1. Rear Derailleur
2016
DESIGN PROJECT
By: Jessica Byrne (C14303401), Stephen Scallan (C12453912), Niamh Fahy (C13490928),
Ryan Palmer (C13363561), Oliver Hughes (C14722449), Benjamin Campbell (C1444963)
DUE: 9TH DECEMBER 2016 |
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Declaration
To the best of our knowledge and belief, this report is our own work, all source have been properly
acknowledged, and the report contains no plagiarism. The report contains 8417 words, 37 figures and 8
tables.
Name: ____________________ Date: _____________________
Name: ____________________ Date: _____________________
Name: ____________________ Date: _____________________
Name: ____________________ Date: _____________________
Name: ____________________ Date: _____________________
Name: ____________________ Date: _____________________
Abstract
This is a report conducted by six students as part of a 12-week design project. This report is done on a
Shimano rear derailleur. This report covers the history, parts list, tolerances, parameters, the design
specifications, standards, manufacturing process, cost, sustainability a risk analysis and a user manual.
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Table of Contents
Declaration ...................................................................................................................................................1
Abstract........................................................................................................................................................1
Table of Tables.............................................................................................................................................3
Table of Figures............................................................................................................................................4
Introduction...................................................................................................................................................5
History of Bicycle Rear Derailleur .................................................................................................................5
Standards.....................................................................................................................................................8
Test method..............................................................................................................................................8
General.....................................................................................................................................................8
Requirements ...........................................................................................................................................8
Testing......................................................................................................................................................8
Testing components..................................................................................................................................9
Safety factor..............................................................................................................................................9
Product Design Specifications ......................................................................................................................9
Performance .............................................................................................................................................9
Maintenance .............................................................................................................................................9
Finish ........................................................................................................................................................9
Materials ...................................................................................................................................................9
Weight ......................................................................................................................................................9
Aesthetics .................................................................................................................................................9
Product life................................................................................................................................................9
Customer ..................................................................................................................................................9
Life in service............................................................................................................................................9
Safety .......................................................................................................................................................9
Environment............................................................................................................................................10
Shelf Life.................................................................................................................................................10
Packaging...............................................................................................................................................10
Ergonomics.............................................................................................................................................10
Competition.............................................................................................................................................10
Marketing................................................................................................................................................10
Manufacturing Facilities ..........................................................................................................................10
Parts List ....................................................................................................................................................11
Tolerances..................................................................................................................................................12
Tolerance discussion ..............................................................................................................................12
Fitments..................................................................................................................................................20
Chain width standards.............................................................................................................................21
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Parameters.................................................................................................................................................22
Sketches ....................................................................................................................................................24
Block diagram.............................................................................................................................................26
Manufacturing Process...............................................................................................................................29
Costing and sustainability...........................................................................................................................30
Costing ...................................................................................................................................................30
Sustainability...........................................................................................................................................30
Environmental Impact .............................................................................................................................31
(calculated using CML impact assessment methodology) .......................................................................31
Component Environmental Impact ..........................................................................................................32
Calculations................................................................................................................................................33
Assumptions made at beginning of calculations......................................................................................33
Aim of Calculation...................................................................................................................................33
Calculations for Average Human.............................................................................................................33
Calculations for Athlete (Bradley Wiggins): .............................................................................................35
Comparison 0.649Nm vs 3.767Nm .........................................................................................................36
Spring Force ...........................................................................................................................................36
Risk Analysis..............................................................................................................................................37
User manual...............................................................................................................................................38
Bibliography................................................................................................................................................39
Table of Tables
Table 1 Job Description................................................................................................................................5
Table 2 Parts List........................................................................................................................................11
Table 3 metal injection moulding tolerances ...............................................................................................12
Table 4 Tolerances.....................................................................................................................................18
Table 5 description of parts in sketch..........................................................................................................25
Table 6 description of parts in block diagram..............................................................................................29
Table 7 Component Environmental Impact.................................................................................................32
Table 8 Metals in consideration for choice of spring ...................................................................................36
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Table of Figures
Figure 1 Parallelogram Derailleur .................................................................................................................6
Figure 2 simplex cable shifter derailleur........................................................................................................6
Figure 3 Campagnolo the Gran Sport...........................................................................................................7
Figure 4 Suntour Cyclone.............................................................................................................................7
Figure 5 manufacturers of derailleurs ...........................................................................................................8
Figure 6 Parts.............................................................................................................................................11
Figure 7 Tolerances....................................................................................................................................12
Figure 8 Pressing Tolerances.....................................................................................................................13
Figure 9 plastic injection moulding tolerances.............................................................................................13
Figure 10 injection moulding Tolerances ....................................................................................................14
Figure 11 Pulley Movement and tolerance..................................................................................................14
Figure 12 Axle fitment and tolerance ..........................................................................................................15
Figure 13 Bicycle chain allowance..............................................................................................................15
Figure 14 Overall Size ................................................................................................................................16
Figure 15 maximum dimensions .................................................................................................................16
Figure 16 Fitments between rivet and front bracket 1 .................................................................................17
Figure 17 Fitments between rivet and front bracket 2 .................................................................................17
Figure 18 Tolerances..................................................................................................................................18
Figure 19 part facts.....................................................................................................................................19
Figure 20 Key Fitments...............................................................................................................................20
Figure 21 retaining rings.............................................................................................................................20
Figure 22 axial fitments...............................................................................................................................21
Figure 23 chain length ................................................................................................................................22
Figure 24 Sketch 1 .....................................................................................................................................24
Figure 25 Sketch 2 .....................................................................................................................................25
Figure 27 pully wheel mould .......................................................................................................................29
Figure 28 Manufacturing and Use Regions.................................................................................................30
Figure 29 Sustainable Design diagram.......................................................................................................31
Figure 30 Environmental Impact Assessment.............................................................................................31
Figure 31 Component Environmental Impact..............................................................................................32
Figure 32 Bike chain with rear derailleur.....................................................................................................33
Figure 33 90 Degrees from Cog to Chain ...................................................................................................34
Figure 34 Bracket bolting............................................................................................................................38
Figure 35 Connecting Gear Cable ..............................................................................................................38
Figure 36 Top Adjustment Screw................................................................................................................38
Figure 37 Lower Adjustment Screw ............................................................................................................38
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Introduction
This is a report that discusses the rear derailleur on a bicycle. A rear derailleur works by moving the chain
between rear sprockets and taking up chain slack caused by moving to a smaller sprocket at the rear or a
smaller chaining by the front derailleur. The table (1) below shows the topics cover in this report and who
done each of the topics.
