1. Seatpost
clamping
You may think that how a seatpost is
clamped to the bike is a yawner. However, with a material like carbon that only
works well in tension and not in compression, it’s a significant issue. A seat
binder generally works by compressing both the top of the seat tube and the
seatpost. But to optimize stiffness of both the frame and the post, both are
built with stiff fibers that can’t tolerate being pinched; the fibers will
crack if deflected very far over a short distance by the seat binder clamp.
Felt’s solution for clamping aero seatposts is unique and game-changing, and
its solution for clamping round posts puts reliability above weight and style
considerations.
Because it
isn’t round, an aero seatpost cannot be clamped inside an aero-shaped seat tube
with a constricting band clamp. Instead, the clamp has to push on the trailing
or leading edge of the post to wedge the opposite edge tightly against the
inner wall of the seat tube or clamp. Felt uses a completely different
seatpost-clamping system that also cuts the weight and the vertical rigidity of
its aero posts. (And its aero posts can be huge, from the UCI-legal (3-to-1
depth-to-width ratio) aero seatposts on its AR-series aero road bikes and
DA-series time trial bikes, to the extremely huge UCI-illegal (more like
8-to-1) aero seatposts on its IA triathlon bikes.)
Instead of clamping around the post or
wedging it from the front or back, Felt clamps each wall of the aero seatpost
against each inner wall of the seat tube by means of a vertical slot running
down each side of the post. On each side, a bolt extending out of a thickened
area at the top edge of the seat tube passes through the seatpost slot and
threads into a separate aluminum plate conforming to the inner shape of the
seatpost wall. Tightening each bolt simply clamps each wall of the seatpost
flat between each aluminum plate and the wall of the seat tube. To illustrate the concept, consider driving
over a flat carbon-fiber sheet on a smooth concrete floor versus driving over a
carbon seatpost. Obviously, the car tire will not crush the sheet of carbon,
because there is no air space to compress it into, but it will crush both a
round and an aero carbon seatpost.
The benefit to
Felt’s clamping system is not just reliable clamping; it is also reduced
weight, increased comfort, and increased frame durability. Since it does not
have to withstand crushing forces to hold it in place, the seatpost walls can
be very thin (you can easily flex the side walls of Felt AR, DA, and IA
seatposts with your fingers) and hence lightweight. This also provides a slight
amount of vertical compliance to a seatpost shape with which comfort is hard to
come by. Finally, it prevents tearing the frame apart by tightening the
seatpost, which is what wedge clamps are doing.
Clamps that wedge the seatpost from the
back are effectively trying to tear the back of the seat tube off (so it has to
be overbuilt and heavier to withstand it), and systems that wedge the seatpost
from the front are effectively working to tear the top tube away from the seat
tube. This may be part of the reason that you sometimes see bikes of pro riders
tear apart in a crash at the wedge clamp inside the top tube that pushes
against the seatpost; the rider standing out of the saddle is twisting at this
area stuffed with carbon in a much less effective layup than throughout the
rest of the frame.
Beyond a great
clamping system, Felt builds a little suspension into its big “Vibration
Reducing Aero” seatposts by encasing 3T’s “Difflock Comfort Module” saddle
clamp in them. This 3T system fits into the large cross-hole in the top of the
post. It surrounds the rail-clamping core with an elastic polymer allowing the
cylindrical clamping module to twist and return when the rider hits a bump. The
clamp also will accept all of the different available shapes of saddle rails
without interchanging clamp parts. Finally, the seatposts are flip-position with
different offsets available.
Even Felt’s
round seatpost-clamping systems are different from the run of the mill. In its
carbon F-series road racing, Z-series endurance road, and ZW-series women’s
road bikes, Felt doesn’t chop weight by using a thin, single-bolt clamp.
Instead, F, Z, and ZW frames all have taller two-bolt aluminum seat binder
clamps, despite the battle to get frames below target weights, like the magical
sub-700-gram weight. The 700-gram Felt F FRD frame does have a pair of titanium
bolts threading into a scandium nut bar in the tall clamp; do does the F1. And
rather than using a single slot, Felt has two slots on opposite sides of the
seat tube, to reduce the amount that any individual fiber is forced to bend.
2. Materials
Carbon frames and
forks used to have a woven top layer for aesthetic purposes that provided
little additional strength or stiffness, while adding weight. Perhaps you
assumed, as I did, that the checkerboard-weave top layer of Felt’s top frames
is like this, but it isn’t. Instead, that layer of TeXtreme
fabric actually saves weight and adds toughness to Felt frames, but it costs
around 10 times as much as the unidirectional fabric it replaces.
TeXtreme Spread Tow Fabric offers the
strength and toughness of two layers of unidirectional carbon in a single layer
of the same weight as one of those unidirectional layers. Unidirectional carbon
layers cannot stand alone for the same reason that a bulletproof vest made out
of fibers all running the same direction could not stop a bullet; an impact can
split the fibers if crossing ones are not there to hold them together.
