These are the official guidelines for Bicycle Fit used by the United
States Cycling Federation. They can be used for Road/Racing bikes, but
would not be applicable for Mountain/Hybrid fit. This is probably the
most comprehensive electronic statement on Bike Fit that I've seen, so
I hope you will find it useful.
Stoots
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USCF Bike Fit instructions:
Taken from United States Cycling Federation & Bicycling Magazine's Weekend
Cycling College Handout, pp 65-71., 1993
For information on attending the Weekend Cycling College sessions, contact
USCF at (719)578-4581 or watch Cycling USA for announcements.
Comments or remarks inside of square braces [comment] are mine and are
things I have added for my own clarity.
BIKE FIT AND ENERGY EFFICIENCY
In terms of distance related to energy expenditure, the bicycle is one of
the most efficient forms of transportation in existence. However, any
human/machine interface can have the relationship fine-tuned with the
purpose of maximizing the performance potential. Scientific research in the
area of bicycle biomechanics has recently begun to define some of these
ergonomic parameters and measurements to assist competitive cyclists in
establishing "position" on their machines. These recommended parameters are
usually specific to events or populations, but they do set a basic outline
for adjusting your bicycle to your body's dimensions.
The amount of improvement possible by properly "fitting" a bicycle is
considerable. In 1981, a group of good USCF Junior riders were tested upon
arrival at the U.S. Olympic Training Center in Colorado Springs. On their
own bicycles, they were evaluated for oxygen consumption at three sub
maximal loads, and a maximal work capacity. Then following a total position
adjustment by the coaches, the testing was repeated. The group was able to
reduce average oxygen consumption by 8 to 14 percent at the same work
levels. The results also demonstrated that as the workloads increased, so
did the oxygen savings. When energy requirements at a set work rate are
reduce, efficiency has been improved. A saving of 10 percent in oxygen
consumption for these Juniors was similar to reducing body weight by 15
pounds while maintaining the same power output. This sizable saving may
have been magnified by their inexperience and lack of coaching, but many
cyclists are in similar situations.
Based upon the studies available, and the input from many reliable coaches,
the parameters outlined below will allow you to optimize your position on
the bicycle for short (less than 60 miles) time-trial competitions. The
recommendations only establish ranges of acceptability, and do allow for
some individual alterations due to riding style or physical variations. We
believe the ideal bike fit may take several months to years. Juniors,
because of their continuing growth, need their position checked several
times a year.
KEY FRAME DIMENSIONS
There are three frame dimensions critical to proper bicycle sizing: seat
tube angle, seat tube length, and top tube length. The seat tube angle
should be from 72.5 to 75 degrees in relation to horizontal. The steeper
the frame angle, the harsher the ride, and the more a frame is limited to
proper position only for short events. At 73.5 degrees a wide range of
positioning adjustments are available to meet most needs. Most modern
manufacturers come close to an ideal range, but there is a trend toward
more upright frames that may limit your choices if you want a more
versatile frame.
If your frame is correctly sized, you still have 11 small component
adjustments that comprise proper positioning. The best way to adjust your
bike is to have it placed on a wind load trainer, use a level to assure
that front and rear axles are perfectly horizontal, and have the assistance
of a trusted partner. The procedure will take about an hour, but take it
slow and easy, because so many of the adjustments interrelate with changes
in one dictating re measurement of another.
Be accurate and be sure to follow the adjustments in the order they are
presented. To create a proper biomechanical relationship, you must adjust
the points where the body actually interfaces with the machine. On the
bicycle, these points are the pedals/foot, the saddle/posterior, and
bars/hands. Each area has sever small adjustments for comfort and
efficiency. (See diagram).
FOOT/PEDAL POSITION
The placement of the foot into the pedal significantly affects power
transmissions, pedaling techniques and potential foot discomfort. Three
adjustments act to secure the body to the machine and act as a baseline
from which to adjust all the other biomechanical relationships.
