The rough road to comfort………….

There is much talk of frame feel and comfort with debates focusing on frame materials and frame design. However, little seems to be reported regarding the science of comfort and feel. So lets have a look at what happens when we ride a bike along a road and just what it may be that is causing the feel and comfort we perceive……………

As we ride along a given road, collisions occur between the road and our bike, at the road / tyre interface of both wheels. The vibrations caused in cycling could be assumed to be a continuous oscillating input (Cardinale et al, 2005), and if we assume the bike to be a perfect transmitter of these forces then the oscillation occur in the bike and are passed directly to the rider. These oscillations continue in the riders soft tissue as a free vibration (vibrating at their natural frequency) where its amplitude will decay due to damping within the tissue. The reality is that the bike system too has a damping effect, which we will come to later.

When the body is exposed to such vibrations it employs a number of strategies to control the effects of such a stimulus. Nigg (1997) suggested that the body can in fact “tune” its muscle activity to reduce the detrimental effect the vibrations can cause. This provides advantageous as the work by Adamo et al (2002) suggest that prolonged exposure to vibration induces muscle fatigue in addition to Bongiovanni et al (1990) findings of reductions in motor unit firing rates and muscle contraction force. The mechanism that causes this is likely to be similar to that of exercise itself. Tiny tears in the muscle can occur, causing pain and reduced muscle function. Active muscles (like our legs turning the pedals) have been shown by Ettema et al (1994) to be more effective at damping externally applied vibrations. However, in order for the body to “tune” itself to reduce the effects of the vibrations, it has to use energy; energy which we may prefer to spend on peddling ! Ultimately however, the vibrations have the potential to cause discomfort and a reduction in performance.

For completeness however, it is worth mentioning the work of Bosco et al (2000) amongst other who have demonstrated that short term (10mins) exposure of specific frequencies (26Hz) and displacements (4mm) have led to an increase in athletic performance (measure by increase in strength and power). The effects of exposure to frequencies ranging from 15 – 60 Hz with displacements of between fractions of mm to 10mm, at accelerations of up to 15g are prevalent in academic literature. These studies have show both positive and negative influence on athletic performance. Interestingly there appears to be some links to the effects of such exposure and the subject fitness levels. So maybe there is a case that untrained cyclist are more likely to suffer discomfort due to a reduced capability at adsorbing the vibrations caused during riding. However, my own view on these studies remains positively on the fence until more robust experimental design has been applied (use of control groups etc). But interesting reading non the less, and demonstrates that it is possible that different frequencies, magnitudes and exposure times are likely to result in different physiological effects for different people.

Anyway back to the problem….

The natural frequency of a vibrating system will depend on its stiffness and its mass. In cycling terms, the vibrations the rider incurs will be dictated by the frequently of the impacts causing the oscillations (e.g. road surface, speed travelling). The oscillation frequency and magnitude may also be influenced by other parameters such as peddling cadence and peddling force profiles. Once the collisions have occurred, their transmission to the rider will be influenced by the mass of the system (rider + bike) and the systems damping characteristics. The damping characteristics being dictated by many things such as (in no particular order) tyre size and pressure, wheels (type, age, spoke tension, spoke quantity, material etc ), frame geometry, frame material, frame tube profiles, frame tube thickness, rider position, rider location (in the saddle, out of it), handle bar type and width, stem length and type, seat post type and height, saddle type and position, bar tape type thickness, clothing worn, fork design and material, bike age, quantity of drink in water bottle, etc…. The list could probably be a page long !

The resulting forces that are transmitted to the rider are likely to be what we perceive as feel. How these messages are “translated” by the bike to the rider and then how the riders body descrambles them could be critical in understanding comfort and bike feel.

So, to summarise, the type of oscillation caused during cycling may depend on the road surface, the speed travelling, the pedalling cadence, pedal force profile and mass of the system amongst other things. The transmission of these forces to the rider will depend upon the riders physiology, their mass and position on their bike in addition to the bike itself.

So what are we left with ? well it is possible that each rider and bike system will have a set of unique vibrations (frequency, magnitude, accelerations etc) and different abilities to deal with them. So, a bike system that is comfortable for me, or one that feels “right”, may not work so well for you. Equally, if I change the way I ride it (speed, position, cadence, pedalling technique) it is likely that the vibrations I receive will change and hence my perception of how the bike feels will also shift.

