure and tube thickness can be reduced at joints (lighter).

Disadvantages

• Fairly expensive and fairly niche. Was perhaps less expensive than carbon early on, but as of late, has been left behind as carbon becomes cheaper and manufacturing techniques increase to make carbon better.

• More expensive than other aluminum alloys. Less tuneable than carbon. Less tuneable and less durable than titanium.

Summary

Scandium ends up (currently) being a very niche material that offers advantages over all other materials, but often only slightly. It's in a weird place as a very, very high end aluminum that one can easily skip buy paying just a bit more to move to titanium or a moderately priced carbon frame. Kona felt like this about scandium in 2008. Eight years later they are introducing carbon MTB frames. To me that says carbon is finally to a place where scandium has become of very limited use based on it's price.

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Scandium (technically a scandium-aluminium alloy) was popular for a short bit - Salsa, voodoo, Kona all made scandium frames at one point. Kona notes:

Scandium is the eighth most abundant rare element on earth. A silvery white metal extracted from the earth’s crust, Scandium is a potent grain refiner that, when added to aluminum alloys, elevates the strength and durability of the material by 50%. It does this by “straightening” out the grains of the alloy, making the metal less susceptible to failure. First used by those crafty Russians during the Cold War, guiding fins built of Scandium alloys on missiles could withstand incredible forces, sustaining no damage even when fired through the polar icecap. Scandium alloys went on to become a highly advantageous addition to Soviet built aircraft giving them incredible weight, maneuverability and range advantages.

It’s this strength and durability that makes Scandium alloys so attractive a material when it comes to manufacturing bicycles. Strength is so much higher (Scandium alloy is twice as strong as 6061 or 7005 aluminum) that we’re able to use much less material to achieve riding characteristics similar to steel. And we like the sexy, compliant feel of steel. With Scandium we’re able to shave weight from our aluminum frames by 10-to-15%.

Source: http://konabikeworld.com/08_tech_scandium.htm

http://salsacycles.com/bikes/archive/campeon

Answer 14

3D Printed

Answer needs completion

Answer 15

Carved Wood

While more expensive than plywood, bamboo or dimensional lumber, frames made from carved wooden tubes (or even monocoques) do exist.

Advantages

• directional strength (somewhat like CF) allows for stiff yet vibration-absorbing frames
• good strength to weight ratio
• potentially eco-friendly
• resistant to denting due to thicker walls
• looks and feels awesome (subjective)

Disadvantages

• needs thicker tubes
• very difficult to use well
• easily damaged by moisture unless specially treated
• very expensive due to labor (and sometimes exotic woods)

Answer 16

Gaspipe Steel

A derisive term for the "high tensile" or mild steel tubing used to build cheap bicycles. Since low-end bicycles are made of low-quality steel, the builders compensate by using heavy, thick tubes.

These tubes are often single-gauge or plain gauge, so they have a consistant wall thickness all the way along the tube whereas higher quality frames are made from butted tubes that may have two or three different thicknessess depending on the loads and distance from a weld.

Difference to other Steel

All steel has the same "Youngs Modulus" (measure of stiffness) What changes between gaspipe and higher tubes is the strength, so gaspipe steel drawn to a thickness of 0.4mm (the thinnest piece of Reynolds tubing) will bend under far less pressure.

Advantages

• Cost. This plain gauge tubing is cheaper.
• Efficiency. Butted tubes have to be made in the lengths required. Plain tube can be ordered in longer lengths and then cut to suit the requirements which reduces wasteage.
• Repairable. Steel can be fixed much easier than most other frame materials.

Disadvantages

• Weight. Approximate weights for a bare steel frame and its fork.

Tubing Weight
Reynolds 531 Superlight/531pro/753 5.5lbs to 5.75lbs or 2.5-2.6 kilograms
Reynolds 531DB/531C 6lbs or 2.7 kilograms
Reynolds 531ST (Standard Tube) 7lbs or 3.2 kilograms
Good quality plain gauge tubing 7lbs to 9lbs, or 3.2-4.1 kilograms
Inexpensive plain gauge tubing 9lbs to 13lbs, or 4.1-6 kilograms

Note: "531" denote different quality tubing types. See the Reynolds entry in this CW for further information.

