MountainBikes It has been a decade in the making, but the mountain
bike has become a passion for many people.Along with this passion it
has also become the most environmental way to get from point A to B. It
hasgone through a very intense evolution process over the past decade.
It all started with some guys from California who took their bikes
out for a ride on their day off,they modified their bikes and turned a hobby
of theirs into a worldwide phenomenon. The mountain bike'srapid
increase in popularity was influenced by social and economic situations,
and by technologicalimprovements that had the needs of bike riders in
mind. The introduction of the mountain bike at a bikeconvention in Long
Beach, California, early in the 1980's coincided with the need for a bike
that combinedtechnical superiority, ease of care, and multipurpose use.
Technological advances came extremely fast after it's introduction
into the world. The advanceshave made riding mountainbikes easier,
which makes it possible for the rider to explore new terrain. I hopethat
this report will be able to provide some information on the subject of
mountain bikes and the advancesin technology that the bike has gone
through, and what might be in the future of the mountain bike. The
road bike has taken more than a hundred years to evolve into the frame
that it is being used ontodays bicycle. Because of the increasingly
popularity of the mountain bike the demand for advances to bemade
have come very rapidly. The evolution of the mountain bike has been a
stormy one over the past decade. Within onedecade the design has
changed radically; this is due to three reasons. First , because geometry
and designwere copied from the first "Stone-Age bikes"; second, because
off-road riding created different problems ;and third, because innovative
frame design mirrored the "spirit of the times": young, new, dynamic,
andstrong. The off-road bike required extra stability.Frame It is
important to know the basic frame geometry and how to measure it. The
combination of tubelength and angle determines not only the
maneuverability of the bike, but also determines the seatingposition and
the transfer of power. Variances of 1° of the headset angle, or a 1' (2cm)
difference in thedistance between the rear-wheel axle and the center of
the bottom bracket, can have very seriousconsequences.Frame
Geometry The basic elements of frame geometry are: A- Height of the
seat tube; B- Length of the top tube;C- Seat-tube angle; D- Headset-tube
angle; E- Trail, F- Distance between the rear-wheel axle and the
bottombracket; G- Distance between the front-wheel axle and the bottom
bracket; H- Wheelbase; I- Height of thebottom bracket; J- Stem angle; K-
Length of the headset tube.A. Height of the Seat Tube This is
determined by the length of the biker's inseam. This measurement is only
of littleimportance, because of the different frame designs and the
different methods of construction used bydifferent manufacturers.B.
Length of the Top Tube This length should correspond to the rider's
trunk (length from the seat to the shoulders). Withmountain bikes this
measurement should be increased by a few inches. This increases the
distance betweenthe two axles, which increases the riding comfort and
makes for a straight and stable ride. Some times thetop tube is slightly
slanted, this is because some bike frames are designed so high off the
ground, the slantedtop tube makes for an easier dismount.C. Seat-Tube
Angle This angle basically determines how the bike will handle. Today
the standard for a seat-tube is tobe set at a 72° to 73° angle. At 69° to
71°, it is a more comfortable ride, but a sharper angle increases thebike's
agility and ability to climb. D. Headset-Tube Angle Along with the fork
and trail, the headset-tube angle determines the steering characteristics
of thebike. A steep angle together with a curved fork reacts more
sensitively when steering; a flatter angle reactsless sensitively. In the
past the angle was set at 68°, but today the standard angle of the
headset-tube is 71°.E. Trail The trail is the distance between two
points marked from the center of the headset to the floor andby the
extension of a line from the center of the front axle to the floor. This
distance depends on thecurvature of the fork and the angle of the
headset tube. A longer trail makes for easy steering; a short trailcauses
the bike to react quickly to every movement of the handlebars.F. Distance
Between the Rear-Wheel Axle and the Bottom Bracket The longer
this distance is, the more comfortable the ride. A shorter distance creates
a "livelyaction" and a good climbing ability. The average span from the
bottom bracket to the rear wheel for amountain bike is 17" (43 cm).G.