Therefore it would appear prudent to develop a bike system that is “customised” to some extent to your physiology, peddling style, fitness and intended end use. To some extent this happens naturally (through your position, tyre choices, saddle selection etc). However, there are a number of frame design influences that could also be applied to help this problem.

In the next Sunday School, we will have a chat about such parameters and see that its never as straight forward as we would like!

Carbon or Ti ?

I’ve raced on some amazing bikes over the years. I’ve also had a few dogs (and I’m talking strictly of bikes here, just for the record). But riding poor equipment is what sometimes happens when you’re not the one paying the bill; you get what you’re given. Here at Sunday we are often asked to explain why titanium is better than carbon. Most customers are surprised when I say, “it isn’t”.

To be more accurate, I should say “carbon could be better”. The thing is, before we can have a constructive conversation as to which material is best, we would need to find out a little more about your needs, and more importantly just what you mean by carbon.

All other things being equal, if I started racing again and could have any bike I could, if it was paid for, and replaced when I broke it, then I may well go for a carbon. Why ? Well it can be super stiff, comfortable, light and the bloke at my local café will think it looks cool. That’s right isn’t it?

Well, it could be, yeah……………..

The problem is we all use the term “carbon” like it’s a single material. We do a similar thing with titanium. But bike manufacturers usually only use 3Al, 2.5V, and occasionally 6Al, 4V Ti. But that’s really about it. So assuming all the manufacturers use ASTM grade material (so the impurities are tightly controlled), chemically you’re getting the same stuff. But carbon is a little bit more complicated. To say a frame is made from carbon is about as accurate as saying my frame is made from metal. It could be anything.

Let me explain………….

Carbon bike frames are made from what as an engineer, I would refer to as a fibre reinforced composite. In essence these material comprise of a matrix (the gluey bit) and a reinforcing fibre (the carbon fibre bit). The properties of the resulting material is dictated by five factors.

The individual properties of the matrix and the fibre.
The proportions of the matrix and fibre in the material.
The length of the individual fibres.
The geometric arrangement of the fibres in the matrix.
The interface between the fibres and the matrix.

The basic approach is to attempt to improve the strength and stiffness of a material (the matrix) by incorporating within it fibres that are actually stronger and stiffer than the matrix.

The carbon is often made by carbonising a polyacrylonitrile (PAN) filament to produce good strength and amazingly high modulus fibre but be aware of cheaper pre-cursers. Typically there are three types of carbon fibres produced, high modulus (HM), high strength (HT) and type A, which has properties somewhere between the two.

Orientation of these fibres is often commented upon in marketing literature. So, to clarify, when tiny fibres are used, they result in optimised isotropy of properties in theory. ie the properties of the material should be the same in all directions and this type of material can be found in frames and forks. However, processes such as injection moulding of such material usually result in great disparity of properties due to flow variation cased by the geometry of the moulded part. In small fibre systems, the percentage of fibres (to matrix) rarely exceeds 40% (by weight). So, most of the frame is glue. Woven reinforcement results, typically, to a maximum of 65% fibre to matrix. Unidirectional alignment of fibres results in the most dense fibre to matrix compositions (up to 90%) and offers the greatest enhancement of properties but at the cost of maximising the anisotropy of the material (it’s very directional!) This is often used to describe a great engineering advantage. Although this could be the case, it is often bad practice to incorporate materials of different stiffness’s as it can produce incompatible levels of deformation resulting in localised concentrations of stress which can lead to local failure.

The matrix is often an epoxy type resin although there are many different materials that could be used.

It is worth noting that controlling the manufacturing processes of carbon fibre materials appears much more difficult that metal forming techniques. I recently saw some data from a world famous composite tennis racket manufacturer where the same batch of production frames were cut up and identical pieces from many rackets were measured for a number of their physical properties (stiffness, etc). The properties varied greatly (and I mean GREATLY). The same factory manufactures bike frames.

Ok, so this brief intro has, I hope, demonstrated that a “carbon” material could have a hugely diverse range of physical properties due to the complex potential arrangements of the reinforcing fibres and composition of the fibres and matrix (properties can vary several 100%). And this is before we have even begun to select material cross sections, and tube geometries. Of course, these parameters can be changed for any other material, but should be done with the materials properties in mind as they can be material specific.

