Bicycle - An Engineering Marvel

8/19/2019 Bicycle - An Engineering Marvel

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Bicycle - An Engineering Marvel

A Quora Book

- Arjit Raj

www.quora.com/raj-arjit

http://crazycuriosity.quora.com/Bicycle-An-Engineering-Marvel-Quora-Bookhttp://crazycuriosity.quora.com/Bicycle-An-Engineering-Marvel-Quora-Book


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1 | P a g e © A r j i t R a j

Contents

How it all started?

A beautiful history of the bicycle (Part 1)

A beautiful history of the bicycle (Part 2)

Wheel - A beauty on its own!

Why does a rolling tire/wheel stop after some time? Rolling friction does no work.

What dissipates its kinetic energy?

Why are the spokes in a bicycle mostly tangential and not radial?

How do the spokes of a bicycle wheel work? How is a wheel able to be light weight and

take such high loads?

Short history of Bicycle tires.

Skeleton to support and hold

Frame of a Bicycle

Transmitting power from the legs What are the different ways in which power from legs is transmitted to rear wheel in

bicycles?

A bicycle does not go reverse when we pedal it in the reverse direction. Why?

High torque gives low speed and low torque gives high speed. How does this happen?

Brakes - Let's slow down

Bicycle Brakes by Raj Arjit

Stability - How do bicycles balance?

Balancing of Bicycles

Miscellaneous What makes a bicycle faster than a regular walking man?

When a wheel spins really fast, why does it appear like it is spinning in the opposite

direction?


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How it all started - I

Bi cycle: An awesome machine with an equally awesome history.

It is hard to think of the so many transformation this machine has gone through.

The quest for human powered, stable, fast and energy efficient vehicle has taken

us a long way. Let’s see how it all started!

1790s – The beginning

The first reference to a two-wheeled vehicle driven by one rider was a toy like

simple machine, with just two wheels attached to a rigid wooden frame. The

rider would sit on the frame and drag using his feet, moving forward.

While it is not precisely known who invented this, Médé de Sivrac, a French

Craftsman, is often credited to have first come up with this design.

There were a couple of strong issues with this tool. It lacked stability as the

moment the rider lifted both of his legs, it started falling over. Along with this,


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there was difficulty in turning. The rider had to lift the front wheel and drag it to

turn, many times this required, stepping out, turning and then using it.

Lack of ability to quickly steer resulted in difficulty in traversing even

moderately rough terrains.

1820s – Velocifere

Before jumping in the invention, it is worthwhile to know of an important event

– the volcanic eruption of Tambora in 1815. This caused a widespread crop

failure leading to starvation and death of horses in huge numbers.

A German civil servant Baron Karl von Drais, was looking for alternatives to

horses for a while. He then came up with modifications to the toy machine and

invented, which became famously known as the hobby horse or Draisene or

Velocifere. He was able to clock speed as high as 15 kmph with this.


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The important modification here was the addition of simple joints to make the

front wheel steerable. As the speed had increased, a backrest was also added for

the rider comfort.

Still the ride was quite bumpy. Also, we were still having the feet on the

ground.

1830s – The first true bicycle

The credit for inventing the first true bicycle – one which could be ridden with

both feet off the ground, is given to a Scottish blacksmith Kirkpatrik

Macmillan.

Macmillan attached two levers on either side of the frame near the position of

legs. While one end was on the frame, the other end carried short lever (known

as treadle) which in turn carried pedals. The rider would simply oscillate pedals

and the complete mechanism would rotate the rocker fixed on the rear wheel.This was given the name Velocipede.


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To understand the mechanism used see the figure below.

The link 4 (called rocker) oscillates while the link 2 (called crank) rotates

complete 360 degrees. Mechies, know the relative length of links required to

cause the oscillation and rotation of different links. :-)

Check the velocipede image carefully. You will notice the presence of small

black color pieces in the center, near the frame. These have threads attached and

goes up to the hand bars. Well, you can guess it. As the speed was increasing,

this was the first one to have brakes. Since dragging by feet, was not a goodthing to do.


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How it all started - II

In Part 1 we saw, how the sheer curiosity of humans led to the rise ofVelocifere, Velocepede and other primitive designs of Bicycles. Let's see

further.

Commercial Failure of Macmillan's Velocepede

Although Macmillan's Velocepede was the first true bicycle, which enabled the

user to traverse without putting his feet on the ground, it failed on commercial

grounds. Not a single product was sold. Probably because oscillating the feet

was much more troublesome than rotating it as in the designs that came later.


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1870s - Michaux’ s velocipede

For the next four decades, there wasn't much strong development and

innovation in the design. A French blacksmith Pierre Michaux is credited to

have come up with a new design which had, for the first-time pedals instead of

treadles. The pedal - crank, system were attached to the front wheel.

The working was much similar to the present day working of children's

tricycles. There was one more piece of innovation though. For the first time in

history of bicycle, "suspensions" were used. Look at the above pic carefully

and see the position of the seat. It is put on a seemingly straight steel bar. Well

that is a simple leaf spring in action. These leaf springs (though more complex

ones) are commonly used in railway carriages, SUVs, trucks and other heavy

vehicles.

Despite the use of suspension, the iron-rimmed wooden wheels offered enough


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shocks to the user, that very soon Michaux's Velocipede was nicknamed as

"Bone Shaker".

Okay, some theory before we jump on the next design.

The aim was to increase the speed of the bicycle.

Speed is simply given by distance travelled divided by time.

Distance travelled will depend on number of revolutions the front wheel

makes.

In one revolution, the distance travelled will be equal to the circumference of

the wheel, which in turn depends on the diameter of the wheel pedalled.