Distance Between the Front-Wheel Axle and the Bottom Bracket This
distance determines the amount of toe clearance. Toe clearance means
that the front tire andthe tips of the rider's shoes never come into contact
as the rider pedals and turns at the same time. To dothis, measure the
distance between the center of the axle at the front-wheel hub and the
center of the axle ofthe bottom bracket.H. Wheelbase This is the distance
between the centers of both the front-wheel and rear-wheel axles. A
longwheelbase makes for ease of handling and good straight-ahead
riding. A short wheelbase makes forsensitive handling.I. Height of the
Bottom Bracket This is the distance between the floor and the center
of the axle of the bottom bracket. A lowerbottom bracket makes the bike
more maneuverable; an elevated bottom bracket means more stability
andbetter straight-ahead riding. A very high bottom bracket makes it
easier to clear obstacles.J. Stem Angle This angle is determined by the
inclination of the headset tube. A wider angle gives an easy,
morecomfortable ride. A narrower angle gives a "sportier" feel. For the
comfortable ride the angle should be setfrom 15° to 25°, for a racer the
angle should be between 0° and 10°.K. Length of the Stem A longer
headset (stem) will distribute the weight of the rider more evenly between
the front andrear wheels. Longer headset tubes are more frequently
found on racing bikes. A long headset tube is about51/8" to 6" (13 to 15
cm); a short tube measures between 4" to 43/4" (10 to 12 cm). All
measurements taken together, and their relationship to each other, define
a bike'scharacteristics. The ability to interpret a frame's dimensions
allows someone to predict a bike'smaneuverability, and allows the biker to
determine if a bike will perform to his expectations.Tube Materials More
than 90% of all the mountainbikes used today are made from steel
tubes. The steel tubes areall made from high quality steel alloys. Other
substances have been added make sure the frame is problem-free as
well as having a high degree of stability and flexibility. Although the steel
tubes are ofexceptional quality, they have one major disadvantage, their
weight. Since weight is one of the basicproblems of a mountain bike,
there has been a search for a material that was light in weight as well
asstrong. Aluminum has rapidly become the tube material of choice in
the past few years. A decade agoaluminum was still an "exotic" metal, a
term used to describe titanium today. The use of carbon fibre andkevlar
are also being used more for the construction of bike frames. In recent
years these materials havebeen used in more industries other than the
aircraft industry, making them more affordable. Today buildersuse these
materials because of their qualities: light weight, and good elasticity, both
combined with goodstrength. Because the tube materials play such an
important role in the way a bike reacts and feels it isimportant for a buyer
to know what the bike frame is made from. It is also important to know
theadvantages and disadvantages of each of the materials.Steel Since
the mountain bike was invented, the frame manufacturers have used
chrome-molybdenum-steel in various thickness' to build high quality
bikes. The two most used steel alloys are 25-CrMo4 and 34-CrMo4. For
25-CrMo4, the 25 means that it contains 25% carbon (carbon makes
steel tension-resistant,and serves as a protection against deformation);
CrMo4 indicates how much of the substances that improvethe quality of
the steel (chrome and molydenum) have been added.
Manganese-molydenum is anotheralloy that may also be added. All of
these alloys reach very good anti-breakage strength. High-quality
steeltubes have seamless joints, and their ends have been reinforced or
"butted". The strength of the walls ofhigh-quality CrMo tubes have been
tripled. Butted tubes are strongest at the point where two tubes
arejoined, and are weakest in the middle of the tube. The advantages of
steel tubes are that it is a relatively inexpensive metal. The soldering the
tubesproduces strong, stable connections. Steel also tolerates a great
deal of stress before it starts to break down. There are two disadvantages
of using a steel frame: it's weight and it's susceptibility to corrosion. The
fight against rust is endless; also, a search for a material that is light is
still an ongoing process. Despite these shortcomings steel remains the
most reliable material for the frame industry.Aluminum The use of
aluminum to make bike frames has increased rapidly in recent years. In
order to makealuminum useful for mountain bike frames, an alloy had to
be produced. Copper, magnesium, zinc,manganese, silicon, and titanium
were each added; all of them increased the strength of aluminum.
Aluminum has a very high resistance to breakage. However, the
maximum load capacity (the amount ofpressure tolerated by a material
before it becomes permanently distorted) of aluminum is not as high as
thatof CrMo steel. Because of this the strength of aluminum can be
increased by widening the diameter of thewall of the aluminum tube.
