Tag: aluminium

Is Frame Comfort a Myth? A Scientific Look at Hardtail Frame Compliance

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

This test compares the vertical compliance of two different hardtails. Image: The Bike Sauce

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)

The accelerometer was attached to the frame’s brake mount. Image: The Bike Sauce

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

Raw vibration data on its own doesn’t provide much insight when it comes to identifying differences in frame comfort. Image: The Bike Sauce

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)

These Power Spectral Density plots show that both frames damp a similar amount of vibration at most frequencies. Image: The Bike Sauce

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

In the 21 to 26 Hz frequency range, the Neuhaus frame showed an ability to damp more lateral accelerations, perhaps making the frame feel more compliant. Image: The Bike Sauce

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.

Between 80 and 120 Hz, the Kona hardtail frame damped more lateral vibration at the bottom bracket. Image: The Bike Sauce

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.

July 27, 2025
Why Frame Stiffness is Critical In Understanding Ride Feel
Frame stiffness has a big impact on how your bike feels beneath you.

Riders often describe overly stiff bikes as feeling ‘dead’, overly flexible bikes as ‘noodly’, and bikes with just the right amount of give as ‘lively’.

After riding everything from ultra-stiff to super-flexy frames, I’m convinced there’s a Goldilocks zone – a sweet spot where subtle frame flex adds to that smooth, responsive ride we all crave.

In this deep dive, we’ll explore what frame stiffness really means, when it matters, how it relates to different materials, whether flex affects speed, and how you can dial in the ideal stiffness for your own bikes.

What Is Frame Stiffness?

A bicycle frame getting stiffness tested at Zedler-Institut. Image: Matt Phillips

We can assess frame stiffness in a few key areas.

Steering stiffness refers to how much the frame twists at the head tube. You’ll feel this most when pushing hard on the pedals while pulling on the bars. A frame with high steering stiffness feels sharp and responsive to your inputs. That said, overall front-end stiffness also depends on your fork, front wheel, and handlebars.

Pedalling stiffness is the amount of flex around the bottom bracket area when you apply power through the pedals. More stiffness here generally translates to better power transfer.

Then there’s vertical stiffness, which relates to how much the frame deflects up and down – a factor I’ve already explored earlier in this article when discussing comfort.

To put it into perspective: the stiffest mass-produced frames are about twice as rigid as the most flexible ones.

Describing Stiffness

The Ritchey Outback has recently been praised for its flex virtues by Morgan Taylor over at The Radavist. Image: Ritchey Logic

I like to think of frame stiffness as a spectrum with two extremes.

At one end of the spectrum, a stiff or responsive frame offers a snappy, direct ride. It feels sharp under acceleration and delivers that unmistakable “up-and-go” sensation. But it can also feel harsh or even dead, transmitting more chatter through the bike when going over bumps. There’s also evidence that excessive stiffness can compromise cornering traction and braking performance – so stiffer isn’t always better.

On the other end, a flexy or forgiving frame mutes feedback from the road or trail, offering a smoother, more compliant ride. However, it can feel slower to respond under power and may flex more with your movements. This can be pleasant – again, up to a point.

What Factors Affect Frame Stiffness?

My friend (and frame builder) Ewen Gellie made himself an intentionally flexy frame using thin, small-diameter steel tubes.

What feels stiff to one rider might feel flexy to another because several factors influence how much a bike moves beneath you.

First, there are rider factors: your power output, body weight, and riding style all play a role. A rider sprinting out of the saddle will flex a frame more than someone casually spinning along.

Next, the bike itself: different riding disciplines demand different levels of stiffness. A burly hardtail built for aggressive trails needs to be stiffer than a featherweight XC race bike, simply due to the greater forces involved.

And finally, luggage: frames designed for load carrying need extra stiffness. Without it, a fully loaded touring bike can feel vague or “noodly” when ridden.

Frame Stiffness For Touring and Bikepacking

My KOGA WorldTraveller-S uses super-stiff aluminium tubes that allow me to carry a particularly heavy load.

Touring and bikepacking bikes are designed to carry luggage at both ends, and the frame acts as the structural bridge resisting the twisting forces between the front and rear loads. To maintain stable handling and predictable ride feel under heavy load, these frames are built significantly stiffer than typical bikes.

The trade-off? A frame designed to resist torsional flex under luggage often feels overly rigid when ridden unloaded. That “lively” ride sensation – created by just a touch of frame flex – is generally only achieved once the bike is fully packed.

It’s also worth noting that belt-drive touring bikes require exceptionally high pedalling stiffness. Because belts have very little tolerance for lateral movement, these bikes are built with especially rigid rear frame triangles to prevent belt slippage under load.

You can read a more comprehensive article about frame stiffness for touring bikes HERE.

Finding The Goldilocks Zone

Paul and I went bikepacking in Vietnam on aluminium Giant Contend SL bikes that offered excellent ride characteristics.

Let’s run through a few rider scenarios to better understand when a rider might benefit from that ideal, subtle amount of frame flex:

Heavier rider with higher power output
Greater frame stiffness is needed to counteract the larger forces from hard pedalling and aggressive cornering.

