Carbon Fiber Bicycle Wheels
 |
| Carbon Rims and Wheels |
Carbon Fiber Bicycle Wheels - Just about everything you need to know to make your purchase.
First let's talk about what a carbon wheel upgrade will do for your ride. A wheel upgrade significantly improves the performance of your bike. Upgrading from entry-level to premium wheels can reduce weight, increase speed, and improve overall performance. Carbon wheels specifically can increase stiffness, making your bike more responsive and ultimately making you more efficient and faster. Carbon wheels can also be more aerodynamic because unlike aluminum, a deeper rim can be created without significantly increasing weight. There are few things you should know before making this investment.
There are 3 main components that comprise a wheel: the rim or hoop, the spokes, and the hub. There is a 4th significant factor in creating a high quality wheel: the actual lacing of the hub, spokes, and rim. The process of lacing involves both the method of lacing of the spokes and truing of the wheel for proper spoke tension. This is generally referred to as a "wheel build". A truly high quality wheel should be built by hand by a master wheelbuilder.
Not all carbon rims are the same:
There are 3 main steps that go into the process of making a carbon rim. Understanding these steps will help you be a smart consumer.
Quality control: Manufacturing a high quality rim is all about controlling the process precisely. Is the wheel mass produced at a factory where the quality control representatives work for the company whose name is on the wheel? Or is the person in charge of quality control a standard factory worker looking over several off brand's wheel production at the same time? The manufacturing process must be well controlled, especially for the products made from carbon fiber, since most of the work is done by hand. This can be hard for the average consumer to figure out. This is one reason to go with established brands. Also, talk to a trusted bike shop about the brands they carry and why.
Selection of the carbon fiber: It’s a fact that carbon fibers or strands are the strongest when they are straight. It is also a fact that sheets of unidirectional carbon require less resin to bond them than woven carbon sheets, which results in unidirectional carbon not only being stronger but also lighter than woven carbon. As a result, the selection of the fibers, how many layers are used, the direction each layer is oriented, whether it be a different direction or different angle, will play a major role in achieving lateral and radial stiffness. This layering will also allow the manufacturer to create a wheel that is stiff in the right directions to optimize ride performance.
Molding: This is another key step in the manufacturing process. If this step is not handled well, the result will be a useless piece of carbon figure that is thrown away. After laying up the material in a rim shape, the carbon fiber sheet(s) is already mixed with resin, and awaits the heating process. As the mold heats, the resin will melt and forms the layers of carbon into a strong fixture. There is a science in the heating procedure. There is a bag inside the rim that is injected with air after the rim is put into the mold. The filled air bag will distribute the pressure equally on the whole inner surface of the rim. This process is fairly detailed so the fabricators play an important role in the quality of the rim.
Finishing: The final step in manufacturing a carbon rim after it comes out from the mold is also critical. The shape will have overflow resin caused by the pressure of the air bag. This is trimmed and a coating is applied over the outer layer to protect the fiber from the exposure to sun and natural elements that occur when riding outdoors.
Now that you understand the multiple, detailed steps required to fabricate a carbon rim, you can see why the manufacturing process is so critical overall quality. You can also appreciate the extensive research and development that goes into how to optimally create use the sheets of carbon to create a high-performing wheel that balances stiffness, compliance, weight and aerodynamics.
Some long-distance off-road riders preferred aluminum wheels because they offer a more comfortable ride. A bit of wheel flex can improve ride quality. Another drawback to stiff wheels is that traction can suffer. Stiff wheels can’t conform to the ground as well as more flexible wheels. On particularly rough or bumpy surfaces, stiff wheels tend to skip around. This reduces friction between your tires and the ground, making it easier to lose traction. To combat this trait, established carbon fiber wheel manufacturers have optimized their wheels for comfort and stiffness. Manufactures can engineer carbon fiber wheels to be stiff in one direction but more compliant in another. Ideally, the wheel should be laterally stiff but vertically compliant. Through their research and design, a high quality carbon wheel can provide the flex and comfort while maintaining the stiffness desired when high torque is applied.
Not all spokes are the same
Spoke type j or straight?