The carbon frames on the market range greatly in terms of their weight, stiffness, ride quality and cost. Although there are some that are fantastic they are not without drawbacks and the market is full of poorer quality products. But all things being equal, carbon could well offer the potential to deliver your dream ride. But it’s a minefield and even the best designs have some limitations.

So is carbon still the material for me? The thing is I’m not racing any more, I have to pay for my equipment, and I don’t (or can’t) replace it several times during the season. I also seem to spend a lot of time flying to Europe to ride the roads I used to race and train on and want something durable enough to cope with the occasional frustrated baggage handler. I ride a 3al, 2,5V titanium frame because I know what it is, what it’s capable of and have confidence that it will remain that way for year to come. I can’t at the moment say the same for most carbon fibre frames.

Yesterday, the guy at my local café picked my “Mondays Child” up. He was amazed how light it was and added that “it looks cool”. That’ll do me.

Introducing Sunday School

According to Wikipedia a Nerd is “a term often bearing a derogatory connotation or stereotype, that refers to a person who passionately pursues intellectual activities, esoteric knowledge, or other obscure interests that are age inappropriate rather than engaging in more social or popular activities.”

And a geek is a slang term, noting individuals as "a peculiar or otherwise odd person, especially one who is perceived to be overly intellectual”


11 years ago I competed in a hill climb competition a month after my road season had finished. I did nothing but train for it. I rode the climb, plotted the gradient from the altitude sensor in my heart rate monitor and worked out what pulse I could maintain for the duration. I studied myself to arrive at my most efficient pedal cadence. I weighed myself and my bike and worked out the power output I would require to go under 16 minutes. I weighed my food and noted my calorie output. I lost wait and gained strength. I knew my lactate tolerance, I trained it, I measured it and I understood it.

The race took 15 minute and 46 seconds. My average heart rate was 196 with a max of 211, my cadence was maintained at 84 exactly as it should have been. The race went perfectly; I did everything I had calculated, I put every watt of power I had through the pedals, I collapsed over the line and coughed up some blood. Job done. I finished second, I lost, but that didn’t matter because I had understood the problem, quantified it and executed it perfectly. I just wasn’t good enough.

And this is what I do. I’ve spent over 10 years in academia, studying, picking up qualifications and experience. I have design engineering and manufacturing degrees and in a few weeks an engineering PhD. I’ve raced in Europe in UCI races too. Now, I’m the technical director of Sunday bicycles and I do design and development consultancy for a number of global sports brands. I often work out of the biggest sports engineering institute in the world, at the famous Loughborough University. But nothings changed, I’m still not good enough. I need to know everything. I need to understand, digest, reconstruct and improve. I’m a Geek. And I’m a cyclist.

When I hear people say, “this frames 18% stiffer than last years” or “its more comfortable” or “its stronger”, you will hear me ask, “how do you know ?” and “why?”. There is so much technology available in the bike industry these days it’s an amazingly exciting area to work in. Yet so much of the technology isn’t fully understood or optimised. Development is often done behind close doors and so much of it is perceived as a black art. It isn’t, its just science, its just engineering.

And that’s what Sunday school is about. It’s here to talk about bike design, but more importantly it’s here to make you ask yourselves a few questions. Why do you ride that size handle bars? Why did you choose those wheels? What is the difference in the material properties of that frame over this one? Are ceramic bearings better ? why do I ride a 72.5 degree seat angle? Is my bike set up correctly? What exactly is carbon fibre? Am I a nerd?

If you don’t know the answers to these questions then you should keep coming back. And you should keep asking yourself the questions too.

The school isn’t here to give you my ungrounded opinions or to give you a glimmer of some black art. It’s here to talk about facts. I’ll do the sums so you don’t have to. But I’ll show you my workings, too.

There are a number of topics I have already been asked to chat about, and if enough of you ask the same question I’ll answer it here, on Sunday.

People are always asking me to explain why titanium is better than carbon. My brief answer is “it isn’t”. A more detailed explanation will be given in the next Sunday School.

Class starts soon, don’t be late.