The Frame is the Foundation of the Bike
A materials strength relates to its behavior when subject to stresses and strains.
- Stress - internal distribution of forces within a body.
- Strain - the deformation of a body caused by an applied stress.
Young's Modulus is a measurement of the stiffness of a solid material.
Metallurgy of the tubes, wall thickness, cross-sectional shape, and size all influence performance. The goal of designing a good bike frame is to put the appropriate amount of material where the bike frame undergoes the most stress—at each end of the tubes. This process is known as butting. The result is a tube with a thin-walled central section and thicker-walled ends.
Different butting techniques: Notice the thickness of the tube in the center and at the end points.
Frame GeometryFitting a Bike to be an Extension of Your Body
Bike Fit Measurements
Reach & Setback
A few of the key measurements for bike fit include:
- Saddle Height: The saddle should be positioned such that there is a slight bend in your knee at the bottom of your pedal stroke.
- Reach: The handlebar should be positioned such that there is a slight bend in your elbow and your back is flat or gently curved.
- Setback: When the pedals are level, your knees should be in line with the pedal spindle.
Frame CompositionUsing the Properties of Elements to Construct Better Frames
Chromoly Steel Frame
Iron - 97.6%
Chromium - 1%
Manganese - 0.5%
Carbon - 0.3%
- Strong, proven material
- Easy to cut, bend and weld
- Takes severe impacts without cracking
- Easily repaired
- Least expensiv e
- Corrodes easily
Aluminum - 97.3%
Magnesium - 1%
Silicon - 0.6%
Copper - 0.3%
Iron - 0.3%
- St rong, low density material
- Weighs less
- Preferred for competitive frames
- Excellent corrosion resistance
- Stiff, creating an uncomfortable ride
- Metal fatigue affects reliability
- Skilled welders needed for repair
- More expensive than steel
Carbon Fiber Frame
Carbon Fiber and Polymer Mix: The properties of carbon fiber-reinforced polymers vary according to weave pattern, fiber density and matrix polymer.
- Non-metallic composite
- Stronger than steel, lighter than aluminum
- Resistant to corrosion
- Absence of design limitations
- Will crack in severe impact
- Costly, much more than aluminum
- Very difficult to repair