Job Description Name
Introduction/ Abstract Jessica
History Stephen
Standards Ryan
Product Design Specifications Oliver
Parts List Stephen
Tolerances Stephen
Parameters Ben
Sketch’s Niamh
Function Block Diagram Ryan
Manufacturing Process Jessica
Costing Jessica
Sustainability Jessica
Calculations Oliver & Ryan
Risk Analysis Niamh
User Manual Niamh
CAD Design (Solidworks) Everyone
Solidworks Assembly Jessica
Presentation Formatting Niamh
Report Formatting Jessica
Table 1 Job Description
History of Bicycle Rear Derailleur
Derailleur gears are a variable-ratio transmission system commonly used on bicycles consisting of a chain,
multiple Sprockets of different sizes, and a mechanism to move the chain from one sprocket to another.
They are referred to as gears in the bike world, these bicycle gears are technically Sprockets since they
drive or are driven by a chain, and are not driven by one another.
Modern front and rear derailleurs typically consist of a moveable chain-guide that is operated remotely by a
Bowden Cable attached to a shifter mounted on the handlebars. When a rider operates the lever while
pedalling, the change in cable tension moves the chain-guide from side to side, "derailing" the chain onto
different sprockets.
Derailleur is a French word, there were many designed during the 19th century but the most prominent is
the Protean two speed Derailleur which was on the Whippet safety bicycle.
Pail de Vivie was a French tourist, writer and cycling promoter who wrote under a different name Velocio he
invented a two-speed rear derailleur in 1905 which was used on his trips in the alps passes
Some of the early designs used rods to move the chain between the various gears,
Other early designs were the Champion Gear which somewhat resembled the modern-day Derailleurs
systems, the technical of this system was that it was chain stay mounted paddles and single lever chain
tensioner mounted on the downtube.
These systems also with the rod systems that I mentioned before were superseded by the Parallelogram
Derailleur which is what out derailleur system is based on.
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Figure 1 Parallelogram Derailleur
Then in 1937, the derailleur system was introduced to the pinnacle of cycling sport, the Tour De France. As
in the modern world they were easily able to change between the multiple gears without having to remove
the wheel to change the gear that is being driven.
This was necessary regularly in stages as the terrain changed. It wasn’t till the following year that derailleur
became common when simplex introduced a cable shifter derailleur.
Figure 2 simplex cable shifter derailleur
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Then in 1949 Campagnolo introduced the Gran Sport which was simply a more refined version of the
previous derailleurs. It didn’t sell well as a cable operated Parallelogram rear derailleur
Figure 3 Campagnolo the Gran Sport
When 1964 came around the next significant derailleur evolution was by Suntour.
They had invented a slant parallelogram rear derailleur, which crucially let the jockey pulley maintain a
somewhat constant distance from the varied sized sprockets which helps the shifting become easier.
Crucially once the patents expired; other manufactures could get in and adopt the design. This has led to
the current trend of Slant Parallelogram rear derailleurs being used in all forms of cycling.
Figure 4 Suntour Cyclone
Before the 1990s many manufacturers made derailleurs including Simplex, Huret, Galli, Mavic, Gipiemme,
Zeus, Suntour, and Shimano. But the successful introduction and promotion of indexed shifting by Shimano
in 1985 required a compatible system of shift levers, derailleur, sprockets, chainrings, chain, shift cable,
and shift housing.
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Figure 5 manufacturers of derailleurs
Today Campagnolo, Shimano, and SRAM are the three main manufacturers of derailleurs, with Italian
manufacturer Campagnolo only making road cycling derailleurs and Shimano making both road and
offroad. American manufacturer SRAM has been an important third, specializing in derailleurs for mountain
bikes, and in 2006 they introduced a drivetrain system for road bicycles.
Standards
Test method
Secure the Rear Derailleur in a fixture that will hold the Rear derailleur firmly but will allow the individual
components to movie freely and without deforming any components. Applying a certain force on the inside
of the arm and on the top arm. This will allow both springs to operate and will prove whether all the
components can move in sync with each other. This will also show the failure rate.
General
Each component has their own stress and failure rate and are all different to each other. For this reason,
the test procedure requires all components assembled and for the tolerances and tightening to be of the
finally selling produced.
Requirements
For the test procedure, all individual components need to be inspected so that there are no flaws in any
component that will throw off the results. These flaws include visible cracking, notches out of the material or
even excess material that may cause friction.
Testing
The results from the tests will show if the Rear Derailleur is strong enough to carry out its procedure. If not,
then the tests will show where and how the failure happened and then a solution can be found. The testing
will also show the maximum force that the springs can with stand and the distance the component can
movie the chain from left to right meaning the number of gears that can be attached to the bike. The
materials for each component will wear differently especially on a different type on material, meaning a
maintains may have to be applied or a different design or material will need to be picked. Therefore, the
test is very valuable.
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Testing components
Test each component separately will show how each component will deform or fail. This can be useful for
starting off, as try with different materials, thickness and shapes will give different results allow the best
material, shape and thickness to be chosen.
Safety factor
Once the Rear Derailleur fails at speed, series injury’s or fatalities may take place. Because of this a high
safety factor is needed to pervert this. A safety factor is the failing force or angle, minus a certain
percentage for the force or angle, meaning the component will never reach its failure rate.
