This is an incomplete listing of terms used in bike fitting. Contact us if you have suggestions for additions or edits!
Using direct measurement and observation without the use of computer aided motion capture and software analysis.
The absolute and relative lengths of body segments eg thigh, lower leg, inseam, torso, arm, shoulders.
Measuring and recording the geometry and size of a bike, including the relationship of component to the frame. E.g. seat height, stack and reach, stem length, seat tube angle, handlebar and seat X/Y
Body Geometry and BG Fit
Specialized Bicycles branded bike components and bike fitting education for dealers. BG Fit is the brand name of bike fitting services available through Specialized dealers.
Body Angles (joint angles)
Used to observe/ record bike fit position of the cyclist’s joint angles either at a static position of flexion or extension, or dynamically through a range of motion.
Measuring and recording the anatomical proportions of a cyclist. Used to predict suitable bike sizes and initial bike fit position.
Published in 1972, this was one of the first cycling manuals to articulate the importance of bike fitting, and to provide guidelines for doing so. Named for the acronym of the Italian cycling organization the published it. Influential in the establishment of early bike fitting protocols.
The study of motion of a person riding a bicycle, usually narrowed down to leg action through the pedal stroke.
A supplier of analysis software for use with video capture of sporting movements, that is popular in bike fitting.
The use of video or motion capture (2D or 3D) to record, observe and interpret body position and fit co-ordinates through software. E.g. Retul uses a digital fit system.
See Saddle to Bar Drop.
The process of observing, assessing and adjusting the position of a cyclist whilst they are pedaling.
The observing can be facilitated by using digital tools like motion or video capture.
The adjusting is most easily achieved using a Size/Fit Cycle.
Effective Top Tube
The horizontal distance from the center of the intersection of the top tube and head tube, to the centerline of the seat tube or seat post.
An adjustable angle finder used for measuring range of motion and body angles.
Fit Institute Slow Twitch. A bike fitting school with a focus on Triathlon fit, operated by Dan Empfield who developed the modern triathlon bike.
The process of adjusting a bike for a cyclist to optimize their comfort, performance and efficiency, taking into account their riding experience, objectives, and physical condition.
Fit Kit System
A proprietary method of predicting a suitable bike size and initial fit position for a rider, based on a combination of body measurements and rider information. The data set is based on empirical evidence rather than algorithms.
Predicting and fitting the bike based on mathematical formula and algorithms, without taking into account personal variance.
Database of bike makes and models including frame size and geometry. Used to help select an appropriate bike for a rider to purchase. This feature is increasingly common in size cycle software.
Originated in Canada. Purchased by Dorel Industries who own Cannondale and several other bike brands. The Guru Experience is a digital fitting system using an electronically controlled and adjustable size cycle (DFU), and 3 D body scanning to record bike and body positions, and simulate different bikes and fit positions.
The inseam length from heel to groin is a body measurement commonly used to determine a frame size and a saddle height. Used on its own, it is inadequate for either prediction. Used on its own, it is most accurate only for estimating standover clearance.
Using Inseam Length only to predict a frame size fails to take into account the upper body proportions and the reach from saddle to bars.
Using Inseam only to determine a saddle height neglects foot length and cleat position and pedaling style which all factor into the saddle height.
See Body Angles
Movement. Cycling kinematics means cycling movements.
A tool for projecting self leveling vertical or horizontal lines onto a surface. A useful bike fitting tool with various applications in the fitting process.
Displaying and recording the movement of a cyclist by detecting and tracking body markers that are attached to key points on the body. Depending on the capture system (infrared or video) the software displays either a stick figure or full image on a computer screen and computes a range of attributes.
2D and 3d versions are available. Pioneered for bike fitting by Retul, but other suppliers have since entered the market.
A basic builders tool that has been applied in bike fitting to assessing the vertical position of the front of the knee in relation to the pedal spindle, in order to establish a suitable saddle setback position. Superseded by digital technology in video and motion capture systems.
Using highly sensitive and thin electronic pads to detect and measure pressure and show it numerically and visually in software. Applications include all direct contact points on the bicycle: feet, hands and butt. Brought to market by German firm Gebiomized.
Rotational Adjustment Device (RAD)
Diagnostic tool that attaches to the bicycle crank, to help examine and align the lower leg’s natural rotation during the bicycle stroke in a cleated bicycle shoe.
