Types of Motorcycle Chassis

When it comes to motorcycles, the chassis is like the backbone of the vehicle - it's the core skeletal structure that holds everything together. From the engine to the suspension, all components are mounted on the chassis, making it a critical element in determining the overall handling and performance of the motorcycle. The design of the chassis is not just about aesthetics - it plays a crucial role in defining how the motorcycle feels and behaves on the road. Different structural components like the Main Tube, Down Tube, and Reinforcement Tube are strategically placed to create a balance between flexibility and rigidity, ultimately affecting the riding experience.

Manufacturers invest a lot of time and resources in designing their own chassis, each with its own unique characteristics and design philosophy. Whether it's for a cruiser, sports bike, or off-road vehicle, the chassis is customized to provide the desired user experience.

In this article, we'll delve into some general perspectives on motorcycle frames that are commonly followed by manufacturers. By understanding the basics of motorcycle chassis design, you'll gain a deeper appreciation for the engineering behind these two-wheeled machines. So, buckle up and get ready to explore the fascinating world of motorcycle chassis design.

 

Six types of Motorcycle chassis are used to manufacture motorcycles.

1. Backbone Frame 
2. Single Cradle Frame                       
3. Dual Cradle Frame      
4. Perimeter Frame               
5. Trellis Frame                                    
6. Monocoque Frame

 

Backbone Frame

The backbone frame is a throwback to the early days of motorcycle design, featuring a long tube that runs down the center of the chassis like a spine. This simple and cost-effective design has the engine mounted directly onto the backbone, giving the bike a streamlined look. While lacking in strength compared to modern frames, the backbone frame is ideal for smaller, economical motorcycles with low-capacity engines. Its minimalist construction requires less steel and is easier to manufacture, making it a popular choice for budget-friendly rides.

Single Cradle Frame

The single cradle frame is a simple yet cost-effective type of frame commonly used in motorcycles. Resembling a traditional bicycle frame with thicker tubular sections, this design often incorporates the engine as a stressed member of the chassis. The engine and other components are typically cradled onto the tubular frame, which is made up of various tubes of different diameters.

One distinctive feature of the single cradle frame is its single downtube that extends downward to support the engine. While this type of frame may not offer the high performance capabilities of other advanced designs, it provides a sturdy and reliable structure for motorcycles. Despite its simplicity, the single cradle frame remains a popular choice for many riders looking for a practical and budget-friendly option.

 

Dual Cradle Frame

The double cradle frame is a design that features two down tubes to support the engine, providing a level of strength and rigidity that surpasses the single cradle frame. This dual structure not only enhances the overall durability of the frame but also offers a cost-effective solution for motorcycle manufacturers. While it may not be the top choice for performance applications, the double cradle frame is a practical option for cost-sensitive markets looking for a reliable and sturdy frame design. Ideal for everyday use in normal motorcycles, the double cradle frame strikes a balance between strength, cost, and functionality in the world of motorcycle engineering.

 

Perimeter Frame

 The Perimeter Frame, also known as the twin spar frame, is a crucial component in high-performance motorcycles, particularly in the world of motorcycle racing. This innovative design features two beams that connect the steering head tube to the swing arm pivot point in the shortest distance possible, greatly enhancing the bike's rigidity. Research has shown that this design not only improves performance but also allows for a lighter overall chassis.

 

 Initially, Perimeter Frames were constructed using steel sections, but with advancements in technology, manufacturers are now turning to lightweight aluminum alloys to ensure both strength and agility. The success of iconic sports bikes equipped with Perimeter Frames is a testament to the effectiveness of this design in high-speed and competitive settings. In conclusion, the Perimeter Frame is a key element in maximizing a motorcycle's performance, providing stability, agility, and strength for riders who demand the absolute best in their machines.