Product Design Specifications
The Rear Derailleur constantly keeps tension on the chain so that the cogs can’t slip as they rotate. It also
guides the chain from gear to gear. The produced Design specification (PDS) for a rear derailleur is as
follows:
Performance
To withstand a heavy impacted without altering the shape or its safety features. To constantly keep the
chain under tension and in line. To have a long-life span so it can last as long as the bike.
Maintenance
The maintenance is minimal on the rear derailleur. The springs and joints need to the greased every few
weeks to prevent rusting and corrosion. This will allow the component to run smoothly and flawlessly. The
cable may need to be adjusted to re a line the chain or to adjust the tension on the chain. This can be
achieved be adjusting the plastic connecter that holds the braided hose in place and allows the cable to fix
to the rear derailleur.
Finish
The Rear derailleur housing needs to have a tough finish to withstand the impacts of the crashes. The
housing needs to be corrosion resistance so that it minimises the possibility of damaging the springs, cable
and chain.
Materials
The materials would need to be light weight so it's easy to install and won’t disrupt the balance of the seat.
The materials would also need to be durable due to the high impact loads. The battery pack or power
source will need a water proof protecting material so it can't fail.
Weight
The total weight of the rear derailleur is 314 grams
Aesthetics
The housing needs to the aesthetical pleasing yet functional, strong and small.
Product life
The life of the product should match that of the bike, unless involved in a serious collision. Then buying a
new rear derailleur or new parts for the damage derailleur can be sourced easy enough by contacting a
bike dealer or the company that produce the rear derailleur its self.
Customer
The main costumer for this produced would be bike manufactures and bike parts provider.
Life in service
Between the chain stretching and the components wearing, adjusting the rear derailleur will take place
every so often mainly when it’s not selecting gear as easy. Besides this the rear derailleur is a heavy-duty
component that should last the length of the bike or even long.
Safety
The rear derailleur needs to be heavy duty due to the speed the bike can achieve. Once the bike is at the
top speed and the rear derailleur fails the back wheel may lock causing the bike to get out of control. The
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rear derailleur housing needs to be safe and secure to prevent the spring force from catching fingers or skin
when adjusting or replacing the component or complements.
Environment
All the components must be able to with stand cold temperatures, for Ireland that would be 1 or 2 degrees
but in Canada that would be -19 degrees. In sunnier countries, the components would need to with stand
temperatures of up to 47 degrees. The housing must be able to with stand moisture, splashes, grit and salt.
Shelf Life
The shelf life for the component would be infinite. As the component is being fitted it will be connected to
the cable and adjusted, so as long as it doesn't get damaged on the shelf, it will fit with ease.
Packaging
The product, once its assembled would be packed into its purchase box, made from cardboard, along with
the instructions on how to recalibrate, the warranty and information on the product. Then that box would be
stacked with the rest of the boxes and placed in a reinforced packaging box made from cardboard. That
box would then be loaded onto a pallet along with other boxes and shrink wrapped together and placed in
the delivery truck.
Ergonomics
The rear derailleur must be easily attached to a various range of bikes easily. The rear derailleur should be
able to be fitted by one person in 10 minutes. The rear derailleur must not protrude from the bike’s frame as
to have a negative effect on the cyclist. . It must also be easy to store, so the packaging can't be an
unusual shape and there can't be pieces that need to be check week, it needs to be durable.
Competition
There’s many competitors for this component but it mainly comes down to price and brand name. The more
the name is known the more likely that company will be selected for the product.
Marketing
This product was designed for a range of bikes, so the marketing would be worldwide in the bicycle
industry.
Manufacturing Facilities
The main facilities that would be needed to produce this product in large quantities would be, a
Manufacturing Facility to produce the parts needed for the rear derailleur, an Assembly facility to assemble
the rear derailleur and a packaging / distribution facility to package and transport the good.
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Parts List
Figure 6 Parts
Number Shimano
Part No.
Product Specifications Planned materials
One Y54W11000 B-axis cap Plastic
Two Y52130010 E-ring (φ6mm) Low quality Steel
Three Y54Y24120 B-tension spring Stainless Steel
Three Y5UU14000 B-tension spring (for the SS type / Seitsume
bracket type)
Stainless Steel
Three Y53X12000 B-tension spring (for the SS type / bracket
type)
Stainless Steel
Four Y53X98020 Bracket (with axis) Seitsume Aluminium alloy
Five Y54M98030 Set bolt (M5 × 11.5) and nut Stainless Steel
Five Y53X98030 Set bolt (M5 × 14.5) and nut Stainless Steel
Six Y52198230 Stroke adjustment bolt (M4 × 14.5) and plate Stainless Steel and Plastic
Seven Y54Y98060 Wire fixing bolt unit Stainless Steel
Eight Y54N98030 Outer casing adjustment bolt unit Stainless Steel and Plastic
Nine Y54Y21000 P axis cap Plastics
Ten Y54Y24110 P tension springs (for the SS type) Stainless Steel
Ten Y52228000 P tension springs (for GS type) Stainless Steel
Eleven Y54Y98020 Right plate (with axis) for the SS type Aluminium Alloy
Twelve Y52472020 4-524 72020 DM pulley bolt unit Stainless Steel
Thirteen Y56398030 Pulley unit Aluminium Alloy
14 Y53922010 Left plate (for the SS type) Aluminium Alloy
14 Y54L09000 Left plate (GS type) Aluminium Alloy
Fifteen Y5UU13000 B-tension spring (SS type / for direct mounting
type)
Stainless Steel
Fifteen Y54Y24100 B-tension spring (GS type / for direct
mounting type)
Stainless Steel
Sixteen Y54Z98080 Bracket axis (with spacers) for with straight Stainless Steel
17 Y54P98060 Bracket (with axis) for direct mounting type Aluminium Alloy
Eighteen Y56398100 Pulley set (10 pairs) Plastic
Table 2 Parts List
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Tolerances
Tolerances are critical to the assemble ability of products but excessively tights tolerances will make the
products excessively expensive. In this document, I will indicate the most critical tolerances on the
component using the below drawing and perform analysis on some of the parts regarding my suggested
tolerances. Due to Shimano still producing a variety of the below derailleur we are unable to have exact
tolerances for the Tourney RD-TY18-GS (Medium Cage)
Engineering tolerance is the permissible limit or limits of variation in: a physical dimension, a measured
value or physical property of a material manufactured object, system, or service.
