"kwalters" <
[email protected]> wrote in message
news:[email protected]...
> Some months ago, it was mentioned here that the MA3 was a good, durable rim, much more so than the
> MA2 & MA40. In 9/01 I replaced a shot MA40 with a MA3, 32h, rear. It currently has ~7000 miles on
> it. It also has 4 cracks radiating out from 4 eyelets. Each crack is 3-5 mm long, all are on the
> drive side in a 17-spoke semi-circle, and all radiate out in the same direction.
>
> I used to get 12K-14K on my rear MA2s & MA40s at a time when I was weighing in at 205-210 lbs. I
> currently weigh 185ish, and have always been a conservative rider: slow down for RR tracks, dodge
> potholes, no curb jumping.
>
> Do I need a new wheel builder? Can anything be done to prevent more cracks from developing?
>
> Thanks for your thoughts. Ken
Ken,
Tension balancing and proper spoke tension are the keys. Double butted spokes also help by spreading
the dynamic loads. We are talking about over 100 kgf in spoke tension on the drive side of a
properly built wheel. Each of those spokes must have the same tension. The author of the book "The
Art of Wheel Building", Gerd Schraner, is quoted at the DT Swiss websit at URL:
http://www.dtswiss.com/en/laufradbau-faq.html "Why are some spokes, especially those on expensive
bikes, thinner in the middle section?
The use of these "reduced" spokes allow longer-life wheels to be built. Spokes with a thinner
mid-section aren't just lighter and more aerodynamic but, more importantly, are much more elastic
than normal straight-edged spokes. When placed under extreme overloads, they react in a similar way
to resiliant bolts used in the machine industry. If a wheel undergoes rapid radial forces, for
example a bump, the spokes spring as they take up the overload, thus protecting the hub."
Gerd talks about protecting the hub, but I know that at the otner end of the more elastic spoke is
the rim. The elasticity of th spoke helps protect the rim as well.
I still think that the statement at the Wheelsmith website at URL
http://www.wheelsmith.com/page4.html bears repeating: "Wheelsmith's wheelbuilding philosophy
emphasizes strength and durability, and the key is high, uniform spoke tension. Spoke tension is the
most difficult and elusive aspect of wheelbuilding. It is the characteristic of the wheel most
difficult to evaluate, yet the most critical to its performance. This approach to wheelbuilding,
based on combining both art and science, and focusing on tension rather than cosmetic trueness, was
pioneered by Wheelsmith and remains at the foundation of our process. Cosmetic trueness can actually
come at the expense of a wheel's strength because it can result in unbalanced tension. So do not be
misled by some builders' claims about trueness, because what really matters is not how true a wheel
is now, but how true it is 1,000 miles from now."
If you wheelbuilder understands these things and applies them properly, stick with him. If you need
another wheelbuilder make sure your budget allows for double butted spokes and the time it takes to
have them properly tensioned and tension balanced. Jobst Brandt's book, Sheldon Brown's website, and
Barnett's Chapter 17 cover these items in detail.
David Ornee, Western Springs, IL
David Ornee, Western Springs, IL