Lighter rider with lower power output
On the other end of the scale, a less stiff frame allows lighter riders to achieve a similar ride feel without the bike feeling overly rigid.

Cruising casually
If your riding style is relaxed and low-intensity, a more compliant frame will feel more responsive to lighter inputs and offer a smoother, more engaging ride.

Aggressive riding style
If you’re out of the saddle sprinting, hammering corners, and generally pushing the limits, a stiffer frame will provide the control and responsiveness you need.

Flat bars or wide drop bars
Wider handlebars give you more leverage over the front end, making it easier to twist the frame torsionally. As a result, bikes designed around wide bars typically require higher steering stiffness to maintain balanced handling.

Are Stiffer Bikes Faster?

The Cannondale System Six has a particularly high pedalling stiffness.

It’s commonly assumed that a stiffer frame is faster because less energy is lost to flex. But unless you’re sprinting for the finish line, a frame with half the bottom bracket stiffness is unlikely to impact your speed in a meaningful way—simply because the amount of deflection is so small.

In reality, aerodynamics and tyre rolling resistance have a far greater effect on performance.

Some have suggested, through hypothesis and field testing, that much of the energy lost to frame flex is returned to the drivetrain. But I find that unlikely. Here’s why: frame deflection builds gradually during the downstroke (from about 1 to 3 o’clock) and releases slowly afterwards – not in a single, clean rebound as some tests assume.

Out on real roads, where dozens of variables are simultaneously storing and releasing energy, it’s improbable that frame flex accounts for most of it. More realistically, some energy might return to the drivetrain, but plenty is lost elsewhere – through your wheels, tyres, crankset, pedals, shoes, and even your body.

What’s The Stiffest Frame Material?

A steel gravel bike by Fairlight Cycles.

The data we’re looking at today comes from the legends at Tour Magazin in Germany.

They’ve developed a standardised static deflection test and have measured over 1,500 road and gravel bikes (all around the same size), giving us an excellent basis for comparing frame stiffness by material. I’ve kept a detailed record of almost every bike ever tested, which allows us to examine stiffness trends across different frame materials.

The test measures how much force in newtons (N) is needed to deflect the head tube or bottom bracket by one millimetre, recorded as N/mm. While static tests don’t fully capture how a frame behaves under a moving rider, the values do broadly align with how bikes are designed for different riding purposes.

For example, Tour de France-style aero race bikes typically show minimal frame deflection, while purpose-built touring bikes often test even stiffer.

Steering Stiffness – Head Tube Deflection Test (Average)
- Aluminium – 105 N/mm
- Carbon – 97 N/mm
- Steel – 88 N/mm
- Titanium – 86 N/mm
This shows that steel and titanium frames generally have lower steering stiffness. Aluminium frames are about 20% stiffer than titanium and steel, while carbon frames are about 10% stiffer.

Pedalling Stiffness – Bottom Bracket Deflection Test (Average)
- Aluminium – 63 N/mm
- Carbon – 62 N/mm
- Steel – 53 N/mm
- Titanium – 53 N/mm
Carbon and aluminium again show higher stiffness, requiring around 20% more force to deflect the bottom bracket by one millimetre compared to steel or titanium.

These lower stiffness values for steel and titanium could help explain their reputation for a distinct ride feel. But that’s not the whole picture – let’s explore the full range of stiffness values by material.

Steering Stiffness – Full Range of Values
- Aluminium – 69 to 145 N/mm
- Carbon – 63 to 131 N/mm
- Steel – 69 to 115 N/mm
- Titanium – 75 to 106 N/mm
Pedalling Stiffness – Full Range of Values
- Aluminium – 45 to 87 N/mm
- Carbon – 39 to 84 N/mm
- Steel – 42 to 77 N/mm
- Titanium – 44 to 68 N/mm
Looking at these deflection value ranges, it’s clear that frame designers can build either a stiff and responsive or soft and compliant bike from any frame material. The material may influence average trends, but it’s the engineering and design that ultimately define how a bike feels.

Small Bike Sizes

An extra-small Marin Four Corners touring bike.

So, how do small frames compare to large ones? Fortunately, Tour Magazin has data on that too.

Steering Stiffness – Head Tube Deflection (Average)
- Aluminium (50cm) – 101 N/mm
- Aluminium (56cm) – 105 N/mm
- Carbon (50cm) – 95 N/mm
- Carbon (56cm) – 97 N/mm
Pedalling Stiffness – Bottom Bracket Deflection (Average)
- Aluminium (50cm) – 66 N/mm
- Aluminium (56cm) – 63 N/mm
- Carbon (50cm) – 62 N/mm
- Carbon (56cm) – 62 N/mm
The good news? Smaller frames aren’t wildly stiffer than larger ones, even though smaller triangles are naturally more resistant to deflection. The data suggests that engineers are doing a decent job of tuning ride quality across sizes.