The disadvantages of aluminum is that the price for high-quality
aluminum is as high as the pricefor steel, but depending on the method
used to connect the tubes, aluminum frames require more time tomake,
which in turn means that it costs more to the buyer. The tubes are either
glued or screwed togetherwith expensive sleeves, or they're welded
together. Both methods are expensive and time consuming. Although
aluminum tubing has only one-third of the rigidity of steel, when the
diameter of aluminum tubesis doubled, the amount of rigidity is not simply
twice but eight times higher. Another disadvantage ofaluminum is its
torsion strength. To improve the torsion strength of the aluminum the
thickness of the wallwas increased, this however, defeats aluminum's
weight advantage. The advantages that aluminum tubing for bike frames
are, that aluminum alloys are rust-free, theyabsorb shocks five times
better than steel, and they're light. Because the aluminum absorbs shock
betterthan steel, the result is a more comfortable ride. Because of these
reasons, the aluminum tubed bike frameis being used more and more
frequently in the industry.Titanium This material is used most often
in fighter planes, but it is now being used for mountain bikeframes.
Because of its superior strength vs. its weight, the finished frame is very
light and very strong. Inthe past titanium turned brittle after time, resulting
in small cracks when under heavy loads. The adjustmentin the
combinations of the metals that were used it the alloys, titanium is now
stronger than steel. Theproblem with this frame material was its price
and its complicated manufacturing process, but the alloy andproduction
problems were solved, and, together with a new welding technique, the
production of titaniumframes has become much easier. The high
price of titanium is titanium's greatest disadvantage. Titanium is three
times as expensiveas CrMo steel. The welding method that weakens
steel and aluminum has almost no effect on titanium. Inthe past it was
necessary to do the welding in a vacuum chamber to protect the material
against oxygen. Agood titanium alloy has approximately the same
strength as steel, but it achieves only 60% of steel's rigidity. This problem
is also solved by increasing the diameter of the tube. A high torsion
strength is titanium'sgreatest advantage, a problem that was solved by
making the walls of the tube thicker. Also, titanium isrust-free and is 40%
lighter than steel.Carbon-Fibre The future of mountain bike frames is in
fibre and resin. The superiority of carbon tubes over steel,aluminum, and
titanium is no longer a secret to mountain bike riders. This material
provides great ridingcomfort, increased rigidity, and amazing shock
absorption. Two types of tube stand out: round tubes thatare glued
together with aluminum sleeves and one-piece Monocoque frames.
Besides carbon fibre, manufacturers are also using glass fibre, graphite
fibre, Kevlar, and Spectra. It is important in themanufacturing process
that a correct, multi-directional arrangement of the fibres is made to
increase thetorsion stress. Poorly made carbon-fibre tubes will fracture
when exposed to heavy loads. There are only two small disadvantages
a carbon-fibre frame has. One is that it costs about four orfive times more
than a steel frame, and the other is that Monocoque frames have a very
limited number ofsizes. Other than those a lot better. Carbon-fibre
frames are three times stronger than steel frames, andhave 35% more
rigidity. They are also well protected from corrosion. Carbon tubes are
20% lighter thansteel tubes; the sleeves used for joining the tubes add
some weight, however, carbon frames are still 60%lighter than steel
frames. Their excellent ability to absorb shocks (the energy flow of the
shocks is diffusedby traveling from fibre to fibre) doesn't diminish the
frame's rigidity. Carbon-fibre is considered to be theultimate material for
frame tubes. Suspension In recent years the trend for mountainbikes is
to be equipped with a suspension system. However, it will take some time
before all the problems with suspension are worked out. The high
demandfor some kind of suspension is because of the heavy load that
the mountain bike's material must bear. Untilnow, the solution was to
increase the rigidity of the frame, but strengthening the material
compromisedcomfort. The solution on today's mountainbikes is by
adding suspension to the wheels. Suspension wasfirst used on racing
bikes, but because of the harsh conditions a mountain bike goes through,
it was only amatter of time before a suspension system was added to the
mountain bike.Front Shock Absorbers The front shock was the creation
of Paul Turner, who engineered the "Rock Shox". This type of
suspension is similar to the suspension used for motocross forks. This
suspension consists of an aluminumfork crown with two telescoping
blades that slide into each other when under pressure. The blades