Okay, so the distance travelled can be increased in two ways - either

increase the number of revolutions per unit time or increase the diameter

of the wheel.

(It was difficult to do both as the weight of the wheel would increase too much).

Keep this piece of information in mind for a while.

While driving bicycle we don't just need longer distance, but also torque -

rotating force, which will give us the necessary traction to propel forward.

Let's do one experiment

Put your bicycle on the stand and try rotating the pedals using hands. Steadily

keep on increasing the speed. You will see that after a threshold RPM

(Revolutions per minute), the force which you are applying starts decreasing.


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This happens because after a certain RPM our hands (or legs) are not able to

deliver the same force at higher speed.

There occurs an optimum RPM at which the force applied is maximum. For

human legs, this comes around to be around 50 RPM.

Great! Now, at that time it was not justified to rotate (or pedal) the front wheel

at that high RPM since it resulted in very large shocks and made the ride highly

uncomfortable.

So we had only one option to increase the speed - increase the diameter!

The increased circumference of the wheel gave longer distance in one

revolution. This led to the increase in speed but yes some problems also came

up!


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1870s to 1900s was the era of these high wheelers. It was a commercial success.

It gave a normal speed of up to 20 miles per hour, which was way ahead of the

previous designs. The problems which came along with the higher speed was

due to its very own size. The center of gravity was very high and closer to the

front wheel. Powering as well as turning the front wheel led to decrease in

stability. Even a small pebble or sudden brakes could make the rider fly off and

fall on the ground facing downwards!

The above design also made it difficult for women and children to use it. It was

commonly used only by brave males and athletes.

Moving towards Modern Design

Englishman called Henry J. Lawson, removed a lot of problems and came with

a new design named as Bicyclette, which soon got famously called as "Safety

Bike".


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As you could see from the pic, the size of front wheel came down and instead of

direct power transmission, chains and sprockets were used. The ratio of

sprocket sizes enabled higher RPM possible.

Soon a series of further small but important changes came up. Both wheels

became equal in size, pneumatic tyres, bells, tangential spokes instead of radial

spokes and other features came, making the bicycle more stable and strong.

(Early Rover safety Bike - 1885 )

(Rover Safety bike 1889)


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The very important diamond shape frame introduced by Rover Safety bikes

became a standard which is still in use today!

If you would like to go through the complete history of Bicycle in just one

minute, I would strongly recommend you to watch this beautiful video.

Evolution of the Bicycle - By Thaalis Vestergaard

Pro tip - Keep your eyes on pedals as well as on the spokes. :-)

Sources

First Chain-Drive 'Safety' Bicycle

The Rover Safety Bicycle 1887 - Starley and Sutton, Coventry

1885: First Chain Driven Bicycle - "The Rover"

High wheeler

historicalcycleclub.com.au

http://vimeo.com/73581450http://vimeo.com/73581450http://vintagegaragecycle.blogspot.de/2010/01/first-chain-drive-bicycle.htmlhttp://vintagegaragecycle.blogspot.de/2010/01/first-chain-drive-bicycle.htmlhttps://vintagebicycle.wordpress.com/2010/09/16/the-rover-safety-bicycle-1887/https://vintagebicycle.wordpress.com/2010/09/16/the-rover-safety-bicycle-1887/https://aehistory.wordpress.com/1885/10/05/1885-first-chain-driven-bicycle-the-rover/https://aehistory.wordpress.com/1885/10/05/1885-first-chain-driven-bicycle-the-rover/http://rebloggy.com/post/vintage-gentleman-penny-bike-wheel-bicycle-penny-farthing-bicyclette-wheeler-hig/29269079920http://rebloggy.com/post/vintage-gentleman-penny-bike-wheel-bicycle-penny-farthing-bicyclette-wheeler-hig/29269079920http://www.google.com/url?sa=i&source=images&cd=&cad=rja&uact=8&ved=0CAcQjB0&url=http%3A%2F%2Fhistoricalcycleclub.com.au%2Fmembersbikes%2F2014%2F2%2F3%2Fmichaux-velocipede&ei=EGbUVOX1HILqaPCagvAF&psig=AFQjCNFNY9w7QCMk8Mv9DCaTakKFd-ma2A&ust=1423292304569532http://www.google.com/url?sa=i&source=images&cd=&cad=rja&uact=8&ved=0CAcQjB0&url=http%3A%2F%2Fhistoricalcycleclub.com.au%2Fmembersbikes%2F2014%2F2%2F3%2Fmichaux-velocipede&ei=EGbUVOX1HILqaPCagvAF&psig=AFQjCNFNY9w7QCMk8Mv9DCaTakKFd-ma2A&ust=1423292304569532http://www.google.com/url?sa=i&source=images&cd=&cad=rja&uact=8&ved=0CAcQjB0&url=http%3A%2F%2Fhistoricalcycleclub.com.au%2Fmembersbikes%2F2014%2F2%2F3%2Fmichaux-velocipede&ei=EGbUVOX1HILqaPCagvAF&psig=AFQjCNFNY9w7QCMk8Mv9DCaTakKFd-ma2A&ust=1423292304569532http://rebloggy.com/post/vintage-gentleman-penny-bike-wheel-bicycle-penny-farthing-bicyclette-wheeler-hig/29269079920https://aehistory.wordpress.com/1885/10/05/1885-first-chain-driven-bicycle-the-rover/https://vintagebicycle.wordpress.com/2010/09/16/the-rover-safety-bicycle-1887/http://vintagegaragecycle.blogspot.de/2010/01/first-chain-drive-bicycle.htmlhttp://vimeo.com/73581450


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Wheel - A beauty on its own!

Why does a rolling tyre/wheel stop after some time? Rolling friction does nowork. What dissipates its kinetic energy?

