On 2 Dec 2006 10:39:36 -0800,
[email protected] wrote:
>
>[email protected] wrote:
>>
>> It takes about 600 pounds of tension to yield a 2mm stainless steel
>> spoke. ...
>
>> You, your twin brother, and a friend can probably hang from a single
>> 2mm stainless steel spoke without breaking it.
>
>But only if the spoke were gripped at both the ceiling end and the twin
>brother end with an attachment capable of 600 pounds! That's not
>going to happen with the plastic tubes slipped over those wires.
>
>Furthermore, the strength of a spoke in tension is tremendously higher
>than its strength in bending. And bending is all that's necessary for
>the spoke to safely pass through the fork-to-tire clearance.
>
>I think you're being extremely over-cautious.
>
>> Please don't test the results of jamming tangled metal debris into the
>> narrow area where the brake arms and fork curve around a high-friction
>> front tire. Hang the tire savers facing forward.
>
>Well, if that's what you prefer, that's fine. But you really ought to
>try them. It sounds like you're in a unique position to test them and
>tell us the results!
>
>- Frank Krygowski
Dear Frank,
Possibly there's a misunderstanding, perhaps people aren't thinking
things through, and maybe some people have never seen jammed tires
after crashes that killed or injured riders.
The scheme proposed (in good faith) was to mount a spoke bent into a U
with enough curves to attach to the brake bolt that goes through the
bottom of the steering tube.
Facing forward, the U-shaped spoke presents no real danger--the tire
motion pushes the bent wire away from everything. It's as safe as
brushing the tire in _front_ of the brakes with the palm of your
glove. There's nothing to jam your hand against the tire, and anything
that catches on the tire will be spat forward to safety.
But facing backward, the U-shaped spoke is as dangerous as brushing
the tire _behind_ the fork. Everything tends to jam between the tire,
the wire, and the spoke, and everything jammed will be dragged forward
with enormous force into the fork, to jam even harder.
Here's a view from the back of my upside-down fork that shows what
will happen within a month where I ride. Just replace the thin
screwdriver blade with a chunk of friendly tumbleweed:
http://i14.tinypic.com/2ep1342.jpg
It's snowing, so I used the easy-to-obtain-and-photograph screwdriver
blade against a 2 mm spoke instead of an actual tumbleweed stalk. The
debris doesn't have to be as hard as metal or even a tree-twig--a
fairly fragile tumbleweed stalk will do. The debris only has to push
the U-shaped spoke against the tire, and everything will jam solid.
Anything that pushes the 2 mm spoke loop against the tire will cause
the tremendous friction of the tire to grab it and try to jam it
through the fork, away from the viewer.
Remember, the spoke is supposed to be bolted to the other side of the
fork, out of sight. (It wouldn't be much better if it were somehow
attached to the recessed bolt on the back of the fork.)
Cutting the bent spoke into two pieces and joining the u-section to a
pair of legs bolted to the fork with high-friction plastic tubing that
only makes them fatter will only to add to the wreckage.
Anyone who doubts the friction involved should try to fiddle a crudely
bent spoke through the fork as shown. I couldn't bend or pull it
through with pliers, not at the angle needed to attach to the bolt.
The easiest way to set up the camera shot was to push the spoke
against the tire with one hand and turn the wheel with the other
hand--and even that was hard to do.
I don't want to be on a bike where a tire spinning at 20 mph tries to
jam such a contraption through the fork.
Cheers,
Carl Fogel
