It’s been quite a few years since my college graduation, yet the details of my senior design project remain fresh in my mind. This project involved the ambitious undertaking of designing a three-wheeled vehicle chassis from the ground up for our university’s solar car team. What started as an academic exercise evolved into a deep dive into automotive engineering, specifically the unique challenges and rewards of 3 wheel car design.
Over a year, my team of mechanical engineering students and I immersed ourselves in the complete design and fabrication of a race car chassis. This encompassed everything from the frame and suspension systems to the hubs, spindles, brakes, and steering mechanisms. Looking back, each of these systems could have been a substantial senior design project on its own. Attempting to tackle them all simultaneously speaks to the perhaps youthful overconfidence we possessed. However, our ambition paid off. We successfully built the chassis, and I gained invaluable knowledge about chassis design and the capabilities of a dedicated engineering team under pressure.
For more visuals and detailed instructions on the design process, you can find comprehensive guides here.
For readers interested in the intricacies of 3 Wheel Cars, I want to share a particularly insightful aspect of our project: the dynamics of three-wheeled vehicles. Specifically, let’s address a fundamental question in 3 wheel car design: What are the advantages and disadvantages of placing two wheels at the front versus at the rear of a three-wheeled vehicle?
To answer this, we need to understand the two primary configurations of 3 wheel cars and compare their performance characteristics across various driving conditions. These configurations are known as:
Delta: Characterized by one wheel at the front and two wheels at the rear.
Tadpole (or Reverse Trike): Featuring two wheels at the front and a single wheel at the rear.
Dynamic Stability: Handling and Control in 3 Wheel Cars
Dynamic stability is a critical aspect of vehicle design. A dynamically stable vehicle reacts predictably and safely in diverse driving scenarios. When designing a 3 wheel car chassis, a key consideration is how the vehicle will behave when pushed to its limits, particularly during fast turns. In such situations, one of two outcomes is inevitable: either the tires will lose traction and slip, or the vehicle will roll over. Ideally, tire slippage is the preferred outcome as it is generally more controllable than a rollover.
Furthermore, in a controlled slip scenario, it’s crucial to design the vehicle so that we can predict whether the front or rear wheels will lose traction first. This is vital because if the rear wheels lose grip first, the vehicle risks spinning out of control, a condition known as oversteer. Oversteer can be challenging to manage, especially for less experienced drivers.
Conversely, if the front wheels lose traction first (understeer), the vehicle tends to push wide in a turn, but it remains more predictable and easier to recover control. Understeer is considered a safer dynamic response and is deliberately engineered into most standard passenger cars. The order in which wheels lose traction is primarily determined by weight distribution and weight transfer during cornering.
Delta 3 wheel cars face significant challenges in achieving optimal weight distribution and managing weight transfer to prevent undesirable handling characteristics. To promote understeer in a delta configuration, designers might consider a front-heavy weight bias. However, this approach increases the risk of the vehicle tipping over during sharp turns due to excessive weight on the front wheel. Conversely, shifting more weight to the rear to mitigate rollover risk can lead to oversteer, making the vehicle prone to spins.
Another dynamic stability concern is “nose diving” during hard braking. This occurs when the vehicle’s front end dips significantly under heavy deceleration, potentially causing the rear wheels to lift off the ground or induce a skid. While a delta design might initially seem advantageous here due to its natural rear-biased weight distribution, real-world braking scenarios are often more complex.
Imagine braking hard while turning in a delta 3 wheel car. The weight transfer to the front wheel can become so pronounced that it can cause the vehicle to flip over sideways. A dramatic example of this can be seen in the early seconds of Reliant Robin car test drive videos, highlighting the inherent stability challenges of the delta configuration.
Category Winner: Tadpole. The tadpole configuration generally offers superior dynamic stability due to its inherent resistance to rollover and more predictable handling characteristics in various driving conditions.
Braking Performance in 3 Wheel Cars
Braking efficiency is paramount in vehicle safety and performance. When a vehicle decelerates, weight shifts forward, placing the majority of the braking load on the front wheels. In fact, the front wheels typically handle approximately 60-70% of the total braking force in most vehicles. Delta 3 wheel cars are inherently disadvantaged in braking due to the weight distribution issues previously discussed and, crucially, because they have one less front tire to contribute to braking force compared to tadpole designs. This reduced front tire contact patch limits the potential braking power, especially in emergency situations.
Category Winner: Tadpole. The tadpole configuration, with its two front wheels, offers a clear advantage in braking performance, providing a larger contact patch and better weight distribution for effective stopping power.
Design Simplicity: Steering and Suspension in 3 Wheel Cars
When it comes to simplicity of design, delta 3 wheel cars present certain advantages, particularly in steering and front suspension systems. Steering design for delta configurations is generally more straightforward. There’s less need to compensate for lateral wheel slippage during turns, simplifying the steering linkage design. In contrast, tadpole designs often require more complex steering systems to approximate ‘Ackermann’ steering geometry. Ackermann steering is crucial in tadpole configurations to prevent tire scrubbing and ensure smooth cornering by allowing the inner front wheel to turn at a slightly tighter angle than the outer wheel.