Tolerance discussion
Figure 7 Tolerances
The three parts above are what I have refenced to do with the below tolerances of
1. Metal Injection moulding
2. Sheet Metal tolerences
3. Plastic Injection moulding tolerances
1. So for the axles which there are two main ones the injection metal mounding would be between the
typical and the best possible, around .1mm. This is down to there not being enough allowable space
in the axle housing.
For the rest of the variables it would come in as between the typical and best possible
The metal injection moulding isn’t relevant to the pulley wheels as the they are made of plastic.
For the side of the cage I would say that it would come in much closer to typical because as long as it is flat
on either face there is enough allowable bolt shaft left to take in some possible poor tolerances.
Table 3 metal injection moulding tolerances
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2. For the Axles only the injection mounlding is relavent.
The pulleys are also not relavent to this kind of manufacture because they are made form a plastic
material.
The sheet metal tolerance are very much to do with the cage sides because this it the most likely way they
were manufactured, But again as long as the tolerance stay belows the bolt shaft length there shouldn’t be
an issue.
Figure 8 Pressing Tolerances
3. Then for the plastic injection moulding is only relavent to the pulley wheels,
We used polypropylene we found that +/- .125mm because our pulley is 8.72mm
As with the cage designs aslong as added material in the design doesn’t do above the bolt length there
should be no issue
Figure 9 plastic injection moulding tolerances
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Figure 10 injection moulding Tolerances
The materials used for our derailleur will generally be cheap due to the mass production of rear derailleurs
for this reason there is no fine tolerances in the derailleurs construction.
Pulley Movement and tolerance
Figure 11 Pulley Movement and tolerance
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Fig. (11) is to show the distance that is set between each of the pulley wheels, this one of the most
important relationships the derailleur has with the bicycle. Without the maintaining this distance correctly for
the entire bike this is fitted to, then this is a problem. Although from the above photo it can be seen that
shimano has made aditions to the pulley wheel, of the solid metal bearing and two metal caps, which allow
little to no tolerance of movment +/- 1mm movement between the pulley wheels
Axle fitment and tolerance
Figure 12 Axle fitment and tolerance
Here is show the tolerance between the axial housing and axial do to the material they are made of and the
relatively low forces they are under I feel there would be no negative tolerance. But as can see there is
nearly a +.5 mm all around the axle. This is also a press fitment.
Bicycle chain allowance
Figure 13 Bicycle chain allowance
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As I have researched tolerances are as simply as the size of a part, for this I have measured between the
two cage walls to find the maximum chain width that can be put into this derailleur. Coming in at 8.72mm
this means that our derailleur can take a five-speed chain of 7.8mm with an allowable tolerance of +/-
.47MM.
Overall Size
Figure 14 Overall Size
From this you are given several figures, but dX is the one that tells us the max height of the derailleur.
Figure 15 maximum dimensions
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The above dY shows the greatest width of the derailleur.
The derailleur can extend further in both directions but only when under severe load.
The following Fig. () are showing the Tolerance/Fitments between the No thread rivet and the front bracket
of the Parallelogram linkage
Figure 16 Fitments between rivet and front bracket 1
Figure 17 Fitments between rivet and front bracket 2
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The below Fig. () shows the tolerance
Figure 18 Tolerances
Table 4 Tolerances
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The Solidworks over all part facts
Figure 19 part facts
The above Fig. (19) was taken from a Solidworks, it is some many dimensions of the derailleur.
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Fitments
Figure 20 Key Fitments
In the above Fig. (20) we have some of the key Fitments shown as this is the contact point between
derailleur and bike chain. Using 2 small pulley bolts, the two sides of the medium length cage are held
together using 2 bolts that have been manufactures into left plate of the cage.
This is seen as interference fit, this is down to the use of the two materials inter fearing which each other
i.e. the thread. This is also an element of friction going on between both metal materials keeping the fit
together.
Figure 21 retaining rings
Above in Fig. (21) is a small step on from Fig. (20) but what can be see here is main working of the
derailleur away from the chain. The two highlighted retaining rings are the key to the entire derailleur. They
attach the cage to the parallelogram linkage which provides the horizontal motions to the derailleur.
Then with the lower retaining ring the entire derailleur is attached via the B knuckle bracket with axle to the
bike.
Both retaining rings are held on using an interference fit (friction/press fit).
They are literally pushed into place and their small diameter keeps a strong fiction fit around the axle which
has a manufactured indent.
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Figure 22 axial fitments
Chain width standards
Fig. (22) is showing the axial tolerance and fitment which is a press fit and the tolerance is around the 1mm
so it would be seen as a fine tolerance
Standards for Metric fits
ISO-R286 and ANSI B4.14831
Here are the external widths for the derailleur chains that you will likely find on transport bikes.
Manufacturing tolerances can be one tenth of a millimetre.
5 speed: 7.8mm
6 speed: 7.8mm
7 speed: 7.3mm
8 speed: 7.1mm
9 speed: 6.8mm
At ten-speed, things get complicated because different manufacturers used different external widths, but
they’re all thinner than 6.8mm.
Nine-speed chains are generally more expensive than eight-speed ones. Ten-speed chains are more
expensive again.
Eight-speed chains are backwards compatible (they work with five-speed, six-speed, seven-speed and
eight-speed cassettes).
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Parameters
Parameters are numerical or other measurable factors that defines a system or sets the conditions of its
operation. Parameters can also refer to a limit or boundary which defines the scope of a particular process
or activity.
