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Retul: The Right “tul” for the Job

By Tom Demerly with Technical Assistance from Craig Bellman

Retul is a comprehensive set of tools and methods for optimizing bike fit and position. In the hands of a skilled and experienced fitter it is a highly effective evaluation process.

No other mechanical factor influences your performance on the bike as much as fit. Period.

In a world of debate over the fastest wheels, lightest frame and most aero helmet no expert or layman can argue away the importance of optimizing bike fit and position. Until your fit is optimized you aren’t performing as well as you could be.

Until your fit is optimized you aren’t performing as well as you could be.

Bike fitting entered the U.S. consumer vocabulary in the 1980’s when New England Cycling Academy (N.E.C.A.) introduced a series of tools and methods for measuring a person to find the optimal bicycle frame dimensions for their body dimensions and adjust pedal cleats optimally. It was called the “Fit Kit”. The early system had shortcomings but was a solid start. Over the next 25 years imaging technology, diagnostics and computing power leaped forward. As the benefits of better virtual capabilities and computing power increased so did the opportunities in bike fit and position diagnostics. The current state-of-the-art diagnostic at the consumer level is likely Retul.


What Retul isn’t.

To appreciate the benefits of Retul you have to know what it is, and what it is not. Retul does not fit you. Only a qualified, experienced bike fitter can wield the tools necessary to optimize bike fit and position. People on Internet forums sometimes debate the merits of a “F.I.S.T.” fitting, a Retul fitting, a Serotta fitting, a Fit Kit, a Guru DFU fitting or some other fit methodology. It is the same as debating the merits of different wrenches. In the hands of a skilled mechanic any wrench can produce a favorable outcome, but in the hands of a novice mechanic the results won’t be as good. All fit systems are reliant on the skill of the person doing the fitting. Steve Merz of’s new retail store in Tempe, Arizona just outside Phoenix is the lead Retul bike fitter at TriSports Tempe. Merz is a Retul Certified fitter with nearly a decade of bike fit experience and formal training across several brands. His skill and experience wielding the Retul system make it the diagnostic tool that is a gateway to improved comfort and performance on the bike.’s Steve Merz brings nearly a decade of professional bike fit and position experience to the TriSports Tempe location. His expertise makes optimal use of Retul’s vast capabilities.

What Retul is.

Retul is a three dimensional diagnostic tool that provides a skilled, experienced fitter like TriSport’s Steve Merz with a level of insight more detailed than any other commercially available fit system. Because the three dimensional level of insight into the rider’s position is better, the ability of the skilled fitter to make improvements is significantly increased. Merz is a perfect example. His insights into practical cycling interface with his formal mastery of the Retul system to provide a customer experience unavailable in any other setting. Steve Merz helps TriSports customers use Retul Frame Finder to find the optimal bike without guesswork, and then uses Retul to optimize their position and performance on that new bike or on an existing bike.

Bike positions have traditionally been evaluated with two dimensional depictions, even with video. Retul provides a three dimensional analysis of a rider’s dynamic movement on their bike.

Consider this: Common bike fit complaints seen on triathlon Internet forums are saddle discomfort, knee pain and lower back pain. Fit pundits usually try to find one cause for one problem. Bike fit and position is seldom that simple. Common bike discomfort issues like saddle pain, sore knees and back pain are usually caused by more than one factor. Retul’s three dimensional diagnostic capabilities provide the skilled bike fitter with an unprecedented capability to identify multiple factors that lead to bike discomfort.

Finding Your Best Bike: Retul Frame Finder.

In addition to optimizing existing bike positions Retul also integrates Frame Finder, a database of major bike brands with detailed fit coordinates. Using data gathered by the Retul dynamic 3D analysis and a trained, experienced bike fitter, Frame Finder models the fit interface between the rider and specific bike models and sizes in the Frame Finder database. This resource completely eliminates guesswork from bike shopping. Retul’s Frame Finder is the data-driven way to find the best bike for you. It relies on empiricals, not the subjective guesswork of a test ride. Since Frame Finder starts with an analysis using the Retul Muve dynamic fit bike it gives you the ability to experience changes in bike fit and position in the visceral sense by actually pedalling with the changes on the fit bike, and via the 3 dimensional digital analysis using Retul motion capture. It is the perfect melding of fact and feel in fit. Retul makes test rides obsolete.

