Semcycle v. XL

I’m trying to understand the differences in basic Semcycle unis. I knowthe
“Semcycle” is stronger and more expensive and the cylindrical portion of the rim
where the spokes join is concave toward the hub. I also noted on the Semcycle
web site that the XL has “a narrower axle [that] gives greater stability for
racing.” (Maybe the “Semcycle” model has this too.)

Can anyone explain the physics of why a “narrower axle” would give greater
stability? Does narrower mean less diameter or less axial length? If the
diameter is smaller, the spokes or flange will be greater (given the same size
wheel); how could that be stronger? If the axle length is smaller, I don’t see
why the stability would be greater.

Of course, I’ll ask Sem himself. Nonetheless, I’m interested in hearing other
perspectives. (Who knows, maybe one of your out there has done something Sem
hasn’t, e.g., ride on the deck of a sailboat. What were the pros and cons of
your particular axel?

I’ve pretty much decided to buy from Semcycle. It’s a pleasure to deal with
merchants who know their product (as opposed to Schwinn (sp?) dealers who don’t
even know they sell unicycles). For just a little more money than it takes to
get a “bottom of the line” competitor, you can get something good — also, with
prompt delivery!

So, I repeat, what is the advantage of (and what is) the “narrower axle”?

RE: Semcycle v. XL

41 Felber wrote:

>also noted on the Semcycle web site that the XL has "a narrower axle [that]
>gives greater stability for racing." (Maybe the “Semcycle” model has this too.)

Narrower means the length of the axle is shorter. In theory, the closer your
feet are to the center of the wheel (from side to side), the less the wheel
will zig-zag when you pedal fast. A narrower axle brings the crank arms
closer together.

Unfortunately your feet can never be right on the centerline, so there will
always be some zig-zag. Some people ride straighter than others, and a bad
zig-zag can probably be helped by training, just like a speech impediment.

But the regular Semcycle has a narrower axle than the XL. What they may be
saying is that the OLDER XL models had a real wide axle, which was one of its
less positive points. I think the Semcycle axle is one of the narrowest out
there. When installing one into a Miyata frame, extra customization is required
to accommodate the narrower width.

>other perspectives. (Who knows, maybe one of your out there has done something
>Sem hasn’t, e.g., ride on the deck of a sailboat.

Most of us haven’t gotten married on it (Sem did), but there are a lot of things
Sem has wisely NOT done. See them on the Things not to do page, at:
http://www.calweb.com/~unifoss/thingnot/dontdo.htm

You will see Sem is only doing one of those things.

>What were the pros and cons of your particular axel?

For me personally, the best thing about an axle is that it doesn’t break. After
that, it’s important that it’s machined properly so the cranks fit tightly with
out chronic looseness (you have to tighten them periodically no matter what).

The two strongest “off the shelf” unicycle axles I know of are Semcycle (not
XL) and Miyata. Everything else is less strong. If you ride off road, or jump a
lot, or practice lots of strange tricks, or are a really big person, a strong
axle is important. If you’re a casual rider who doesn’t stress the unicycle,
any axle will do.

John Foss Miyata frames with Semcycle axles (carbon fiber uni on the way!)

RE: Semcycle v. XL

A wide hub causes the wheel to wobble more as you peddle wasting energy, causing
a more pronounced “S” curve to your straight line riding. (Ride on a wet street
sometime and notice the path of your tire.) Excessive wobble at high speed will
contribute to a loss of control. A narrow hub makes the wheel less rigid from
side to side which is not good. It’s all a tradeoff. Narrow is better for track
racing. Some experts have even gone to the extreme of narrowing stock axles. The
XL is an excellent all around unicycle.

    ----------
    From: 41FELBER@cua.edu[SMTP:41FELBER@cua.edu] Sent: Tuesday, May 12,
    1998 1:32 AM To: UNICYCLING@winternet.com Subject: Semcycle v. XL

    I'm trying to understand the differences in basic Semcycle unis. I
    knowthe "Semcycle" is stronger and more expensive and the cylindrical
    portion of the rim where the spokes join is concave toward the hub. I
    also noted on the Semcycle web site that the XL has "a narrower axle
    [that] gives greater stability for racing." (Maybe the "Semcycle" model
    has this too.)

    Can anyone explain the physics of why a "narrower axle" would give
    greater stability? Does narrower mean less diameter or less axial
    length? If the diameter is smaller, the spokes or flange will be greater
    (given the same size wheel); how could that be stronger? If the axle
    length is smaller, I don't see why the stability would be greater.

    Of course, I'll ask Sem himself. Nonetheless, I'm interested in hearing
    other perspectives. (Who knows, maybe one of your out there has done
    something Sem hasn't, e.g., ride on the deck of a sailboat. What were
    the pros and cons of your particular axel?

    I've pretty much decided to buy from Semcycle. It's a pleasure to deal
    with merchants who know their product (as opposed to Schwinn (sp?)
    dealers who don't even know they sell unicycles). For just a little more
    money than it takes to get a "bottom of the line" competitor, you can
    get something good --- also, with prompt delivery!

    So, I repeat, what is the advantage of (and what is) the
    "narrower axle"?