Bendy
spokes
Independent developments from the US and the UK both
combine composite materials and innovative designs to improve
the performance of traditional spoked wheels
Dating back to the late 19th
century, spokes provide a
rigid and lightweight wheel
structure. They remain
omnipresent in bicycles and motorcycles,
although have been superseded by forged
solid steel or aluminium alloy rims in
motor vehicles. Spokes, of course, are
wire rods that lace into a wheel’s axle
hub and run radially outward to the rim,
the outer perimeter that holds a tyre.
Screw threads cut into their far ends
mate with headed nuts set in the interior
of the rim. There are usually two sets of
spokes coming off either end of the hub.
As the wheels turn, spokes experience
alternating cycles of tension and
compression, depending on their position
relative to the hub that imposes part of
the vehicle’s weight on them. Spokes
in the top hemisphere of the wheel are
pulled taught, as the hub hangs from
them; spokes in the bottom hemisphere
are squeezed by the hub that tends to
bear down on them.
Not that the rider feels it; these
wheels themselves offer almost no give.
For mountain bikers and motorcyclists,
the work of softening bumps along
the way may be done by various
arrangements of shock absorbers
mounted in the frame. But for others, the
only cushioning is provided by the small
pillow of air enclosed in the pneumatic
tyre. That group includes users of
wheelchairs, which also ride on spoked
wheels, a feature that makes them
almost impossible to ride comfortably
off-road.
A UK innovation promises to change
that by reducing vibration up to 70%
compared to spoked wheels. Six years
ago, Jelly Products launched a design that
makes use of carbon bre springs instead
of spokes. That ‘loopwheel’ design
provides a much greater hub movement,
relative to the rim, than spokes. Its
particularly rigid rim passes on shocks
and bumps to the carbon bre springs,
which ex in response to minimize the
shock on the hub. De ection might be as
much as 70mm on a 559mm-diameter
wheel, according to inventor Sam Pearce
(pictured, right, with partner Gemma
Pearce). Arranged at 120° apart around
the rim, they ensure that the hub is
supported from above and below at any
time (and, in fact, from any side, allowing
the wheel to also counter horizontal
bumps equally well as vertical ones.)
Pearce contends that the reduction
in mechanical ef ciency caused by
the spring assembly – a physical
inevitability – has a negligible effect on
rolling resistance. However, weight can
affect that. Its double-loop wheels are
a lightweight 1.8kg without push rim or
tyre. And in September, the company
launched two even lighter-weight models,
Loopwheels Extreme and Loopwheels
Urban (pictured inset, above), which
feature only three springs. Although they
work in the same way, they are more than
400g lighter.
Pearce explains that the company
faced two principal engineering
challenges in creating the design. The
rst was reducing the width of the
carbon- bre springs to dimensions that
are reasonable for a wheelchair, but
24 www.ied.org.uk
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