The technology behind fitting a triathlete to a bike is advancing as fast as the triathlon bike itself. (LAVA Archives/June 2015)

As a 15-plus year veteran of bicycle retail and bicycle fitting, I still find it inspiring to help athletes take an educated approach to getting set up properly on the bike. Bicycle fitting has evolved over the years into a highly technical, quantifiable and exacting process. Bicycles have gotten more specialized, and as athletes work to eke out every last bit of performance from the bike, bike fitting tools have evolved to meet their needs. I would like to break the process down by separating the new generation of bike fitting tools from the actual process of fitting.

But the process of matching the rider to the bike has evolved and there are now a myriad of choices.

Essentially, our plumbing has stayed the same. The way we need to move with the bike has stayed the same. But the process of matching the rider to the bike has evolved and there are a now a myriad of choices. One of the first big revolutions in the fit studio was the fully adjustable fit bike. The ability to easily change angles and proportions without having to struggle with the rider’s actual bike was a real boon. Now the fitter and client are free to explore different positions and hone in on the ideal. Once the contact points are determined on the fit bike, that information can be used to set up the current bike, select a new bike, or even to draft a custom frame.

The Serotta Size Cycle was one of the first fit bikes to be widely used and is still in use today. The Size Cycle is manually adjustable through the use of quick-release levers and a digital angle finder to measure seat angle. It looks very much like a regular bike when set up and ready to go. The Size Cycle generates the X and Y coordinates, and will give basic frame geometry information and contact points in space that make it easy to apply the information across various platforms. There are many high-quality, manual, accurate fit bikes—Calfee, Waterford and Exit are a few more that come to mind.


Chris Lieto dialing in his position before Kona 2010 at the San Diego Low Speed Wind Tunnel.

The next generation of fit bike streamlines the process further by making it possible to adjust the position of the rider while they are still on the bike. The use of hydraulics and manual cranks can greatly increase the efficiency of finding the ideal position. A good example of this sort of equipment is the Guru Dynamic Fit Unit (DFU), a completely computer-automated system that can capture unlimited riding positions for comparison. This feature of the software allows the fitter to toggle back and forth between various riding positions to quickly help the rider assess which choice is the best.

Another example of a next-gen fit bike is manufactured by Purely Custom. It looks less like a bike and more like two towers that run on a track. One tower is for the saddle and the other for the bars. This tool also allows on-the-fly adjustments while the athlete is riding and also makes the fit process more efficient. Both the Purely Custom and the DFU rely on software to generate a report with the fit coordinates that can be used to set up a current bike or to find a match with the perfect bike by tapping into a database of manufacturers’ frame geometries.

Clearly there are now sophisticated fitting tools. But how do you quantify those measurements? The answer is motion capture. The combination of high-quality motion capture systems with a good fit bike is where the magic really happens. Now the rider can be moving under real-world resistance levels and the effect of the effort on the position can be accurately measured. The Guru DFU integrates 3D motion capture into its suite of analytics. Other current examples of this technology can be found in the Dartfish 2D and Retül 3D motion capture systems.

Retül is a motion-capture system that measures the rider dynamically in three dimensions and displays those measurements in real time. Sensors are placed on the rider at various points, and an array positioned along the side of the rider picks up the signals within less than a millimeter of accuracy. Retül can measure movements in 3D, meaning that the fitter can look at the degree of flexion in the leg through the bottom of the pedal stroke and also see if the knee is flaring out or dropping in simultaneously.

Dartfish is a software package that allows videos to be captured from a variety of sources in 2D and has a number of measurement tools that can be overlaid on the videos to quantify motion. Besides being a measurement device, video of the rider in motion is helpful as a teaching tool about posture and form. Videos can be taken from any angle, so assessment from the front, back, top and side of rider can be made simply by moving the camera. Both Dartfish and Retül are portable, so fitters, trainers, coaches and physios can use this technology outside a dedicated fit lab and in the field as needed. Outside the fit lab, the work could be done on a bike set up on a trainer. For smaller adjustments, follow-up sessions and assessments on the bike, these motion capture tools are fantastic.


OK. So now we have some great fit bikes and ways to quantify motion. How do we get to a great fit? It’s all about methodology. All of these great tools mean nothing if there isn’t a robust protocol to guide the fitter and rider to a good position.

There are many ways to approach bike fit and in my experience, people fall into one of two camps. One camp is the fitter-guided, rider-selected approach used by F.I.S.T, which was developed by Dan Empfield of Slowtwitch fame. The other is based on first assessing the athlete’s mobility, goals and functionality and then using those strengths and weaknesses as guidelines to help the fitter recommend the best position. This protocol is practiced by innovators such as Paraic McGlynn, founder of Cyclologic. Both of these approaches are valid; they aim for the same result, but do so from different points of view.

The F.I.S.T. protocol stems from a top-down approach: it posits that all elite triathletes adopt a somewhat similar position on the bike and that fit, mobile age-group athletes can get into similar postures with training and practice. F.I.S.T practitioners believe that the body is smart and can be trusted to find its own nexus of strength and balance.

Cyclologic takes a bottom-up approach: it uses mobility assessments to establish the athlete’s ranges and limits first and optimizes the position within those limits. Both of these protocols are currently being taught and are always being improved on as new ideas come to light.

One last critical point about the bike fit process is that the body is not static. Fitness and mobility change over time, so fit coordinates that worked to get you set up for a fast, short-course event are probably not going to be ideal for a long-course race, for example. Communication between the athlete and the fitter will influence the result and is critical to a good result for both parties. A single fit session will absolutely give an athlete a great foundation to work from, but that one fit doesn’t need to be set in stone. Cyclologic takes this point to a new level. It has dispensed with the term “fitting” in favor of “cycling analysis” and is constantly developing and integrating new tools to allow the athlete to quantify changes over time.

To pull all of this together, I think it is critical to know that all of these tools, methodologies and ideas are valid. As a potential client, an athlete should ask questions about the approach that the fitter will take. Does that fitter have experience setting up bikes in the way you are looking to ride? How many fit sessions has the fitter performed? How are they going to provide the information to you and how can it be applied? How will they follow up? Once you’re satisfied with the answers to these questions, go for it. You will be faster and more comfortable. Guaranteed. LAVA

Adam Kaplan, head cycling analyst for Get a Grip Cycles in Chicago, has been fitting and designing bicycles for over 15 years. Looking to create long-term relationships with it’s clientele, Get a Grip Cycles pioneered a fit-first philosophy to ensure the bike truly meets the needs of the rider, regardless what it says on the downtube.