Since the broad
packets (“tows”) of TeXtreme fibers cross at 90 degrees, forming the
checkerboard pattern, they provide the toughness of two crossing layers of
unidirectional fabric with a single layer. Furthermore, the weaving allows
thinner fibers to be used in the fabric without it being too delicate for human
hands to wrap around a frame shape.
For added
security, Felt uses a TeXtreme layer on the inside of the frame as well — the
first layer workers put down. This can prevent “mystery” carbon frame failures
by preventing fibers from imploding inward on impact. If a carbon frame takes
an impact, it is often difficult to tell that there has been damage on the
surface. But the sharp application of force can break internal fiber layers,
which can splay out inside of the frame. Cracks can then propagate from there,
and a rider’s frame may suddenly fail while JRA (“just riding along”), but the
failure was actually due to a prior crash. Felt’s layer of woven TeXtreme
inside can prevent severed unidirectional fabric fibers from splaying into the
interior of the frame tube on impact, and can therefore stop the propagation of
a crack.
TeXtreme
fabric is made in Sweden, and due to laws intended to prevent strategic
materials from falling into the hands of the Chinese military, Felt had to
import it to the United States, have it impregnated with resin certified as
being non-weapons-grade, and then send the pre-preg fabric, refrigerated, to
China for use in its frames. You can imagine the added costs. Once Felt bought
enough of it, TeXtreme went through a certification process with the U.S.
government so that it sends the fabric to China directly, and it is pre-pregged
there; this cost savings has made it possible for Felt to now use TeXtreme in a
second model from the top in each frame series.
3. Molding methods
Carbon
bikes are no longer made by laying fabric pieces into mold cavities because the
layers can’t overlap properly at the seam, and the molds are too hot from the
previous frame to lay pre-preg fabric in without becoming sticky. Instead,
workers (in a cool room) drape cold carbon pre-preg fabric pieces around a
mandrel shaped like a smaller version of the finished piece. Heat and pressure
make the resin flow like water; computers calculate the resin viscosity with
temperature to optimize flow through the layers. Mold channels let resin and
air escape. For premium frames, the mandrel is often EPS foam (Styrofoam)
dipped in latex. Once the clamshell mold closes around it, air is pumped into
the latex bladder, applying pressure against the carbon layers.
Felt’s top
models, by contrast, are done with “inside-out” molding. Rather than molding a
solid mandrel out of EPS in a clamshell mold with two female halves, Felt molds
two separate “coffee-cup”-like mandrel halves, which, when put together, form a
hollow version of the frame made out of a thin and tougher, denser foam. This
takes two male-female clamshell mold halves for each clamshell “coffee-cup”
mandrel half, or four molds total for just the mandrel.
The hollow
mandrel halves are taped together, and, rather than dipping the resulting
mandrel in latex repeatedly to get the desired thickness, it is coated with
silicone. Jeff Soucek, Felt’s director of R&D, said the silicone layer is
smoother and more uniform than multiple layers of latex, which can form drips
and be uneven in thickness and surface finish, and it has higher a heat
resistance. Soucek said the precision of the shape of this mandrel means the
layup moves very little during molding, so he can reduce the frame weight by
minimizing overlap of layers. He said with an EPS foam mandrel, overlap must be
around 5mm, whereas 1mm overlap is possible with the clamshell mandrel.
Air is pumped
into a nylon bladder inside of the clamshell mandrel, which is uniform and
tough and can’t blow out with temperature or due to uneven thickness the way
Soucek said a latex bladder can, causing a section of the frame to not be
compacted properly. On Felt’s second-tier frames, which are done with a solid
EPS-foam mandrel, it is encased in a nylon bladder rather than a latex one.
4. Bottom bracket
shells
Many of today’s
carbon frames are “net-molded;” nothing is machined or bonded in afterward to
make the bearings in the bottom bracket or headset fit. Thing is, there is no
shortage of riders complaining about their carbon bikes creaking, caused by
movement of the bearings or bearing cups in the frame.
As a bike mechanic, especially if you are installing internal electric wires
for electronic shifting, it may be beautiful to look inside the bottom bracket
shell of a top end carbon frame and see that it is completely hollow; you can
look right up inside the seat tube, down tube and chainstays. It’s obviously
very light, and it’s easy to route cables and wires through. However, you can
imagine that the bottom bracket bearings of, say, a press-in BB30 bottom
bracket may be more free to move around relative to each other if there is
nothing but a big hollow space between them.
By contrast, even on the 700-gram F FRD frame, Felt molds a separate carbon
cross-tube — a bottom bracket shell — and then bonds and molds it into the
frame. This keeps the bearings lined up with each other so they don’t creak and
to extend their life. Of course, you don’t have such easy access to the big
hollow tubes to stuff the rat’s nest of internal electronic wires and junction
box into them.
