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by Matt Wikstrom
June 7, 2016
TECH NEWS BROUGHT TO YOU BY BIKEEXCHANGE
The bicycle may be a simple machine but there are many aspects to its performance. Indeed, cyclists can go to great lengths to dissect and compare the various traits and behaviour of different bikes when deciding on the best one for their needs.
And in general terms, it’s fair to say that we have developed a sophisticated understanding for many of the factors that influence the performance of a bike. For example, frame geometry is now well defined and clearly understood, both for the behaviour of the bike as well as it’s suitability for any given individual and/or riding discipline.
The notion of bicycle engineering is no longer ridiculous and the science behind bicycle design has grown considerably in the last two decades, providing the industry and consumers alike with much more data on the way that a bike performs. Some manufacturers have even resorted to publishing white papers based on the findings of their research so that consumers can better understand the benefits of their products.
Despite our growing sophistication, there is at least one aspect of the bike has yet to be defined with such clarity: ride quality. It’s an evocative term that can used to refer to the mystique of any given bike, yet it’s not critical for its performance, and in practice, is largely open to interpretation.
So what do we know about the nature of ride quality?
In the past, there was lot of emphasis on frame material when it comes to deciding the ride quality of a bike but it is not as simple as that.
In keeping with its elusive, even esoteric, nature, there is no clear definition for ride quality. The spectrum of opinion ranges from vague, artistic notions to precise engineering terms.
Ben Serotta is a well-known framebuilder with a long history in the bike industry that has worked with every frame material. Despite his experience, he believes there is an element to ride quality that continues to defy our understanding:
“I’ve thought about this phenomenon during my rides. You might give the same sheet of music to two musicians. One plays it perfectly, but when the other plays you get goose bumps. How? It’s impossible to define. With the bike, it’s part technology, but I’m pretty sure it’s also part magic that infiltrates the bicycle.”
By contrast, Damon Rinard, an engineer who has worked for Trek and Cervélo, and is now manager of road bike engineering for the Cycling Sports Group (which owns Cannondale, Schwinn and GT) is far more pragmatic:
“To me, many bicycle characteristics that some might include in ride quality are better characterised on their own. There’s a list: handling, stiffness, weight, aerodynamics, etc. are a big part of what we experience when riding (thus they affect the quality of the ride, thus may be considered part of ride quality), but to me, these other characteristics are well understood technically, which leaves ride quality as mostly bump and vibration isolation.”
This second view pervades academic research on the matter, and while there is a risk that this approach may overlook other components, by reducing ride quality to a single measurable trait, researchers have been able to more effectively investigate the factors that influence it.
Direct measurement of vibrations travelling through a road bike while in use has provided insight on the nature of ride quality and how it is experienced by cyclists. Photo courtesy VÉLUS.
Professor Jean-Marc Drouet is an engineer and head of VÉLUS, a research group at the University of Sherbrooke in Canada that has been studying ride quality for over a decade. He’s ready to admit that he’s still not clear on what ride quality is, but he draws an important distinction between it and the comfort offered by the fit of the bike.
“The fit of the bike, or its static comfort, depends upon the position of the handlebars and the saddle, and how well each suits the rider. That is quite different from ride quality, or dynamic comfort as I’ve come to refer to it, which seems to depend upon energy transmission to the rider.”
Ultimately, ride quality is largely a subjective phenomenon, so it remains open to interpretation. For the purposes of this discussion, though, I’m going to define ride quality as the set of sensations experienced by a rider while the bike is under load.
Any rider that has ever compared different bikes or noticed what kind of effect a change in wheels, tyres, or even tyre pressure can have on the comfort and/or feel of the bike will understand that every part of the bike can influence ride quality. Even minor components like the handlebar tape have a role to play.
The rider is also a crucial component, so the influence of shoes, gloves and shorts can’t be overlooked either. What is more important though, is the rider’s perception and interpretation of the sensations travelling through the bike. Variations in both account for a lot of the difference in opinion on the behaviour of any given bike or component.
There is more to the influence of the rider than just their perception. Studies have demonstrated that their height and weight is important, as is their power output, weight distribution and riding position. Even seemingly minor variations, such as the angle of the wrist, can have an impact on the perception of ride quality.
The hands are very sensitive to vibrations so it makes sense to use an active suspension unit at the front end to improve the ride quality of the bike.
