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Rating Methodology
The stem ratings were determined on three basic
design variables - performance, price, and
durability.
Performance
Performance of stems is primarily based on mass,
with some subjective improvements to be had by
increased stiffness. It could be assumed
that once a stem has an "acceptable" stiffness,
any additional improvements will have diminished
effect. Furthermore, at this point in time
the relative contribution to overall steering
column stiffness of the stem is unknown.
It could be speculated that the bar itself is
the primary contributor to the perceived amount
of flex in the overall steering system due to
its length - stiffness being proportional to
length cubed. However, the stem does
provide the boundary condition, or "fixity-ness",
for the handlebar and is therefore an important
part to evaluate.
Based on these two variables of stiffness and
mass and the preceding logic, a relative
weighting scheme was determined to help quantify
stem performance. Overall stem performance
was rated using a weighting of 80% for the
importance of mass and a 20% weighting for the
importance of stiffness.
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Durability
A minimum value of 1 was assigned to a stem that
survives what one might consider to be a maximal
loading condition (approximate 200 lb horizontal
load) for 25,000 cycles. It should be
remembered that since this is a comparative
rating system, this value of 1 does not
necessarily mean that the product should be
considered unsafe. The author has been
riding a stem that ranks in the 3-4 range for
nearly 100,000 kilometers. The upper end
of the durability scale was determined by the
capacity of my compressor/air cylinder system
which is in the 900 lb range.
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