My co-worker has been hounding me to buy a Seven bike. Please critique this little essay he sent me:
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I know you're sick of hearing about ti bike company comparisons, but here goes. I know that you're
into the local idea, and if you were considering a custom steel frame, I'd say why not? But there
are still massive qualitative differences b/w Ti manufacturers' products, and you need, therefore,
to immerse yourself more into the research process. And, what's more fun than that anyway?!
There are three primary differences between Seven and the other guys:
1. Seven uses butted tubing, and they have the longest experience working w/ butten ti (a difficult
thing to find in frames).
2. Seven uses a space industry grade 3Al-2.5V ti instead a sports or commercial grade, and also
instead of 6AL-4V (a lower quality alloy for frames), which is what you'll find in some of the
Moots frame sets.
3. Seven doesn't do final surface treatments (peening or texturizing), as this can cause stress
risers and hides sloppy welds (like linings in Gore-Tex jackets).
Seven allows for a truly custom frame with the axiom not just limiting a customer to tubelengths and
handling characteristics but also tube dimensions and butt placement. They also use the best
domestically sourced ti tubes available and as far as i know, they are the only ones to do so
(though, i think the real world implications of this fact are probably non-existant). welds are
clean, finish is luxurious. handling is a little risky to comment on as they are custom bikes. mine
handles like a dream though. ride characteristics also vary with each frame... mine is on the
steel-like side.
for the money, Sevens are a terrific value. keep in mind that non-custom Merlins made with
comparable design considerations (ala butted tubes) cost just as much as fully custom sevens do.
Litespeeds, anything other than the arenberg and tuscany will cost a pretty penny too. Moots (best
welds!) and Ibis probably are my favorite Ti bikes after Seven and both only offer straight-gauge
tubesets at a price comparable to Seven's Alaris model. With Moots, custom will cost extra too. also
on the side of value is the longevity of Ti. most people complain about the cost of Seven's, but in
reality, they are not that bad compared with other truly high performance bicycles. plus, why would
you want a couple of thousand dollars when you could have a great bicycle instead.
one gripe is that i asked for the bike to be set-up with DT shifter bosses - not because i like the
way the look or think they are more accessible than STI braze-ons, but because i was actually
planning to use DT shifters! the boss was inserted so far up the downtube that not only did it look
funny, but my fingers would get caught in the brake cable housing when i reached for the left
shifter. i can theorize that the reason was to place the boss at the thickest part of the butt, but
they could have run the butt longer to lower the boss. another gripe is the ST H20 braze on. it's
too high at midway down the seattube. it looks odd, and i suppose it raises the bike's center of
gravity. this, i admit is getting nit-picky. i only wish that i had thought about both of these
issues (shifter boss & H20 boss) and told Seven _exactly_ where i wanted them placed.
Overall rating reflects that this is indeed a solid bike and as good if not better than any
currently available. Still, i don't consider it one of the truly great bikes of all time. Given the
chance to buy it again though, i'd do it without a second thought.
Types of Ti In addition to unalloyed titanium, which is called commercially pure or CP, there are
two alloys commonly used in the cycling industry today: 3AL-2.5V and 6AL-4V.
3AL-2.5V 3-2.5 titanium is an alloy consisting of 3% aluminum, 2.5% vanadium, and 94.5% pure
titanium. The properties critical to bicycle tubing are best served by a high quality 3-2.5 seamless
tube. Excellent fatigue life, property consistency, formability, and corrosion resistance are but a
few of the reasons 3-2.5 is still the premier frame material.
In the U.S., bicycle frames are commonly manufactured using 3-2.5 certified to either an ASTM B-338
or a sports grade specification. ASTM B-338 meets all Aerospace Material Specifications for
hydraulic tubing. Sports grade, certified according to a less stringent set of chemical and
mechanical specifications, is typically less expensive.
Some builders may use surplus material or "scrap", which meets neither aerospace nor sports grade
specifications. Certification is not available for scrap, making it impossible to determine whether
the material is of inferior quality.
6AL-4V An alloy of 6% aluminum, 4% vanadium, and 90% titanium, 6-4 titanium offers some very
favorable raw material properties, which is why Seven uses it to fabricate dropouts and other frame
parts. One of the properties that makes 6-4 an optimal material for dropouts is its toughness. But
this toughness also makes it unattractive as a material from which to make tubing. Applying the
techniques used to draw 3-2.5 tubing to 6-4 tubing costs more and wears tooling very quickly. In
addition, tube wall consistency, concentricity, and finish quality-both inside and outside-are
limited. At the time of this printing, no U.S. mill offers seamless 6-4 tubing. However, some do
offer 6-4 seamed, or welded, tubing.
Two major issues prevent Seven Cycles from favoring this method of tube manufacture. First, seamed
tubing is fabricated by rolling 6-4 sheet into a tube shape while simultaneously welding the seam
that is created in the rolling process. The result is a tube that has a welded seam-a potential
failure point-along its length. This seam acts as both a hard point and a stress riser since the
weld bead is thicker than the tube itself and the weld creates an inconsistency in the tube.
Second, 6-4 sheet is designed to be used as a sheet, not as a tube. If it is formed into a tube, its
grain structure can lead to premature tube failure. Indeed, a 6-4 tube will fail through fatigue
cycling (repeated flexing) before it should, and independent fatigue tests show that tubing made
from 6-4 sheet does not have the fatigue life of a properly drawn 3-2.5 tube.
In addition, an examination of some other high-tech industries that depend on high strength alloys
like 3-2.5 and 6-4 reveals that none use 6-4 small diameter tubing, primarily for the reasons
mentioned above. Consultation with titanium mills over the past decade tells us that seamless 6-4 is
not on the near horizon.
CP A small number of titanium frame builders incorporate Commercially Pure (CP) titanium into their
frames. CP has, at best, half the strength of 3-2.5. A CP frame must be made heavier than an
equivalent 3-2.5 frame in order to have comparable strength. Even most steels used in high quality
frames have higher strength than CP. The overall quality of CP tubing is lower because it is
typically used in low-cost applications-not bicycle building. CP is used mainly in industrial
applications when corrosion resistance is most important.