Bicycles

Unit 3 of the WJEC engineering course is an examined unit. There is ALWAYS a question about bicycle engineering within it (usually question 1!). Sometimes this is an extended answer *+ mark question, sometimes it is a shorter question but it will always be there. This page will hopefully help prepare you for this type of question. 

The question is usually based upon how the bicycle has evolved over the years, how it functions, how it is designed, manufactured and the choices of materials that it has been made from. 

You should be aware of the common components of a bike and what they do.
The image to the right will help you. Further down the page there are some descriptions of their purpose and how they work. 

• Tensile Strength:
  The ability of a material to resist being pulled or stretched apart. While not the main factor in bicycle frame failure, it contributes to overall strength and durability.  The spokes. handlebars and frame all need to possess this property. 

• Density:
  How much a material weighs for a given volume. Lower density materials are lighter, which is desirable for easier handling and acceleration. Can you say which of the following three materials is less dense: aluminium, steel or carbon fibre? 

• Stiffness:
  The material's resistance to deformation under load, influencing how efficiently power is transferred from the rider's pedals to the wheels. Higher stiffness can improve pedalling efficiency, but too much can lead to a harsher ride. 

• Durability:
  The ability of the frame to withstand regular use, considering rough terrain, and repeated stresses, different weather conditions and general 'wear and tear'. 

• Fatigue Resistance:
  The ability of the material to withstand repeated stress cycles, such as from pedalling and road bumps, without fracturing. 

• Toughness:
  The material's ability to absorb impact energy before fracturing, which is important for crash-worthiness. 

• Weight:
  A lighter frame is generally desirable for easier handling, acceleration, and climbing. 

• Corrosion Resistance:
  The ability to resist degradation from environmental factors like moisture, which is particularly important for outdoor cycling. 

• Elongation:
  How much a material can be stretched before it breaks, contributing to the frame's ability to absorb impacts. Brake cables will elongate over time and in high temperature conditions (due to thermal expansion). 

• Safety:
  The frame must be strong enough to support a range of rider weights and different riding conditions, resisting impacts, ensuring a safe ride over the extent of the bike' service life. The brakes must be able to continue to function effectively, handlebars retain shape and robustness and the suspension (if fitted) must be reliable.

• Steel:
  Strong, durable, and relatively inexpensive, but heavier than alternatives. 

• Aluminum:
  Lighter and stiffer than steel, but can arguably be less comfortable and may not be as easily repairable. 

• Carbon Fibre:
  Lightest and stiffest, but also the most expensive and susceptible to hidden damage, which can only be seen using non-destructive-testing.  Carbon fibre is a composite material (not a metal) and requires complex manufacturing techniques to shape and form. 

• Titanium:
  Offers a balance of strength, durability, and comfort, but is expensive.