That said, there’s still room for improvement. Smaller riders tend to be lighter and produce less power, meaning they’d likely benefit from more frame flex to achieve the same ride feel as a heavier, more powerful rider on a larger frame.

Here’s the challenge: bike frames need to be strong enough for the most powerful riders in any given size. Take Caleb Ewan, for example—an elite sprinter riding an XS frame. His power output is significantly higher than that of an average rider his size. Designing for him means overbuilding for many.

The Custom Bike Advantage

The Bastion bikes are constructed with titanium 3D printed lugs and filament-wound carbon tubes.

While many people choose custom bikes primarily to perfect their fit, an even better reason might be to fine-tune the ride feel.

Since most bikes are designed to accommodate the heaviest and most powerful riders, those who are lighter and produce less power stand to gain the most from a frame tailored to their needs.

Shoutout to Bastion Cycles for letting customers specify their desired frame stiffness – both torsional and vertical – during the ordering process. They can offer this because they 3D-print their own titanium lugs and build their own filament-wound carbon tubes, which is seriously impressive.

What’s more, Bastion’s order form includes stiffness data from several popular bikes, helping riders get a clear idea of how their custom frame will feel under them before it’s even built.

Aluminium and Carbon Bikes With Similar Stiffness Values To Steel/Ti

The Trek Emonda ALR5 aluminium road bike has a similar bottom bracket deflection to a steel or titanium bike.

We now know that steel and titanium frames tend to be less stiff on average than carbon and aluminium frames.

However, since there’s a wide range of deflection values across all materials, let’s say you want to match the flex characteristics of a typical titanium or steel bike – or maybe you’re lighter and prefer a bit more compliance.

Bikes with Lower Stiffness (More Compliance)

Aluminium: Trek Emonda ALR5 (road), Giant Contend (endurance), Giant Revolt (gravel)
Carbon: Trek Emonda (road), Trek Madone (road), Felt AR (road), Trek Domane (endurance), Giant Defy (endurance), Look (all models)

Most Trek and Look road bikes are designed with more torsional flex built in. Specialized’s latest Tarmac SL7 and Aethos road bikes are trending toward a softer frame feel as well. Giant’s endurance and gravel models also rank among the more forgiving options.

Bikes with Higher Stiffness (Less Compliance)

Cannondale System Six (road), Specialized Allez Sprint (road), Specialized Venge (road), Cannondale CAAD Optimo (road), Specialized Sequoia (gravel), Merida Silex Carbon (gravel), Felt Broam (gravel), Cube (all models)

Aero race bikes and budget aluminium frames tend to be the stiffest overall. Data also shows that Cube builds its bikes with particularly high stiffness.

For bikepacking and touring, the Specialized Sequoia, Merida Silex, and Felt Broam perform best when loaded with luggage, thanks to their robust frames.

DIY Frame Stiffness Tests

Cycling through the Mars-like landscapes of Bolivia.

A great way to gauge the stiffness of different bike frames is by comparing them side-by-side.

Here are two simple static tests I do before taking a new bike for a ride:
1. Front End Wiggle Test: Hold the seat firmly between your legs and push and pull on the handlebars. You’ll be able to see and feel how much the frame twists.
2. Bottom Bracket Deflection Test: With both brakes engaged, apply pressure to the forward pedal and observe the frame flexing sideways.
Keep in mind these static tests only offer a snapshot of frame stiffness – they don’t fully capture how the bike will feel on the road. So, be sure to take the bike out for a test ride as well.

I recommend jotting down your impressions of stiffness from both the static tests and the actual ride. Trying multiple bikes this way will help you identify the ride characteristics you prefer.

And if you’re test riding a touring or bikepacking bike, try to do it with luggage loaded to get a more realistic feel.

Other Ways To Determine Frame Stiffness

The Curve GMX+ uses large, oversized titanium tubes to maximise the frame stiffness.

If you don’t have access to test bikes, it’s much trickier to gauge how a bike will feel beneath you.

A good starting point is the bike’s intended use: racing road bikes are generally stiffer than endurance road bikes, and touring bikes tend to be stiffer than bikepacking bikes.

With steel and titanium frames, predicting ride characteristics is easier because the largest-diameter tubes typically determine stiffness. That’s due to the fact that doubling a tube’s diameter and wall thickness can increase stiffness by up to 16 times.

Carbon and aluminium frames are less predictable since their stiffness depends on many design variables. In those cases, it’s worth reading reviews from trusted journalists – ideally ones who share a similar height and weight as you – to get a better sense of how the bike might ride.

Summary

Finding the ideal “Goldilocks zone” for frame stiffness involves considering your body type, riding style, bike setup, and how you plan to use the bike.

The data shows that bikes made from any frame material can be designed to feel either forgiving or responsive. While titanium and steel frames tend to have lower average stiffness – potentially making them a better fit for lighter riders – this isn’t always the case. Some of the stiffest steel and titanium frames exceed the stiffness of many aluminium or carbon models.

Ultimately, I recommend trying out a variety of bikes to discover the ride qualities that suit you best, then making your choice from there.

