DYNAMIC BIKE SIZING
Bike Set-up Measurement Procedures
Measured from the Center bottom bracket (middle of crank axle) to top of seat along
seat tube. Mark your seat post at the top edge of the seat tube by etching or with a permanent marker/paint.
Seat post extension is measured from the top of the seat tube clamp to the bottom edge of the seat rails.
Your seat height was determined by your leg angle with the crank arm at bottom center. It is now within the optimal
range for maximum power, efficiency, and injury prevention (145-150 degrees). If you begin to feel a knee pain in the
back of your knee, you may need to lower your seat. If you feel pain in the front of your knee, you may need to raise
your seat. Do not lower it more than one half centimeter at a time. Improving the flexibility of your hamstring muscles
and lower back will also help alleviate knee pain.
Seat Set-back (fore/aft)
Set-back is the horizontal distance from tip of the seat to the center of the bottom bracket(cbb). Use a plumb line for
this measurement. Drop plumb line from tip of seat to top tube (tt). Mark TT. Next drop plumb line from tt to cbb.
Mark tt then measure distance in cm between two lines on tt. This is your set-back measurement. Mark your seat
rails at the leading edge of the clamps.
Stand Over Height
This is the distance from the floor to the top of the top tube, measured at the center of the top tube.
Knee-Over-Pedal Axle (KOPS)
This is the distance of the tibial tuberosity of your knee (bump under kneecap) in relationship to the middle of the
pedal spindle when the crank arm is horizontal. For general road riding KOPS should be “0” (directly over) to 1.0 cm
behind. This will typically provide optimal weight distribution between hands and seat.
For time trial events, your KOPS can be as far as 2.0cm to 4.0cm or more in front of the axle (by moving saddle
forward). This forward position allows for a flatter back and more aerodynamic profile and a more comfortable
pedaling position while riding in aerobars. You will need to raise/lower your seat ~5mm for every 1.0 cm moved
forward/backwards. For hilly TT courses a typical road position usually works best. You may need to raise the height
of your aerobars for more comfort.
This is the vertical distance from the top of the saddle (at center) to the top of the handlebars or aerobar pads. If
experiencing neck and shoulder pain, or you feel like your are “reaching” too far, consider decreasing the drop by
raising the stem and/or purchasing a positive rise stem. Lowering the handlebars (increasing drop) will flatten your
back for better aerodynamics, but may compromise comfort, efficient breathing, and pedal stroke mechanics. It is
essential that you are comfortable in aerobars for the duration of your race distance.
This is the distance from the back, tip, and center, of the saddle to the center of the stem-handlebar intersection. A
general rule of thumb for road riding is that the end of the stem should obstruct the view of the front wheel hub when
riding on the hoods with arms slightly bent. This may not apply if you have a forward geometry bike, as used in time
trials and triathlons, or when riding in aerobars. Consider a shorter stem if experiencing neck, shoulder, or back pain,
or you feel like your are “reaching” too far. Consider a longer stem if you feel “crunched” or if breathing is
Aerobar Armpad Reach:
A rule of thumb: The angle of the upper arm relative to your torso should be approximately 90 degrees to for optimal
support and comfort.
Elbow Pad Width
Your elbows should mask the outer edge of the thighs. However, widen them if you feel “pinched”, feel you have less
control, or you feel your breathing is being impaired.
Research has shown that this angle has little effect on aerodynamics and overall speed, unless the angle is too steep.
The key is to adjust them at an angle which provides maximum comfort. A slight upward angle of about 5-12 degrees
is usually most comfortable, but current theory suggests the aerobars/arms should be level; parallel to ground. This
can be achieved with “S” bend style aerobar extensions.
Upper Torso Height/Back Position
Your upper torso height as determined by your handlebar stem has been positioned for optimal aerodynamics and
comfort. For better aerodynamics, keep your upper and lower back flat and relaxed. Avoid unnaturally tightening and
arching your back as you ride. The height of your torso is dictated by comfort, the distance you ride, breathing
efficiency, and the level of aerodynamics you want to achieve. For more comfort raise your handlebars
To improve efficiency, pedal in smaller horizontal ovals by “pushing” the foot over the top of the pedal stroke. Then at
about the 5 O’clock position start “pulling” back and up (“unload” pedal) before the pedal is at the bottom of the stroke.
THESE SHOULD NOT BE FORCEFULL MOVEMENTS. The sole of your shoe at the cleat (ball of foot) should be
parallel to the ground when the pedal is at the 3 O’clock position. Pedaling should be smooth and without a pulsating
sound. Riding on an indoor trainer is an excellent way to “hear” how efficient you are. It has been suggested that
riding rollers can smooth out your pedal stroke.
For better hill climbing, as your foot passes the 3 O’clock position, lower your heel as if scraping mud off the bottom of
your shoes and exaggerate push-pull pedaling technique.
Bike Geometry and Set-up Diagram
A = Seat Tube Length Center to Center
B = Top Tube Length Center to Center
C = Seat Height
D = Reach From Back of Seat (RBOS)
E = Reach From Nose of Seat (RNOS)
F = Drop (Top of Saddle to Top of Handlebars and/or Aerobar Armpads)
G = Seat Set-back. Set-Back is the horizontal distance between the tip of the seat and the center of the Bottom
H = Reach From Center of Seat as measured through centerline of seat-tube
IMPORTANT: If you change saddles, measure the length of your current saddle and account for any differences
when measuring Reach and Set-back. Re-measure seat height as your new saddle may sit higher or lower on the
rails. The thickness of the padding or internal design may also be different from your old saddle.
Vern LaMere, M.S.
Precision Bicycle Fitting, Performance Testing and Multi-Sport Coaching