J-Bend - The most common spoke type has a 90-degree bend at the end that connects to the hub. The J-bend prevents this area of the spoke from twisting, which helps with the wheel building process and during spoke replacement. Hubs are more simple and less expensive to manufacture when designed to work with J-bend spokes. Some riders say J-bend spokes are inferior to straight pull spokes because they bear too much stress at the bend. However, with high-quality spokes and a sound wheel build, very few riders report any issues at this junction.
Spoke Quality - Brand Matters
While any manufacturer can buy the same wire, there are many trade secrets in the manufacturing processes and it’s those processes that determine the quality of the spokes. Spokes can be categorized into three categories: straight gauge, butted, and bladed.
Straight gauge spokes are generally either 13 gauge (2.3 mm), 14 gauge (2.0 mm) or 15 gauge (1.8 mm). Virtually all high quality steel spokes are made of stainless steel. The top brands mostly use a Sandvik 18/8 alloy (18% chromium and 8% nickel) that can be hardened by cold working (important for the butted and bladed spokes).
Butted spokes are made by cold working the center to a smaller diameter than the ends. Interestingly, the process involves peening the center with many small anvil type heads. The thinner the spoke, the more it’s been peened and therefore the more it’s been cold hardened and the stronger it is. Spokes are never stretched to reduce their gauge.
Typically a 14 gauge spoke will be either 1.8, 1.7, or 1.5 mm in the middle. The thinner the middle, the lighter the spoke but more care is needed in building because with the thinner center they have a tendency to wind up. A butted spoke with a 1.8 mm section is about 6 grams. One with a 1.5 mm section is a little over 4 grams. The difference, times 44 spokes is 88 grams for a set of wheels – that’s a lot of wheel weight considering it’s just the spoke diameter changing. As an added bonus, because fatigue causes spoke failure, the lighter spokes are stronger because they stretch a little better (and have been hardened more).
One of the major recent developments is the increase in spoke strength allowing for fewer spokes. Sapim brand has risen to the top of the high end spoke brands along with DT Swiss.
As bladed spokes have became widely popular as the increasing importance placed on aerodynamics. The most popular bladed spoke being the Sapim CX Ray which is both extremely light (a little over 4 grams) and very strong (the strongest spoke Sapim makes (except for their 13 gauge spokes). Both DT Swiss and Pillar have similar spokes.
Not all wheel builds (lacing and truing) are the same:
Radial, 1 cross, 2 cross, 3 cross
A higher cross-pattern (3-cross) means you’ll need slightly longer spokes (because the distance from the hub to their rim-hole is greater), so the wheel will weigh slightly more than a 2-cross or radially laced wheel, but that’s a small trade-off for the improvement in strength.
Tension - properly and evenly tensioned with lateral relief through the process
Spoke Tension:
Hubs, rims, and spokes all have a tension operating range as recommended by their respective manufacturers. If a rim manufacturer say their rims can be built to 140 kg/f and a hub manufacturer sets their limit at 120 kg/f, default to the lower number in the wheel build. In general terms, most wheels are built to 120-130 kg/f unless there is a limitation from some of the components.
Building the wheels with an even tension from one spoke to another and falling within the appropriate tension range, coupled with proper wheel building practices like stress relieving, will result in better build quality. If your wheel builder does not use a properly calibrated tension meter or says they build “by feel”, that’s a red flag for considering another option - for example, let us build the wheelset for you before sending them off. Especially for carbon wheel builds, the wheel building process and components should be high quality only. It doesn’t pay to take shortcuts.
Where are the shortcuts
When choosing off brand wheels, look into the company's research and development of the testing performed, carbon they choose and how they choose to lay it up in the mold.
Much of the cost the consumer pays is in the research and development of the wheel.
Bike Hub Anatomy:
Hubs are at the center of your wheels. Following, discusses
almost everything there is know about bicycle hubs.
The front hub is simply designed to enable the wheel to spin,
while the rear hub is a little more complex as it also forms part of the bike’s
transmission – the cassette or sprocket which drives the rear wheel and is
attached to the rear hub, which on most bikes also features mechanism to allow
you to coast or freewheel (exceptions being fixed-gear or ‘fixie’ bikes and
track bikes).
Both front and rear hubs have the following components:-
Hub shell/body: This is the main
component of a hub. It is the “body” or “shell” to which the spokes and the
brake rotors (if disc brakes are used) are attached.
