Engineering Report

Materials for Bicycle Frames



Contents: 2

Synopsis: 3

Introduction: 3

Analysis: 4

Result Summary: 10

Conclusion: 13

Acknowledgments: 14

Bibliography: 14


This engineering report contains information on the different types of materials used to construct tricycle frames. The types of materials present in this report are compared and contrasted with each other and a judgment is made to evaluate the best material out of the selected to be used by a fictional small business. Cost and Weight are the major factors considered in the evaluation of the best material.


This reports main purpose, as stated in the synopsis, is to compare and contrast specific materials and make a judgment for which material is best for a fictional recumbent tricycle small business based on the properties each have and most importantly the weight and cost.

The analysis section provides research done on each of the possible materials used for the tricycles. It displays significant properties each material has required to justify the best possible selection for the small business. It displays fatigue and resistance capabilities, assembly compatibilities, disadvantages and gives reasons for possible costs for each material.

The Results section displays all information required to meet the aims or main purpose of the report.

The conclusion sums up the report, giving a personal decision, based on the information gathered, as to which material is best for the small business

The Acknowledgements and Bibliography section gives the relevant sources acknowledgement for the assistance given in researching the topic.


Reynolds 853

The Reynolds 853 is a steel alloy created by Reynolds Cycle Technology, a manufacturing company based in Birmingham, England. It is composed of several elements solely including iron, carbon, chrome and molybdenum but also includes silicon, copper and manganese.

The Steel??™s physical properties include a stiffness level similar to mild steel. With the addition of chrome and molybdenum the steel can be strong enough to butt or be thinned down in the middle, thus making the material lighter.

It has an excellent strength to weight ratio obtained from heat-treatment used in its formation. The heat treatment used for this steel does not use quenching rather uses air cooling or air hardening. This results in the steel having a finer grain and raises the yield strength in the material. Subsequently due to air hardening the material??™s strength increases as the materials temperature cools. This unique air hardening property of Reynolds 853 provides additional stiffness through reduced micro-yielding at the joints, allowing stiffer products with excellent fatigue strength. This gives it an added resistance to all loads put on it and a resistance from damage.

In assembly Reynolds 853 steel is suitable for TIG welding and brazing, using lugged or lugless construction. The production process ensures tight tolerance, gauge tubes. The strength to weight ratio of 853 is close to that of quality titanium frames. It however can not be brazed.

The cost of the material can be relatively cheap once equipment used for making the product is obtained, i.e. casts, assembly lines, elements, etc. Maintenance to production equipment is the only other factor needed to take into account

Reynolds X100

Like the 853 steel alloy, Reynolds X100 is a product of Reynolds Cycle Technology, based in Birmingham, England. It is an aluminum alloy composed of both aluminum and lithium. The material was derived from aerospace projects and commonly used for custom bike builds but has limited production due to the uncommon availability of the raw materials.

Behind steel, aluminum is seen as the second most common material and is most likely to overtake steel as most popular material used for frame design. It is 12% stiffer and 20% lighter than steel in its most common bike frame design. Aluminum is rust proof and dampens vibrations 20% faster than steel.

With the addition of lithium to the alloy its strength and stiffness properties significantly increases while its density decreases. As a consequence to the increased stiffness the frame has very little flex. The power produced by the rider is transmitted very well however it poorly absorbs shock from rough roads and coarse chip bitumen. The frame is recommended to be used by sprint cyclist and not so much the average rider.

In order to obtain the strength and stiffness that is provided by the material the aluminum must be very thermally treated after being welded, then quenched, and then artificially aged before assembled. To further increase the stiffness and decrease the weight of the material the diameter of the tubes of the frame can be increased while maintaining the wall thickness, making a tube that is eight times as stiff, but only twice the weight. Though using this method runs the risk of being unstable if the walls of the tubes are thinned out to much.

The cost of the initial materials is relatively cheap but in the case of mass production the availability of the materials may be too small. Also the precision of the above method with heat treatment may both cost money and time and may be too much trouble for mass production.

Titanium Alloy

Titanium alloys are metallic materials which contain a mixture of Titanium and several other elements such as aluminum and vanadium. Most titanium frames are 3% aluminum and 2.5% vanadium though a stronger alloy, 6% aluminum and 4% vanadium is increasingly used.

Titanium alloy has a very high tensile strength and fracture toughness. At room temperature its strength is roughly 1200MPa and toughness range from 50 ??“ 60MPa. It is half as stiff as most steels though is half as dense making it 20% lighter than steel. For stiff titanium frames it is required to have a larger diameter, than comparable steels, though not as large as aluminum. The frame is also very corrosive resistant. With the addition of silicon the alloy can obtain significant grain refinement and it can be said that titanium alloys have a perfect balance of properties for frame building.

Welding must be done carefully to avoid contamination and machining must be done precisely. Titanium is very reactive to atmospheric gases and can result in degradation in the material. Titanium is weldable in annealing conditions but provide limited weld ductility and heat affected zone ductility. It can also be significantly strengthened by cold working.