areeither made from aluminum or steel. The distance of the spring action
is about 21/8" (5.5 cm). The degree oftension can be adjusted. There
are two ways to absorb shocks: oil-pressure or air-pressure suspension,
orwith springs and oil. Plastic parts can also give good results. Bikes
that are equipped with front-wheel shock absorbers don't lose contact
with the ground ,which allows for more control, and thereby making
driving at higher speeds possible. However, thisadvantage only comes
into play when riding at high speed, and when the shocks occur in quick
succession. Suspension prevents shocks from reaching the tire, and
thereby prevents damage to the rim; rims aren't aseasily deformed. The
greatest disadvantage is the change in the geometry of the bike. The
steering-tubeangle gets smaller, anywhere from 2° to 2.5°; the trail gets
larger, which changes the handling of the bikefrom characteristically quick
to a "sluggish" steering reaction. Add to this the additional weight of the
shockabsorber. A fork with a shock is around 171/4 oz. to 21/4 lbs (500
to 1000 g) more than a Unicrown orswitchblade fork. Suspension forks
are particularly useful for a biker who doesn't or can't avoid obstacles and
whenriding at high speeds is the goal of the rider, like in racing
competition, and especially in downhill races. Forthe average biker the
suspension system won't become useful until the system has been
improved to : 1.Minimize geometrical changes; 2. Design the suspension
in such a way that it can be turned on or off ascircumstances require; 3.
Reduce weight.Rear-Wheel Suspension After the front-wheel suspension
systems gained acceptance, it was only a matter of time beforeengineers
designed a suspension system for the rear-wheel. This was considered to
be an ambitiousundertaking, because it meant jeopardizing the stability of
the rear frame, a vital part of the frame structure. At the end of 1990,
Cannondale, Offroad, and Gary Fisher introduced the first rear-wheel
suspension. Cannondale and Offroad used similar systems. They both
have elevated chain stays providing lateral sway,with the pivot point
located in the front of the seat tube. Cannondale uses an oil-pressure
suspension, theOffroad rear frame is protected against shocks by plastic
devices. These suspension systems are well madeand designed, but
they also contribute to some problems: Stiff wishbone construction at the
rear framelessens lateral stability; interference with the important
geometry of the rear frame by adding shockabsorbers will also cause
considerable loss to the bike's lateral stability, changing the ride of the
bike. GaryFisher installed plastic devices to absorb shocks. They're
located behind the bottom bracket. Chain tension,however, makes the
rear frame more rigid (due to the lowered seat-stay position); traction is
not affected. Rear-wheel suspension is great for riding downhill, because
potholes are smoothed out, and tiresare protected from severe
punishment. However, uphill riding can be an ordeal when the rear of the
framebounces with every pedal stroke. This can drain the energy from
the rider quite rapidly. A bike equippedwith rear-suspension is also
heavier. At this time no satisfactory solution has been found; the
manydifferent versions are all still in the experimental stages. This
technology is still recent and still has room forimprovement. A rear-wheel
suspension that is standard to most bikes has not yet been found.Gears
Shifting and drivetrain have undergone enormous evolutions.
Today four different methods ofshifting gears are available: single shift,
double shift, rotation-grip, and grip shift. All four of the systems
aredifferent. The one thing that they all have in common is that they are
all indexed. The functions of the frontand rear derailleurs have reached
high standards, technologically and functionally. In combination
withnumerous gear positions this is (at this time ) the most perfect gear
shifting system. The only disadvantageis that it needs frequent attention
and adjustment. To shift gears smoothly and silently before the
invention of the indexed system was truly difficult. It was a process of
slow learning, and only professionals knew how to do it properly. The
indexed system,however, made it possible for even a novice rider to
master the art of shifting gears properly and with ease. The indexed
system has a built-in mechanism that enables the derailleur to move in
such a way that thechain rests securely on the chain ring as well as on
the sprockets. Single Shifter Today, as in the past, the single shifter
is the one that most bikers prefer. It is close to thehandgrip, and top
mounted, this one is the lightest (51/4 oz or 150 g) and reaches every
sprocket within a turnof 90°. This system also makes it possible to
disengage the indexed system, so that in case of difficulties,the gears
and derailleur can be used manually, using the friction system. The only
disadvantage is that theposition of the lever isn't ergonomically perfect.