You can read about frame comfort HERE and different frame materials HERE
February 26, 2021
Why It’s Impossible For Steel Frames To Be More Comfortable Than Aluminium
We’ve all heard the claims: aluminium frames are “harsh” and will rattle your bones, while steel and titanium frames supposedly glide like magic carpets.

But is that really true, or is it just a placebo?

The more I’ve explored the science behind bicycle comfort, the clearer it’s become: frame material plays a surprisingly minor role.

In fact, my own experience flies in the face of popular belief – the most uncomfortable bike I’ve ever ridden (an ’80s steel road bike) was made from the very material that’s supposed to offer a smooth ride. But as you’ll discover throughout this article, the discomfort wasn’t caused by the steel frame itself.

Before we go any further, let me be clear – I’m not denying that different frame materials can influence how a bike feels to ride. For example, a frame with small amounts of horizontal flex can feel more ‘lively’ under power.

However, this article is focused purely on comfort – specifically, vertical compliance – not on subjective ride feel or handling traits.

Diamond Frames: Built to Resist, Not Flex

Riding the rough roads of southern Bolivia on my aluminium touring bike.

When comparing the comfort of different bikes, there’s one key metric we can actually measure: vertical compliance. This refers to how much your body moves up and down in response to bumps, vibrations, and rough surfaces. A bike with higher vertical compliance can better absorb road imperfections, making for a smoother ride.

So, how much vertical compliance do frames really offer? Surprisingly little. Studies show that there’s virtually no measurable difference in vertical compliance between most frame materials or designs.

The reason is that a diamond frame functions like a truss – a design purposely built to resist vertical forces. Simply put, your frame isn’t made to flex vertically.

The Astonishing Difference Between Frame and Seatpost Flex

The KOGA Test Centre in the Netherlands measures the strength and performance of their frames.

There are very few tests that isolate and measure the vertical deflection – or “comfort” – of a bicycle frame alone. That’s because most experiments include a seatpost inserted into the frame, which makes sense: we don’t mount our saddles directly to the top tube.

Back in the 1990s, Bob Bundy tested four steel road frames from the ’80s. To flex the rear triangle just one millimetre vertically, it took between 7,158 and 14,316 newtons of force.

To put that in perspective, a high-end carbon flex seatpost can achieve the same deflection with just 69 newtons of force.

That’s 100 to 200 times less force, clearly showing where the real compliance comes from.

Modern Testing Confirms Seatposts Dominate Vertical Compliance

The Canyon S13 VCLS seatpost is in for testing at the Microbac Lab. Image: BikeRadar

Today, the most reliable frame deflection testing comes from Tour Magazin in Germany. They’ve measured the vertical compliance of over 1,500 road bikes! But it’s important to note that their tests include both the frame and seatpost together.

What’s fascinating is how closely Tour Magazin’s combined frame+seatpost results align with seatpost-only tests conducted by Microbac Laboratories. This strongly suggests that the seatpost is doing almost all the work when it comes to vertical deflection. In fact, based on the data, it wouldn’t be surprising if the seatpost contributes around 99% of the compliance, leaving the frame with less than 1%.

Here are three clear examples:
- Ergon CF3 Seatpost
  • 69 N/mm with the Canyon Endurace CF SLX frame (Tour Magazin)
  • 67 N/mm measured alone (Microbac Labs)
- Canyon S13 VCLS Seatpost
  • 84 N/mm with the Canyon Ultimate CF SLX frame (Tour Magazin)
  • 77 N/mm measured alone (Microbac Labs)
- Syntace P6 Hi-Flex Seatpost
  • 123 N/mm with the Müsing Aviator frame (Tour Magazin)
  • 114 N/mm measured alone (Microbac Labs)
The slightly lower values from Microbac likely reflect a greater exposed seatpost length during testing. More exposed post equals a longer lever arm, which requires less force to flex. In contrast, Tour Magazin used around 230 mm of exposed post, 20–30 mm shorter, which naturally results in higher stiffness values.

You can read more about seatpost comfort HERE.

Why Tyres Are Key Players in Vertical Compliance

Deformation graphs on a flat surface from the study ‘Deformation of an inflated bicycle tire when loaded‘ (University of Girona). Interestingly, these tyre sidewalls were ground down so they had a consistent sidewall thickness to help create mathematical models to predict deformation.

Tyre deformation is a complex topic, with many variables influencing how much a tyre can compress. Factors like tyre width, casing materials, puncture protection layers, sidewall thickness (which often varies across the tyre), tread pattern, rim width, and whether the tyre is tubed or tubeless all play a role.

The type of surface the tyre interacts with also matters – its hardness, texture, and bump shape all affect how the tyre responds.

Unlike a seatpost, tyre deformation isn’t linear. Each additional millimetre of compression requires more force than the last, making the relationship between force and deflection non-uniform.

But let’s not get too deep into the weeds. The key takeaway is this: it takes very little force to deform a tyre by one millimetre, making tyres one of the most significant contributors to ride comfort.