That's Scaffold tube, inch and eighth gas barrel, inch and eighth 531 tubing (⌀ ≈29 mm), inch gas barrel and inch 531 tubing. Where 'gas barrel' means the material that was actually used as conduits for gas.

Here's a gaspipe bike - an "olmo" You couldn't tell by looking that its heavy.

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Note technically pipe is made from flat metal which has been rolled, and is joined with a seam weld. Tube is formed as a closed shape and does not have a seam.

See also Reynolds and Ishtawa steel entries elsewhere in this CW.

Answer 17

Aluminum Alloy

History

The first Aluminum bicycles were made around the turn of the century. That is: the 19th century. The earliest documentation of Aluminum being used as a bike frame material is three examples made for a Parisian trade show by Clement Cycles in 1893. This bicycle was not made of tubes, but was a solid single piece aluminum casting!

This of course was quite impressive for its time as Aluminum was only first industrially produced in 1856. However, as you can imagine, these solid frames were very heavy and not very good.

Aluminum as a frame material remains a curiosity for the next 80 years while steel frames dominate the performance and utilitarian market. This doesn't change until TIG welding is developed and becomes common in the 70's. This advancement allows construction from extruded hollow tubes and the possibility of much better performance.

In 1974, the MIT mechanical engineering student Marc Rosenbaum decides to try building an aluminum bicycle for his senior thesis. He took advantage of the low density of Aluminum and built his bike with large diameter tubes and very thin walls. The result of his efforts was a track bike lighter than any other in the world at 12.3 lb!

Here's a great article on it. https://www.sheldonbrown.com/AluminumBikeProject.html

The industry followed soon after. Gary Klein patented the wide tube Aluminum bike frame in 1977 and started Klein bicycle company. Cannondale introduced the first model of the CAAD in 1983 and Al joined the pro peloton shortly after. Miguel Indurain won the first TdF on an Aluminum Pinarello Keral Lite in 1995 and they were the material of choice until replaced by carbon in 1999.

Today, Aluminum bike frames are the majority of new production, having displaced steel as the lowest cost option. You can buy Aluminum framed bikes from every department store. Aluminum also lives on at the highest levels in the pro peloton, with Jonny Brown's Specialized Allez winning the 2018 US Road Championships.

Material Properties

Most structural metals have similar maximum strength to weight ratios. This is due to the physics of metallic bonds. Aluminum alloys follow the same curve as steels and Titanium alloys, but have lower density and strength per unit volume. This has some implications:

Aluminum is not very good for high strength applications where size is limiting. Aluminum will never be very good for screws, bolts, or rivets because it will be a fraction the strength of steel.

However, for bike tubes, the case is opposite. Tubes with large diameter and thin walls are lighter for the same stiffness. This is because the stiffness (moment of inertia) of a tube under torsion scales with the cube of radius, maintaining the same total material. However, sufficiently thin tubes are vulnerable to local shell buckling. This effect limits the thinness that steel tubing can be made. Because Aluminum is much less dense, the same mass of it can be made into a tube that is both larger in diameter and wall thickness, and therefore stiffer. Alternatively, an equally stiff frame can be made lighter than steel. Most aluminum frames today have much wider tubes than steel bikes, but these tubes are actually less wide than the theoretical optimum. Some compromise is made for the sake of resisting handling loads and to improve aerodynamics.

Aluminum is self-passivating in air, meaning the oxidized metal protects the underlying metal from corrosion. This means Aluminum does not rust in fresh water or air. However, aluminum is vulnerable to pitting corrosion by solutions that attack the passivating film, including salt water. This is a problem for marine environments and during winters where roads are salted, and you should cover any exposed aluminum.