The thumb has to move up above the handlebars each timethe gears
have to be shifted. However, the single shifter system is preferred for all
racing bikes.Double Shifter For ergonomic reasons, a few of the
professional mountain bike racers, moved the shifter belowthe
handlebars. The lever worked well of the biker pushed the lever away
from himself. It was pulling itback that was the problem. To solve this
problem the double shifter was introduced in 1989. The shifterwas split
into two separate levers. The lower lever moved the chain to a larger
sprocket and the upper levermoved the chain to a smaller sprocket. The
whole procedure became more complicated; instead of onemovement in
two directions, using one lever; now two movements, using two levers in
two directions,, wasnecessary. To shift gears it was necessary, even for
trained bikers, to learn the whole new procedure. despite the improved
position of the shifter the double shifter system has a disadvantage;
although by usingthe lower lever the largest sprocket or chain ring can be
reached, to shift to a smaller sprocket (to the right),it's necessary to push
the lever six or seven times, causing a slight slowdown. Although it is a
minorinconvenience for the recreational biker, it is a concern for mountain
bike racers.Rotation-Grip Shifter Handle bars with a diameter of 7/8"
(22.2 and 22.7 mm) are equipped with a 61/4" (16 cm) longrotation grip
with two or three mechanisms inside. The springs, activated by pressure,
cause a mechanismeither to tighten or to loosen the gear cable. In order
to shift to another gear, the grip must be rotated. Adial lets the rider know
on which sprocket the chain is riding on. Every sprocket can be reached
within a90° turn of the shifter. Later a lever inside the rotation grip was
made that prevents the gears from jumpingwhen riding in rough terrain.
Despite the perfect ergonomical placement of the shifter, it does have
twodisadvantages; the increasing number of handlebar accessories
leaves little room for mounting new ones,and accidental shifting can't be
totally eliminated.Grip Shift The "Grip Shift" is a system that can be
mounted at several different places on the handlebars. A21/8" (5.5 cm)
wide by 13/4" thick rotation ring can be mounted on either the inside or
outside of the grip andused on any handlebars that have a 7/8" diameter
(22,2 and 22.6). This system has an intricate systemconsisting of three
ring-cups that turn within each other that tightens and loosens the gear
cable by pulling itacross a wedge. The only disadvantages is that a 270°
turning radius is needed to reach all the sprocket. The greatest
advantage is its light weight. At only 2 oz (66 g) the "Grip Shift" is even
lighter than the singleshifter. Other handlebar accessories may also be
added if desired.Front Derailleur The front derailleur transports the chain
rings. This is done by a chain guide, which can be movedfrom side to
side by a cable, and is moved back with a retracting spring. Indexed
systems also functionwith the derailleur, but still need further refinement.
All too often the chain rubs against the cage and mustbe adjusted at the
shifter. While it is quite easy at the shifter, it's much more complicated
with the rotation-grip shifter. Adjustments don't last, and frequent
attention is necessary. This is a main complaint about therotation-grip
shifter.Rear Derailleur In order to accommodate the wide
arrangement of the gears, the mountain bike's chain housing hasto be
much longer than that of a road bike. The chain housing has to
accommodate the largest sprocket. The most popular type of mechanism
is the "slant" mechanism, almost all rear derailleurs are built accordingto
this model. With the slant mechanism, a much better functioning shifting
system has evolved becausethe guide pulley "wanders" back and fort at
the same distance over every sprocket.Brakes Brakes are the only
components that haven't significantly changed in the evolution of the
mountainbike. Today, the simple cantilever brake system has proven the
most reliable for off-road riding. Thefuture, however, belongs to disc
brakes, which at this time, are still going through a trial and error period.