Bearings: The bearings allow the
wheel to rotate smoothly while remaining attached to the bike. Front Hubs
typically have two bearings, one on each side. The rear will typically have 3
to 4 bearings as there are an additional set of bearings in the free hub body.
Freehub body: The freehub is found
on the drive side of the rear hub. It is a splined component to which the
cassette is installed. There are additional bearings in it that allows it to
rotate independently of the hub body. It contains a ratcheting mechanism which
transfers power to the cassette but also allows you to coast.
Bearing sleeve or axle: The
bearing sleeve is like an axle and it joins the two bearings and interfaces
them with the wheel axle. The end caps are also attached to the bearing sleeve.
End caps: These are the parts of
the hub that attach to the fork dropouts of the bike and keep the wheel in the
correct position. They can be changed to make a hub compatible with different
axle standards.
Rear hubs usually have these additional components:-
Ratchet mechanism: As mentioned
above, this is the device that lets the freehub spin independently of the hub
body in one direction, in other words, when coasting. But it also locks them
together when you want to transmit power to the rear wheel and pedal in the
forward direction. There are three types of mechanisms that are responsible for
this – sprag clutches, ratchet-and-pawl mechanism, and ring-drive systems.
Types of Bearings
Nearly all bike hubs out there have one of two types of
bearings. Cup and cone bearings are
the older and more affordable type. These contain rings of loose ball bearings
that rest inside ‘cups’ in the hub body, and are fixed in place by ‘cones’
which are conical nuts. Other than being cheap, cup and cone bearings also have
the advantage of being easy to service at home. However, it can be tricky to
adjust them perfectly.
The other, more expensive, type is called cartridge bearings. These consist of ball bearings
or needles that rotate in a single unit called the cartridge. The cartridge can
be removed for servicing or replacement when worn out. Most high end hubs will
manufactured to accept cartridge bearings.
Materials
The majority of bike hubs are made of aluminum which is both
lightweight and strong. Higher-end carbon fiber hubs are also available for the
super the weight watcher. On the other end of the spectrum, are steel hubs which
can and durability but also weight.
Brake Rotor Attachment
Most higher end bikes now will be set up for disc brakes. Disc
brakes have a rotor that is attached to the hub of the wheel. This attachment is
either a: Six bolt or Centerlock.
As the name suggests, six bolts are used by fixing a six bolt rotor to the hub.
Meanwhile, a centerlock rotor attaches directly to the hub splines via a
special lockring. Both types have the same level of performance and one is not
really better than the other. It is useful to know that there are adapters that
can make centerlock rotors attach to six bolt hubs and vice versa.
Axle Standards
Axle standards can be confusing for most people. The main
standards are Quick Release, Thru-Axle, Boost and Non-Boost. Thru axles and
quick-release skewers have frame specific sizes. Therefore, you have to choose
a hub or a wheel according to the frame and fork of your bike.
Below are some major points to consider when
selecting a Rear Hub-
Points of Engagement
This describes the number of points at which the cassette is
engaged by the freehub’s ratchet mechanism. Generally referred to as POE,
higher-end hubs will usually have 36 POE or more while low-end hubs typically
have somewhere around 18 to 24 POE.
Points of engagement and angle of engagement
You’ll see some brands quoting points of engagement and
others referring to the angle of engagement for their hubs. The number of
points of engagement is the number of discrete positions in which the freehub
can lock to the wheel in each complete turn of the wheel, once you stop
freewheeling and start to pedal.
So a freehub with 36 points of engagement, for example, will have a 360/36 = 10-degree angle of engagement. If there are 72 points of engagement, the angle of engagement drops to 5 degrees.
Generally, higher points of engagement are found on more
expensive hubs. This is because more points of engagement means there is less dead crank travel or gap time before power is applied to the rear wheel. The bike can accelerate just a tiny bit faster. More points
of engagement is not as vital in road riding or time trialing as the rider is
continually pedaling. It is however more vital in mountain biking where the
rider will encounter technical terrain and need a fast engagement to quickly apply
power to the wheel and avoid dabbing.
When you are shopping for a new hub to replace a wheelset,
you will have to buy according to the number of spoke holes and their type(j-bend
or straight pull) available on the hub flange to that of the spoke holes
drilled into the rim. As an example, a 24-hole hub can only work with a a 24-hole rim.
Comments
Post a Comment