Rimpact TMD Development Blog Part 5 - Hold Up, A Revelation!

In earlier blog posts, we detailed the development process for our Tuned Mass Damper (TMD), designed to improve rider comfort and performance by reducing vibrations in the front end of mountain bikes. We discussed the initial concept, the calculations, and the prototyping stage. We also shared the results of our placebo testing, which demonstrated the TMD's effectiveness in providing a smoother and faster ride.  

Initially, we planned to share raw data from our vibration and accelerometer testing in this post. However, during our analysis and concurrent development of another product, the Chain Damper, we made a significant realization that shifted our understanding of the TMD's functionality. We will still share the data, but in the next post, as this revelation has us excited to share our new found understanding and perspective on this product type and how it fits into the spectrum of performance enhancing components for the Mountain Bike. It is important you have this context so that the data makes more sense.

A Revelation: Not a true Tuned Mass Damper?

Our initial design for the TMD followed the conventional approach, targeting a specific frequency to optimize the damping effect. However, the dynamic nature of mountain biking, with its variable terrain, rider inputs, and suspension dynamics, creates a wide range of frequencies and amplitudes passing through the bike. We knew this was the case from the outset, but felt that by targeting the most dominant frequencies on a range of trails, we could make a TMD that was effective ‘most’ of the time. However further analysis of our Chain Damper led us to a better understanding of how our prototypes were so effective which in turn led us to question the effectiveness of a fixed-frequency TMD in such a dynamic environment.  

By design, the Chain Damper acts to ‘smooth’ out the effects of un-damped chain energy. In layman’s terms this means that the chain, which can weigh 260g on average, will flail around when riding and move around at as much as 8m/s with over 5 joules of energy. This is significant force, yet this chain energy is not controlled by a system in the same way our suspension controls the movement of our wheels. The Chain Damper captures this chain energy in it’s springs temporarily and returns it to the system when the chain has settled. This results in the rider not feeling the energy ‘spike’ which is described as drivetrain feedback, chain slap and even ‘pedal kickback’. When we were working on the Chain Damper we suddenly realised the overlap between the Chain Damper’s action and the TMD’s action. They both did the same thing, capturing input energy temporarily and releasing it when the moment has passed.

Our TMD testing showed that even when targeting a single frequency, the TMD still provided noticeable benefits, confirmed by both accelerometer data, rider feedback and timed testing. This led us to two important discoveries:  

1. Energy Smoothing: The TMD's mass, suspended between two springs, can be displaced freely. When an impact occurs, the forces that pass through the fork and crown, into the headtube displace the TMD’s mass. The mass's momentum is temporarily stored in the springs, smoothing out the energy transfer through the headtube and reducing the sharp spikes in compression that riders feel at the bar. This results in increased front-end grip, chassis stability, and reduced rider fatigue as the rider experiences a lower total amplitude in force, followed by a more consistent feeling in the time after the moment of impact, until the bike has settled.   

2. Mechanical Advantage: We observed that adding a static mass to the head tube provided some benefit, but the active TMD offered a significant improvement over this static mass. We concluded that the TMD acts as a "mass with mechanical advantage," effectively providing the benefits of a heavier weight without the actual weight penalty. Riders who add weights to their frame could achieve the same performance change with significantly less weight added as the TMD is acting above and beyond it’s weight on paper in terms of effectiveness.

These findings revealed that our TMD, while not a tuned mass damper in the strictest sense, functions more as a Mass Damper, Vibration Damper, or even a Harmonic Damper. Call it what you will, it’s effective. As we have been sharing the development of the project for a couple of years under the name 'TMD' we elected to stick with it.

The TMD: Available Now

Despite the shift in our understanding of its mechanics, the TMD's effectiveness in making the bike faster and smoother remains unchanged, as proven by our extensive testing and data analysis.  

The TMD is now available for purchase and is being assembled in-house. It comes with a premium protective case and two sets of spare springs with different spring rates, allowing riders to fine-tune the TMD to their specific needs and trail conditions.  

We are excited to offer this innovative product to the mountain biking community, providing riders with a smoother, more controlled, and ultimately faster ride.