Due to titanium being rather expensive it is rarely used for cycles. It is expensive not only because of the material costs, but also because of the care and time that must be put into the welding process.

7005 Aluminum

Like the Reynolds X100, 7005 Aluminum is an aluminum alloy but consisting of Zinc and Magnesium. Due to its cost and inconvenience of heat treating, 7005 aluminum has gained considerable popularity with smaller companies.

7005 Aluminum has similar properties to the Reynolds X100. It is seen as the second most common material and is most likely to overtake steel as most popular material used for frame design. It is 12% stiffer and 20% lighter than steel in its most common bike frame design. With the addition of zinc, its resistance from corrosion significantly increases. It however has a low fatigue strength when compared to steels.

It is apparent that the most important thing when considering aluminum is the effortlessness in which it can be welded and the strength provided by the weld. When welded the area affected becomes annealed and (specific to 7005 aluminum) it under goes age hardening which recovers some of its previous strength before the weld over time. The result is a joint that is roughly 90% of the strength of the base material. To ensure an efficient bike however the frames should be made from material that is 30% thicker than is necessary which subsequently raises the weight by 30%.

Like Reynolds X100, the cost of the initial materials is relatively cheap but its cost would also decrease due to the fact that a post heat treatment is not essential to get an efficient product. The simplicity of its assembly would also positively affect cost effectiveness therefore mass production would be plausible.

Carbon Fibre

Carbon Fibre is a very strong and light composite material similar to fibre glass and is commonly referred to as reinforced fibres. The material consists of extremely thin fibres about 0.005-0.01 mm in diameter composed of mainly carbon atoms and polymers which are bonded by microscopic crystals which are aligned parallel to the axis of the fibre. Each carbon filament thread is a bundle of many thousand carbon filaments.

For the same strength, carbon fibre weighs considerably less in comparison to both aluminum and steel. The crystal alignment makes the fibre very strong for its size. Carbon Fibre does not suffer from stress rupture and have a very high tensile strength between 3450-4830 MPa. When protected from the sun Carbon fibre filaments can last almost indefinitely but unlike steel alloys the have no endurance limit when exposed to cyclic loads.

The material is excessively expensive due to its great strength to weight ratio and the process in which it needs to take during construction. The series of molds required for its manufacture are a key factor in its high cost despite improved manufacturing techniques which can reduce costs. During its construction 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.

Recycling Carbon fibre can be an issue as it can not be melted down in air due to the many polymer elements in its composition. They can however be thermally decomposed in an oxygen free environment and milled or shredded at low temperatures. It can then be harvested from the remains though the process dramatically shortens the fibre. The recycled material is also much weaker than the original piece.

4130 Chromium Molybdenum Steel

4130 Chromium Molybdenum Steel, also known as Chromoly steel, is a low alloy steel which is considered as an all purpose steel. This steel has relatively low harden ability; nevertheless, it is one of the most popular alloy steels because of its good formability and weld ability along with an excellent mechanical properties.

Chromoly is used in the normalized or in near normalized condition and does not require heat treatment. In the normalized state the maximum allowable tension stress is 95 ksi. At this value it has good toughness and excellent elongation properties. In comparison to Reynolds 853 it has 30% less fatigue stress resistance, considerably less tensile stress resistance and a lower strength to weight ratio. Temperature has significant effect on the material. Its strength decrease as temperatures rise but would this would have little effect from day to day sun. At sub-zero temperatures the material undergoes a change in its ductility to brittleness which can effect its impact resistance.

Its low carbon content makes it easily joined with silver, brass or even TIG welding, although it does suffer some annealing in heat effected area. Like Reynolds 853, chromoly steel can be welded quite easily. Relieving internal stresses within the welds can be accomplished by heating the general area of the weld and then letting the area air cool. This is isn??™t absolutely necessary as the internal stresses aren??™t that much higher then the level trying to be accomplished but it may help to have a metal more resistant to fatigue when being used as transport. Sufficient strength and toughness can be acquired by normalizing the material.

The material itself is fairly cheap and due to its high availability and the fact that it??™s easy to manufacture the cost of the material is even less. It also has a notably good strength to weight ratio.


Material: The type of material
Composition: The make up of the material
Strengths of the Material: Materials positive properties
Fatigue and Resistance: The materials resistance when under different loads.
Ease in Assembly: The effort required to assemble the material together
Disadvantages: Faults
Weight and Cost: The Rough weight and cost of the material

