Frame comfort or compliance is one of the most talked-about yet least quantified aspects of mountain bike design. Riders often claim that one hardtail feels smoother or more forgiving than another, but what’s happening beneath the surface?

To investigate, Nolan from The Bike Sauce set out to compare two steel hardtail frames using real-world trail testing and a scientific approach to vibration measurement. For a deeper dive into his methods and analysis, be sure to watch his full video.

His baseline was the Kona Honzo ST, a burly, overbuilt frame known for its stiffness. In contrast, the Neuhaus Metalworks Hummingbird, a boutique frame designed with refined tubing and geometry, promised a more compliant ride. By controlling all other components (ie. wheels, tires, fork, cockpit, drivetrain, and tire pressure), Nolan isolated the frame as the only variable.

With a compact accelerometer mounted in strategic locations, he gathered data over repeatable trail segments to reveal how each frame filtered vibration. The results were surprising and challenged a core belief about what makes a hardtail comfortable.

Frame Comfort While Riding Seated

I’ve previously outlined why steel frames cannot be more comfortable than aluminium when it comes to vertical compliance.

In short, when you consider all the components that contribute to vertical movement (tires, saddle, seatpost, and even your body), the frame material itself plays a minimal role. The frame’s vertical compliance is just a small part of the total system’s spring rate and becomes almost negligible when viewed in the context of all the “springs” working together.

Krysztof has also explored this topic, using accelerometers to compare how titanium and carbon frames damp vibration. By controlling variables and keeping most components consistent, his tests showed both frame materials offered similar levels of damping on different gravel test courses. The takeaway? Component choice matters more than frame material when it comes to vibration reduction.

However, these findings mostly apply to seated riding. So what happens when you’re out of the saddle, when your body is no longer part of the suspension system?

Frame Comfort While Standing

Nolan had been riding the Kona Honzo ST hardtail, and he found it to be an exceptionally fun and capable bike, but it tends to ride on the ‘harsher’ side. The frame appears overbuilt, with extra gussets and reinforcement to prevent failure, which also makes the frame extremely stiff.

Enter the Neuhaus Metalworks Hummingbird, a boutique steel hardtail frame. Nolan tested a Medium Plus frame size, comparable in size to the Kona.

The goal of this project was to explore whether frame comfort, a commonly used but rarely measured concept, can be quantified with actual data.

It’s worth mentioning that I’ve previously explored the relationship between frame stiffness and ride quality in depth, including how steering and pedalling stiffness affect performance. In that article, you’ll learn how to identify the ideal level of frame stiffness for your specific riding style.

Vibration Test

To ensure a controlled and fair comparison, Nolan kept the components identical between the two frames. The wheels, tires, cockpit, fork, drivetrain, and dropper post were all the same, and both bikes ran matching tire pressures at 20 psi. This meant that any differences in ride quality or vibration could be confidently attributed to the frame alone.

To measure vibration, Nolan used a Yost Labs 3-Space Mini Data Logger. This compact scientific device includes a 9-degree-of-freedom inertial sensor and internal filtering. It’s sensitive enough to detect frame-level vibrations, yet small and light enough to avoid interfering with the ride itself.

To isolate different aspects of frame compliance, the data logger was mounted in two specific locations: first at the rear dropout, and then at the base of the seat tube near the bottom bracket. Each frame was tested with both sensor placements, and two runs were completed per configuration, resulting in a total of eight data sets.

Both bikes were ridden on the same trail section; a short but representative 400 metre long descent with a 7% average grade. The terrain featured a consistent mix of ruts, loose-over-hard fire road, and smoother singletrack, offering a balanced variety of trail inputs.

This repeatable test environment gave Nolan a solid foundation for comparing how each frame filtered out vibrations under real-world conditions.

Rear Dropout (Control)

With the sensor at the rear brake mount, vibrations travel through the wheel but not through the frame itself. This acts as a control.

In all four runs (two per frame), the PSD plots were nearly identical. This confirmed that trail conditions, tire pressure, and wheel setup were consistent between tests.

In other words, this was a valid apples-to-apples comparison.

Time vs Frequency Domain

Before diving into results, it’s worth understanding a key concept: frequency-domain analysis.

Raw accelerometer data, when viewed in the time domain, appears chaotic. But applying a Fourier transform reveals where vibrational energy is concentrated. This is visualised in a Power Spectral Density (PSD) plot, which displays the intensity of vibration across frequencies.

Trail vibrations typically occur in the 10 to 30 Hz range, which was the primary area of interest in this study.

Bottom Bracket (Vertical Compliance)

When looking at vertical acceleration at the bottom bracket, the results were unexpected: both frames produced nearly identical data.

While the bottom bracket signal was damped compared to the rear axle (as expected), there was no measurable difference in vertical compliance between the Kona and the Neuhaus at the bottom bracket.

Despite how different the Neuhaus feels on the trail, the measurements suggest that double-triangle hardtail frames simply don’t flex vertically in a meaningful way. The structural layout of the frame, particularly the chainstay/seatstay connection, inherently limits vertical compliance.

Lateral Compliance

To dig deeper, Nolan analysed lateral acceleration data from the same test runs.

Here, a clear difference emerged. In the 21 to 26 Hz range, the typical bandwidth for off-road trail vibrations, the Neuhaus frame consistently showed 2 to 7 dB less lateral vibration compared to the Kona. On a logarithmic scale, this is significant: a 3 dB change represents a doubling (or halving) of energy.

This strongly suggests that the Neuhaus feels more compliant not because of vertical flex, but due to lateral compliance – side-to-side flex in the frame structure that helps dissipate trail impact.

Nolan also validated this mechanically: by leaning the bike and pressing down at the bottom bracket, the Neuhaus visibly flexed more than the Kona.

Interestingly, the Kona showed greater vibration damping at the bottom bracket in the higher frequency range. This isn’t unusual; materials or structures that absorb vibration well at certain frequencies often perform worse at others.

One possible explanation is the Kona’s increased frame weight, which can alter how vibrations are absorbed and dissipated throughout the system.

Caveats & Considerations

This was not a lab-controlled test. The data for each bike was collected three weeks apart. However, the identical rear axle data confirms that all test conditions were effectively controlled.

Further studies, ideally with more frame types and a range of rider weights, would enhance these findings. But even this limited sample points toward a compelling conclusion: lateral compliance, not vertical compliance, is what contributes most to perceived comfort in hardtail frames.

Summary

When tested with an accelerometer, the Neuhaus Hummingbird is more compliant than the Kona Honzo ST – but not in the way most riders (or marketers) might expect.

The idea that hardtail frames flex vertically under load just doesn’t hold up when tested. Instead, comfort appears to result from engineered lateral flex (side to side), achieved through tubing selection and frame geometry.

Nolan’s testing shows that while the bike industry often markets “vertical compliance,” the real story likely lies in how a frame manages lateral forces. That’s what mountain bikers are likely feeling on the trail.

Adblock test (Why?)