Sigurd said:*Ok, I always thought that there was just one type of aluminum. So
the best trials cranks are the better grade of aluminum? I guess for
the uni I'm using and what I'm doing I don't need that much crank.
The ones I have now are steel and they started to bend when I started
hopping. I have a 24" wheel and I'm looking to get 140-150. I have
150s now. I like the torque for hills, but I like to cruise too.
Almost leaning more towards the 140s.
Thanks for the help. =) *
There are many different grades of aluminum. Aluminum bicycle parts are
all made from aluminum alloy, they're not made from pure aluminum.
There are many different aluminum alloys. Different alloys have
different properties. Some will be softer and more malleable, while
others will be harder and stronger. Some alloys are less expensive and
easier to machine while others are stronger and more difficult to
machine. The choice of what alloy to use makes a big difference in the
final strength of the crank. The more expensive cranks generally use
the stronger alloys.
In addition to the choice of alloy there is also the manufacturing
process. Some cranks are made from cast aluminum. Cast aluminum cranks
will be very weak (think Lasko). Some cranks are machined from a solid
block of aluminum alloy. The better cranks are first forged and then
machined. The more machining required the more expensive the cranks are
going to be.
All aluminum cranks are not created equal. The choice of alloy and the
manufacturing process are very important factors in determining the
strength of a crank.
Unless you plan on spending big bucks for a custom set of cut down Kooka
cranks, you're going to be better off getting steel cranks. The steel
cranks will eventually bend, but they're also cheaper than good strong
aluminum cranks. Steel also has the advantage that it will first bend
before breaking in two. When aluminum cranks fail the fail quickly and
catastrophically (meaning the break in two with little warning).
In the 140 mm length, there's the Schwinn steel cranks. In the 150 mm
length, there's the Bicycle Euro steel cranks along with others. The
Bicycle Euro cranks have a reputation for being stronger than the
others.
Keep an extra set of cranks on hand so that when you do eventually bend
the cranks you have something to replace them with.
If you continue to have constant problems with bending cranks then it's
time to consider one of the splined setups. The splined cranks are
bigger, beefier, stronger.
--
john_childs - Guinness Mojo
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