5. Head tubes
Again, veering
from the “ideal” of a net-molded frame, Felt does not depend on molded carbon
seats to hold the headset bearings. Rather, it bonds in thin aluminum bearing
seats to ensure precision of the bearing function.
6. Aerodynamics
No, Felt does not
have its own wind tunnel. However, it has a legacy in aerodynamics that started
with Jim Felt, while he worked at Easton, making custom aero frames for
triathletes out of special aero Easton aluminum tubes. Furthermore, Felt does
not restrain itself from making no-holds-barred aero bikes that the UCI does
not allow. While other manufacturers tend to sell their UCI-approved time trial
bike as a triathlon bike and make some changes in components to speed it up a
bit, Felt just went ahead and made the fastest bike it could, with some parts
of the frame being over twice the 3-to-1 aspect ratio mandated by the UCI. Felt
claims its IA frame has net lift in crosswinds (negative drag, so an
aerodynamic propulsive force rather than a drag force) and that the AR road
bike and DA time trial bike also have an exceptionally “high yaw profile,”
meaning they can go to high yaw (sidewind) angles before the bike “stalls” (the
point where the drag force suddenly increases dramatically).
Felt claims its “soft airfoil” shape on
many of its aero-bike frame tubes performs better in crosswinds by improving
reattachment of air after passing the tube, has a higher frame stiffness, and
interacts better with a water bottle than sharper or truncated airfoil shapes.
It’s also lighter than a sharp airfoil because added material is required to
form the sharp edge, as carbon cannot make a sharp bend like that. The company
says other shapes have a place; it uses sharp airfoils for the trailing edges
of handlebars and truncated airfoils (Kammtails) on vertical tubes that don’t
have a wheel or any other parts behind them. Judging by our test of the Felt
AR3 against other aero road bikes in the wind tunnel (August 2014 issue of Velo)
Felt’s tube shapes work, as the AR3 was the clear winner in any kind of
crosswind.
Felt claims its
UCI-legal time trial bike, the DA, is the fastest UCI-legal bike straight out
of the box (i.e., with no changes in component spec). However, it claims that
its UCI-illegal IA triathlon bike is faster yet: 4.5 minutes faster over an
Ironman than the DA — a full 100 watts of power savings over a road bike!
Felt’s road product manager Dave Koesel recommends that triathletes NOT buy
bikes with the UCI-approved sticker, saying, “that thing is a parachute” (in
order to get the UCI certification, a manufacturer must make the bike slower
than it otherwise could).
There are other items to mention as well –
things that Felt has quietly been doing for some time that now others are
trumpeting loudly about doing. Hollow dropouts are one example — where the
chainstay and seatstay form a continuous hollow loop past the dropout area, and
only the last small bit where the wheel clamps is compression-molded. This
allows Felt to make the F1 PR frame — the frame Thor Hushovd and Magnus
Bäckstedt used at Paris-Roubaix — that has become more relevant due to the
surge in popularity of racing road bikes on gravel. By bonding custom aluminum
dropouts into the hollow chainstay/seatstay loop (in place of
compression-molded carbon ones) of the top-end F1 road frame, raising its brake
bridge, and lengthening its fork (with bonded-in compression-molded carbon
dropouts), Felt has lengthened the rear end and wheelbase and kicked the seat
and head angles back by 1.2 degrees. This allows it to easily accept 28mm (and
even bigger tires) and increases the bottom bracket drop (so that the bottom
bracket is lower with a 25mm tire and about the same with 28mm or 30mm tires as
the F1). This amounts to a super light, confident-handling bike for cobbles and
gravel roads.
The hollow
dropouts forming a loop can also be used as a leaf spring; this feature is
incorporated into the Edict 4-inch-travel cross-country race 29er. The Edict is
a single-pivot bike that behaves like a linkage bike because of this flex at
the dropouts. When you remove the Edict’s shock, the shock-actuation lever
snaps down (you have to pull up on it to fit the shock back in) because the spring
formed by the hollow stays at the dropout springs open. This means the bike
springs to its sagged position, even without the rider on it, so the frame is
doing more of the work and the shock less, similar to the anti-squat built into
a linkage frame.
Another example of something Felt has been
quietly doing for a long time that is now being touted by major brands is
size-specific tube diameters and layups. Just like it did to Jim Felt when he
was making custom aluminum frames, Felt always made carbon tubes smaller in
diameter and with different wall thickness for small bikes than for big ones.
The only area where this doesn’t hold true is for specific aerodynamic shapes
for aero frames, but the wall thicknesses are still thinner on the smaller
frames.
Felt has invested
heavily in its product — in its engineers and the designs, tools, and materials
they come up with — and not much in marketing. So consumers just may be
surprised at how light, fast, snappy, and tough a bike they’ve barely heard of
can be.
Read more at
http://velonews.competitor.com/2014/08/bikes-and-tech/6-reasons-felt-making-worlds-best-bikes_339460#Gx0FTIdeSsCHhkgw.99
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