Many people think they know but they don't!

The first thing to know is that Rolling resistance is differentthan Rolling friction!

There are 4 different causes that dissipates the kinetic energy and causes

the tyre/wheel to stop.

1.

Deformation at contact - Prominent in all rolling bodies.

2. Hysteresis Losses - Prominent in tyres.

3. Rolling Friction - This not necessarily opposes motion.

4. Slippage - At higher speeds or at watery/slippery surfaces.

Deformation at contact

This is the most prominent factor responsible for slowing down of bodies

like a steel ball/ring/sphere. To understand this, the first thing you have

to keep in mind is this - no body is perfectly rigid. Although we say,

the rolling bodies make a point contact at surface, it is not true in

practical sense. Rolling bodies make an area contact.


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Source: H.C. Verma's Foundations of Physics I

Now because of this area contact and irregular deformation, the Normal

force (the reaction of surface corresponding to its weight) doesn't pass

through center. Instead, it gets shifted slightly towards right and gives

counter-clockwise torque which causes net deceleration.

The magnified view of the contact area and the normal forces is shown

below. You can easily notice the normal forces are higher on the right

side than on the front.


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Hysteresis Losses

Hysteresis is derived from a Greek word meaning "Deficiency" or

"lagging behind."

It is simple to understand in this way: You pull a rubber band and make

it longer. You spend some amount of energy in doing this. Now when you

leave the rubber, the energy released is lesser than the energy spent.

Another way to understand is in terms of force. It is harder to deform by

loading than by unloading.

The above figure shows the Elastic hysteresis of an idealized rubber

band. The area in the centre of the hysteresis loop is the energy

dissipated due to internal friction. Pic source Hysteresis.

http://en.wikipedia.org/wiki/Hysteresishttp://en.wikipedia.org/wiki/Hysteresishttp://en.wikipedia.org/wiki/Hysteresishttp://en.wikipedia.org/wiki/Hysteresis


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Rolling Friction

This is the force analogous to friction in case of planar bodies. The value

of rolling friction coefficient is much less, varying from 0.01 to 0.001.

Slippage

Slippage occurs when the wheel rotates more but translates less. This

causes loss in power. This is more prominent in watery surfaces or at

very high speeds.

If you liked the articles so far, you may enjoy learning the Fundamentals of -

How a car works through my Udemy Course.

https://www.udemy.com/automobile-engineering-from-zero-to-100-for-everyone/?couponCode=RedditS


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Why are the spokes in a bicycle mostly tangential and not radial?

Short answer – better transmission of torque at lower weight.

Detailed answer

Once, all bicycles had radial spokes. In fact, when the wheels were first

originated, they had no spokes at all – a simple flat disc type wheel. Soon

it was realised that the wheels could be made lighter by connecting the

centre (hub) to the rim through straight rods. The wooden wheels used

6/8 spokes which were all radial. From no spokes, we went to radial

spokes then to tangential ones.

Now tangential spokes are not the exact technical term used in this field,

since no spoke is exactly tangent to the flange. The correct term is

crossed-spoking.


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The pattern of bicycle spokes is defined by the number of times each

spoke crosses adjacent spokes on its way from the hub to the rim.

Cross-zero refers to radial pattern – the ones which go straight from

the hub to rim along the radius.

Cross-spokes are somewhat tangent to the hub (flange, to be precise)

and cross adjacent spokes on its way from the hub to the rim. The

maximum number of crosses can be obtained by dividing the number of

spokes by 9. (I don’t know why!) For example, in 36 spokes maximumcrosses are 4 and for 32, the maximum is 3. Maximum occurs when the

spokes are closest to tangential to the flange.

There are also mixed patterns having both radial and crossed spokes as

shown below.


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So how does this crossing help, exactly?

Spoke crossing is much more important for the rear wheels, which have

to transmit the torque from the hub to the rim via spokes.

If radial spokes are used, then the hub will sort of pull each spoke with it,

making the pattern of spokes spiral. This results in excessive shear force

acting on the spokes. Because of this, stronger spokes are needed and the

strength of coupling at the hub has to be increased. Many times the

spoke nipples are reversed and fastened to the hub if radial spokes are

used.

The above problem gets eliminated to much extent in tangential or cross

spoked case, because the force gets transferred along the direction of the

spokes.

Try visualising any two spokes in the same line. Each supports each

other. This effect is not present in radially spoked wheels.


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Spoke Nipples are those parts (shown in color in figure below) that holdsthe spokes to the rims. It is used for tightening of the spokes and

keeping it tensed.

Axles, bearings and tires are not that important from the structural

strength point of view.


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Working

Basics

Some materials, for example, concrete pillars support load in

compression. These will fail when applied stretched from both ends

(tensile loads). In a similar manner, there are materials that can support

load only in tension (when stretched and tight). Examples are ropes,

threads and Bicycle spokes! These materials will simply bend and twist

under compression.

But when I sit on a bicycle, its spokes gets compressed, so why it doesn’t

fail?

Agreed the spokes are compressed, but even after compression it is in a

net tension. See the figure below to understand what happens to a bicycle spoke - in 3 condition:-


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1. When it is not fitted in the rim – Free state.

2. When it is fitted in the rim – it is stretched and tension is applied

3. When a person sits and load is applied – it gets compressed. But the

amount of compression is less than the amount of tension given in

step 2. This leads to net tension - always.

All the spokes work together and share the loads (not equally) and are

able to support high loads.

A common misconception

There is a prevailing misconception (or confusion) regarding whether

the hub hangs from the upper spokes or stands on the lower spokes?

http://en.wikipedia.org/wiki/Spo...

The correct answer is - the hub stands on the lower spokes.