The table above, sourced from the Silca Blog, illustrates how much force is needed to deform a test tyre across different surface shapes. The left column shows deformation on a perfectly flat surface, the middle on a rounded ‘cobblestone’ (8cm radius), and the right on a much sharper ‘pavement lip’ (8mm radius).

What’s clear from the data is that tyres require less force to deform over sharper surfaces. This makes sense; sharper bumps concentrate the load over a smaller area, leading to more compression with less effort.

Interestingly, on flatter and moderately rounded surfaces (like cobblestones), a high-quality flex seatpost can actually deform more than a 23–28mm tyre! But once you get into wider tyre widths, the tyre quickly becomes the dominant source of vertical compliance.

For context, here are some additional tyre deformation figures on flat surfaces, compiled by Damon Rinard:
- 100 N/mm – 25mm tyre at 87 psi (6 bar)
- 150 N/mm – 23mm tyre at 116 psi (8 bar)
These numbers reinforce just how firm narrower, high-pressure tyres are—and how much comfort can be gained by switching to wider, lower-pressure setups.

Do Rear Wheels Contribute to Ride Comfort?

Graph showing rim deformation. Image: Killa’s Garage

But what about the rear wheel? It plays a central role in the ride experience, so does it contribute much to vertical compliance?

As it turns out, not really.

Testing from Killa’s Garage shows that bicycle wheels offer very little vertical deflection. Under a 70 lb load, the wheel deflects just 0.002 inches. At 120 lb, that increases to 0.005 inches, and at 170 lb, 0.0075 inches. Converting these into metric and calculating stiffness, we get a range of approximately 891 to 1378 N/mm.

To put that into perspective, a flex carbon seatpost deforms 13 to 20 times more under the same force. In other words, your rear wheel is far stiffer than your seatpost—and contributes very little to ride comfort.

Springs in Series: Explaining Overall Ride Compliance

Almost every component on a bicycle offers some amount of vertical deflection – however microscopic – meaning they all act like springs to some degree. From the ground up, the system consists of a series of springs in this order: tyre, rim, nipples, spokes, hub shell, bearings, axle, frame, seatpost, and saddle.

Using the formula for calculating rate of springs in series, we can better understand how these parts work together to deliver overall vertical compliance.

The key takeaway? When multiple springs are combined in series, the total spring rate is lower than the rate of the softest individual spring. That softest spring is usually the tyre, but if you’re running narrow, high-pressure tyres, it could be the seatpost instead.

This means that simply adding a wide, low-pressure tyre or a quality carbon flex seatpost can significantly improve ride comfort – regardless of frame material. Even the notoriously stiff steel frame tested by Bob Bundy in the ’90s (at 14,000 N/mm) would feel comfortable with a compliant seatpost in the mix.

In the table above, I’ve calculated the combined spring rates* for various flex seatpost and tyre combinations.

The data clearly shows how the softest spring dominates the overall system. Even with high-pressure road tyres, the presence of a flex seatpost significantly lowers the force required to move your body vertically by just one millimetre.

As you can see, flex seatposts have a smaller impact on bikes equipped with wide tyres. Conversely, when using narrow tyres, flex carbon seatposts provide a noticeably greater comfort benefit.

Understanding springs in series also explains why components that require high force to flex vertically (ie. the frame) have minimal effect on overall comfort – they’re essentially “overridden” by the softest spring in the system.

*These spring rates apply specifically to the initial millimetre of deflection. As tyres deform further, their spring rates increase to varying degrees depending on their construction and pressure.

Do Frame Materials Affect Vibration Damping?

If you tap a metal frame, it tends to “ring” because metals have relatively low damping. Tap a carbon frame, on the other hand, and you get a dull “thump” — that’s carbon fibre’s natural ability to absorb vibrations better than metals.

This sounds promising, but remember the frame is just one part of a larger system. Softer components – like your tyres, saddle padding, and even the contents of your luggage – offer far more effective vibration damping than the frame itself.

Factors like wider tyres, lower tyre pressures, thinner tyre casings, thicker saddle padding, and softer luggage all play a much bigger role in making your ride feel smoother.

In my experience, once tyres get wider than around 40mm, the damping difference between carbon and metal frames becomes nearly undetectable.

However, you might still notice a difference between carbon and metal frames on bikes running especially high-pressure tyres. And when you add luggage to any bike? Suddenly, every bike feels surprisingly smooth to ride.

Summary

If you absolutely swear that your steel or titanium frame feels more comfortable, the data suggests it’s probably a placebo effect – but honestly, that’s not a bad thing if it works for you.

When you look at all the components involved in vertical movement, the frame material – whether steel, aluminium, titanium, or carbon – has virtually no impact on ride comfort. Frame compliance makes up only a tiny fraction of the overall spring rate, and it becomes practically irrelevant once you consider the combined effect of all the springs in series.

The real game-changers for comfort are your tyres, which deform anywhere from 10 to 250 N/mm depending on pressure and width, and your seatpost, which can flex as easily as 69 N/mm. A flex carbon seatpost will compress up to 15 mm vertically before your frame even shifts by a fraction of a millimetre.

