A rigid frame gives the motorcycle that nostalgic look that is favoured by many. The lack of rear suspension reduces costs, making it the popular choice of chopper builders. After all, a chopper is meant to be inexpesive, lightweight and free of all but the essentials. Its main disadvantage is the lack of comfort for the rider.

1. The frame

  

The basic dimensions of the frame are the same as those of the one designed for the Old School bike. It’s a hardtail frame, designed to accept a 140 mm rear tyre using a belt drive. It has a 33-degree neck rake and is constructed using 1-1/4″ x 1/8″ and 1″ x 1/8″ diameter tubing. The frame’s total mass is 22 kg.

2. Finite element model, material properties and boundary conditions

The model is discretized using tetrahedral (TETRA10) elements in SolidWorks Simulation module. The element size is 10 mm and there are 54102 elements and 105584 nodes in total.

The material used is AISI 4140 Chrome-Molybdenum high tensile steel, which has the following properties: Modulus of Elasticity: 200 GPa, Poisson’s ratio: 0.285, Density: 7850 kg/m³.

The model is considered as a free body.

3. Results

  
Mode Shape Number 1 – 72.3 Hz             Mode Shape Number 2 – 102.9 Hz

  
Mode Shape Number 3 – 106.6 Hz            Mode Shape Number 4 – 149.3 Hz

  
Mode Shape Number 5 – 171.6 Hz            Mode Shape Number 6 – 192.1 Hz


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