As the sole interface for the bike with the terrain, it’s not surprising that tyres have a profound effect on the ride quality of a bike. Most riders will already have an intuitive understanding of this notion, and have probably experimented with it by testing different air pressures and/or brands of tyres.
High tyre pressures generally reduce the rolling resistance of the tyres, but it comes at the expense of comfort and grip, all of which colour the ride quality of the bike. Similarly, the width of the tyres and rims is important along with the construction of the tyre and the type of inner tubes (butyl rubber versus latex).
According to Silca, “a 10% change in tyre pressure at 100psi can have a greater effect on ride quality than changing frame materials.” That’s because the change in vertical compliance is equivalent to the difference in vertical compliance for carbon and steel frames. Of course, there is more to ride quality than just vertical compliance, but it serves to illustrate the magnitude of influence that tyre pressure can have on the feel of the bike.
Road cyclists have traditionally favoured high tyre pressures with the hope of reducing rolling resistance but over-inflated tyres typically create more vibrations for the rider to contend with.
It is generally held that different frame materials have distinct ride qualities. Aluminium alloy has a reputation for being harsh, steel and titanium less so, while carbon fibre is well recognised for its damping characteristics. However, as popular as these notions may be, there is no hard data to support such broad generalisations.
What may be more important is the final size, shape, structure and mass of the frame. Steel frames from previous eras that used relatively small diameter tubing were often smooth and silent, even on rough roads. By contrast, contemporary composite designs with much larger frame members can be very noisy and tend to offer a very distinct ride quality.
But such associations are spurious at best. One of the harshest bikes that I’ve ever ridden was a steel Eddy Merckx from the late ‘80s. Scott’s new Foil also defies expectations, providing a smooth, comfortable ride despite the frame’s large aerodynamic tube profiles. Clearly, it’s possible to manipulate any material to influence the ride quality of the frame but just like the proverbial book, it’s impossible to judge the ride quality of a frame without putting it to the test.
Interestingly, it appears as if frame compliance has increased in recent years, not because of a change in materials, but as a matter of design. In this regard, composite materials seem to offer the greatest advantage for creating local regions of flex (eg. at the seat tube) for extra compliance.
Composite materials are renowned for the amount of compliance they have to offer but this is not a product of the materials per se, but the way that they are used.
Our understanding of the relative influence of different parts of the bike on its ride quality is rudimentary at best. Popular wisdom holds that any part that is larger (eg. rim profile, handlebar diameter, seatpost diameter) is going to be stiffer, and therefore, more uncomfortable but there is no evidence in support of this notion.
Similarly, there is widespread belief that carbon fibre composites can improve the comfort of parts like the seatpost, stem and handlebars, but as I will discuss below, this is not the case. Indeed, some components have surprisingly little impact on ride quality.
With a marketplace awash with of plethora of alternatives for any given part, the scope for variation is immense. The question therefore arises, is there any way to predict what kind of effect a new part will have on the ride quality of a bike?
Not really. Ultimately, the only way to answer this question is through trial-and-error testing by the individual. Nevertheless, our understanding of ride quality has progressed in recent years, and while it is far from complete, some interesting concepts have emerged from research on the phenomenon.
The majority of academic research on ride quality has focussed on the vibrations that arrive at the cockpit and saddle when the bike is in use. Such vibrations can be measured with sensitive strain gauges and accelerometers, but to do so in a reproducible manner is quite challenging.
Jean-Marc Drouet (on the bike) and Mathieu Dorion (at computer) carrying out impact testing on a treadmill in the VÉLUS lab. Photo courtesy VÉLUS.
The VÉLUS group has been studying vibrations in road bikes for more than a decade and is the leading authority on this kind of research. The team has collaborated with a variety of manufacturers (Trek, Cervélo, Look, Argon18, Procycle, Devinci) and published a number of research papers, all with a view to understanding how vibration affects the comfort of the rider.
Their testing rig essentially comprises an instrumented bike that is mounted on a large treadmill or hydraulic shakers. Different sized bumps are attached to the former to serve as the terrain, while the latter can be programmed to deliver a range of insults to the bike. In both instances, VÉLUS has validated its results with real-world testing.
Using this approach, VÉLUS investigated the effect of different frame, fork and component materials on vibrations measured at the saddle and cockpit before going on to establish a hierarchy of influence for different parts of the bike.