Oh, and about the most uncomfortable bike I’ve ever ridden (an ’80s steel road bike) — it was equipped with narrow, high-pressure 22mm tyres, had almost no exposed seatpost, and featured a firm racing saddle. Hopefully, it’s clear now that it wasn’t the frame causing the rattling, but those components providing very little vertical compliance.
May 4, 2020
Why Frame Stiffness Matters On Touring Bikes (And Less On Bikepacking Bikes)
After years of bike travel, I’ve come to really value lateral frame stiffness. While it’s not an absolute necessity, a stiff frame makes a noticeable difference in handling, stability, and the overall ride feel of a bike.

In this article, I’ll cover when frame stiffness actually matters and when it doesn’t. I’ll show you how to spot a stiff touring bike without even taking it for a ride, and we’ll also explore how stiffness relates to rider comfort, frame size, belt drivetrains, and different construction materials.

This article was originally published in December 2018 but has been updated in February 2020.

Why Stiffer Is Better When It Comes To Bike Travel

Most touring bikes are designed to carry both front and rear loads, and it’s the frame that has to resist the twisting forces created between these two points. A stiffer touring frame offers several advantages.

Extra Stability

At certain speeds, a fully loaded touring bike can develop a bit of front-to-rear wobble. While frame stiffness isn’t usually the root cause (it’s more often due to an unbalanced front load or a slightly out-of-round wheel), a stiffer frame is better at resisting this oscillation. This becomes even more important on drop-bar touring bikes, where you have less steering leverage to correct a wobble once it starts.

Unbalanced Front Loads

Perfectly balancing front panniers isn’t always realistic. I pack mine based on accessibility (kitchen gear on one side, camping gear on the other), which leaves one pannier slightly heavier. With a very stiff frame, I’ve noticed these weight differences are less likely to induce oscillations, even when the load is uneven. In short, more stiffness gives you greater flexibility in how you distribute your front luggage.

Confidence-Inspiring Ride

The torsional rigidity of a stiff frame makes a touring bike feel more predictable and controlled. With less noticeable flex in the top tube and down tube, the bike feels planted and stable under load—something that naturally inspires more confidence on long journeys.

Frame Materials And Stiffness

My KOGA WorldTraveller-S is a particularly stiff aluminium touring bike frame.

The good news is that you can build a very stiff touring bike out of any common frame material – aluminium, steel, titanium, or even carbon. Ultimately, it all comes down to the frame’s engineering and design.

Take titanium, for example. Compared to steel, a titanium frame with the same strength is roughly half the weight and about half as stiff. To bring stiffness up to a practical level, manufacturers typically use larger-diameter tubing. The result is a frame that’s strong and stiff, often lighter than steel, but also more expensive.

Aluminium behaves a bit differently. Using the same tube dimensions, aluminium is about one-third as stiff, one-third the weight, and only about half as strong as steel. To compensate, aluminium frames are built with oversized tubing and thicker walls, which helps achieve the necessary stiffness and durability.

To read more about frame materials and bike travel, head over to my in-depth article HERE.

How To Tell If A Bike Frame Is Stiff

The Trek 520 received a larger diameter down tube in 2019 to increase the overall lateral frame stiffness of the bike.

Measuring frame stiffness isn’t an exact science, but there are a few reliable indicators. In general, stiffer frames use larger-diameter tubes with thicker walls. Factors like frame size, tube butting, ovalization, and material quality also play a role – though those details are rarely shared by manufacturers.

While ultra-light, thin-walled, oversized tubing does exist, you won’t find it on touring frames. That kind of tubing is reserved for high-performance road bikes. For example, Columbus Spirit OS steel tubing can be as thin as 0.4mm in the tube centre – far too delicate for a loaded touring rig.

Another good sign of stiffness is an oversized head tube (especially if it houses an internal upper headset assembly). A larger head tube gives frame builders more surface area to connect big tubes, which helps increase overall torsional rigidity.

If you can’t test a frame fully loaded, here’s a quick guide to spotting stiffer touring frames based on tubing dimensions:

Steel
- Down tube: 34.9mm or larger (e.g. 38.1mm, 42mm, 44mm)
- Top tube: 31.7mm or larger (e.g. 34.9mm)
- Double or triple-butted tubing
Titanium
- Down tube: 41.5mm or larger (e.g. 48mm)
- Top tube: 34.9mm or larger (e.g. 37.3mm, 38.1mm)
- Double or triple-butted tubing
Aluminium
- Down tube: 44mm or larger (e.g. 48mm)
- Top tube: 38mm or larger (e.g. 44mm)
- Double or triple-butted tubing
Bike Size And Frame Stiffness

Co-Motion uses the biggest diameter steel tubing available to maximise the frame stiffness of their touring lineup.

If you’re a smaller rider, you’ll generally notice less variation in stiffness between touring frames. That’s because shorter tubes naturally make smaller frames (44 to 52 cm) stiffer. In fact, tubing with slightly smaller diameters is usually more than adequate for these sizes.

