Small but Mighty
Although a small company in the French Loire Valley, with an absolute annual production capacity of about 2,000 frames, CYFAC nevertheless boasts a Ph.D. in Sports Biomechanics among its small staff. Dr. Matthieu Papin worked jointly with CYFAC and the French National Institute of Sport in Lyon to develop the CYFAC POSTURAL FIT CABINE, a fit study system which produces a frame design and rider fit protocols. The Postural Fit Cabine has taken CYFAC from their already pristine reputation as one of the top custom frame builders in the world, to an entirely new level.
Cadence Performance Cycling Center in Philadelphia is the world’s largest dealer of CYFAC frames and works closely with CYFAC and their USA distributor, VeloEuropa, Inc. Recently, Cadence and Pez had the opportunity to pose a series of questions to Dr. Matthieu Papin, CYFAC’s Sports Ergonomics Engineer, and Aymeric Le Brun, CYFAC’s Product Manager. The result was a fascinating and wide-ranging interview on the art and science of proper bike fitting.
Why Go Custom?
Pez: Cyfac is extremely well-known for their custom built (sur mesure) framesets. Is there a distinct advantage for having a custom frame as opposed to a production-size frame?
Dr. Matthieu Papin: The mechanical properties of a bike frame are a function of the fabrication techniques and the materials used (alu, steel, ti, carbon) whereas the dynamic handling of a frame is principally tied to its geometry. As such, with the view to optimizing the human-machine pair (reactivity, comfort, handling), the frame’s geometry has to correspond perfectly to the characteristics and expectations of the cyclist. It is necessary to adapt the frame to the rider’s measurements but also to “type” the frame with respect to the cyclist’s level, type of riding, and expectations.
A custom frame allows for the precise geometry that ensures optimal aesthetic and handling characteristics for the individual rider. However, it is possible that the optimal geometry for rider X corresponds with a frame’s “standard” geometry. In this case, the standard frame will be just as effective as a custom frame.
Pez: Describe for us the toughest/most challenging custom bike fit you have done for an individual, pro or otherwise. What made it challenging and how did you approach it?
Matthieu Papin: A cyclist has multiple goals. As such, in the search for performance, comfort, or health the positioning of each rider represents a real challenge. And, the positioning of certain cyclists affected by crippling pathologies presents even greater difficulties.
Notably, I remember a cyclist affected by a nervous system injury after fracturing vertebrae during a fall while mountain climbing. This injury is characterized by a loss of angular movement at the ankle joint, meaning that the flexing and extension of the ankle are nearly impossible.
After 3 hours analyzing the rider’s movement, I succeeded in repositioning him with the use of some atypical techniques. Principally, I resolved the joint deficiency by placing the cleats beneath the heel of the shoe. And, ultimately, we built a very particular custom frame (seat angle 81 degrees) because any standard geometry could not respond to his needs and peculiarities.
Bike Fit Trends
Pez: What is the most common fit mistake that you see?
Matthieu Papin I see lots of positioning errors including poor saddle set-up (set-back). But I mostly see cyclists who are too stretched-out and very uncomfortable. Reach measurements, as well as differences in saddle-bar heights that are too extreme are generally the causes. The results are lumbar and cervical pain, tendonitis, and altered pulmonary ventilation. In short, the result is a decrease in performance potential.
Pez: Is there a difference between what professional riders use and even high-end recreational riders should have as a position?
Matthieu Papin The fundamentals of positioning are the same across the entire range of riding levels, but the precision of the individual fit changes relative to the fitness level, annual mileage, and presence or lack of pathological problems. Healthy professional riders certainly tend to be more fit, have less body mass to impede breathing/body function, and are clear with respect to pathological problems. Consequently, a professional’s position will tend to feature a slighter higher saddle height, greater set-back, longer reach, and greater saddle to bar height measurement than if it were the same rider (same physical measurements) but with a lower fitness level, less annual mileage, with the presence of some pathological issues (e.g. lumbar or cervical pain).
Because of the significant amount of testing we’ve conducted we see that the physical body measurements aren’t the only things to consider when determining a position/frame design. It is not like making a custom suit! The whole comprehensive picture of the rider must be considered – body measurements, riding level, type of cycling discipline, age, gender, the peripheral equipment used – to get an accurate accounting of the rider and his or her physiological properties. Only then can the proper position for THAT person be determined.
The interesting thing is that amateur cyclists are actually even better tuned in to positioning than the professionals who are typically the victims of misinformation!
Pez: What have you seen as a change in position for high end athletes?
