I’ve been reading the discussion of cottered and cotterless cranks. I’d like to
pass on an observation made by Tom Miller of The Unicycle Factory:
Cotterless cranks are indeed superior mechanically to cottered cranks. Cottered
used to be common (back in the 70’s) but they had problems as discussed here.
Basically they needed frequent inspection and tightening to work well but when
(not if) they went bad usually a pair of 25 cent replacement pins was all it
took to fix it. Back when I rode a 10 speed the bike shops usually had my size
except on rare occasions but these days they are getting much harder to find at
least in the Midwestern United States.
Cotterless came along later and was an improvement mechanically. Neater looking,
no nut to scrape your ankle and much stronger. But you could ruin an entire
crankarm if they work loose (especially alloy crankarms) and you don’t tighten
it right away.
That was a basic summary of the differences. OK here’s the bit of wisdom:
Cotterless cranks are especially suited for unicycles due to the need to pedal
both forward and backward. They have a four shouldered taper which mates to the
crank axle much like a box end wrench on a nut–much less chance of slippage due
to increased surface area to withstand the stress.
Cottered cranks on the other hand are strong enough for forward pedaling (if
properly tightened) but weaker for reverse pedaling. If you have never seen one
of these cotter pins removed, they are tapered and have a flat along the length.
This flat is wider at the end opposite the threads and takes the majority of the
stress during the power stroke of normal bicycle pedaling. When you pedal
backward, the narrower part of the pin must take that same load on a smaller
surface area. So the relatively soft cotter pin eventually deforms and you have
a wobbly crank to deal with.
I would recommend that anyone shopping for a unicycle insist on cotterless
cranks. Just keep a crank puller-installer tool (about the size of a roll of
Lifesavers) and a 6 inch adjustable wrench handy. Check the tightness of the
axle nut regularly. Unless your are the Incredible Hulk, you won’t have to worry
about overtorquing the nut with that size wrench. If it starts squeaking as you
ride, stop immediately and tighten it before riding again.
Now here’s an anecdote: I was cruising the campus of Syracuse University in
Syracuse New York last spring. I noticed my right crankarm start to squeak but
I was 10 blocks from my car and tools. I knew of a bike shop about half that
distance so I started riding that direction. The campus is on a big hill so it
was too steep for me to try to ride the whole way one footed. I rode using
both pedals but pressing as little as possible on the right. I made it to
within two blocks of the shop when the crankard simply fell off on the
sidewalk with a clank.
It just so happened there was a small group of female college students standing
about 6 feet away when this happened. One of them said rather facetiously said
“Awww!” (as in “too bad–so sad”). I dismounted, picked up the crankarm and
remounted one footed. I idled a bit, then wound up and pedaled on to the bike
shop that way. It was great!
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| Dennis Kathrens | “Hey, where’s your other wheel?” |
|d. kathrens@genie.com | “On my OTHER UNICYCLE” |
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