Sizing a bike is not the same as fitting a bike!
Understanding that "Everybody" is custom, the bicycle must be
a continuation of the cyclist. You need to make very sure that the
frame allows you to mount and dismount safely. A more compact frame
is fine, as long as you can raise the saddle to your specific height
needs. Make sure you don't exceed the maximum-extension mark on
the seat post. We feel that at least 2.5 to 3 inches of seat post
down in the seat tube is needed. Check with your seat post company
to see what they suggest.
Sizing a bike can be a problem if your only concern is the stand-over,
rather than top tube and stem length concerns. Of more concern is
to find the "Effective Body Extension" for your hip, spine, shoulders,
and arms. This can only be done after you find the correct cleat
placement, saddle height, saddle aft and the correct saddle angles.
Then and only then can you determine the correct stem length, stem
rise, spacers, and handlebar rise. For optimal placement and handling,
the handlebars should not exceed 140 mm. If the measurement from
you saddle, to the top and center of the handlebars does not fall
within these parameters, your top tube length is short.
Note: You may need to replace component
parts to achieve the correct fit.
For handling and dismounting the bike, the frame needs to fit you
in terms of crotch clearance above the top tube. Have your bikes
shoes on and hold the top tube between you legs. Look for at least
2 inches clearance as you stand just ahead and over the bottom bracket.
Many pros will have as much as 4.5 inches of clearance.
Another method is to pull the top tube firmly up into the crotch,
again with your bike shoes on. There should be 2 inches to 4.5 inches
from the ground to tires.
Determining Frame size
The only tools needed to size your bike are 1) level or book, 2)
a metric tape, and 3) a calculator!
This is a very simple sizing process!!! It takes very little time.
- Take your inseam length while standing in your socks with your
feet about 4 to 6 inches apart, back against a wall.
- Hold your level or book under your crotch (pull up firmly).
- Use the tape from the top of the level or book, and measure
to the floor.
- Read the tape in centimeters.
- Multiply the (cm) measurement by .67
- Mountain Bikes, subtract 11 cm and round to the lower number,
road bikes round to the nearest even cm.
- This should roughly be the length of the seat tube on a properly
This should give you a good reference point on size, so that you
can obtain a precision fit.