Standing, in this case, means that the spokes at the bottom are the ones

that change stress; they are being shortened and respond structurally as

rigid columns. They are rigid as long as they remain tensioned.

We could have said that it “hangs”, had the stress changes in the upper

spokes been more than in the lower one. But exactly the opposite

happens. The increase in tension of the upper spokes is less than 4% of

the stress changes in the bottom spokes.

http://en.wikipedia.org/wiki/Spoke#Reaction_to_loadhttp://en.wikipedia.org/wiki/Spoke#Reaction_to_loadhttp://en.wikipedia.org/wiki/Spoke#Reaction_to_load


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Loads - Static and Dynamic

The spoke tension and tire pressures forms the major source of static

loads on the wheel, while the rider's weight, braking load, loads due

to surface irregularities, torsional loads from hub to rim via

spokes (during pedalling) forms the sources of dynamic loads.

Note - Rider's weight is dynamic and not static, because the revolution

of the wheel causes a periodic change of loads on different spokes

and regions of rim.

Failure

A common type of failure is due to the breaking of spokes and cracking

of rim. Although spoke failure appears instantaneous and the blameis often put on the a particular event, like going through sudden

surface bumps (around which it failed), the reality is different.

Most of the time spokes failure is due to the fatigue. And also, it is

not the exact bump in the road that caused failure. The spokes break

(due to fatigue) after leaving a bump - while returing to its normal

tension and not while meeting the bumps.

Sources

1. Bicycle Wheel by Jobst Brandt

2. http://en.wikipedia.org/wiki/Spoke

http://en.wikipedia.org/wiki/Spokehttp://en.wikipedia.org/wiki/Spokehttp://en.wikipedia.org/wiki/Spokehttp://en.wikipedia.org/wiki/Spoke


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Short history of Bicycle tires

The first bicycle "tires" were iron bands on the wooden wheels of

velocipedes. One similar wheel (though, not of a bicycle is shown

below)

These were followed by solid rubber tires on penny-farthings. The

first patent for "rubberized wheels" was granted to Clément Ader in

1868. In an attempt to soften the ride, rubber tires with a hollow core

were also tried.

The first practical pneumatic tire was made by John Boyd

Dunlop in1887 for his son's bicycle, in an effort to prevent theheadaches his son had while riding on rough roads. (Dunlop's patent

was later declared invalid because of prior art by fellow Scot Robert

William Thomson.) Dunlop is credited with "realizing rubber could

withstand the wear and tear of being a tire while retaining its

resilience". This led to the founding of Dunlop Pneumatic Tyre Co. Ltd

in 1889. By 1890, it began adding a tough canvas layer to the rubber to


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reduce punctures. Racers quickly adopted the pneumatic tire for the

increase in speed it enabled.

Finally, the detachable tire was introduced in 1891 by Édouard

Michelin. It was held on the rim with clamps, instead of glue, and

could be removed to replace or patch the separate inner tube.

Source: Wikipedia - Bicycle tire

http://en.wikipedia.org/wiki/Bicycle_tire#Historyhttp://en.wikipedia.org/wiki/Bicycle_tire#Historyhttp://en.wikipedia.org/wiki/Bicycle_tire#Historyhttp://en.wikipedia.org/wiki/Bicycle_tire#History


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Skeleton to support and hold

We will be discussing the commonly used Diamond Frames in Bicycle.


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Different Parts and Functions

Head Tube: This houses the handle bars and the fork, which holds

the front wheel.

Top tube: Acts as a connector from head tube to the top of seat tube.

In most cycles it is parallel to the ground, while in case of some racing

cycles it be sloped downwards to allow for more space while...

Down tube: This connects the head tube to the bottom joint. It also

possesses small attachments to allow for various cables (coming from

from handle bars) or a cage for holding small bottles.

Seat tube: This houses the seat post of the cycle. The seat post can be

inserted at varying degrees in the seat tube. This provides space for

adjusting the position of seat saddle at different heights.

Chain stays: It runs parallel to the chain and connects the bottom

joint to the rear end. Seat Stays: Finally this connects the top of seat tube to the rear end

Why Triangular Shaped?

The diamond frame consists of two triangles ( the front half is notprecisely a triangle, though). There is a reason for the use of triangular

shapes.

Triangle is structurally the most rigid and strongest shape of all simple

geometries. Let's understand why without going much in mechanics.

Consider a rectangular shaped arrangement of links. Now, even if all the


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links are welded properly at joints, an uneven force can easily change the

angles (slightly) and convert it into the other shape.

This type of misalignment doesn't occur in case of triangles because for a

given set of 3 members, a unique triangle is possible with fixed angles.

Hence triangle forms the simplest rigid structure. A triangle cannot be

distorted to form another shape (keeping the members straight).

Now we can use various combination of triangles as per our need. The

various combination of triangles must follow a simple rule:

N = 2 J - 3

where, N= Number of links and J = Number of Joints.

For a simple triangle N and J both are 3. Whereas for a diamond frame N

= 5 and J = 4.


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What we have discussed in last paragraphs falls in the domain of a

subject known as Truss. You can find many application, where triangles

are used in different combinations to provide strength. Examples include

various bridges and towers and monuments.

Sources:

Bicycle frame

Bike Frame Geometry

http://en.wikipedia.org/wiki/Trusshttp://en.wikipedia.org/wiki/Trusshttp://en.wikipedia.org/wiki/Trusshttp://en.wikipedia.org/wiki/Bicycle_framehttp://en.wikipedia.org/wiki/Bicycle_framehttp://www.bikeframerepair.com/BikeFrameGeometry.htmlhttp://www.bikeframerepair.com/BikeFrameGeometry.htmlhttp://www.bikeframerepair.com/BikeFrameGeometry.htmlhttp://en.wikipedia.org/wiki/Bicycle_framehttp://en.wikipedia.org/wiki/Truss


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Transmitting power from the legs

What are the different ways in which power from legs is transmitted

to rear wheel in bicycles?