A typical plot of the vertical force (top), acceleration (middle) and power (bottom) transmitted to the brake hoods during a bump-test for the front wheel. Measurements were carried out on a treadmill with two circular aluminium dowels attached to the surface to provide two closely spaced impacts, repeated three times. The force and the acceleration were measured using an instrumented brake hood. The power is calculated from the force and acceleration signals.
The raw data resemble a seismogram, where the various peaks and troughs reflect the magnitude of vibration over a range of frequencies. Any reduction is presumed an improvement in the comfort of the bike, where low frequencies (<50Hz) are especially significant since they are generally the most unpleasant. Higher frequencies (up to 100Hz) can be generated, but it’s not clear what kind of effect they have on the rider.
VÉLUS has not published an exhaustive comparison of materials but the results from one study demonstrate that it is futile trying to generalise on the effect of different materials. For example, while 3T’s alloy Ergonova Pro handlebar transmitted more vibration than the carbon version, FSA’s carbon K-Wing behaved more like the alloy Ergonova than the carbon version.
Results from the same study also showed that Cervélo’s R5ca frame transmitted less buzz than the R3 or a steel Masi Gran Criterium frame, a Specialized Roubaix fork was significantly more comfortable than Easton’s EC90SL fork, as were Zipp 202 wheels when compared to Fulcrum Racing 7s. Interestingly, the study could not identify any differences for three types of stems (3T ARX Pro, 3T ARX Ltd, FSA OS-99 CSI).
During the course of this study, the team experimented with various ways of expressing their results, and found that the amount of power absorbed at the saddle and cockpit was the most robust. Thus, a small bump transmitted 1.5-4W to the rider’s hands and buttocks, while the difference between some components could be as much as 0.5W.
Purpose-built instrumented brake hoods allow researchers at VÉLUS to measure the force and the acceleration transmitted to the hands of the rider. Photo courtesy VÉLUS.
The handlebars and forks had the greatest influence on vibrations transmitted to the brake hoods, while the wheels and frame were more important for the vibrations felt at the saddle. A smaller effect was noted for the wheels on vibrations measured at the brake hoods, however the stem had no effect. Some components, like the seatpost and saddle, went untested since they comprised the measuring apparatus, while other aspects, such as tyre pressure, remained consistent throughout the study.
Jean-Marc Drouet admits that he’s still uncertain as to how the results on absorbed power actually relate to comfort and ride quality. As mentioned above, it is assumed that any reduction in absorbed power will be perceived by the rider as an increase in comfort, but this has yet to be formally proven.
Interestingly, the results agree reasonably well with a recent survey and academic study where 244 participants were asked to rank the importance of each part of the bike to their comfort. Saddle design emerged as the most important part, followed closely by the frame and handlebars. Wheels were considered less important and were ranked alongside the pedals, shifters and forks.
While there is room for more work on this topic, the correlation between objective and subjective measures seems to suggest that most riders have an intuitive understanding of the relative importance of each part to the feel of the bike, at least in terms of comfort. Having said that, the survey participants underestimated the importance of the wheels (including tyres and tyre pressure).
I mentioned in the discussion above that the perception of the rider is important to the whole phenomenon of ride quality. It turns out that individuals can be more or less sensitive to ride quality according to a threshold of perception that applies to all of the senses. Formally referred to as “just-noticeable difference”, it is defined as the smallest change in stimuli that can be detected by an individual.
The VÉLUS group has been studying how this threshold applies to cyclists with a small survey on how well a group of seven riders could detect a drop in front tyre pressure. Each rider spent about an hour on the same bike fitted to a treadmill where a dowel rod (9.5mm diameter) served as a bump. Matching front wheels with different tyre pressures were swapped throughout the test to determine what kind of pressure difference each rider could reproducibly identify.
A closer look at the terrain that is added to the treadmill for impact testing at VÉLUS. Photo courtesy VÉLUS.
There was a broad range of sensitivity between individuals: one rider in the group was able to identify a drop of around 10psi, while others didn’t notice a difference until it was 30psi or more. The average for the group was around 20psi, while the starting tyre pressure was 100psi.
The group went on to examine this notion with more rigour for a larger group of cyclists, but rather than vary tyre pressure, they employed a testing rig with hydraulic shakers to provide the input for each cyclist to interpret. On average,the participants were able to reliably identify a 15% decrease in vibration, and the hands proved to be more sensitive than the buttocks.