On the other hand, if you’re tall like me, it’s worth seeking out frames with the largest possible tubing diameters – you’ll feel greater differences in stiffness. Tall riders carrying heavy loads may even benefit from a marathon tube, an extra reinforcement that connects the head tube to the seat stays. That said, these designs are less common today, as modern tubing is available in much larger diameters than in the past, making additional reinforcement less necessary.

When Frame Stiffness Matters Most

This Hilite features a massive 48mm titanium downtube.

When You’re Carrying Heavy Loads

A typical touring setup distributes weight across both ends of the bike. The heavier the load, the more stiffness the frame needs to manage the twisting forces. For example, I usually carry about 8 kg up front and 15 kg on the rear. With this setup, the aluminium tubing of my KOGA touring frame (or oversized steel tubing of my Co-Motion) feels noticeably stiffer and more stable than my previous steel Surly Disc Trucker.

If you’re riding with less luggage weight, say 5 to 10 kg total, frame stiffness is generally less important and won’t have a major impact on your ride.

When You’re Running a Belt Drivetrain

Belt-drive frames demand a particularly stiff rear triangle; otherwise, the belt can derail from the cog. In fact, both Gates and Rohloff set minimum stiffness standards for frames designed to work with their systems. Beyond simply keeping the belt in place, extra stiffness has another benefit: it allows you to run lower belt tension, which can reduce drivetrain resistance at low power outputs.

What About Comfort?

Seatposts such as the Ergon CF3 or Canyon VCLS 2.0 provide significantly more vertical flex than any bike frame ever could, regardless of its stiffness.

It’s often assumed that stiff frames are uncomfortable to ride. But even if that were true, it helps to put frame comfort into perspective.

Most bike frames require over 500N of force to flex just one vertical millimetre. In real terms, that means your body weight only produces about a millimetre of frame flex. Compare that to a carbon seatpost like the Ergon CF3 Pro, which takes only 69N of force per millimetre, so it can easily flex around 10mm just by sitting on the saddle.

And neither of those is your bike’s primary source of suspension – that role belongs to the tyres. With as little as 10N of force, a wide tyre can deform by a millimetre or more.

When you look at it this way, tyres and seatposts contribute vastly more vertical compliance than the frame itself. Which means in practice, you’ll be hard-pressed to notice any meaningful difference in comfort between frames of varying stiffness.

Read more about why seatposts are overlooked yet critical for comfort HERE.

Summary

Frame stiffness plays a key role in the stability of a loaded touring bike. By adding just a few hundred grams of extra material, you get a bike that feels more planted, predictable, and confidence-inspiring on long tours. Combined with a good seatpost and wide tyres, even a very stiff touring frame can be just as comfortable as any other bike.

You can usually gauge the stiffness of a touring frame by checking its tube diameters. While it’s not an exact science, the stiffest frames almost always use the largest-diameter tubing available.

For light bikepacking setups, or for bikes carrying heavy loads primarily at one end, a high frame stiffness is less critical.

Find Out Whether Steel, Aluminium or Titanium Is The Best For Bike Travel HERE
February 28, 2020
Frame Materials for Bicycle Touring: Aluminium vs Steel vs Titanium

A robust and long-lasting touring frame can be made from aluminium, steel, or titanium. While the frame materials play a role, the most important factors are that the frame is designed specifically for touring, built with precision, and backed by a manufacturer known for producing reliable and durable touring bikes.

Let’s explore this in some extra detail.

Frame Materials: Which is Most Comfortable?

Road Vibrations and Bumps

There is surprisingly little difference in comfort between frame materials. The biggest source of comfort: your tyres.

You’ve probably heard that steel and titanium touring bikes are more comfortable, while aluminium frames give a harsher ride.

Surprisingly, the frame itself actually contributes very little to overall vibration damping, especially once your bike is loaded with panniers. Most of the road’s bumps are absorbed by your tyres, seatpost, and saddle.

Think about it: when your tyre hits a bump, it deforms, dissipating most of the shock, ranging from a few millimetres on a narrow tyre to centimetres on a wide touring tyre. Your rim, spokes, and hub pass along the remaining energy, but their effect is minimal. The shock then travels through the frame and seatstay up to the seatpost, which can flex significantly – up to 25 mm on some carbon posts. Finally, your saddle absorbs more vibration before it ever reaches your body.

So, while aluminium, steel, and titanium frames may differ by a couple of millimetres of vertical flex, this difference is tiny compared with the combined damping effect of tyres, seatpost, and saddle.

With the right tyres, a flexible seatpost, and a comfortable saddle, any frame material can provide a smooth and enjoyable touring ride.

Resonance

An aluminium, steel and titanium touring bike.

All bikes have natural resonant frequencies – they vibrate to some degree, just like everything around you. While resonance is sometimes said to affect ride comfort, most road vibrations are actually absorbed by your tyres, grips, seatpost, and saddle.

Resonance only becomes a real issue when it builds to the point of causing a “speed wobble” at certain speeds. Bikes prone to wobbling often lack sufficient frame stiffness.