There are many different ways in which power transmission is done.

Let's see how it is done in following types of bicycles :-

1. Single Speed Bicycles

2. Variable Speed Bicycles (Geared Bikes)

3. Fixed Gear Bicycles

4.

Tandem Bicycles

5. Miscellaneous

Single Speed Bicycles

One large sprocket is connected to the pedals. A chain passes over it and

is connected with a smaller sprocket (this is connected with the rear

wheel).

In this a larger sprocket is rotated by pedaling, which in turn rotates the

smaller sprocket at the rear. One revolution of larger sprocket brings

multiple revolutions of the rear sprocket (and hence, the wheels). The

ratio of diameters of both determines how much revolution the rear

sprocket will make on one revs of front sprocket.


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It is called single speed, since, for any particular speed of pedaling, you

can have one and only one speed of rear wheel.

Variable Speed Bicycles

Here Derailleurs are used for achieving the variable speeds. The basic

theory is that you need to drive sprockets of variable diameters to

achieve different speed - torque combination.

See this answer for more info - High torque gives low speed and lowtorque gives high speed. How does this happen?

The rear derailleur serves two functions. One of switching the chain from

one sprocket to another and also it keeps the chain tight.

The front derailleur just serves one main function of shifting chain from

larger ring to another.

Note: Derailleurs is originated from term De-rail. It derails the chain

and moves it to different cogs.

https://www.quora.com/High-torque-gives-low-speed-and-low-torque-gives-high-speed-How-does-this-happen/answer/Raj-Arjithttps://www.quora.com/High-torque-gives-low-speed-and-low-torque-gives-high-speed-How-does-this-happen/answer/Raj-Arjithttps://www.quora.com/High-torque-gives-low-speed-and-low-torque-gives-high-speed-How-does-this-happen/answer/Raj-Arjithttps://www.quora.com/High-torque-gives-low-speed-and-low-torque-gives-high-speed-How-does-this-happen/answer/Raj-Arjithttps://www.quora.com/High-torque-gives-low-speed-and-low-torque-gives-high-speed-How-does-this-happen/answer/Raj-Arjithttps://www.quora.com/High-torque-gives-low-speed-and-low-torque-gives-high-speed-How-does-this-happen/answer/Raj-Arjit


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A more close- up view of rear derailleur is shown.


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Fixed Gear Bicycles

These refers to those bicycles having drive train without a freewheel.

Freewheel are attached the rear wheel which helps in coasting (ride

without pedalling using forward momentum) and also prevents from

driving backward.

See this answer to know more about freewheel working:

A bicycle moves forward when we pedal it in the forward direction. But

why does it not go reverse when we pedal it in the reverse direction?

Such bicycles are simple, lighter but for many people tougher to handle

and control, especially during turnings. Fixed gear bicycles are also

commonly called Fixies.

In Fixies, the rear sprocket is threaded or bolted directly to the hub of

the back wheel, so that the rider cannot stop pedalling. When the rear

wheel turns, the pedals turn in the same direction. This allows a cyclist to

apply a braking force with the legs and body-weight, by resisting the

rotation of the cranks. It also makes it possible to ride backwards

although learning to do so is much more difficult than riding forward.

Tandem Bicycles

The tandem bicycle or twin is a form of bicycle designed to be ridden

by more than one person.

https://www.quora.com/A-bicycle-moves-forward-when-we-pedal-it-in-the-forward-direction-But-why-does-it-not-go-reverse-when-we-pedal-it-in-the-reverse-direction/answer/Raj-Arjithttps://www.quora.com/A-bicycle-moves-forward-when-we-pedal-it-in-the-forward-direction-But-why-does-it-not-go-reverse-when-we-pedal-it-in-the-reverse-direction/answer/Raj-Arjithttps://www.quora.com/A-bicycle-moves-forward-when-we-pedal-it-in-the-forward-direction-But-why-does-it-not-go-reverse-when-we-pedal-it-in-the-reverse-direction/answer/Raj-Arjithttps://www.quora.com/A-bicycle-moves-forward-when-we-pedal-it-in-the-forward-direction-But-why-does-it-not-go-reverse-when-we-pedal-it-in-the-reverse-direction/answer/Raj-Arjithttps://www.quora.com/A-bicycle-moves-forward-when-we-pedal-it-in-the-forward-direction-But-why-does-it-not-go-reverse-when-we-pedal-it-in-the-reverse-direction/answer/Raj-Arjit


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There are two common configurations used :-

Crossover rear drive: In this the forward crankset is connected by a

left-side timing chain to the rear crankset, which in turn is connected

by a right-side chain to the rear wheel. This requires both of the cranks

to be in tandem.


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Single side rear drive: The forward crankset is connected by a

right-side timing chain to the rear crankset, which in turn is connected

by a right-side chain to the rear wheel. This does not require both the

cranks to be in tandem.

Miscellaneous

There are many other different types of bicycles like Sociable, Pedibus,

Conference bike etc. (I wish someone comments the working of

transmission in these machines).

Sociable Conference Bike


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Party bike or Pedibus.


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A bicycle moves forward when we pedal it in the forward direction. But

why does it not go reverse when we pedal it in the reverse direction?

Welcome to the "Awesomeness of Mechanical engineering"!

The reason for this, is the presence of a simple but beautiful mechanism

called the Freewheel, which is attached to the rear wheel hub. To

understand the working, see the figure below.

