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Bicycle
Size and Fit
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The fit of a bicycle is very
important. If you are not comfortable, you won't ride.
If the fit is not right, you will be less efficient.
There are some general rules of thumb for determining the
bike fit, but they are only approximate. To further
complicate matters, many manufacturers measure their bicycles
differnetly, so the same size from one company will not be the same
size as from another company. Companies also have
different geometries, some position the rider in a more stretched out
aggressive position while others have the rider in a more upright
postion.
Frame Size
- Frame size is a measurement of the length of
the seat tube. Some companies measure from
the center of the bottem bracket to the top of the seat
tube (measurement A in the diagram below).
Others measure from the center of the bottom bracket to the
top or center of the top tube. On road bikes the measurement
is usually given in centimeters. On mountain bikes
it usually done in inches. Some manufactures don't provide a
measurement, but rather make a few size frames and label them small,
medium and large
Stand over height and clearence
- The stand over height is the distance from the ground to the
top
of the top tube (measurement K in the diagram). The clearence
is the distance from your
crotch
to the top of the top tube when you straddle the bike. The standover
height is not a mesurement that manufactureer usually give, but it is
very useful to buyers. (Tip to sellers - Put the standover height in
your ad.) This measurement wiil let you know if you can
straddle the
bike
and if you will have clearance. For a road bike you should
have
at least an inch of clearence. For a mountian bike, it should
be
at least two inches of clearence.
Top tube
length
- The top tube length is the distance labeled C in the above diagram.
The top tube length and the stem will determine how upright
or
stretched out you will be when riding. Replacing the stem can
change your position. However the stem can be
expensive, so
if you buy a bike that does not fit and you plan to correct the fit by
replacing the stem, just be aware of the potential cost of the stem and
the installation.
What size do
I need?
- Are you confused by this point. Between the different ways
that manufacturers measure bikes, individual differences and personnel
preferences, it is difficult to give a size just based on your height
or inseam. Never-the-less, the table below provides a good
starting point.
To use this table, you will first need to get an accurate measurement
of your inseam. The easiest way to get a good measurement is
to stand against a wall and hold a
book between your thighs, with its spine snugly against your crotch in
the same way a bike seat will be, then have a friend make a mark on a
wall at the top of the (horizontally straight) spine.
Stepping away from
the wall, measure the distance to the floor. This is your
inseam
length. A road bike frame's "height" is generally thought to
be ideal if
it is 67 percent of your inseam length. A mountain bike is
ridden on a
much smaller frame: as a guideline, use your road bike size and
subtract 10-12 cm.
| Height (feet & inches) |
Inseam (inches) |
Frame Size (inches) |
Frame Size (cm) |
Top Tube (cm) |
| 5'3" |
28.5 |
19.3 |
49 |
51 |
| 5'4" |
29 |
19.7 |
50 |
51 |
| 5'4.5" |
29.5 |
20 |
51 |
52 |
| 5'5" |
30 |
20.5 |
52 |
53 |
| 5'6" |
30.75 |
20.9 |
53 |
54 |
| 5'7" |
31.25 |
21.3 |
54 |
54.5 |
| 5'8" |
32 |
21.7 |
55 |
55 |
| 5'8.75" |
32.5 |
22.1 |
56 |
55.5 |
| 5'9.5" |
33 |
22.5 |
57 |
56 |
| 5'11" |
33.75 |
22.9 |
58 |
56.5 |
| 6'0" |
34.25 |
23.2 |
59 |
57 |
The size from this table is just a starting point. Find the
row
that is closest to your height and inseam measurement in the first two
columns. If your exact height and inseam are not on the
table,
look at the row that is closest. This table will give you an
approximate range of the frame size that you need. Go to a
bike
store and try some different sizes or try a friend's bike to
validate the size that is best for you.
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