BTW, speaking of expensive cranks :
With splined crank arms, from what I understood, the attachment to the
axle is much stronger because of the splined grooves. OK, now is the
crank body itself much stronger also - I mean is the splined attachment
impacting on the stress limit of the crank before it snaps or bends ?
Oli-
-----Original Message----- From: Jeff Lutkus
[mailto:lutkus@unicyclist.com] Sent: Thursday, July 05, 2001 10:12 AM To:
Olivier Paugam; Jeff Lutkus
Cc: unicycling@winternet.com Subject: RE: crank arms
My limited knowledge physics tells me that yes, the crank arms will be
deformed to a certain degree, before returning back to their original
shape. If, however, the force you land with excedes the elastic limit of
the crank arms, they will not spring back.
My impression is that as you get into the “better” materials, the elastic
limit is not increased, but the amount that the pedals tend to flex with
the same force is decreased. By this logic, cheaper cranks would tend to
bend out of shape, whereas the more expensive ones would more likley snap
(though a lot more force would be required).
My uneducated guess would be that that this bending feeling is more due to
a flex in the spokes then anything with the cranks. It makes me wonder,
though, just how much flex the average set of crank arms have before they
break or become permanently misshapen. I would suspect if the cranks are
long enough, and have a good amount of flex, you very well could feel it.
Jeff Lutkus
— “Olivier Paugam” <opaugam@aptilon.com>
> wrote:
>That’s funny, this strange feeling happened to me yesterday actually
>with
>my monty uni.
>I was doing a 2’ drop on a steep slope, landed quite brutally and
really
>felt the right crank bending. When I reached flat ground I checked the
>crank
>and mysteriously it was intact.
>
>I’m wondering if a crank can really deform slightly and get back to its
>primary shape or it’s just an illusion maybe due to the shock on the
>lower
>leg / unprepared / over-contracted muscles ?
>
>As a matter of fact I never bent my bicycle euro 140mm on trials.
>
>Oli-
>
>-----Original Message-----
>From: Jeff Lutkus [mailto:lutkus@unicyclist.com]
>Sent: Thursday, July 05, 2001 8:42 AM
>Subject: crank arms
>
>
>I discovered today that inexpensive crank arms may be fine for street
>riding, but not for muni. So, does anyone have any recommendations on
>who makes a good (yet still, hopefully, inexpensive) crank arm? As the
>terrain is quite flat around here, I’m probably looking at a 6" size.
>
>I borrowed the crank arms from my Coker because they were the right
>length. I really should have thought that through before I took them
>into the woods. I had to make a 6" jump up to a bridge, and I landed
>just hard enough to bend one crank to the point where I could feel, but
>not see the bend. Well, after that, I figured it wouldn’t make much
>difference if I went for a 3’ drop.=20
>
>http://www.rit.edu/~jvl2957/bent_crank.jpg
>
>That drop had the oddest feel – I felt the shock of the landing as it
>was absorbed by the pedal… which, unlike other drops I’ve made on my
>20" uni, did not apply any of that force back to my foot.
>
>Also learned that day, riding a mile on a dirt trail with two bent
>cranks can be interesting.
>
>Jeff Lutkus
>
>
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