Begin with the fore-aft placement of the foot on he pedal. While standing
erect in your cycling shoes, place a white dot on the shoe over the inner
ball of each foot. This is located on the distal head [ Anatomically
located far from a point of reference, such as an origin or a point of
attachment] of the first metatarsal bone [The middle part of the human foot
that forms the instep and includes the five bones between the toes and the
ankle] (the point forward of the arch that prominently protrudes toward the
midline of the body). Be sure to mark the point specific to the bones of
your foot, and not the area created by the manufacturer of your shoe.
These points may be very different. Also, locate these bones on each foot,
as there is always variation between foot sizes and shape on the same
person. Place the shoe into the pedal with the cleat loosened enough to
allow easy fore and aft movement. Position the dot so that it is directly
over the pedal spindle. This is the neutral position, best for the
majority of riders. There remains a degree of adjustability from this
point based upon racing distance, foot size, and riding style. If you have
exceptionally long feet or toes for your size, you may find moving the shoe
forward of the axle more secure.
If you have one available at a local bike shop, the Fit Kit's Rotational
Adjustment Device (RAD) does an excellent job of alignment. When you have
decided on placement, again trace the cleat with a permanent line and fix
the cleat bolts with a blue Loctite (available at hardware store, it keeps
nuts and bolts from loosening).
Note: A person using the rotational adjustment device for cleat position
should not be looking down at his or her feet, as this will change your
foot position giving you an improper fit.
The last foot adjustment is the correct use of toe clips and straps, if you
don't use a clipless pedal system, toe clip length should he selected to
assure at least l/4" of clearance between the toe of the shoe and the clip,
when power is being applied to the pedal. The clip size can be adjusted by
stacking washers behind the mounting washers or positioning the clip flange
inside the pedal cage rather than in front. The clip should also parallel
your foots rotational adjustment. Don't be afraid to use some pliers to
bend the toe clip for a customized fit. The only place the toe should touch
the shoe is at the top strap retainer. The toe-strap buckle should rest on
the outside edge of the shoes sole and not on the top of the foot.
Recently, many pedals have been designed to become narrower at the rear
cage to increase cornering angles. If you have wide feet or supinate [To
turn the foot or leg so that the sole is outward] while riding, this
prohibits proper support and strap placement. Purchase wider pedals and
your discomfort should disappear.
SADDLE PLACEMENT
The location of the saddle in relation to the pedals has the greatest
influence on the rider's ability to produce power. Research has been
conducted to determine saddle heights that produce the most raw power, the
greatest aerobic efficiency, and the best aerodynamic position.
Unfortunately, the results have shown that different goals produce
different recommended saddle heights. Time trialist need to position
themselves with a saddle height designed to produce the greatest aerobic
power at the lowest oxygen cost over a time period greater than one hour.
These are essentially the same requirements of Olympic-level time-trial
competitors.
A range of seat heights approximately 20mm wide allow the most efficiency.
Only slightly above the range, oxygen consumption rose significantly.
Below this range, the oxygen consumption increased less dramatically, but
the trend was obvious and the power production capability was reduced. The
range was from 94.5 to 96.5 percent of trochantric leg length (determined
by measurements from the top of the femur at the hip socket, passing
through the knee, to the lowest edge of the foot). This was slightly higher
than the coaches had considered optimal. The acceptable range of variation
(about one inch) was much wider than most people had assumed. Additionally,
the seat heights that the riders had been training at prior to the study
were nearly as efficient as the best possible fits in this range. All the
riders had instinctively set their heights at 96 percent to allow the
highest power at the lowest oxygen cost.
To set your seat height:
1. With your bike on a wind load trainer, remove both toe clips.
2. Measure the thickness of your cycling shoes at the heel and at the
cleat. Record the difference in sole thickness between the two
measurements. Some styles have a uniform thickness throughout (Adidas),
while other may have a sole that thickens under the cleat dramatically
(Sidi).
3. Set the saddle so that it is perfectly horizontal. Use a level. (We
will finalize the seat angle later.)
4. Put on your cycling shorts, and mount the bike. Pedal for at least 10
minutes at moderate load and regular cadence to settle in to your normal
seating position. Stop pedaling, remove your right foot from the shoe, and
have your partner bring your right crank down to a vertical position. (This
should he straight down in line with the seat tube.) Position of rider
should be with the hands on the brake hoods.