One other interesting observation to come out of this work is that the position of the rider can have a profound impact on the transmission of vibration. Any rider that has tackled rough roads will immediately understand this point: riding in the drops and/or with a sharp wrist angle generally exaggerates road chatter, and this is exactly what the group observed. Furthermore, variations in stem weighting and wrist angle could reverse impressions of the relative comfort for two different wheelsets because of their influence on vibrations travelling to the stem and seatpost.
When it comes to fatigue testing, purpose built jigs are very effective for testing the durability of the frame but fail to provide any meaningful data on ride quality.
This last point, when combined with variation in just-noticeable differences, goes a long way towards reconciling conflicting, even contradictory, experiences that individuals can have with the comfort of any given bike or component. And while this notion has yet to be formally proven for other traits of the bike — like stiffness, handling, and responsiveness — I expect it will apply to them all.
Frame builders and bike manufacturers have long made use of prototypes and trial-and-error to refine the performance of their bikes, but research on vibration and absorbed power/energy promises to bring new sophistication to bicycle engineering.
Jean-Marc Drouet says that more work is required though. For example, there is no clear understanding on how cyclists interpret vibration. Missing too is a meaningful metric that can provide an absolute measure of comfort and/or ride quality that can be applied universally to different bikes and components.
Researchers at VÉLUS have validated their lab testing protocol with real-world testing. Here, Julien Lépine (right) checks the acquisition system and wiring prior to an on-road measurement session with Jean-Philippe Pelland-Leblanc (left). Photo courtesy VÉLUS.
Nevertheless, Drouet is satisfied with the progress VÉLUS has made, having established an effective test protocol that has provided some insight on ride quality and can also be used to test the efficacy of different strategies and/or products. This last point is something that Drouet sees as a concern with an increasing number of unsubstantiated claims permeating the marketplace.
Thus, his team recently investigated the impact of damping materials on vibrations travelling through the frame and to the cyclist. They looked at the behaviour of the frameset on its own as well as when it was put to use by a cyclist and found that small gel inserts positioned in the frame and forks had no significant effect in either setting. In contrast, wrapping a frame in damping material managed to reduce the magnitude of some frequencies travelling through the frameset when it was tested on its own, but it had no effect on vibrations travelling to the cyclist.
As a consequence, Drouet doubts that any damping material incorporated into a frameset will affect the comfort of the bike. The results also emphasise the importance of testing the performance of the bike with a rider rather than without.
One important thing to note about the studies discussed above is that they generally concentrate on the response of the bike to sudden changes in terrain with bump tests. While this kind of approach is well suited to understanding ride quality in terms of comfort, are there other aspects that bear upon the ride quality of a bike?
At present, it’s difficult to find a bike engineer that believes there is anything that’s been missed, but perhaps a technological breakthrough will make the difference. This seems unlikely though, since it’s possible to measure differences in the characteristics of different frames, forks and components that cannot be felt by the rider.
Where once there was a strong emphasis on stiffness for a road bike, now it has shifted to favour compliance with a tangible effect on ride quality.
If there is truly nothing else to measure for ride quality, then perhaps what is lacking is a thorough understanding of how all the parts and characteristics of the bike come together to produce the final impression of its performance. Maybe this is where the “magic that infiltrates the bike” can be found.
In this regard, it’s worth noting that our understanding of how a bicycle is able to self-steer only came to fruition recently despite a century of study. The breakthrough came, not from discovering a new dimension, but in understanding how some very familiar characteristics work together.
All of the available data suggests that the ride quality of a bicycle is related directly to vibration and the amount of energy that is transferred to the rider. The remainder of the impressions that cyclists associate with riding a bike can probably be attributed to other traits and characteristics of the bike, such as its stiffness, weight, geometry, and handling.
Regardless, our understanding of ride quality is far from complete. One important concept that bears upon our understanding of the phenomenon is that individuals vary in their sensitivity to vibration according to a sensory threshold. Some riders will notice a small change in energy transmitted to the handlebars while others will be unaware of it until it is much larger. This goes a long way to reconciling variation in opinion on the ride quality of any given bike or component, and likely extends to other traits.
In considering the nature of ride quality, Ben Serotta likened a bike to a sheet of music, and I think the analogy is very apt. The bike comes together like an orchestra, where each part has a role to play in forming the music, while the rider is like an auditorium, each with his or her own set of acoustics that will determine how the music is perceived.