William O'Hara writes:
>> http://www.whiteind.com/ENO_Products/cranks.html
>> Shimano, Sugino and Campagnolo seem to be your other options. I am
>> using a set of the Shimano FC-M460 on a mountain bike that gets a
>> lot of riding, and they have been excellent. Not too expensive.
>> I agree with others, they are not going away completely. I'm
>> planning to stick to square taper on all my bikes.
> I am totally confused by the bike industry. Read my question on
> head tubes. I just read that square taper is more efficient than
> any of these crazy things such as external BB or ISIS by a huge
> magnitude. Obviously Campy knew something. I've been trying to
> read everything on this since my ISIS drive BB lasted only 2000
> miles(yet another post).
I think you are using the wrong term to describe the crank/spindle
interface. There is no efficiency in that joint but rather reliability
and durability. You could say the cottered crank was ideal if you
ignore that it only worked well with steel cranks and that the
bearings were too small in diameter, and that it took skill to install
properly.
The square taper inherited the cottered crank spindle, ball bearings
and cups and has been burdened with them ever since. Not only do the
spindles spall, the square taper is a mystery to most bicycle
mechanics. For this reason there is a division about assembly with
and without grease. Cranks have been split from excessive press fit
but how these came about seems to still mystifies the manufacturers,
having never themselves been able to reproduce such failures...
although to cause it is simple. As a rule they don't read wreck.bike
and seem not to know how.
http://pardo.net/bike/pic/fail-001/FAIL-001.html
picture 011 or the seventh picture. This was achieved by repeatedly
tightening the spindle bolt after use. It did not require grease. A
spindle bolt will break before damaging force can occur on the crank.
The ISIS method fails on several fronts and doesn't address the
bearing problem, using the same old cottered crank spindle diameter
and bearing cups. Besides, the spline is difficult to manufactured
and solves a non existent problem.
Shimano built the Octalink that has had a backlash flaw since its
beginning. Shimano didn't understand that and came out with a second
version with deeper splines that had the same failing as the first.
The current state of the art is the overhung bearing and no pressed on
cranks. Shimano using the pinch bolt design on a spline at the left
crank, and Campagnolo meshing a hollow spindle with a saw toothed
spline in the center. Both of these solve the torque and force
problem, although the Shimano method is simpler and less expensive.
What they don't do is address the BB thread forces that have required
a left hand thread or extreme torque to not unscrew. The left hand
thread is proof that the threads move or the thread direction would
make no difference. The bearing cups are supplied with Loctite type
thread retention, which does not work with such high loads. This is
the current weak spot and we will have to wait and see how they work.
Jobst Brandt