The concept of the disc brake is of interest for mountain bikers, because
mountain biking makes such greatdemands on the brakes. These
demands are best served by disc brakes for three reasons: First, the
amountof space that disc brakes allow for the fat tires, so that mud
accumulation won't create problems; second,the brakes should weigh as
little as possible; and third, they must function under both wet and
dryconditions. But first we have to the learn the basic, and still the most
common type of brake system.Cantilever Brakes The best system is
also a simple one, and one that works. The cantilever brake is a
perfectexample. Two moveable brake arms with brake shoes are
mounted on bosses that are soldered to the seatstays, or to the chain
stays. On many models both brake arms are connected by cables. At
the end of thecable, which originates at the brake lever on the
handlebars, are cable carriers to which a linking wire isattached. The link
cable can be disconnected either at the left or right brake carriers. This
release thetension and allows the rear of front wheel to be removed. On
newer models the brake cable, which comesfrom the brake lever, is
attached directly to one of the brake arms, and guided by a round cable
carrier,connected to the other brake arm. On traditional cantilever
brakes, brake arms extend rather far to the outside for the best
possibleleverage. Sometimes this causes the rider's feet to come in
contact with the brake arms. This problem wassolved by "Low Profile"
brakes. Brake arms became longer, but the angles became much tighter.
ThePedersen cantilever brake makes use of the direction of the rim
rotation to give more power to the brakeshoes. The brake shoes are
pulled in the direction of the wheel's forward movement, creating
acorrespondingly higher brake action. When releasing the brake shoes,
a spring action pulls them back intothe neutral position, which results in
an energy saving of 20%.Brake Shoes Most brake shoes are made from
a hard, friction-resistant, special material consisting of
vulcanizedrubberlike plastic, which has been constantly been improved
over the years. New combinations made fromsynthetic rubber and pheol
ressin have increased deceleration, but overall they lose an enormous
amount ofeffectiveness when the rims are wet. Effectiveness when the
rims are wet is the big disadvantage of all rimbrakes. Since the rim
becomes part of the brakes in cable-carrying systems, the effectiveness
of the brakesvery much depends on the surface condition of the rim. The
most recent rims have a layer ceramic on theoutside which have
improved the effectiveness of the brakes under all weather
conditions.Hydraulic Brakes Hydraulic brakes operate by an
enclosed oil tube made from polyamide. Pressure applied to thebrake
lever is transferred to a cylinder and the brake shoes. In spite of many
advantages, these brakes arebeing used less and less, even though the
last disadvantage has been eliminated. The disadvantage was thatin
order to remove the wheels, you would have to let the air out of the tires.
This was solved by designing abrake so that the brake arms could be
opened up so that the wheel could be taken off with out letting the airout.
Disc Brakes Despite the good track record of the cantilever brake, the
search for an effective disc-brake systemhas started. A new bike
company in California, Mountain Cycles, introduced a hydraulic "Pro
Stop" disc-brake system in 1990. Aluminum discs (located at the hub of
the wheel) have brake shoes made from a low-temperature fibre material.
These brake shoes grip the disc in a "pinching" fashion. The brake
shoes,together with the aluminum disc, don't lose power under wet
conditions. Power from hand pressure isperfectly transferred to the brake
shoes. These disc brakes were developed in conjunction with a
front-wheel suspension system. Their weight including fork is 53/4 lbs
(2.6 kg). This system can also be mountedon conventional Unicrown
forks. Brake Levers The brake lever has been used ever since the
mountain bike was invented. It has gone throughimprovement over the
years in ergonomics, size, weight, and the way it performs. The lever
pulls a brakecable, which transfers the pulling action of the brake arm of
the cantilever to the brake shoe. The lever wasshortened after it was
discovered that it can be operated with only two fingers. There is also a
brake leverwith a roller mechanism, called the "Servo Wave". When this
lever is used, the pivot point changes therelation to the cable carrier,
which causes the brake shoes to come closer to the rim. The closer the
brakeshoes get to the rim, the more effective the transfer of power from
the lever to the brake shoes. Allaccomplished with a minimum amount of
pressure applied to the brake lever at the handle bars.
. riding mountain bikes easier, which makes it possible for the rider to explore new terrain. I hopethat this report will be able to provide some information on the subject of mountain bikes and. guys from California who took their bikes out for a ride on their day off,they modified their bikes and turned a hobby of theirs into a worldwide phenomenon. The mountain bike'srapid increase. Mountain Bikes It has been a decade in the making, but the mountain bike has become a passion for many people.Along with this