A sprocket is fitted over this freewheel, which is pulled/rotated by the

chain.

Now when you have to move forward (counter-clockwise in above

figure), the red color link - called pawl, acts like a hook and gets locked

with the teeth - called ratchet and transmits the torque. The complete

mechanism is called ratchet and pawl mechanism.

But when you reverse pedal, it falls back and becomes "free". The yellow


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color link is actually a spring that prevents it from falling permanently.

This is the reason why you hear the distinct "click-click" sound when you

reverse pedal. Also, there are multiple "pawls" placed along the

circumference too.

The figure above is very simple diagram for the freewheel. The actual

part diagram is shown below with the names of each.

This is what it looks from inside in real.


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and this is what you actually see!

A close view of the hub:


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High torque gives low speed and low torque gives high speed. How

does this happen?

You can understand it without any equations!

To get an analogous example of cycling:

Case 1

Level Road: Let's say you are pedaling the wheel with your full body

power. You will see the speed is high, but you will "feel" as if you areapplying very less effort (Less torque). It makes you enjoy the cycling.

(High speed)

Case 2

Inclination: Now again you are applying full power as you wish to

reach destination as early as possible. Now you will see speed is low, but

you feel as applying greater effort (High torque).


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Make the understanding strong.

The Power supplied by you for a particular load is constant.

Now Power is the product of Torque and Angular velocity .

So Lower torque implies Higher velocity and Higher torque implies

Lower Velocity for the same power output.


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Bicycle Brakes

There are different types of Bicycle brakes. All of them have 3 majorcomponents.

1. A mechanism through which the rider apples the Braking force.

2. A mechanism to transmit the force to the wheels.

3. A mechanism that ultimately applies force on wheels.

In this article the most commonly used braking system is discussed. It is

quite simple with the rider pressing the brake handle, which is directly

connected with a cable (usually Bowden cable). This cable transmits the

force and pulls the levers (shown in blue and red). This brings the brake

pads (shown in black) closer to each other. The brake pads then applies

force on the rim of the wheels.

http://en.wikipedia.org/wiki/Bowden_cablehttp://en.wikipedia.org/wiki/Bowden_cablehttp://en.wikipedia.org/wiki/Bowden_cable


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Balancing of Bicycles

There are very few engineering machines, where knowing how it works

is difficult than actually working on it. Bicycles are one of those things!

It is true that the exact reasons validated by both theoretical proof and

experimental evidence has not been found for which all

factors contribute to the balancing of bicycles and by how much.

Currently we talk only in terms of major and minor factors for this sort-

of magical stability of bicycles.

Even then, there are confusion regarding which is the most important

factor and how much it accounts for it. In this article, I will be

mentioning the major reasons that have been proved experimentally.

There are 4 important factors that contributes to balancing of bicycles.

1. The ability of the front wheel to turn into the fall.

2. The trail of steering axis

3. Gyroscopic Precession (Secondary reason - Earlier this was

considered to be the primary reason

4. Operator skill that many times acts effortlessly.

The ability of front wheel to turn into the fall

To understand this reason, try to balance a pen (with flat base) vertically

on the center of your palm. If you see carefully, you will notice that you

always try to move your palm in the direction in which, the pen starts


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falling.

The same thing happens with the front wheel. The front wheel turns

(rapidly) on the side the bicycle starts falling. You would have also

experienced this, while just walking and taking a bicycle from one point

to another, by holding the seat (saddle) and the handle bar. If you tilt the

cycle and don't hold the handle it falls (we call it turning, but

scientifically it is just falling).

Understanding Gyroscopic Precession is easier and helpful in getting the

feel of first reason - the trail. So let's start with that.

Gyroscopic Precession

Check this video to understand this seemingly complex topic clearly.

https://www.youtube.com/watch?v=ty9QSiVC2g0

https://www.youtube.com/watch?v=ty9QSiVC2g0https://www.youtube.com/watch?v=ty9QSiVC2g0https://www.youtube.com/watch?v=ty9QSiVC2g0


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You may like to see this video too - Gyroscope

So, a spinning wheel resists change in its angular momentum and

prevents itself from falling. Okay, this could be the main reason for the

stability of bicycles. Many people believed that this was the case (even

now, some people believe the same).

This has been proved wrong, by carrying simple experiments in which

another wheel was attached to the bicycle wheels and made to rotate inopposite direction. This cancels the total angular momentum, which in

turn removes the gyroscopic effect. Had this been the major factor, the

bicycle should have become unstable. But it was not the case. The

impact was much less.

It was concluded that while GP effect is there, its effect is a minor factor

rather than being a major one.

The trail of steering axis

http://goo.gl/Us6meYhttp://goo.gl/Us6meYhttp://goo.gl/Us6meYhttp://goo.gl/Us6meY


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The point of contact of front wheel "trails" the point where the steering

axis meets the road. Because of this, when a bicycle leans, a torque is

developed that turns the front wheel. The result is similar to that of

Gyroscopic effect but the reason is different.

In fact, the stability of bicycle increases on increasing the amount of trail.

The problem that prevents in having excess trail is that it becomes

difficult to steer.

In the figure above the trail is referred as positive. Experimental bicycles

with negative trail were found to be extremely unstable.

The above three reasons coupled with the skill of operator is responsible

for the balancing of the bicycle.

This article is a part of a Quora Book on the topic Bicycle - An

Engineering Marvel.

You can download the entire book as a free pdf for offline reading -

Visit this link - E-Book Download

Sources:

1. The stability of Bicycle by David E. H. Jones

(http://socrates.berkeley.edu/~fa...)

