The design and optimization of two-wheel vehicle suspension provides an exciting design challenge due to the multitude of potential layouts and interrelated variables to consider. Balancing these design factors to achieve the desired comfort and road holding performance while also ensuring the vehicle achieves the desired trim state under the various operating conditions, termed chassis control for the purposes of this paper, requires a deep level of technical understanding to execute successfully. Consequently, a specific area of two-wheel vehicle suspension development that has received little attention is defining the nominal vehicle trim state in terms of target sag and the associated proportion of vertical wheel travel to be used in compression versus that available for extension. For closed course racing vehicles, both on-road and off-road, the suspension travel and target sag are determined experimentally based on simulation or testing to obtain the primary objective of minimum lap time. However, for commercial on-road vehicles, suspension travel and target sag are often constrained by numerous vehicle design requirements such as aesthetics, seat height, and packaging limitations. These design constraints require production-intent suspension travel and target sag to be selected early in the product development cycle. Until now, limited literature has been published regarding nominal target sag and how best to proportion suspension travel between compression and extension, though a general guideline proposes ~33% target sag as the starting point. The intention of this paper is to provide a deeper technical understanding of suspension performance trade-offs between available suspension travel and target sag using physical vehicle testing and multibody simulations.

A key component in the mountain bike industry is the telescopic front suspension, which offers the advantage of improved performance when traversing obstacles, rough terrain, and high impact landings. Despite the popularity of telescopic forks in the market and their incorporation into vehicle level simulation, the details and modelling assumptions around this subsystem have received limited attention in the literature... This paper presents a system identification and modeling approach that promises a deeper understanding of the dynamic behavior of mountain bikes with telescopic front suspensions. The mountain bike front suspension subsystem is modelled initially using the classic quarter car model with the suspension and tire both included as second-order systems, each with spring and damper elements in a Kelvin-Voigt arrangement stacked in series. The paper then incrementally increases the complexity of the quarter car model by performing a parameterization study of the fork and tire. The model results are compared to data from an impact sled test of a telescopic mountain bike front suspension subsystem. The correlation between the quarter car model response and the test data varies with the complexity and inclusion of parameters suggesting that the inclusion of key parameters in the model is an important aspect of modeling the mountain bike front suspension system.

Quantifying the suspension performance implications for suspension displacement and target sag and their impact on comfort, road holding and chassis control on a cruiser motorcycle

Mountain bikes are essentially ruggedized versions of a standard bicycle with geometry and features suited to off-road cycling. Their intended use case has them encountering jumps, bumps, drops, and impact. As such, their designs have evolved to include front and often rear suspension systems composed of springs and dampers in sometimes elaborate kinematic arrangements. Despite extensive design resources spent optimizing and tuning mountain bike suspension systems, very little has been published regarding the in-plane behavior of their tires or bicycle tires in general. In this work, a drop test bench is utilized to measure the dynamic radial stiffness and damping of numerous mountain bike tires including four common sizes spanning 29er, plus-sized, and fat tire variants, as well as various constructions ranging from trail, through enduro, and downhill. The tire is treated as a classical, lumped Kelvin-Voigt model with a parallel arrangement of a spring and damper. Identification of the system parameters is accomplished by treating the tire as a bouncing ball and using the coefficient of restitution from pre and post impact velocities to determine the dynamic stiffness and damping. The advantages of this approach in comparison to a classical logarithmic-decrement approach are discussed. Results suggest that due to its viscoelastic nature mountain bike tire dynamic radial stiffness is appreciably higher than its quasi-static value. Furthermore, although its damping is relatively low (spanning 2 to 5% of critical), it can affect subjective “trail feel” and can be perceptibly influenced by tire selection, size, construction, and inflation pressure.

A key component in the mountain bike industry is the telescopic front suspension, which offers the advantage of improved performance when traversing obstacles and rough terrain and during high impact landings. Over the last three decades these suspensions have become more widely adopted and more complex in design. Despite their popularity, there has been limited reported literature focused on the behavior of the telescopic front suspension as a dynamic subsystem in models commonly used in both the motorcycle and automotive industries, e.g., half moto and quarter car models. This paper presents a system identification and modeling approach that promises a deeper understanding of the dynamic behavior of vehicles with telescopic front suspensions.