the early 1900's the hirth joint, or more correctly in the industry,
the Hirth coupling, was develop by Hellmuth Hirth as a type of
fool proof, high strength locking joint used to connect two ends
of a shaft together.
It is characterized by a set of teeth on the end faces of each
half shaft that mesh together in a self centering and self aligning
locking joint. It offers a high strength connection on relatively
small diameters for reversing gears in ships and cooling water
pumps in almost every industry.
Today the Voith Turbo Corporation, incorporates this design into
power transmission components for the automotive, rail, nuclear
and marine industries. In fact Voith Turbo adapts this technology
to all industries that can utilize its simplicity of design to
transmit high torques at both small and large dimensions.
it is no wonder that Campagnolo was interested in incorporating
such a proven technology into their newest line of cranksets.
After all it has withstood exhaustive technological testing for
performance and reliability in the most extreme environments of
nuclear energy and jet engines.
Advantages of Using the Hirth Joint
in Crankset-Bottom Bracket Design:
- The axle of the new ultra-torque Campagnolo Crankset can be
spliced in the middle of the bottom bracket shell without the
use of external flanges or bushings. These are not necessary
with the geometry and design of the hirth coupling. With no
additional flanges, there is less rotational mass and thus greater
pedal efficiency and smoother riding.
- External bearings can now be mounted on the half spindles
tight up to the crank leaving the entire circumference of the
bottom bracket shell available to allow for a larger hollow
spindle. With greater spindle diameter the bicycle gains rigidity
- With the larger spindle diameter, the crankarms can be made
thinner and still yet still create a rigid crankarm-spindle
connection. Thinner crank arms allow Campagnolo to maintain
a consitant Q-factor (lateral distance between pedals), uncommon
in typical external bearing designs.
- On both the drive and the left side of your bicycle the Campagnolo
crank arm can be fused to each half axle, so no added length
is needed on the spindle to allow pinch bolts to hold the crank
in place. This offers a weight savings and no risk of the pinch
bolts coming lose and dropping a crank arm.
- The final benefit of using a hirth joint in the ultra torque
crankset is that Campagnolo can promote themselves as having
THE most easily installed crankset in the industry. The cups
are threaded into the bottom bracket shell, then each half "L"
shaped axle is positioned, and lastly a 10mm bolt is torqued
in place to hold the two halves of the crankset together.
With a quick review of the Hirth advantages, what's not to love
about the Hirth
Joint/Ultra-torque Campagnolo Crankset combination.
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