Introduction
A bicycle rear derailleur allows gear changes. It moves the chain up and down the cassette, which is a set
of increasing diameter gear sprockets, on the rear wheel of the bicycle.
Bicycle derailleurs look like a complicated mechanism at first sight, but this is just a false impression. The
basic principle behind them is quite simple. They rely on the mechanism of a mobile parallelogram.
The travel of the whole bike derailleur is limited by two adjustment screws which act as maximum and
minimum stops.
Key Parameters
Parallelogram Mechanism
Modern rear derailleurs are built as a parallelogram which has one end attached to the frame, while the
other one has a mobile arm that guides and tensions the chain. The parallelogram is actioned thanks to a
lever and a cable, which are in turn actioned by the shifters. The shifters are operated by the cyclist and are
positioned on the handle bars of the bicycle. Also, the derailleur is responsible for keeping the mobile arm
parallel with the sprockets so that it aligns perfectly with them.
Stops
The stops are adjustable screws to keep the derailleur within the minimum and maximum gear sprockets.
The stops can be adjusted depending on how many different number of gear sprockets are on the bicycle’s
cassette. If there were no stops on a derailleur, nothing would be preventing the chain from falling off and
onto the ground or falling onto the spokes. For this reason, it is very important that the stops are measured
perfectly in the manufacturing of the rear derailleur.
Cage
The derailleur cage is a swinging link, with two pulleys. As the chain moves between different size
sprockets, the amount of chain required changes.
If a smaller diameter gear is selected on the cassette, there will be a shorter chain length required.
The derailleur cage’s movement picks up this slack.
Figure 23 chain length
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Tensioner Spring
The tensioner spring moves the cage to provide gear changes and to keep the chain in tension. If the
spring wears over a long period of time, it may cause the chain to start ‘skipping’. This is when the chain
slips off the teeth while cycling because there is not enough tension on the chain.
Chain Capacity
Chain capacity is the amount of potential slack chain the rear derailleur cage can handle. It is the
measurement of how well it can keep a chain in sufficient tension. Since it’s expressed as a number of
teeth, it’s derived by the following equation:
Chain capacity = (biggest cog teeth – smallest cog teeth) + (biggest chainring teeth – smallest chainring teeth)
Because it’s based on the number of teeth of the entire drivetrain, the effective chain capacity varies from
bike to bike. Drivetrain manufacturers therefore have to cater for these variations
Different Cage Sizes
The manufacturer Shimano, who manufactures the rear derailleur we used for the project has three
different sized derailleurs. They are SS (short-cage), GS (medium-cage) and SGS (long-cage) derailleurs.
The derailleur we used has a GS medium cage size.
The SS derailleurs have a maximum chain capacity of 33 teeth or less. These are usually built for road
bikes. Some down hill mountain bikes also use a short-cage derailleur.
The GS derailleurs have a higher maximum chain capactiy of 37T to 39T or less. This is usually the longest
cage offered for road bike rear derailleurs, but also the default “short” option offered for their mountain bike
counterparts.
The SGS has the longest cage and this is exclusively the domain of mountain bikes or any unit marketed
for touring bikes. A typical unit sees chain capacity well into the 43-44T range.
Indexed gears
‘Indexing’ is a system where the shifter clicks into preset positions corresponding with individual gears. This
allows for a smoother and more efficient gear change than the older system which relied on friction alone.
Indexed rear derailleurs have a different action than friction ones. However, indexed derailleurs are
compatible with friction shifters. Certain types of shifter have both index and friction modes.
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Table to Accompany Isometric Sketches
Identifying number Name Number Required
1 B- Axle Cap 1
2 Stop Ring 2
3 B-Tension Spring 1
4 Adapter w/Mounting Shaft 1
5 Adapter Screw & Nut 1
6 Stroke Adjusting Screws & Plate 1
7 Cable Fixing Bolt Unit 1
8 Cable Adjusting Bolt Unit 1
9 P-Axle Cap 1
10 P-Tension Spring 1
11 Outer Plate w/Mounting Shaft 1
12 Pulley Bolt 2
13 Pulley Unit 2
14 Inner Plate 1
15 Casing 1
Table 5 description of parts in sketch
Figure 25 Sketch 2
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Block diagram
Below is a chart that describes how a rear derailleur works.
The Gear Selector is
rotated to the required
gear.
Adjusting the
gear selector
cable.
Displaying
the gear that
is chosen.
The gear selector cable travels through a braided
hose until it reaches a notch in the frame of the bike
which is located underneath the frame.
The cable is now bear and as it reaches the bottom
bracket there is a plastic guide that guides the cable
to the second notch.
As the cable reaches the second notch, which is located
at the back of the bike where the seat stay and chain
stay meat, the cable is fed back through a braided hose.
The cable is then fixed to the barrel adjuster which is
connected to the outer hinge of the rear derailleur.
As the hinge moves diagonally up and down from
the cable being adjusted, the inner and out plate that
hold the plastic cogs are moved in parallel with the
hinge.
The barrel adjuster,
adjusts the distance of the
derailleur from the
sprocket cluster (rear
gears), to allow smoother
gear changing.
Braided hoses are used
so the cable stays under
tension and protected
from the elements and
from being snagged.
As the cable moves,
the hinge adjusts
causing a spring to
compresses or release.
The hinge puts the
chain under enough
tension to prevent the
chain from slipping and
to away maximum
power transfer to the
rear wheel. This allows
the hinge to stay in the
desired location. The
plastic cogs have inner
steal sleeves to
prevent the plastic cog
from wearing. The
plastic cogs allow the
chain to rotate
smoothly and freely.
The inner and out
plates prevent the
chain from disengaging
these plastic cogs.
The chain
converts the
movement from
the chain rings to
the sprocket
cluster (rear
gears). To allow
the chain to move
up and down the
sprocket cluster
the rear derailleur
is needed.
The cogs are used for
guiding the chain to the
right gear.
Once the right gear has
been engaged then. The
possess is over until a
new gear is required.