Front suspension design is also typically simpler in delta 3 wheel cars. A common and effective approach is to utilize a ‘telescopic fork’ system, similar to those found on motorcycles. Positioning this fork with a caster angle helps ensure straight-line stability when the steering input is released. Rear suspension design in delta configurations offers flexibility, with various options available depending on the desired performance and complexity.
Conversely, tadpole 3 wheel cars present more complexity in front suspension design, requiring more intricate systems to manage the two front wheels effectively. However, the rear suspension design in tadpole configurations is often simpler. A ‘swing arm’ design is a common and straightforward choice for the single rear wheel. Consider the design of a child’s tricycle; delta configurations are the norm. It’s rare to see a tadpole tricycle due to the added complexity in steering design.
Category Winner: Delta. Delta configurations generally offer greater simplicity in steering and front suspension design, making them potentially easier and less costly to manufacture in some applications.
Aerodynamics and 3 Wheel Car Design
Aerodynamics plays a significant role in vehicle efficiency and performance, especially at higher speeds. The tadpole configuration lends itself more naturally to an aerodynamically efficient teardrop shape, which is known for minimizing drag. Achieving the optimal length-to-width ratio (approximately 0.255 for a teardrop shape) is more easily realized with the tadpole layout compared to the delta. The delta configuration, conversely, struggles to conform to this ideal aerodynamic shape. As illustrated in aerodynamic studies, the teardrop shape fits poorly with the delta layout, often requiring designers to encase a larger volume of empty space to achieve a streamlined profile. This increased volume translates to greater drag and reduced aerodynamic efficiency.
Category Winner: Tadpole. The tadpole configuration offers superior aerodynamic potential due to its natural compatibility with the efficient teardrop shape, leading to reduced drag and improved fuel efficiency or range.
Powertrain Considerations for 3 Wheel Cars
Powertrain selection and implementation present distinct challenges and advantages for both delta and tadpole 3 wheel car designs. Delta configurations face several powertrain-related disadvantages. Opting for front-wheel drive in a delta car exacerbates the dynamic stability issues already associated with their front-heavy weight bias. Placing the drive components at the front further concentrates weight at the front, potentially worsening rollover risks and negatively impacting handling. Furthermore, integrating steering and front-wheel drive in a delta configuration requires careful engineering to avoid conflicts and ensure smooth operation.
Choosing rear-wheel drive for a delta 3 wheel car introduces another layer of complexity. To power the rear wheels effectively, particularly in cornering, a differential gear is generally necessary. Without a differential, the single driven rear wheel can cause stability issues due to uneven force distribution during turns. This is similar to the challenges faced by early four-wheeled vehicles before the widespread adoption of differentials.
In contrast, tadpole 3 wheel cars with rear-wheel drive offer a more advantageous powertrain configuration. Rear-wheel drive in a tadpole design avoids the weight distribution and steering integration challenges of front-wheel drive deltas. Moreover, a differential is not strictly necessary for rear-wheel-drive tadpoles. The single rear driven wheel simplifies the powertrain and can maintain good traction, especially when approximately 30% of the vehicle’s weight is positioned over the drive wheel. This weight distribution helps ensure adequate grip without requiring complex differential systems.
Category Winner: Tadpole. The tadpole configuration, particularly with rear-wheel drive, generally offers a more efficient and less complex powertrain solution compared to delta designs.
Conclusion: Tadpole Configuration Dominates for Most 3 Wheel Cars
In conclusion, when considering the overall performance and practicality of 3 wheel cars for most applications, the tadpole configuration emerges as the clear winner. Its advantages in dynamic stability, braking, aerodynamics, and powertrain outweigh the delta’s slight edge in design simplicity. Tadpole 3 wheel cars offer a more balanced and predictable driving experience, enhanced safety features, and greater potential for aerodynamic efficiency, making them a superior choice for a wide range of vehicle types.
However, the delta configuration of 3 wheel cars still holds value for niche applications where simplicity and cost-effectiveness are paramount. For example, in low-speed, lightweight vehicles or specialized industrial applications, the delta’s simpler design may be preferred. Despite its limitations, the delta 3 wheel car remains a viable option for specific use cases.
PS: If you found this exploration of 3 wheel car dynamics insightful, don’t forget to check out the detailed Instructables guide here. It provides a 15-step walkthrough of the chassis building process, offering even more in-depth information on each stage.
For those wanting to delve deeper into solar car design or race car engineering, I’ve compiled a list of recommended books that were instrumental in my learning journey. These resources were invaluable in understanding the principles and practices discussed in this article.
Recommended Books:
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