Matthieu Papin For several years cyclists have begun taking into consideration the idea of comfort. This thought was put aside for far too long in the search for hypothetical aerodynamics that actually made performance suffer. Consequently I’ve noticed many cyclists raise their bars to straighten out the torso and limit tension on the back/spinal muscles. This helps relieve potential muscular-skeletal stress (a detriment to performance) and improves pulmonary function (a strong determinant of good performance). Of course, raising the bars beyond where they need to go will not have any additional comfort benefit and will start to cause aerodynamic/handling problems.
Pez: Frames built for 700c wheels are more common than ever. Even for more petite riders, it seems that manufacturers are pushing 700c wheels on compact frames rather than offering frames for 650c wheels. How do you feel about this? Is there any downside to a petite person riding a 650c bike?
Matthieu Papin: First of all, building a 650c frame is possible for any size cyclist. However, for cyclists taller than 1m75/5’9”, 650c wheels do not provide any significant advantage with respect to the dynamic road manner of the bike under “standard” conditions (provided that the optimal frame angles are still respected). On the other hand, because of a circumference that is 16cm less when compared to a 700c wheel, the lower inertia of the 650 does allow for more active accelerations (important for climbers).
Not all cyclists can expect to have an optimal geometry on a 700c frame. In fact, for “smaller” cyclists, a 700c frame will not respect the optimal angles needed for proper handling. As such, there are purely geometric constraints that determine the choice between 650 and 700. In general terms, the 650c bike proves to have the optimal dynamic handling/manner for riders less than 1.70m/5’7 Ѕ” and is a must for those less than 1.60m/5’4”.
How Stiff is Stiff?
Pez: I recall reading that the Gitane-branded bikes built by Francis Quillon, founder of Cyfac, and ridden by the Renault team in the early 1980’s were among the most flexible ones ever tested. This was also true of the Vitus 979’s, but it has not stopped these bikes from being incredibly successful in professional racing (Fignon winning 2 Tours, Kelly winning lots of races including Paris-Roubaix). So besides bike “feel,” just how important is stiffness from an engineering or efficiency perspective?
Aymeric Le Brun: To explain the ride of a frame, “stiffness” and “power transfer” are two terms easily cited, made generic, and these days often vulgarized. While these are indeed important factors, they aren’t the only qualities to look at with respect to a frame. Cyfac considers what we call the “reactivity” of the frame relative to the power of the rider using it.
Stiff for one person may not be stiff for another. Or, for certain events/distances/types of riding, an overly stiff frame can have a significant performance disadvantage for the rider. This is why we look at 1) the rider-machine as a symbiotic pairing and 2) the performance of the frame relative to the morphological and physical characteristics of the individual using it.
Sean Kelly rode on the Vitus frames and Laurent Fignon, as well as the entire Gitane Team, rode on Cyfac-built Reynolds series bikes. They were ultra-light for the time and considerably flexible. But this flex actually permitted these riders to have a frame that was “reactive” under all circumstances. As long as the flexibility isn’t too great (i.e., it still permits the transmission of the rider’s energy) it is important—indeed, fundamental–in the reactivity, or dynamics, of the bike. In these examples the frames were of the proper stiffness/reactivity for Kelly and Fignon to have such successful performances. However, for a larger/stronger rider these frames may not have been optimal and, conversely, a super light-weight rider may have even found them too stiff!
We like to look at the example of the pole-vaulter Sergei Bubka who was the only athlete capable of bending the ultra-stiff pole that he used. That was the right piece of equipment for him because he could realize its potential. Other competitors couldn’t even begin to use his equipment; they had to find the right combinations of stiffness/reactivity that were suited to them. The same principle applies with a frame (at the bottom bracket).
Pez: When building up an entire bike, how important is it to match the stiffness of the frame/fork with that of other components (handlebars, stem, seatpost, wheels)? How is that done?
Aymeric Le Brun: A frame equipped with the wrong wheels or components can see its road manner and power transfer affected negatively. A bike’s manner is the result of the association of the entire ensemble of parts (especially the frame and the wheels).
A stiff frame (like the Cyfac TIGRE or NERV CARBON) can be further enhanced by the use of rigid wheels or more stiff handlebars.
Alternately, these frames could have a more versatile set-ups with the use of parts that are less rigid or non-oversized bars/stems (like the ITM MILLENIUM with a strada-bend bar). Of course, the overall ensemble of frame and parts should be set up to fit the profile of the individual rider, the type of riding, and the desired feel.
Our Cyfac Expert shops (as well as many other fine dealers) are capable of selecting the right parts for the rider.
Pez: When deciding handlebar width, you’re facing two apparently contrasting goals: 1) aerodynamics dictate narrower bars, 2) ease of breathing suggests wider bars. What is the best way to determine handlebar width. Would that differ for different disciplines (e.g., track vs. road).