28. 27 | P a g e
below is a block diagram of how a rear derailleur works.
30. 29 | P a g e
Number Description
1 Gear Selector, rotates forward and back
2 Gear selected shown on plastic display and the tension in the cable coming from the
gear selector is changed.
3 Cable in Braided hose travels down the front of the bike to the underneath of the frame.
4 Cable travels through a guide on the bottom of the crank.
5 Cable becomes bare from the guide under the crank to the braded hose at the rear of
the bike.
6 The braided hose at the rear of the frame is connected to the rear derailleur.
7 The rear derailleur is connected to the rear of the frame that holds the chain in place and
under tension.
8 The chain travels through the rear derailleur, the back gearing and the front gearing,
linking the three components together.
9 Front gearing.
10 This is a diagram the shows the chain, rear derailleur, front gears and rear gears all in
position and linked together.
Table 6 description of parts in block diagram
Manufacturing Process
There are two main types of manufacturing processes required to make a rear derailleur these are;
Injection Moulding and Stamping.
Injection moulding is a manufacturing process for producing parts by injecting material into a mould. For
manufacturing a derailleur both metal injection moulding and plastic injection moulding are used. Fig. (27)
shows the mould used for producing the pully wheels.
Stamping (pressing) is the process of placing flat sheet metal into a stamping press where a tool and die
surface forms the metal into shape.
Figure 26 pully wheel mould
31. 30 | P a g e
Fig. (28) below shows that the derailleur is Manufacturing in Asia and the bulk of the derailleurs made are
sold in the USA. This is due to a lot of bicycle companies are American.
Manufacturing Region
Use Region
Figure 27 Manufacturing and Use Regions
Costing and sustainability
The costing and sustainability have effects on the price, human opinion, and the environment. Over the
past couple of years’ people have become more concerned about how products they us effect the
environment. With a lot of laws and regulation about how products affect the environment. Both these
factors increase the costing and therefore the price of a product.
Costing
How a product is made, the quality of materials used in production, the efficiency of a manufacturing plant
all have an influence of the costing. Material prices are as followed aluminium alloy (€1.89 per kg)
polypropylene (€1.62 per kg), stainless steel (€5.23)[8], as it can be seen the steel is much more expensive
per kg compared to both the aluminium alloy and polypropylene. The reason behind this is that the
components that are made of steel are much more critical to the overall derailleur because it these fail it will
have a greater effect on the derailleur.
Sustainability
Product lifecycle sustainability is an approach to managing the stages of a product's existence so that any
negative impact on the environment is minimized. Environmental Impact Assessment is the process that
anticipated the effects on the environment of a product is measured.
Carbon-dioxide and other gasses which result from the burning of fossil fuels accumulate in the
atmosphere which in turn increases the earth’s average temperature. Carbon footprint acts as a proxy for
the larger impact factor referred to as Global Warming Potential.
Sulfur dioxide, nitrous oxides other acidic emissions to air cause an increase in the acidity of rainwater,
which in turn acidifies lakes and soil this is called Air Acidification. These acids can make the land and
water toxic for plants and aquatic life.
Total Energy Consumed is the measure of the non-renewable energy sources associated with the part’s
lifecycle.
When an overabundance of nutrients is added to a water ecosystem, eutrophication occurs which causes
an overabundance of algae to bloom, which results in the death of both plant and animal life. This is called
Water Eutrophication.
32. 31 | P a g e
Figure 28 Sustainable Design diagram
Fig. (29) shows the important areas of product lifecycle sustainability. These areas need to be carefully
looked at when an environmental impact assessment is carried out.
Environmental Impact
(calculated using CML impact assessment methodology)
Figure 29 Environmental Impact Assessment
33. 32 | P a g e
Fig. (30), show the Four Areas of Environmental Impacts of one product. As it can be seen the majority of
the negative environmental impact is caused due to the choose of the materials used on the sustainable
design diagram Fig. (29) this is the raw material extraction and processing. The manufacturing of the
product causes the second amount of negative impact on the environment again in the sustainable design
diagram Fig. (29) this is the part manufacturing and part assembly stages are causing this. There is no
negative environmental impact caused by the use of the derailed. Both transportation and end of life
respectably have a very small amount of negative impact on the environment compared to the
manufacturing and materials.
Component Environmental Impact
Component Carbon Water Air Energy
Bracket 0.278 6.4E-5 1.9E-3 3.4
Outer plate 0.253 5.8E-5 1.8E-3 3.1
Inner plate 0.198 4.5E-5 1.4E-3 2.4
Front Bracket 0.153 3.5E-5 1.1E-3 1.9
Pulley Wheel 2 0.102 2.3E-5 7.1E-4 1.2
Big Spring 0.093 2.1E-5 6.5E-4 1.1
Back Bracket main
body
0.074 1.7E-5 5.1E-4 0.902
Small Spring 0.028 1.3E-5 1.7E-4 0.339
LBracket 0.027 6.1E-6 1.9E-4 0.326
Inner Spring 0.021 9.1E-6 1.2E-4 0.246
Table 7 Component Environmental Impact
Figure 30 Component Environmental Impact
it can be seen from the table. (7) and Fig. (31) above that the components that are red are the most
unsustainable, the grey components are the more sustainable. The green components are products the
company buys rather than manufactures due to the availability of these products such as the rivets and
springs. The Carbon footprint, Air Acidification, Water Eutrophication and the Total Energy Consumed are
all considered when determining the sustainability of the different components
34. 33 | P a g e
Calculations
Assumptions made at beginning of calculations
1. No friction on the bearings
2. The terrain at which the bike was speeding across does not slow it down in any way i.e. Flat smooth
surface
3. No environmental elements in which a bike would encounter whilst speeding
4. Bike was in a vacuum
5. A gearing ratio was excluded
Aim of Calculation
Aim of calculations is to find out how much force and torque is required in a chain on a bike to move the
rear derailleur and its bike with it. A material will then be determined for the multiple springs in a selected
rear derailleur.