The Retul Process.

A key feature of Steve Merz’s use of Retul is the “beginning, middle, end” process of interview, evaluate and position. A Retul fit makes efficient use of client’s time with most fits lasting about 2 hours. This enables busy customers to get the precise fit results they need in a reasonable amount of time and enables Merz to service up to four clients in an 8 hour day.

TriSports’ bike fitter Steve Merz begins the Retul process with a client by interviewing them to identify key goals and experience to optimize the outcome of the fit session.

Merz begins each Retul session with an interview to identify the customer’s goals and experiences on the bike. This interview reveals the key items the customer wants to leave TriSports Tempe with, whether it is a new bike, an improved position to moderate discomfort or assistance with injury moderation. While a bike fitter is not a substitute for a trained physical therapist if a cyclist is injured, improving position is often a key to preventing discomfort from becoming injury.

After the interview Merz actively evaluates the client for functional mobility and screens for significant assymetries including leg length discrepencies and other pre-existing indications that may influence fit and position.

Following the brief interview process Steve Merz conducts a series of physical evaluations to screen for leg length discrepancies, gait anomalies and functional mobility. This active interaction provides the first insights into how the bike will be configured to accommodate the cyclist for optimal comfort and performance.

Once the baseline configuration on the Retul Muve fit bike hase been set up, Steve Merz begins the attachment of the LED emitter harness to the client.

Once the oral and functional evaluations are complete Merz configures the Retul Muve fit bike in a start-point position that may be based on an existing bike, a potential new bike  or a data-generated start point. The advantage of fitting and positioning on a Retul Muve fit bike instead of an actual bicycle include ease of adjustment. Clients can experience stem changes, different saddle positions and even different crank lengths without getting off the bike. Once a baseline position is established on the Retul Muve adjustable fit bike the fitter can attach the LED emitter harness to the client’s anatomical landmarks. This series of LED emitters enables the Retul system to provide three dimensional motion capture analysis and modelling of the rider’s dynamic pedal stroke on the bike.

The LED emitter harness is mounted to the fit client. As the client pedals the Retul sensor unit acquires and tracks the LED emitters creating a detailed three dimensional depiction of the pedal stroke while quantifying all the angular relationships on monitors for the fitter’s diagnosis.

The three dimensional analysis of the rider’s movement on the bike is a key capability to Retul. Early video fit diagnostic systems relied on a two dimensional or “flat” representation of the rider with evaluation of the position usually done on a static image. You could not understand what was happening as the rider actually pedalled the bike. The position was diagnosed as literally a flat snapshot in time. The Retul sensor detects and records not only the angular relationship between the LED emitters, it also records their proximity to the Retul sensor, tracking the movement of the human body through three dimensions in real time during the pedal circle. This level of insight into the client’s movement on the bike extends beyond optimizing a static position. It enables the fitter to observe the fluid movement of the rider in all planes, providing a level of insight into the rider/bike interface previously only available in the most advanced engineering settings.

Retul produces a dynamic depiction of the rider with all the attendant angular relationships displayed on a monitor for the fitter to evaluate. As the client pedals the “stick figure” depicting the relationship between the LED emtters also moves, showing the movement in three dimensions.

With the three dimensional motion analysis running the bike fitter can observe data and graphic depictions of the rider’s landmark points then make improvements based on the observed data. Once adjustments are made the fitter re-evaluates the position to verify the improvements.

A key benefit to the bike fit consumer, and the fitter using Retul, is not only a much higher level of diagnostic capability of the bike position, but must faster processing of the data for evaluation by the fitter. Using Retul, the fitter can perform a depth of analysis previously unavailable in only a fraction of the time of previous fit methodologies. Bike fitting is more in depth, more accurate, more quantifiable and more efficient. It saves the client’s valuable time being fitted and makes the bike fitter more productive, turning out more, and better, fits in less time.

Retul is the bike fitter’s dream “tul” for achieving a level of insight into rider position previously only available to the top professional triathletes and cyclists, many of whom have now used Retul to optimize their positional interface with the bike. When combined with an experienced bike fit professional like Steve Merz of TriSports Tempe the level of capabilities available to the bike buyer and athlete wanting to improve their position and performance is without equal.

Retul is the optimal diagnostic tool for a master bike fitter like TriSports Tempe’s Steve Merz.