The distance between the seat and the handlebars. May be described in general observational terms of the rider eg “long”, “short” or in bike measurements eg tip of saddle to center of bars.
Handlebar reach refers to a horizontal measure of the bar’s dimensional shape.
Also see Stack and Reach
One of the pioneers of using motion capture technology in bike fitting. Purchased by Specialized Bicycles and now only available to Specialized dealers. Often promoted in conjunction with BG Fit.
The term “Retul Fit” has become synonomous with using motion capture in the fitting process.
Saddle / Seat
Seat Angle or Tilt
The angle of the saddle from the rear to the front, expressed either in general terms Eg nose up or nose down or level, or in degrees from the horizontal using a digital level from nose to tail.
a/ distance from the center of the Bottom Bracket to the top of the seat, along the seat tube and post
b/ distance from the center of the pedal spindle to the top of the seat, with the crank at the bottom of the stroke and in line with the seat tube
There are various methods for determining the measurement reference point on the top of the saddle.
Seat Tube Angle
The angle of the seat tube from the horizontal. A steeper seat tube is closer to the vertical and positions the rider more forward on the bike, than a relaxed seat tube. Relevant in terms of the relationship of the saddle to the bottom bracket.
Seat to Bar Drop
Distance of the vertical displacement between the top of the saddle and the top of the handle bars.
On a drop bar, this is to the top of the bars adjacent to the stem clamp.
On a flat bar, this is to the center of the hand grips.
Relative to the seat height, the bars may be negative (lower) or positive (higher).
Inserts used between a cleat and cycling shoe to adjust for a difference in leg lengths.
Serotta International Cycling Institute. Originally founded by frame builder Ben Serotta. Now an independent Bike Fitting School. Introduced the concepts of XY co-ordinates for recording the position of a rider on a bike; the use of a size cycle for fitting; and places strong emphasis on cycling anatomy and biomechanics.
Size Cycle / Fit Cycle
A simulated and stationary bicycle with adjustable frame or fit co-ordinates to simulate different bike geometries and rider positions. Some are manually adjusted and some are electronically adjusted via internal motors.
Used to project and predict a bike fit for stock bikes and custom frame builders. There are two broad categories:
a/ bike geometry simulators into which actual frame dimensions can be set;
b/ XY co-ordinate fit bikes for documenting the rider’s fit position, which rely on software to determine a bike geometry appropriate for that.
Bike sizing is the process of predicting an appropriate frame size and geometry for a rider that could be well adjusted (fitted) to suit them.
Sizing may also include predicting a fit position through a combination of rider interview and formulas, or by position simulation on a size cycle.
A Fit Kit Systems data input based on the responses to four questions, and used as a protocol in determining a suitable bike length and handlebar drop.
Stack and Reach
Originated by Dam Empfield as a bike sizing reference measurement.
The location of the top of the head tube in relation to the center of the bottom bracket, expressed as an XY co-ordinate.
i.e how far in front of the BB is the top of the headtube, and how high above the BB is the top of the headtube.
Commonly used to represent frame sizes as it takes into account both the height of the headtube in relation to the BB, and the distance forward from the BB.
A bicycle fit performed based solely on measuring a rider while they are not moving. i.e sitting on the bicycle but not pedaling.
A set of philosophical, mathematical and procedural models used to define a bike fitting process.
Trek Precision Fit
The current name for the bicycle fit services offered by Trek Bicycle dealers, and for their inhouse fitter training.
Varus and Valgus
Typically used in reference to the feet. The inward or outward angulation of the foot in relation to the lower leg. May be a factor in identifying knee or foot-pedal issues.
Video Capture / Analysis
Capturing is recording a rider whilst pedaling in some movie format / media.
Analysis is being able to review it through software that allows for the use of digital tools like joint angle analysis, point tracking, replay speed adjustment, etc in order to better observe and interpret the cycling kinematics.
Used to cant the cycling shoe or foot and compensate for foot tilt and uneven pedal pressure.
May be in the form of in-shoe orthotics, or tapered inserts applied between the cleat and the sole of the cycling shoe. Developed and promoted by Paul Swift of BikeFit.
A 2D mathematical way to record a riders fit position.
2 sets of coordinates are used, both using the center of the bottom bracket as the reference point:
a/ saddle XY, being the center of the saddle rail position;
b/ handlebar XY, being the center of the handlebar stem clamp.
An adjustable measuring tool designed to quickly and accurately measure these locations.