|Material |Reynolds 853 |Reynolds X100 |Titanium alloy |7005 Aluminum |Carbon Fibre |Chromoly Steel |
|Composition |iron, carbon, chrome, |Aluminum, lithium |Titanium, aluminum and |Aluminum, zinc and |Carbon atoms and |Iron, carbon, |
| |molybdenum, silicon, | |vanadium |magnesium |various polymers |Chromium and |
| |copper and manganese | | | | |molybdenum |
|Strengths of Material |Excellent strength to |12% stiffer and 20% |very high tensile |12% stiffer and 20% |For the same |does not require heat|
| |weight ratio, great air|lighter than steel, is |resistance and fracture|lighter than steel, |strength, carbon |treatment for a good |
| |hardening properties, |rust proof and dampens |toughness, strength is|resistance from |fibre weighs |product, Sufficient |
| |ability to become |vibrations 20% faster |roughly 1200MPa, |corrosion, retains |considerably less in |strength and |
| |stronger as temp. |than steel, strength |toughness range from 50|great strength in welds|comparison to both |toughness can be |
| |drops, additional |and stiffness |??“ 60MPa, very |due to age hardening |aluminum and steel, |acquired by |
| |stiffness can be |properties |corrosive resistant | |choice of weave can |normalizing the |
| |acquired |significantly increases| | |be carefully selected|material, good |
| | |relative to the | | |to maximize stiffness|formability and weld |
| | |decrease of density | | | |ability along with an|
| | | | | | |excellent mechanical |
| | | | | | |properties |
|Fatigue and Resistance |Excellent fatigue |Poorly resistance to |very high tensile |Has a low fatigue |does not suffer from |the maximum allowable|
| |resistance |shock |resistance and fracture|strength in comparison |stress rupture, very|tension stress is 95 |
| | | |toughness |to steel |high tensile strength|ksi, good toughness |
| | | | | | |and excellent |
| | | | | | |elongation properties|
|Ease in Assembly |Fairly easy assembly, |Complex assembly, |Difficult assembly, |Can be welded with |Complicated assembly,|Its low carbon |
| |Suitable for TIG |must be very thermally |Welding must be done |barely any effort. |carbon atoms and |content makes it |
| |welding, using lugged |treated after being |carefully to avoid | |polymers are bonded |easily joined with |
| |or lugless |welded, then quenched, |contamination and | |by microscopic |silver, brass or even|
| |construction. |and then artificially |machining must be done | |crystals which are |TIG welding |
| | |aged before assembled |precisely, weldable in| |aligned parallel to | |
| | | |annealing conditions | |the axis of the fibre| |
|Disadvantages |can not be brazed |frame has very little |Must be precisely |Needs to be made from |have no endurance |it has 30% less |
| | |flex due to stiffness |welded and machined |material that is 30% |limit when exposed to|fatigue stress |
| | |level, poorly absorbs |carefully to avoid |thicker than is |cyclic loads |resistance and |
| | |shock on rough roads |contamination which |necessary which | |considerably less |
| | |and coarse chip bitumen|results in degradation |subsequently raises the| |tensile stress |
| | | | |weight by 30%. | |resistance in |
| | | | | | |comparison to 853 |
| | | | | | |steel |
|Weight and Cost |Excellent strength to |20% lighter than steel,|20% lighter than steel,|cost of the initial |expensive due to its |Notably good strength|
| |weight ratio similar to|the cost of the initial|really expensive due to|materials is relatively|great strength to |to weight ratio, |
| |titanium, |materials is relatively|the material and time |cheap but its cost |weight ratio, |material itself is |
| |Cost relatively cheap |cheap but in the case |and care required to |would also decrease due| |fairly cheap and due |
| | |of mass production the |work it. |to the fact that a post| |to its high |
| | |availability of the | |heat treatment is not | |availability and the |
| | |materials may be too | |essential to get an | |fact that it??™s easy |
| | |small | |efficient product | |to manufacture |


By looking through the results the best choice for this fictional recumbent tricycle company would be to choose a material that is a steel alloy. Steel alloys would be the best choice for this company for several reasons.

Looking at Titanium it has roughly the same strength to weight ratio though is 20% lighter. Steel however is much easier to weld and assemble while still having excellent fatigue resistance. It is also a much cheaper product which is of great consideration to a small business. Also the risk of contamination in titanium would be too great for a small company considering the expensive price.

Looking at Aluminum it may be 12% stiffer and 20% lighter than steel but has poor shock absorbing properties which is needed in a tricycle for everyday use and has low fatigue strength in comparison to steel. Steel is again much easier to assemble as it has no need to be thermally treated after the joint is complete (X100) which makes mass production more cost effective. 7005 Aluminum needs to be purchased with 30% thickness excess which also seems a waste of product in order to get what is needed. Also steel has a greater availability than aluminum.

Looking at Carbon Fibre for the same strength it weighs considerably less than steel. It has good stiffness with considerably high tensile strength and does not suffer from stress rupture. However it is extremely expensive for a small amount which is too extravagant for a small business to use for its key material. Carbon fibre also has a poor endurance when placed under cyclic loads where steel is very versatile under different loads.

In specifics Reynolds 853 steel alloy is a better selection than Chromium molybdenum Steel alloy. Both have similar simplicity in assembly but Chromoly Steel alloy has 30% less fatigue stress resistance and considerably less tensile stress resistance in comparison to Reynolds 853 steel alloy. Reynolds 853 air hardening property is quite unique and would be a valuable asset to the small business. It also has a higher strength to weight ratio.


Special acknowledgements to the Reynolds website as it provided the foundation for most of the information obtained in research.


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