2. Bicycle and motorcycle dynamics

http://crazycuriosity.quora.com/Bicycle-An-Engineering-Marvel-Quora-Bookhttp://crazycuriosity.quora.com/Bicycle-An-Engineering-Marvel-Quora-Bookhttp://crazycuriosity.quora.com/Bicycle-An-Engineering-Marvel-Quora-Bookhttp://crazycuriosity.quora.com/Bicycle-An-Engineering-Marvel-Quora-Bookhttp://goo.gl/forms/brLInlPFN2http://goo.gl/forms/brLInlPFN2http://goo.gl/forms/brLInlPFN2http://socrates.berkeley.edu/~fajans/Teaching/MoreBikeFiles/JonesBikeBW.pdfhttp://socrates.berkeley.edu/~fajans/Teaching/MoreBikeFiles/JonesBikeBW.pdfhttp://en.wikipedia.org/wiki/Bicycle_and_motorcycle_dynamicshttp://en.wikipedia.org/wiki/Bicycle_and_motorcycle_dynamicshttp://en.wikipedia.org/wiki/Bicycle_and_motorcycle_dynamicshttp://en.wikipedia.org/wiki/Bicycle_and_motorcycle_dynamicshttp://socrates.berkeley.edu/~fajans/Teaching/MoreBikeFiles/JonesBikeBW.pdfhttp://goo.gl/forms/brLInlPFN2http://crazycuriosity.quora.com/Bicycle-An-Engineering-Marvel-Quora-Bookhttp://crazycuriosity.quora.com/Bicycle-An-Engineering-Marvel-Quora-Book


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What makes a bicycle faster than a regular walking man?

Vertical motion of Center of Mass

This has been mentioned by Jack Dahlgren. The diagram below shows

the different position of the center of mass of a human while walking. A

good amount of energy is wasted in the up-down motion.

Applied force is Discontinuous

The power you supply is not continuous while walking. If you do the

same thing on bicycle by applying force on pedal for every 1 second

followed by a brief pause - your speed will reduce drastically.

The figure below shows how the reaction from ground varies on the

https://www.quora.com/What-makes-a-bicycle-faster-than-a-regular-walking-manhttps://www.quora.com/What-makes-a-bicycle-faster-than-a-regular-walking-manhttps://www.quora.com/Jack-Dahlgrenhttps://www.quora.com/Jack-Dahlgrenhttps://www.quora.com/Jack-Dahlgrenhttps://www.quora.com/Jack-Dahlgrenhttps://www.quora.com/What-makes-a-bicycle-faster-than-a-regular-walking-man


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body. You can see it drops to zero periodically.

Higher Surface Resistance

The resistance offered to ground is higher to our feet than to wheels.

Please not that at very high speeds, wind drag becomes very high too, but

yes, you can't reach that speed by mere walking.


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Unwanted Motions

You generally swing your hands (and slightly neck too). Energy losses

takes place here.

The result of all above is that a person can lose upto two-thirds of the

power he spends while walking.

To know more on the resistance thing:

Raj Arjit's answer to Why does a rolling tyre/wheel stop after some time?Rolling friction does no work. What dissipates its kinetic energy?

Source of the figures: Biomechanics of Walking and Running,

by Claire. T. Farley.

https://www.quora.com/Why-does-a-rolling-tyre-wheel-stop-after-some-time-Rolling-friction-does-no-work-What-dissipates-its-kinetic-energy/answer/Raj-Arjit?srid=iMqW&share=1https://www.quora.com/Why-does-a-rolling-tyre-wheel-stop-after-some-time-Rolling-friction-does-no-work-What-dissipates-its-kinetic-energy/answer/Raj-Arjit?srid=iMqW&share=1https://www.quora.com/Why-does-a-rolling-tyre-wheel-stop-after-some-time-Rolling-friction-does-no-work-What-dissipates-its-kinetic-energy/answer/Raj-Arjit?srid=iMqW&share=1https://www.quora.com/Why-does-a-rolling-tyre-wheel-stop-after-some-time-Rolling-friction-does-no-work-What-dissipates-its-kinetic-energy/answer/Raj-Arjit?srid=iMqW&share=1https://www.quora.com/Why-does-a-rolling-tyre-wheel-stop-after-some-time-Rolling-friction-does-no-work-What-dissipates-its-kinetic-energy/answer/Raj-Arjit?srid=iMqW&share=1


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When a fan spins really fast, why does it appear like it is spinning in the

opposite direction?

A rotating wheel can appear to rotate faster, slower, reverse or even

stationary to the human eye. Such illusions happen in two forms.

1. While watching a video.

2. While seeing in real life.

The illusion while watching Video

Short answer

The rotation of the object (let's say a spoke-wheel) happens continuously

while the camera records it as "instances" in form of frames. Now

humans perceive motion by, sort of, comparing the one frame with theprevious frame (very quickly). Depending on what gets recorded in the

consecutive frames, different types of illusions occur.

Long answer

Consider a wheel with 4 spokes at at equal angles from each other.

https://www.quora.com/When-a-fan-spins-really-fast-why-does-it-appear-like-it-is-spinning-in-the-opposite-directionhttps://www.quora.com/When-a-fan-spins-really-fast-why-does-it-appear-like-it-is-spinning-in-the-opposite-directionhttps://www.quora.com/When-a-fan-spins-really-fast-why-does-it-appear-like-it-is-spinning-in-the-opposite-directionhttps://www.quora.com/When-a-fan-spins-really-fast-why-does-it-appear-like-it-is-spinning-in-the-opposite-directionhttps://www.quora.com/When-a-fan-spins-really-fast-why-does-it-appear-like-it-is-spinning-in-the-opposite-direction


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Consider the wheel to be rotating in clockwise direction. The wheel is

rotating continuously but the camera will be recording it in frames. Let's

focus on the top most spoke. The current position of it is 12 o'clock.