 

Trellis Frame

The Trellis frame is a popular choice among bike makers for its innovative design and performance benefits. Similar to a perimeter frame, its primary goal is to connect the steering head with the swing-arm efficiently. However, the trellis frame sets itself apart by utilizing a network of short steel or aluminium tubes welded together to form a distinctive trellis-like structure. This construction method not only enhances rigidity but also keeps the frame lightweight. One of the key advantages of the trellis frame is its simplicity in design and construction, making it a cost-effective option for manufacturers. Despite its straightforward approach, the trellis frame boasts impressive strength and stability. It has become a preferred choice for many bike manufacturers due to its effectiveness in providing a solid foundation for high-performance motorcycles. The combination of strength, lightweight construction, and cost-efficiency makes the trellis frame a standout choice in the world of bike frame design.

 

Monocoque Frame

Monocoque frames are a specialized type of frame commonly found in high-performance cars, but also utilized in select extreme motorcycles. These frames are constructed as a single, super-stiff piece of metal, providing unparalleled torsional rigidity and lightweight construction. While typically more expensive to produce due to their complex and precise construction, monocoque frames are reserved for machines with extreme power and demanding performance requirements. Some hyperbikes that balance high-speed thrills with touring capabilities opt for the superior strength and rigidity of a monocoque frame. These frames often incorporate exotic materials such as carbon fiber and magnesium, further adding to their exclusivity and expense. While not as common as other frame types, monocoque frames offer a level of precision and engineering excellence that sets them apart in the world of high-performance motorcycles.

 

 

Project SR Perspective of Selection of Chassis Frame

At our company, we are dedicated to creating the best possible chassis for off-road racing applications. To achieve this, we work closely with professional riders and closely monitor international races to gather feedback and insights on what it takes to build a winning chassis. By understanding the structural flex and twist required for optimal performance, we set the standards for our chassis to excel in even the most abusive conditions.

To ensure our chassis are up to the task, we put them through rigorous testing both in Computer-Generated Models (CAD, CAE) and on our Extreme off-road Moto-cross Track – both of which are proprietary assets of our company. Our chassis frames are constructed using a trellis structure with Topologically Optimized Reinforcements, designed to meet our exacting standards for performance and durability.

Some of the tests our chassis have successfully passed include a 16ft long jump and 8ft high jumps, as well as continuous riding on extreme off-road tracks for more than half an hour. These tests demonstrate the strength and resilience of our chassis, ensuring that they are ready to perform like champions in any racing situation.

 

SR 14 Frame

 

Difficulties Faced during manufacturing of chassis frame.

Material Sourcing: Our chassis frames are made of high-grade steel tubes (AISI 4130). The steel tubes got various types of 3D bends to match rider’s ergonomics. Our motorcycles fall under the premium category and are very much custom built for the specific purpose. We make motorcycles like one out of ten production volume precision. So, we need perfect material in small quantities. Here we faced a lot of challenges to source the steel tubes as the suppliers are unwilling to send such small quantities. We partnered with some agencies in such a condition that we will procure steel from them for all our current and future motorcycles.

Pipe Bending: After getting the material we need to shape them by bending. Initially we failed to find a supplier who will make the bend pipes, so we made our own machine and develop methodology to bend the pipes in 3direction simultaneously.

Welding Fixture: We made our in-house welding fixture to maintain the alignment of frame as frames got distorted after welding. Our fixtures are quality certified by state-of-the-art CMM machines.

 

 

This chart is based on Project SR experience.

PARAMETER	SINGLE CRADLE	DOUBLE CRADLE	PERIMETER	TRELLIS	MONOCOQUE
Cost	Low	Low	High	High	Very High
Complexity	Low	Low	Low	High	Very High
Weight	High	High	Low	Low	Very Low
Stability	Low	Low	High	Very High	Very High
Rigidity	Low	Low	High	High	Very High
Cornering	Poor	Poor	Good	Very Good	Excellent
Stiffness	Low	Low	High	High	High

 

 

In conclusion, we have found inspiration in the steel trellis frame structure and have successfully created a lightweight and flexible frame for our motorcycles. By incorporating additional guard tubes, we have enhanced the protection of our sophisticated electronic components from potential accidents. It is worth noting that trellis and perimeter frames are ideal for low to medium volume production due to their cost-effective nature, requiring less tooling than monocoque frames. On the other hand, monocoque frames are better suited for high-speed vehicles where cost is not a limiting factor. Overall, our innovative approach to frame design has resulted in a successful fusion of functionality and aesthetics in our motorcycle line-up.