Matthieu Papin: Contrary to the general belief among cyclists, the choice of optimal bar width doesn’t pit respiratory and aerodynamic efficiency against one another. The latest studies and research show that the ideal bar width positions the arms in the axis of the scapular-humeral joint. This corresponds exactly to the biomechanical width of the shoulders, which is the distance between the two acromions (the outermost, leading edge of the shoulder).
First of all, this minimizes muscular efforts and therefore limits the cervical and trapezium tensions/stress on the rider. Consequently, this proper bar width favors oxygen transfer thanks to an optimization of pulmonary ventilation. Additionally, wind-tunnel tests show that this biomechanical width does not affect the cyclist’s drag because the position of the arms does not increase the frontal area exposed to wind.
Bar width can be adjusted based on the specific cycling discipline undertaken. For example, mountain bike riders use larger bars to benefit from better maneuverability whereas track riders opt for tighter bars in order to negotiate better through on-track traffic/competitors. But, when we speak of optimization of the rider-bicycle pair, we focus on the biomechanical shoulder width.
Pez: Describe for us how the typical rider should select crank length. What are the factors they should consider and what are the general guidelines?
Matthieu Papin: Cyclists typically select crank length based solely on the measure of their inseam. To do so, some apply a constant coefficient such as I*0.2 (inseam measurement x 0.2) or trust a value table that was developed empirically. In all honesty, these methods do not allow for satisfactory results on either the medical-scientific or sporting fronts. With the development of the Cyfac Postural System we scientifically determined a multi-factor mathematic formula that permits the definition of the optimal crank length. This formula was defined after having done the following scientific observations:
During the pedal cycle, crank length dictates the joint amplitudes of the ankle, knee, and the hip. The longer the crank length, the greater the top-to-bottom cycle each joint must accomplish. Medical-scientific data does, however, define certain angular limits that are specific for each one of these joints. The closer to the limit (or beyond it) the more stress the system feels.
With the use of shorter cranks and a higher pedaling cadence we limit the forces applied to the muscular-tendon system. In overview, cranks that are too long put too much stress on the joints. The increase in pedaling cadence with shorter cranks also increases the kinetic energy of the pedal stroke. Consequently, the cyclist’s energy output is improved by an inertial effect. The scientific results show that muscular coordination of lower limb muscles is facilitated with the use of shorter cranks. As such, at the same power, pedaling is more fluid and cadence is increased. This is more efficient, less stressful, and leads to a better performance. Using the Cyfac Postural System, the 5 major parameters that determine crank length are: inseam, age, gender, level of riding, pre-existing pathologies.
Pez: Besides personal preference, are there specific times when free pedal float is NOT desirable from an ergonomic/biomechanical perspective? Is there such a thing as too much pedal float?
Matthieu Papin: Only the track sprint races necessitate, for safety reasons, a complete blockage (fixing) of the foot on the pedal. For all other cycling disciplines it’s preferable to allow some movement at the foot-pedal interface in order to respect the biomechanics of the lower body. The heel must have some measured freedom of movement in order to limit muscular-joint stress but also to minimize the loss of propulsive energy. For the majority of cyclists, the heel’s variation of longitudinal angle stays between 3 and 6° and should never go past 9°.
Pez: There have been a number of claims about platform size on pedals, with some companies touting the largest platform, and others (e.g.,Speedplay) counting the cleat as part of the platform. What is your analysis?
Matthieu Papin: The latest research on the biomechanics of pedaling shows that pedaling efficiency is optimized by:
1. having greater contact surface between the pedal and the cleat
2. the distance between the cyclist’s foot and the pedal axis (affected according to the thickness of shoe sole and the height of the pedal/cleat ensemble).
Currently, the Look Keo, Time RXS, Speedplay, and Shimano SPD-SL pedals meet these biomechanical characteristics.
Get more info at:
• The US Importer – VeloEuropa website
• Cadence Cycling website.
Aymeric Le Brun:
Aymeric Le Brun is Cyfac’s Product Director. With a DESS degree in Sports Economics, Aymeric is responsible for product development, material acquisition, and communication. He has logged many miles as a national level cyclist and has been steeped in cycling since his youth in the Brittany, France’s cycling heartland. Intensely passionate and dedicated to the development of bicycle technology, Aymeric also remains faithful to the hand-made techniques and high-end craftsmanship synonymous with Cyfac.
Matthieu Papin is Cyfac’s resident Sports Ergonomist. An accomplished cyclist, triathlete, and runner, Matthieu backs up his love of sport with a Ph.D. in Sports Biomechanics and a degree in Sports Engineering. He is responsible for the development of Cyfac’s Postural System and works closely to optimize the dynamic inter-working of the cyclist-bicycle pair.