Note: Frames refer to one of the many still images that make up the

entire video.

After one frame, consider the top spoke to have rotated 3/4th of the

circle (270 degrees) and is now at position 9 o'clock. After another frameit will be at position 6, and then back to 3. So in reality the spoke moves

-

12 - (3) - (6) - 9 - (12) - (3) - 6 - (9) - (12) - 3

in clockwise direction.

but when our eyes sees it in form of frames it is easier to relate it in

counter-clockwise direction and it appears the spoke to be moving in -

12 - 9 - 6 - 3

in counter clockwise direction.

This creates the impression of wheel moving in reverse. Had after every

frame the spoke was at 12 o'clock position, it would had appeared to be

stationary. If after each frame it had made slightly more than one

revolution then it will appear to be moving in right direction but slowly.

Another example is shown in figure below.


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Image source: Sciencelet.com

The illusion in real life

This type of illusion also occurs while seeing the wheels of fast moving

car or blades of a fan.

Now while the reason is quite similar considering that our eyes are also

like camera. The actual reason is debated since we do not know how

exactly our eyes work (in frames?).

Neuroscientist Dave Purves and colleagues in a 1996 issue

of Proceedings of the National Academy of Sciences, posits that humans

perceive motion in a manner similar to a movie camera, just like frames.

But in 2004, researchers led by neuroscientist David

Eagleman demonstrated that test subjects shown two identical wheels

spinning adjacent to one anotheroften perceived their rotation asswitching direction independently of one another. This observation is

http://www.sciencelet.com/2013/05/how-come-wheels-rotate-backwards-in.htmlhttp://www.sciencelet.com/2013/05/how-come-wheels-rotate-backwards-in.htmlhttp://www.sciencelet.com/2013/05/how-come-wheels-rotate-backwards-in.htmlhttp://www.ncbi.nlm.nih.gov/pmc/articles/PMC39674/http://www.ncbi.nlm.nih.gov/pmc/articles/PMC39674/http://www.ncbi.nlm.nih.gov/pmc/articles/PMC39674/http://www.ncbi.nlm.nih.gov/pmc/articles/PMC39674/http://www.ncbi.nlm.nih.gov/pmc/articles/PMC39674/http://www.eaglemanlab.net/http://www.eaglemanlab.net/http://www.eaglemanlab.net/http://www.eaglemanlab.net/http://www.sciencedirect.com/science/article/pii/S0042698904002731http://www.sciencedirect.com/science/article/pii/S0042698904002731http://www.sciencedirect.com/science/article/pii/S0042698904002731http://www.sciencedirect.com/science/article/pii/S0042698904002731http://www.sciencedirect.com/science/article/pii/S0042698904002731http://www.sciencedirect.com/science/article/pii/S0042698904002731http://www.sciencedirect.com/science/article/pii/S0042698904002731http://www.eaglemanlab.net/http://www.eaglemanlab.net/http://www.ncbi.nlm.nih.gov/pmc/articles/PMC39674/http://www.ncbi.nlm.nih.gov/pmc/articles/PMC39674/http://www.sciencelet.com/2013/05/how-come-wheels-rotate-backwards-in.html


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inconsistent with Purves' team's discrete-frame-processing model of

human perception, which, reason suggests, would result in both wheels'

rotations switching direction simultaneously.

A "better" explanation for motion-reversal, Eagleman and his team

conclude, is a form of "perceptual rivalry," the phenomenon by which the

brain generates multiple (or flat-out wrong) interpretations of a visually

ambiguous scene.

Sources 1. IO9

2. Wagon-wheel effect

3. Sciencelet.com

Thanks for reading. I hope you enjoyed it.

About myself – A passionate mechanical engineer, with interests in sharing and

gaining knowledge. I am Quora top writer and instructor on Udemy as well.

You can connect with me here and check my online courses and free articles.

Udemy profile - https://www.udemy.com/u/arjit/

Quora profile - https://www.quora.com/Raj-Arjit
http://en.wikipedia.org/wiki/Multistable_perceptionhttp://en.wikipedia.org/wiki/Multistable_perceptionhttp://en.wikipedia.org/wiki/Multistable_perceptionhttp://io9.com/why-do-wheels-sometimes-appear-to-spin-backwards-1593807400http://io9.com/why-do-wheels-sometimes-appear-to-spin-backwards-1593807400http://io9.com/why-do-wheels-sometimes-appear-to-spin-backwards-1593807400http://en.wikipedia.org/wiki/Wagon-wheel_effecthttp://en.wikipedia.org/wiki/Wagon-wheel_effecthttp://en.wikipedia.org/wiki/Wagon-wheel_effecthttp://www.sciencelet.com/2013/05/how-come-wheels-rotate-backwards-in.htmlhttp://www.sciencelet.com/2013/05/how-come-wheels-rotate-backwards-in.htmlhttp://www.sciencelet.com/2013/05/how-come-wheels-rotate-backwards-in.htmlhttps://www.udemy.com/u/arjit/https://www.udemy.com/u/arjit/https://www.udemy.com/u/arjit/https://www.quora.com/Raj-Arjithttps://www.quora.com/Raj-Arjithttps://www.quora.com/Raj-Arjithttps://www.quora.com/Raj-Arjithttps://www.udemy.com/u/arjit/http://www.sciencelet.com/2013/05/how-come-wheels-rotate-backwards-in.htmlhttp://en.wikipedia.org/wiki/Wagon-wheel_effecthttp://io9.com/why-do-wheels-sometimes-appear-to-spin-backwards-1593807400http://en.wikipedia.org/wiki/Multistable_perception

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Bicycle - An Engineering Marvel