Fortunately, most purpose-built touring bikes are stiff enough to carry heavy loads without issue, so speed wobbles are rarely a problem – unless you’re running very heavy front panniers.

Sizing and Components

Comfort isn’t just about how stiff the frame is. Choosing a frame that fits your body and matches your riding style has a major impact on how good your bike feels on long rides. Equally important are a well-fitted saddle, a seatpost that absorbs bumps, and grips that feel right in your hands – they all make a noticeable difference.

Which Frame Material Is The Stiffest?

A diagram showing stiffness testing on a bike frame.

Any material – aluminium, steel, or titanium – can be used to build a stiff bike.

Frame makers achieve different characteristics by adjusting frame tube diameters and wall thicknesses, balancing stiffness, strength, and weight. Touring frames are often the stiffest of all bike types (and usually the heaviest) because they need to handle heavy loads on both the front and rear without twisting.

When test riding touring bikes, frame stiffness is one of the first things I notice. It’s crucial for bikes carrying front and rear panniers, as a stiff frame improves high-speed handling and helps prevent speed wobbles.

Which Frame Material Is The Lightest?

A diagram showing the differences in tube butting.

The goal of any good frame builder is to use material only where it’s needed. Aluminium and titanium are often considered lighter than steel – but the reality is a bit more nuanced.

A process called butting reinforces the ends of frame tubes to make them stronger. By removing material from the tube’s middle section while keeping the ends thicker, manufacturers can optimise stiffness and strength while also reducing weight.

High-quality frame makers adjust tube diameters, wall thicknesses, and butting patterns across their size ranges, tailoring the frame for touring (strong, stiff, and reliable).

A titanium frame with the same strength as steel is roughly half the weight and half the stiffness. To make it stiff enough for loaded touring, titanium frames use larger-diameter tubes, resulting in a frame that is strong, stiff, and often lighter (though more expensive) than steel.

Aluminium frames, in contrast, are about one-third as stiff, one-third the weight, and half as strong as steel frames with similar tubing. Like titanium, aluminium frames need large-diameter tubes with thicker walls to maintain strength and stiffness. Even with this extra material, aluminium frames typically end up lighter than both steel and titanium, making them a popular choice for riders prioritising weight savings.

Which Is The Easiest To Repair and Modify?

Getting It Fixed

Gripsport in Australia completes frame repairs using gussets and sleeves to ensure the frames are repaired back to their original strength.

All bike frames can be repaired, but some are easier than others.

Steel is the simplest to work on, though a roadside repair – say, in Kyrgyzstan – is unlikely to be permanent. Steel tubing is thin compared with industrial metal, so unless the welder specialises in bike frames, there’s a real risk of damage during welding. That said, a quick fix can often keep you riding.

Aluminium and titanium frames are also repairable, but they require more specialised tools and expertise. A simple weld over a crack is rarely enough; to restore full strength, new material (usually a gusset or sleeve) is added to reinforce the frame.

Modification

Steel frames are the easiest to modify. Professional builders can replace or redo almost any part of the frame. You can add mounts for bottles or racks, fit disc brake tabs, or even swap out individual tubes, head tubes, and rear dropouts to suit your needs.

Which Will Last The Longest?

Frames can break in many different ways.

The durability of a bike frame depends far more on engineering and build quality than on the material itself. A high-quality frame is unlikely to fail on a tour unless it experiences a major trauma, like a serious crash.

Fatigue

Steel and titanium frames have a fatigue limit, meaning they can endure repeated flexing indefinitely without failing. Aluminium, in contrast, has no true fatigue limit, so it will eventually fail after enough stress cycles.

This sounds alarming, but aluminium touring frames are engineered to be three times (or more) the strength of a typical steel frame, easily handling the demands of loaded touring. In practice, a well-designed frame of any material won’t be affected by fatigue during normal use.

Defect Tolerance

If a frame develops a defect, some materials give you more warning than others. Steel and titanium tend to bend or dent before breaking, giving you time to notice a problem. Aluminium frames, however, can develop cracks quickly and fail with far less warning.

Bolt Threads

Aluminium threads are softer than steel and can strip if bolts aren’t handled carefully. Using a little grease and ensuring bolts are threaded straight can prevent this issue.

Rust

Steel is susceptible to rust, but it rarely causes frame failure.

Many steel frames over 30 to 50 years old are still on the road. Rust isn’t a major concern because the steel tubing is thick and painted. Still, it’s wise to apply anti-rust spray inside the frame occasionally – especially if you ride in wet climates or near the ocean – and touch up paint chips as needed.

Summary

Whether aluminium, titanium, or steel, the most important thing is choosing a frame designed specifically to handle the demands of touring.

Manufacturers with a long history of building reliable, rugged touring bikes ensure your frame can last for decades of riding.

Some notable examples: Santos and KOGA excel with aluminium, Co-Motion and Surly are renowned for steel, and Idworx makes top-tier titanium touring bikes.

For a deeper dive into the technical details (and plenty of terminology), check out SheldonBrown.

January 26, 2015