Newsgroup: it.sport.ciclismo
Titolo: Per acidjam@yahoo.com circa la scelta della bici (luuuungo)


Subject: How to fit a Bicycle
Sergio,
I'm glad you found the article worth while.
HOW TO FIT A BICYCLE
by Peter Jon White
Copyright 1997
Bicycle fit is always a series of compromises. You're always finding
the best balance of comfort and performance.
When I fit a rider, I start at the bottom bracket. I believe that the
most important aspect of bicycle fit is the rider's fore-aft balance
on the bike. The fore-aft position of the saddle relative to the
bottom bracket determines that balance. Too far forward, and you'll be
supporting your upper body with your arms. Too far back, and the
handlebars will need to come back so far for a comfortable reach that
the bike will be very inefficient while climbing in the saddle, and
awkward to ride out of the saddle. This part of fitting seems to be
the least well understood, and getting it wrong, I believe, leads to
the most discomfort.
Before doing anything else, try to position the angle of the saddle so
that the points of the saddle that your sit bones rest on is level.
Too many people ride with the saddle angled down in the front. This
causes you to be constantly sliding forward on the saddle, (onto the
narrowest part), forcing you to push back against the handlebar.
Obviously, some people can't have the nose of the saddle up too much
in order to level the rear. If raising the front of the saddle to
level the rear causes discomfort, I would suggest looking for a
different saddle, one that allows the most level section for your
pelvic bones. Once you can rest comfortably on the saddle, you can
start the process of fitting the bike.
The technique I use is to have the rider sit on the bike clipped in
with the hands on top of the brake hoods and a little bend at the
elbow. Now take your hands off the hoods and see if you can
comfortably keep the same position of your torso. If it's a strain,
you now know that in that position, you're going to be using your arms
to support you while riding. That can cause a lot of discomfort,
especially in the shoulders and neck.
I generally recommend the furthest forward position of the saddle that
allows you to lift your hands from the bar without feeling like you're
falling forward. I have found that that usually means having the
saddle further back than most fitting systems recommend. Don't worry
too much about handlebar position until the saddle is where you want
it, but while positioning the saddle, try not to have the bar be a
long stretch away. If you current seat post won't allow the saddle to
be placed far enough back, there is an accessory clamp available that
positions the saddle 1 inch further back on most seat posts. It's
called the "Torque Platform".
Saddle height is best found by trial and error. I don't think that a
systematic approach works here at all. Some say the saddle height
should be some percentage of some leg measurement. Some would have you
place your heel on the pedal without shoes on, etc. No system accounts
well for the variations in riding styles, foot angle, and different
leg lengths individuals have. Perhaps the best starting point is to
find the highest saddle position that allows you to pedal without
rocking side to side in the saddle and maintain some bend in the knee
at the bottom of the pedal stroke. But I stress starting point here.
An interesting point is that while some people are very sensitive to
minor changes in saddle height, most people don't seem to be.
Variations of one half inch or so don't seem to matter much.
There are two parts to finding the best handlebar position; height and
reach from the saddle. A higher position, to a point, is more
comfortable and affords a better view of the road and scenery. A lower
position is more aerodynamic, helps your muscles work more
efficiently, gives better high speed stability, and makes climbing
easier. A handlebar position closer to the saddle is more comfortable,
and positions the torso more upright, but a longer reach helps in
climbing, (especially while out of the saddle), and in high speed
control. I recommend the lowest position and longest reach you feel
comfortable with. I use an adjustable stem that allows a wide range of
vertical and horizontal adjustment. The customer can take his own bike
out with this stem in place and try lots of combinations on the road. 
I would suggest using your present bike to, first, find the ideal
saddle position for you, then the ideal handlebar bar position. Once
the old bike fits, write down these measurements: Vertical distance
from BB axle, to a horizontal line across the top of the saddle:
Distance from a plumb line dropped from the nose of the saddle to the
BB axle. Distance from the nose of the saddle to a vertical line
through the center of the stem's handlebar clamp. Distance from a
horizontal line across the top of the saddle to the center of the
stem's handlebar clamp. Distance from the center of the stem's
handlebar clamp to the front of the handlebar drop, (the reach of the
bar). Then when you're looking at new bikes, choose one that allows
you to position the saddle and bar where you need them. Be sure to use
your own saddle when sizing the new bike.
You may end up with a choice of sizes. I like to maximize stand over
clearance so I usually recommend the smallest frame that gets the job
done. The trade-off there is that smaller frames give you less room
for water bottles and other accessories, another compromise!
Notice that in all of this there is no mention of measuring body
parts, dropping plumb lines from knees, positioning handlebars so they
block views of front hubs, etc. My methodology is quite different from
what most people are doing in bike shops. The Fit Kit and other
marketed fitting systems are based on the measurements of lots of
different riders and their bikes. It assumes that the averages of
those measurements are somehow going to result in a good fit for you.
But take the case of two riders; Rider A, and Rider B. Rider A has
very little upper body muscle but very strong legs. Rider B is
identical to Rider A but has been working out at Ralph's Gym and looks
like a body builder. The fore aft position of the saddle will be
different for the two riders. The extra upper body mass of Rider B
will require a slightly further back saddle position to give the same
balance. 
Different riders of identical physical proportions are likely to make
different compromises in the fit of their bikes. The main difference
between sizing a racing bike and a touring bike is that you might
choose a different handle bar height and reach. But the fore-aft
saddle position may be different as well. Racers are less concerned
with looking at scenery than tourers, and a lower bar position
definitely helps the power output. Also, a more forward saddle
position allows the handlebar to be more forward, a definite help in
fast climbing. This is likely to be more important to the racer than
the tourer. 
Remember that fitting is a series of compromises between power output
and comfort. Take a look at a track sprinter. The torso is almost
horizontal. The arms are reaching down to the handlebar. This is not a
comfortable position. But it does allow the sprinter to get the
maximum power to the pedals because he can pull more effectively on
the handlebar while pushing the pedals. The average cyclist wouldn't
want to make the extreme compromise in comfort to achieve the fastest
sprinting position. But we all have to make a decision about what
compromises we do want to make.
Most likely, many of us have ridden a three speed bike like a Raleigh
Sports at some time. The three speed is designed around comfort rather
than efficiency. It couldn't be more different from the track bike.
The saddle is way back, the handlebars are close to the saddle and are
at or above the saddle height. One of the reasons why the traditional
three speed bike is so slow is the riders position, which doesn't
allow the muscles of the body to work together as well as the racing
bike does.
Somewhere between the fit of the three speed and the track bike is
where most of us want our bike to be. But each of us has to find that
point for ourselves. No "expert" can tell you how much comfort you are
willing to give up to be able to climb a hill better. Nor can he tell
you how much speed you should give up to make the bike more
comfortable for tomorrow's century.
Peter White Cycles
666 Massachusetts Avenue
Acton, MA 01720
978 635 0969
Pe...@PeterWhiteCycles.com
Peter Jon White
Peter White Cycles
666 Mass Ave. Route 111
Acton, MA 01720
(978) 635 0969
 Voice, 
(978) 263 0181
 Fax
mailto:
Pe...@PeterWhiteCycles.com
http://www.PeterWhiteCycles.com

Grazie!
Nico