Figure 31 Bike chain with rear derailleur
Prior calculations, a bike ratio must be known.
A selected bike with rear derailleur has wheel size 26 inches which is approximately 0.7m in diameter. Bike
chains depend on the speed at which a bike is designed for example a racer bike is designed to go at a
faster speed than a normal road bike therefore it has a thinner chain and wider gap between the sprockets
in a chain [1]. It’s also to allow correlation between the gears, the chain and the wheel size of a bike as
miscorrelation can cause a chain to wear faster. This shows that a mountain bike has a thicker chain and
less gaps between the sprockets in its chain typically. A selected bike with a selected rear derailleur has a
gear of speed of 7 [2].
Calculations for Average Human
An assumption was made based off a reference [3], that a normal human being i.e. not an athlete, could
make a bike move from 0 – 22 Mph in 20 seconds, with all assumptions stated at the start of this section.
22 Mph = 35.4 Km/Hr
This was the speed a selected rear derailleur would have to move at. A speed equation was then brought
into account: 𝑎 =
𝑢𝑡+𝑣
𝑡
35. 34 | P a g e
It was assumed that:
U = 0 𝑚/𝑠
T = 20 seconds
V = 35. 4 Km/Hr = 9.80 𝑚/𝑠
From this it can be calculated that the acceleration is 0.49150 𝒎/𝒔−𝟐
It is known that the force of an object is equal to its mass multiplied by its acceleration. A known weight of a
bike and an average human was found.
Weight of bike: 16.9 kg [2]
Weight of average human (Global): 62kg [4]
Total weight= 78.9kg
Using formula 𝐹 = 𝑚×𝑎 with a equal to 0.49150 𝑚/𝑠−2
F = 38.779N
In order to find a torque required for a specific chain, the diameter of a derailleur’s cog teeth must be known
in order to know specific chain size.
The diameter of a cog tooth on a specific derailleur is 32.55mm.
Torque can be found by multiplying a radius by a force by sine of an angle:
T = 𝑟𝐹𝑆𝑖𝑛∅
Figure 32 90 Degrees from Cog to Chain
The angle at which a chain meets a cog tooth on a derailleur is 90° as shown in Fig. (33).
Sin (90) = 1
36. 35 | P a g e
F = 38.779
r = 16.275mm
Torque required to move cog tooth in derailleur is equal to 0.6495Nm.
Based off this figure, the right chain size can be determined.
Calculations for Athlete (Bradley Wiggins):
An assumption was made off the basis of athlete Bradley Wiggins, famous athletic cyclist ref [5], to make a
comparison between a normal human and an athletic cyclist. The same method approach was used.
In cycling, however, there is a maximum bike weight that the Union Cycliste Internationale (UCI) which are
the union in charge of competitive bike racing, allow competitive cyclist to race with. This weight in
kilograms is 6.8kg [6]. For this comparison, this very fact was ignored as it would be unfair to an average
human.
Bradley Wiggins weighs 76kg [5]
76 + 16.9 = 92.6kg
Total weight = 92.6kg
80.5 Km/Hr [7] = 22.36 m/s
This was the speed a selected rear derailleur would have to move at. A speed equation was then brought
into account: 𝑎 =
𝑣−𝑢
𝑡
It was assumed that:
U = 0 𝑚/𝑠
T = 20 seconds
V = 22.36 m/s
acceleration = 2.5 𝒎/𝒔−𝟐
Using formula 𝐹 = 𝑚×𝑎 with a equal to 2.5 𝑚/𝑠−2
F = 231.5N
Repeating the same method that was found to acquire a torque from an average human, a torque for
Bradley Wiggins was acquired.
Although there is a change of bike weight, the same rear derailleur was used in calculations.
Therefore;
Diameter of cog teeth is 32.55mm
Torque can be found by multiplying a radius by a force by sine of an angle:
T = 𝑟𝐹𝑆𝑖𝑛∅
Sin (90) = 1
F = 231.5N
r = 16.275mm
T = 3.767Nm
37. 36 | P a g e
Comparison 0.649Nm vs 3.767Nm
This means that a chain that could last longer and maybe was made of a stronger material would be
needed for Bradley Wiggins compared to an average human. For an average human, not a lot of torque is
needed. This would suggest that a typical 7 speed chain would be needed compared to chain that is closer
to 9 or 8 speed for an athlete.
Spring Force
The diameter of the rear derailleur as stated prior to this calculation is 32.55mm. Upon further investigation
on the teeth of a selected rear derailleur, it was found that from a Solidworks CAD model to be 10.77mm.
7mm was taken away from this to obtain a tooth height.
10.77 – 7 = 3.37mm = 0.037m
From prior calculations, it was seen that the max load on a bike from an average human was equal to
78.9kg. With both figures, a torque and spring force can be acquired for a spring in a selected rear
derailleur.
A known metal must be determined for a selected spring before calculating the spring force. The software
known as CES Edu pack 2016 [8], was used to find a material. Table. (8) shows the comparison between
the different materials to determine a suitable metal. Price per kg, young’s modulus, shearing modulus,
Poisson’s ratio, elongation, hardness Vickers and tensile strength are the criteria that was used to choose a
suitable material for a selected spring.
After careful consideration, stainless steel was chosen mostly due to its elongation and tensile strength.
Although low alloy steel is the cheapest metal in consideration, it lacks the elongation needed for a spring.
Mass manufacturing was also taken into consideration. Stainless steel springs are very common compared
to low alloy steel springs which are none existent. It is also easier to mould the stainless steel compared to
a low alloy steel material. With a material selected the calculations were finalised.
𝑇 = 𝑟𝐹𝑆𝑖𝑛∅
r = 0.01685m
F = 774.009
∅ = 90
T = 13.042Nm
A spring constant would then have to be found to know displacement. This was done with calculations from
spring calculator [9]. By knowing an outer diameter, wire diameter, number of coils and the selected
material a selected spring is, a spring constant can be found.