5. Drop your heel down toward the pedal and position it just above the
top of the pedal surface. Straighten your leg, but do not reach by moving
your hips. Do not even look downward. The foot is still not touching the
pedal. Have your helper position your foot in a flat position and measure
from the bottom of the sole at the heel to the top of the pedal. There
should be at least 5mm clearance.
6. Now add the difference in sole thickness that you measured earlier to
the gap. If your shoe is 1Omm thicker at the cleat than at the heel, the
foot should have a 15 millimeter space above the pedal.
7. If you have large feet as compared to your height, or if your pedaling
style is decidedly toe-down, add another 4mm to the gap.
8. Now check the other leg with the same procedure. It is quite normal to
have a few millimeters of difference between leg lengths. If it is
pronounced (more than eight millimeters), visit a sports-oriented
podiatrist or orthopedist to confirm this discrepancy and compensate for it
with orthopedic inserts or a built-up sole under the cleat is recommended.
This should give you a very good, efficient seat height in the middle of
the acceptable range. Remember, if you err, be on the short side as the
penalty for a too-high saddle is severe. Mark your setting and record it.
It you are competing in ultra distances and train more than 300 miles per
week, lower your saddle five to eight millimeters from this position. Its
not quite as efficient as the higher position, but will reduce stress on
the knee, which becomes more vulnerable to injury with mega-mileage.
The fore/aft adjustment will effect seat height so don't put everything
away yet. With your foot in the cleats, pedal for five minutes to settle in
again. Have your partner bring your right crank arm to horizontal (three
o'clock). Drop a plumb line from the tibial tuberosity toward the pedal.
(The tuberosity is the small bump on the front side of the shin hone below
the knee). Move the seat fore or aft on its rails until the plum line
bisects the pedal spindle. This is the maximum forward position for the
seat, and should only be used by short-distance riders that spin a high
cadence with lower gears. A neutral position would be with the plumb line
falling one centimeter behind the pedal axle.
After your fore/aft position is finalized, mark the seat rail and repeat
the seat height measurement procedure. As you moved the seat rearward. your
saddle height was increased. Finalize the seat height again, placing a
piece of tape around the seat post to mark your extension, and recheck the
fore/aft position to make sure that it did not change. You may have to
repeat these two adjustments several times until you are satisfied.
As an addition, it should be noted that crank arm length will have an
effect on fore/aft foot position. Crank length is the distance from the
central movement of the bottom bracket to the central movement of the pedal
spindle. This distance is generally dictated by the following rule: A rider
with a body height of 175 cm uses a 170 mm crank length. Each 5 cm of body
height makes a difference of 2.5 mm in crank length. For example, rider of
180mm height may use a 172.5 crank length. A rider of 170 cm height may use
a 167.5 mm crank length.
The angle of the saddle is a matter of personal anatomy and comfort more
than biomechanical position. A horizontal saddle allows the cyclist to move
back and forth across the surface to change position as the terrain
dictates. Some male riders prefer slight upward tilt (3-4 degrees) with the
nose of the saddle, and many women riders feel an equally small downward
tilt is more comfortable. Whatever you select, keep it conservative and
comfortable for your own anatomy. A common error for beginners is to tilt
the nose of the saddle slightly downward for comfort, which results in neck
and shoulder soreness from the strain of constantly pushing themselves back
onto the saddle.
HANDLE BAR PLACEMENT
The handlebar position determines upper body support, leverage for hard
efforts, and respiratory limitations while riding. To a large degree, the
top tube length of your frame sets the limits of adjustability for your
bars. Incorrect handlebar placement does not affect power production much,
but it does create rider discomfort. The items to he considered are stem
height, stem length, handlebar bends, bar angle, brake hood location and
bar width.
Stem Height: The top of the stem should be no more than 4 to 6 cm below
the highest point of the saddle. Going lower than that will do nothing to
improve aerodynamics, but will increase neck strain. Most riders have
their stems too low and assume a greatly bent over position. This is
partially due to the fact that many stems do not have a sufficient range of
height. If your thighs contact your abdomen, this is a sure sign that your
stem sits too low in the head tube.