Aluminum alloys melt at about 600C, and they are relatively easy to cast. However, high strength applications prefer forged aluminum because this can align the grains in a favorable direction. Aluminum is also much easier to machine than steel or titanium and it does not significantly harden with heat. Many high quality modern aluminum frames are made by hydroforming, in which very high pressure water forces the aluminum tubes into a female mold. This process allows for considerable design freedom, and Aluminum tubes can be made more freeform than steel, though to a lesser extent than carbon.

Aluminum alloys are often said to not have a fatigue limit. This means that at sufficiently high cycle counts, any load will eventually cause failure. Therefore, aluminum frames can be seen to possess a finite useful life. This is in contrast to materials such as steel which have a (practically) unbounded cycle limit at loads below the fatigue limit. This is not entirely true, and Aluminum alloys have specified fatigue strengths at the highest ranges of cycle count. However, Aluminum's fatigue strength is less well defined than for steel as its fatigue diagram does not inflect sharply at any point. In my experience, well designed Aluminum frames will last longer than most people keep them running. My daily driver is twenty years old. Most people (though maybe not the reader) don't own a bike that long.

6061T6 is the most common grade of Aluminum Alloy used in cycling. It is widely available, moderately strong and it's easy to weld by TIG. 7075 is about twice as strong, but cannot be welded and is susceptible to micro-cracking. Many bike manufacturers have their own trade names for the alloys they use, and these may or may not be the same as above. Many exotic alloys exist with elements such as Magnesium and Scandium.

Al 6061T6

• Density: 2700 kg/m^3
• Yield Strength: 276 MPa
• Ultimate Strength: 310 MPa
• Young's Modulus: 69 GPa
• Elongation at Yield: 0.4%
• Elongation at Break: 12%
• Fatigue Limit: 97 MPa
• Brinell Hardness:95

Al 7075T6

• Density: 2810 kg/m^3
• Yield Strength: 503 MPa
• Ultimate Strength: 572 MPa
• Young's Modulus: 72 GPa
• Elongation at Yield: 0.7%
• Elongation at Break: 11%
• Fatigue Limit: 159 MPa
• Brinell Hardness: 150

Just for comparison:

4130 Chromoly

• Density: 7850 kg/m^3
• Yield Strength: 435 MPa
• Ultimate Strength: 670 MPa
• Young's Modulus: 205 GPa
• Elongation at Yield: 0.2%
• Elongation at Break: 25.5%
• Fatigue Limit: 320 MPa
• Brinell Hardness: 195

Ti6Al4V

• Density: 4430 kg/m^3
• Yield Strength: 880 MPa
• Ultimate Strength: 950 MPa
• Young's Modulus: 114 GPa
• Elongation at Yield: 0.8%
• Elongation at Break: 14%
• Fatigue Limit: 510 MPa
• Brinell Hardness: 334

Toray T700S Carbon Fiber (UD)

• Density: 1800 kg/m^3
• Ultimate Strength: 2550 MPa
• Young's Modulus: 230 GPa
• Elongation at Break: 1.7%

Answer 18

Reynolds Steel

this answer needs completion its just notes at this point

Reynolds butted tubing was first patented in 1897.

There are many different grades of Reynolds steel. The most commonly known is 531 (pronounced "five, three, one") which was first produced in the 1935 but is no longer available outside of New Old Stock, or by Special Order. This steel was also used on Jaguar XKE car chassis, and assisted in 27 Tour de France victories. The replacements are 520 and 525, which are similar to 531 but can also be welded.

list some other codes and their meanings and usages 753 (required certification by Reynolds), 953, 725, 631, 853, 525.

explain the numbers 531 gets its name from the composition. Five parts manganese, three parts carbon, and one part molybdenum.

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Advantages

• Classy steel tubing
• Considered as a "forgiving" material for building and daily use

Disadvantages

• Many different grades available
• Heat treating requirements vary across different grades
• Some grades do not permit cold-setting of frames
• Steel can suffer from corrosion issues

References

http://bikeretrogrouch.blogspot.co.nz/2013/12/reynolds-tubing.html

https://en.wikipedia.org/wiki/Reynolds_Cycle_Technology#Tubing_types Big list of tubing codes here.