Spoke Selection Guidelines
At
first glance it would appear there is not much
left to consider after
the rim and hub are selected. In fact the
spokes play a very important role in supporting
static loads and transmitting power to the
road. Spokes also contribute to weight, ride
quality, strength, stiffness, and aerodynamics
of a wheel.
1) Weight: Spoke weight is pretty
straight forward. Thinner spokes weigh less
than thicker spokes right? True, however
there are several important trade-offs involved
with thinner spokes. Thinner spokes are harder
to true because they tend to twist during the final
stages of the wheel build when tension is at its
highest point. Thinner spokes are not as
strong as thicker spokes and are therefore not
recommended for some mountain applications where
spoke overload can be common. Also, thinner spokes
tend to fit loosely in the hub holes and should
be used with spoke washers to improve fatigue life.
Double butted spokes can help reduce weight and
distribute load throughout the spoke better. These
spokes are designed similar to a high stress fastener
that necks down in the center. Double butted
spokes have a springy characteristic that enhances
ride quality.
Exotic materials have been successfully used in
spoke manufacturing, however cost and availability
can sometimes be limiting factors. Titanium,
and Carbon/Kevlar spokes are currently in use on
several manufacturers production wheels. Titanium
spokes weigh significantly less than stainless
spokes. Due to their inherent flexibility
the Ti spokes give a very unique ride sometimes
described as comfortable, plush, soft, Flexi, and
even sloppy by some riders.
2) Spoke Lacing Patterns: Spokes can be
laced in a variety of different patterns that can
enhance appearance, strength, and durability. Spoke
patterns are usually designated by the number of
times each spoke crosses other spokes. Common
lace patterns are zero-cross or Radial (0x), one
cross (1x), two cross (2x), three-cross (3x), and
four-cross (4x). These spoke patterns are
sometimes combined on rear wheels. Additionally,
there are many exotic lace patterns, which are
not commonly used in racing wheels. Some
of these include the Crows foot, Three leading-Three
trailing, and patterns that use spokes twisted
about themselves or other spokes. These and
other interesting patterns can be found on the
web.
As the number of spoke crossings increase the
angle in which each spoke leaves the hub approaches
90o (tangential). Wheels with
3x or 4x lace patterns will usually transfer power
more efficiently than those with 2x patterns. As
the number of spoke crossings increase the length
of each spoke increases. Longer spokes are
more flexible and contribute to decreased radial
stiffness, which improves ride quality. Consequently
wheels with more spoke crossings have lower lateral
stiffness, which is important to cornering stability.
The ideal number of crossings is not easy to determine
since the stiffness of the rim plays an important
role in the overall stiffness of the wheel. Generally
2x and 3x patterns can be used successfully on
road wheels. 3x and 4x patterns should be
used for wheels subjected to higher torque inputs,
such as track racing. Radial lace patterns
should only be used for front wheels since they
tend to twist when the hub is subjected to torque
inputs from the rider.
Mixed spoke patterns can be found on many modern
race wheels. These patterns commonly consist
of a 2x pattern on the drive side mixed with a
radial pattern on the non-drive side. One
exception is Mavic's Isopulse lace pattern used
on their Ksyrium wheels, which uses a radial pattern
on the drive side. Mavic claims this pattern
helps transfer load from highly stressed spokes
on the drive side to the spokes on the left side
of the rear wheel. This system is intended
to improve the poor distribution of loads caused
by the asymmetric geometry of the rear hub.
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