Table 8 Metals in consideration for choice of spring
Cast Al-Alloy Low Alloy Steel Stainless Steel
Price per Kg (€/Kg) 1.89 – 2.176 0.5 – 0.544 5.23 – 5.425
Young’s Modulus (GPa) 72 - 89 205 - 217 189 - 210
Shear Modulus (GPa) 25 – 34 77 - 85 74 - 84
Poisson’s Ratio 0.32 – 0.36 0.285 – 0.295 0.265 – 0.275
Elongation (%Strain) 0.4 - 10 3 - 38 5 – 70
Hardness = Vickers (HV) 60 -150 140 - 693 120 - 570
Tensile Strength (MPa) 65 - 386 550 – 1.76𝑒3
480 – 2.24𝑒3
38. 37 | P a g e
From a Solidworks CAD model, these parameters can be found
Wire Diameter :1.6mm Number of coils :10.5
Outer Diameter :12mm Material : Stainless Steel 17-7ASTM A313
With all this information, the spring constant for a selected spring is found to be 1.255N/mm [10]
Risk Analysis
This section, Risk Analysis, outlines the risks and failures that are associated with the rear gear derailleur.
It discusses potential ways in which the derailleur could fail as well as evaluating these risks and the
actions taken to combat them.
It will make use of Failure Mode and Effects Analysis (FMEA) system, which has two types; design and
process. Design type is undertaken before the part is produced and highlights its function, while process
type is analysing the assembly process of the product after its completion. [11] [12]
The failure most associated with the derailleur is actually its attachment to the bike frame. The derailleur is
attached by a bracket, known as the derailleur hanger. This hanger can snap but is more likely to bend.
The effect of the hanger snapping is that the derailleur is only partially attached, only through the chain, and
gears cannot be changed. The cause of this failure is due to the fact most derailleur hangers are made
from stamped aluminium [13] [14]. Stamped aluminium is relatively fragile [15]. However, this material is
chosen purposely so that the bracket will bend/bracket rather than the frame of the bike breaking. A new
bracket cost under €20 [16] [17] and therefore can be sacrificed to preserve the more expensive frame. The
cause of this failure can occur from simply heavy duty use such as long haul journeys, rugged terrain and
mountain biking. However, it can also occur from having the wrong gear combination for the type of terrain,
but this is rare. With these heavy uses mentioned the occurrence of this failure can be as little as every six
months.
A resulting risk of this failure is the fact that if the bracket bends by snagging on the cogs, it can bend in
such a way that the spokes become damaged. A much more severe outcome, is if the entire derailleur
interacts with the wheel. This can occur from the bracket snapping, or bending far too much, as well as the
limiting screw being incorrectly set. If the lower limiting screw is set incorrectly, set too loose, it allows the
derailleur to travel too far inwards –past the cogs and towards the wheel. This could entirely destroy the
derailleur, cable, housing and the wheel itself. More so, the human injury it could cause is quite dire; a
locked back wheel or the entanglement of the derailleur and chain could cause huge damage. If traveling at
any speed and suddenly stopping, the cyclist may be thrown from the bike. This then leads in to the
aspects of, if the cyclist is wearing a helmet and the surrounding environment for which they will be falling
on. The most severe case would result in death, from either a head or neck injury. Paralysis could also
occur.
However, it is rare for this to occur, with the more likely outcome being the derailleur partially interacting
with the wheel, but still allowing for the bike to move until the cyclist can slowly stop –resulting in little injury.
The precautions in place are, that if the derailleur hanger breaks, the metal snaps so that the derailleur
hangs on the chain but does not interact with the wheel. The position of the derailleur also makes it unlikely
for interaction with the wheel as well as the gear cable attaching to the derailleur.
The other failures can occur from ordinary metal fatigue and everyday cumulative damage. Such as the
wearing of the sprockets, which results in unsmooth gear change. These can be easily replaced when worn
too low. The other obvious failure that could occur, is if the bike itself was in a crash, where there is a side
impact which could smash and bend the derailleur.
39. 38 | P a g e
User manual
Tools required:
Torque wrench Bike Stand, as rear wheel will need to be elevated
Philips head Screw driver
1. Attach the rear derailleur to the bikes derailleur hanger.
Before tightening the bracket spindle, make sure to not to cause
deformation of the hanger/dropout tab due to the B-tension screw.
2. Tighten the bracket spindle bolt through the bracket, frame and
bracket nut just enough so that the derailleur will stay on.
3. Using the torque wrench tighten the bolt until it makes a click,
setting a value between 3-4 Nm.
4. Starting from the shifters feed the gear cable down to the derailleur, but hold off on securing the
derailleur to the cable.
5. Using the Philips head screw driver turn the high/top adjustment screw to line the pulley just below the
smallest sprocket. When this screw is turned clockwise the
pulley will move inwards to the wheel spokes, and
anticlockwise, outwards from the wheel spokes.
6. To connect the gear cable, pull slack and feed it through the
groove of the rear derailleur, give tension to the cable by pulling
with a pliers.
7. With the cable connect, shift the derailleur
to just below the largest sprocket by turning
the low/bottom adjustment screw. When this
screw is turned clockwise the pulley will
move outwards from the wheel spokes, and
anticlockwise, towards the wheel spokes.
8. To use the B tension adjustment screw, place the chain on the
largest sprocket and smallest chain ring, and turn the crank arm
clockwise. Adjust the guide pulley so that is as close as possible
to the sprocket, but not touching. Then, place the chain on the
smallest sprocket and repeat the steps, making sure the pulley
and sprocket do not touch and the chain has correct tension.
Note
• Wash and lubricate the derailleurs moving parts if shifting gears
does not feel smooth.
• Replace the derailleur if adjustment is impossible due to the links being too loose.
• The Derailleur should be periodically cleaned and all moving parts lubricated.
Figure 33 Bracket bolting
Figure 34 Connecting Gear Cable
Figure 35 Top Adjustment Screw
Figure 36 Lower Adjustment Screw
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