Linear Static Analysis and Material Evaluation of a Bicycle Frame Under Two Rider-Loading Scenarios

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1. Problem Definition

This study investigates how a bicycle frame behaves structurally under typical rider loads. Using ANSYS Static Structural, the goal is to evaluate stress, deformation, and material performance to determine which material; structural steel, aluminium, or assumed carbon fibre offers the best combination of stiffness, durability, and weight efficiency for the same frame geometry.

The analysis also identifies critical stress regions, explains the physical reasons behind them, and provides design recommendations for improving real-world frame performance.



2. Simulation Setup

2.1 Geometry and Constraints

The bicycle frame geometry was kept constant for all cases. The supports were applied at the wheel axles as follows:

  • Front axle: fixed in Y and Z; free in X
  • Rear axle: fully fixed in X, Y, and Z

These constraints simulate a rigid wheel–ground interaction without suspension compliance.

2.2 Loading Scenarios

A 100 kg rider load was divided into two realistic scenarios:

Load Case

Seat & Pedals

Handlebars

Case 1

70%

30%

Case 2

50%

50%

Case 2 simulates more aggressive riding, with greater load on the handlebars.

2.3 Materials Evaluated

Property

Structural Steel

Aluminium

Carbon Fibre (Assumed)

Elastic Modulus (GPa)

200

70

~140

Approx. Yield Strength (MPa)

250

280

Very high (assumed)

Total Frame Weight (N)

103.29

35.51

Very low

 

 

Boundary Conditions followed the original model:

  • Front axle fixed in Y & Z, free in X.
  • Rear axle fully fixed in X, Y, and Z.

These conditions simulate the frame supported by wheel axles without suspension compliance.

 

Simulation Results

a)     Structural Steel

Case

Max Deformation

Max Stress

Case 1

0.209 mm

33.49 MPa

Case 2

0.273 mm

42.94 MPa

 Case 1 Deformation


Case 2 Deformation


Case 1 Stress


Case 2 Stress


b)     Aluminium

Case

Max Deformation

Max Stress

Case 1

0.586 mm

32.97 MPa

Case 2

0.7667 mm

42.27 MPa

 

Case 1 Deformation


Case 2 Deformation

Case 1 Stress


Case 2 Stress


3.3 Expected Carbon Fibre Behaviour (Assumed)

  • Stress levels similar or lower due to tailored stiffness
  • Deformation between steel and aluminium
  • Significantly lower weight

4. Discussion of Results

4.1 Where Maximum Stress Occurs and Why

For all materials and both loading cases, stress concentrations consistently appear at:

  • Head tube junction (top tube + down tube intersection)
  • Seat tube and bottom bracket region

These regions experience the highest stresses because:

  1. They act as load transfer nodes, where multiple tubes meet.
  2. Bending moments are largest where the load path changes direction.
  3. Welded joints and sharp geometric transitions create natural stress risers.

Smoother transitions, fillet improvements, and gussets would reduce these peak stresses.

4.2 Deformation Behaviour and Stiffness Differences

Although steel and aluminium show similar stress values (~33–43 MPa), their deformation differs greatly:

  • Steel (E = 200 GPa) → Very stiff, lowest deformation
  • Aluminium (E = 70 GPa) → 3× more deformation
  • Carbon fibre (E ≈ 140 GPa) → Moderate deformation, but extremely lightweight

These trends exactly match theoretical predictions, confirming that the material stiffness not strength dominates deformation.

4.3 Effect of Load Distribution

Case 2 (50–50 weight distribution) produces:

  • Higher stresses
  • Larger deformations
  • More bending in the front triangle

Therefore, Case 2 is the more critical loading scenario for design evaluation.

4.4 Comments on the Boundary Conditions

The fixed axle model is a simplified representation.
In reality:

  • Tires, joints, and suspension absorb some loads
  • Peak stresses shift and may reduce in some regions
  • New stress concentrations appear at suspension mounts

A more realistic simulation would include tire stiffness, joint stiffness, and dynamic effects from road impacts.

4.5 Design Improvement Opportunities

  1. Increase tube diameter
    • Bending stiffness scales with diameter.
    • Major reduction in deformation with minimal weight increase
  2. Add gussets at high-stress joints
    • Reduces bending stresses
    • Improves stress distribution
  3. Improve joint transitions
    • Larger radii reduce stress concentrations
  4. Material-specific enhancements
    • Aluminium: increase tube size for stiffness
    • Steel: possible wall thickness reduction to save weight
    • Carbon fibre: tailor fibre orientation along load paths

5. Conclusion & Material Selection

  • Structural Steel offers the lowest deformation, excellent durability, and high fatigue resistance, making it ideal for robust and long-lived frames where stiffness and reliability are priorities.
  • Aluminium provides considerable weight savings at the cost of reduced stiffness and potentially shorter fatigue life; however, its strength-to-weight ratio remains attractive, and stresses stay well below yield in the simulated cases.
  • Carbon Fibre (with assumed high strength and increased stiffness relative to aluminium) would offer the best strength-to-weight ratio, with moderate-to-high stiffness and extremely low mass, though with increased sensitivity to impact damage and more complex repair requirements.

Final Material Recommendation

Considering performance, manufacturability, durability, and weight efficiency, carbon fibre provides the best strength-to-weight ratio, steel provides the best durability and stiffness, and aluminium offers a balanced compromise with significant weight reduction compared to steel.



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