Stem Extension: The length of the stem extension determines the horizontal
distance between the handlebars and the seat. To determine a proper stem
extension. assume a normal riding position with your hands on the brake
hoods. Have a helper drop a plumb line from the tip of your nose while you
look down at a 45 degree angle toward the road surface. The line should
pass about one inch behind the handlebar. A long ride can also give you
evidence about the stem extension. If you develop soreness in the triceps
and deltoid (upper arm) muscles, the stem extension is too long. A short
stem will cause your neck and trapezius (shoulder) area to ache. Women
generally need stem extensions in the 80 to 110mm range (measured from the
front edge to the back edge), while men's longer arms accommodate 90 to
120mm lengths.
If you find yourself needing stems too much longer or shorter than those
ranges to get a proper fit, the top tube length of your frame is the real
culprit. Do not try to get away with bizarre stem lengths to compensate for
a poorly fitting frame. Steering, weight distribution, and center of
gravity get so fouled up, that at best the bike will always feel
"squirrelly," or unpredictable in its handling; at worst it will be
dangerous to ride.
Handlebar Shapes: Select a bar that has a straight top section with no
forward bend for at least 25 centimeters across the top. The bars should
not curve downward like track bars, or upward, as do some touring shapes.
The drop, or the vertical distance from the top of the bars to the bottom,
should he a minimum of four inches, and for larger riders as much as
six-and-a-half inches. Cinelli Model #64 and Model #66 are two excellent
examples of good road bars.
The width of the bars should equal the distance between the forward,
rounded edge of the shoulder joint. Bars that are too narrow inhibit
complete respiration while wide bars act to increase aerodynamic drag.
Hold the bars up to your shoulders and the ends should hit you outside of
the ends of your collar-bones, but inside the edge of your shoulder. Women
generally use 38 centimeter bars, while men are more likely to need 40 and
42 cm widths.
Handlebar Angle: The best rotational angle for the bars creates a neutral
position for the wrist---you should be able to grip the drops or brake
hoods without extreme bending of that joint. Position the bars by rotating
them in the stem clamp until the ends of the bars are pointing at the
mounting bolt for the rear brake. The wrist should be able to maintain a
relaxed grip on the drops and still be able to reach the brake. If this is
uncomfortable for you, you can rotate the bars upward, but not beyond
parallel to the ground.
Brake Lever location: The neutral placement for the brake levers is
achieved with the brake lever tips in line with the bottom of the handlebar
drops. Because you spend 50 percent of your riding time with your hands on
the hoods, avoid the temptation to bring them up much higher by changing
their position or rotating the bars. As long as you can safely reach and
operate the brakes from both normal hand positions, strive for the lowest
profile that is comfortable. If your stem has the proper extension, and
your levers are properly placed, your upper body/back should lean forward
at a 45 degree angle when you're on the hoods. When you move to the drops,
your back should be nearly flat, with your upper arms vertical, and the
elbows bent at 110 degrees. For women to be comfortable, buy brake levers
designed for women, or bend levers toward handlebars to accommodate a
females smaller hands and reach.
Now if you have taken your time and double checked everything, you should
have achieved an optimal position on the bike. A last check is to measure
the weight distribution of the bike. Put a scale under the front wheel and
an identical thickness of wood under the rear wheel and mount the bike.
Have your helper steady you while you assume your best racing position.
Record the weight on the scale. Reverse the scale and support and repeat
the weighing. Add the two weights together, and then divide each separate
weight by the total. A properly balanced bike and rider should have 45
percent on the front. Any more than 60 percent on the rear or 50 percent on
the front will make for an unstable bike.
Record all your final measurements and permanently mark them on the
equipment itself in case you have to disassemble the bike. Ride the bike
for a few long rides, and listen very carefully to your body. It may feel
strange at first, but give the body time to adapt to its new location. All
the measurements allow for some individual adjustability but do not tinker
continually. When you end up with a comfortable position on the bike, don't
change it! Now all you have to do is concentrate on training to go fast.
.
Last edited by:
stoots: Mar 3, 05 8:36