In principle, a G-Boxx system has the advantage of eliminating many common problems associated with a derailleur based system. Since the drivetrain components of a typical bicycles are all exposed and attached as separate parts to the frame they are exposed to the elements, dirt, water, etc. This causes the excellent efficiency of a derailleur drivetrain to deteriorate over time, which in turn means that you spend more time overcoming this inefficiency than providing forward momentum. Of course, debris, rocks and other similar elements may also cause considerable damage to the drivetrain, making the entire system inoperable. Finally, a derailleur based system also utilizes some form of chain tension device in order to prevent the chain from derailing when moving it from one cog set to a lower. G-Boxx provides a unique, simple and clean solution to all of these problems by enclosing all drivetrain based components inside an encapsulated system. This allows the efficiency of the G-Boxx to remain constant and provide the rider with constant and continuous forward momentum.
A platform strategy is a concept whereby one platform is utilized to manufacture several different models. One of the biggest examples of this strategy can be found in the automobile industry, where this has been long common. Volkswagen for example utilizes this strategy by building several different models based on the Golf sub-chassis; with a different body it becomes the Jetta, or Audi may utilize it to build the TT sports-coupe. The main benefit is of course the cost factor; no longer do you have to build different chassis, instead you utilize one for many different models. Bicycles have traditionally been built around a non standard framework. First, the frame was designed and built, then all components where attached onto the frame. For the first time, G-Boxx allows bicycles to be manufactured based on a platform strategy. Using G-Boxx as a platform, all main system components such as gearbox, suspension, even dynamo's and brakes are attached within the G-Boxx framework facilitating a simple and clean solution.
The relationship between sprung and unsprung weight on a bicycle is of critical importance. The heavier the unsprung weight to sprung weight factor is, the more critical the bike handling becomes. A higher weight rear wheel will not be as efficient in actuating the suspension as a lighter weight wheel. Therefore it is most important to design and implement light weight rear wheels to get the most out of the suspension. Bikes with G-BOXX systems do have much lighter wheels compared to bikes with deraileurs or hub based drivetrains, because no shifting components are attached to the wheels.
In a G-Boxx system, all parts and components necessary for changing gears are contained within an encapsulated system. Therefore, they are not affected by the outside elements common to on or off-road cycling. Water, dirt, debris, etc is no longer able to penetrate the system and the owner therefore does not have to spend as much time keeping the system clean and free of debris. Further, since all critical components are free from contact with debris, a long-life and hassle free operation is virtually guaranteed, unlike derailleur based drivetrains, where even the most expensive components must be maintained and upgraded at some point during aggressive riding. Most importantly, no G-Boxx contained parts will become damaged due to impact or other harmful contact with rocks, roots, etc.
Traditional single-pivot suspension systems are designed with the main pivot rotating around the middle (front) chain ring. The reason is that in this scenario drivetrain elements are least likely to hinder the suspension movement and action. However, due to the main pivot being located fairly low the rear wheel now follows a path where first has it has an upward movement, then, during the second have of travel, arcs forward. However, the force which actuates the suspension does not act from either under the bike or from behind the wheel; rather, it is determined by a factor acting from under and one factor from behind the wheel. The resulting wheel path would therefore be arcing towards the back and the top. A single-pivot design can implement this wheel path by moving the pivot higher up. A derailleur based drivetrain however also works against this by acting as a negative force on the suspension during pedal induced forward movement; typically riders will complain about a severe bouncing effect whilst pedaling the bike. Optimally configured G-Boxx bikes have their main pivot exactly in the middle of the aforementioned wheel path. This results in a good wheel path without the negative influence a derailleur based drivetrain will have on the system. As G-Boxx was designed from the outset to work with a multitude of different suspension designs, other solutions to this problem are also to be implemented.
The following simple examples will demonstrate why there is a tremendous benefit to shifting without pedaling. Mountainbikers encounter the following situation frequently - following a downhill is a tight corner, followed by an uphill section. Typically, the rider would select a tall gear for maximum speed; while standing on the bike however, pedaling really becomes difficult (fear of cranks catching a rock, rut or roots) therefore, the biker mostly coasts downhill. Just before the corner, the brakes are applied and since you are not able to shift gears while in the turn, you are left with having to shift sometime after exiting the turn (Note: downhill racing has become an extremely popular sports venue where frequently titles are won and lost within 1/10th of a second). A G-Boxx based rider on the other hand would have no such problems; he could simply engage any of the available gears while coasting, even braking for the turn. He therefore already has the optimal gear in place to tackle the forthcoming uphill section. Citybikers on the other hand can also benefit from G-Boxx systems; imagine a scenario where a speeding biker needs to suddenly stop for a light or other sudden conditions; upon reapplying his energy to the pedals, the wrong gear is selected and forward movement becomes difficult. Utilizing a G-Boxx, this problem is eliminated.
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Q-07 · Why is a derailed chain dangerous?
A derailed chain can be dangerous under conditions such as the aforementioned downhill rider; the chain became offline without the riders knowledge - he applies power to the pedals and due to the chain not having any resistance, the rider is typically ejected off the bike. A derailed chain can also cause major damage by jumping between the cassette body and the spokes, thereby sometimes effectively locking the wheel from any forward movement and the rider again being ejected off the bike.
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Q-08 · What is chaingrowth?
Within the context of the bicycle drivetrain, no physical chaingrowth takes place; the term merely implies that under certain circumstances the distance between the rear cassette and main chain ring up front can change. One example is the use of derailer based drivetrains combined with rear suspensions. This problem is further exaggerated by having multiple gears in the front and at the rear wheel; a slack chain will cause problems as it will no longer allow for proper power placement on the drivetrain system. The simple solution to this problem was the implementation of a chain tensioner device. With the use of a G-BOXX transmission, it is possible to design a full suspension bicycle without this problem of chaingrowth.
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Q-09 · Why is the use of chain tension devices not the best solution?
During the aforementioned example, most suspension bicycles have a chaingrowth problem during any suspension movement. The chain therefore must be longest when the wheel is at the maximum distance from the main chain ring; shortest at the exact opposite. Of course, no biker will ever adjust and readjust their chain length for varying conditions, which is why the use of a chain tension device is essential to the overall performance of the bike. The problem here is that all chain tension devices are mounted externally on the frame, thereby being fully exposed to the elements surrounding the rider. Frequently, collisions with rocks, roots, trees, etc. might cause a complete system failure in chain tension devices.
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Q-10 · What are the advantages of a light weight bike?
A simple rule of physics is that it takes far less energy to move a lighter object than an equal, heavier one. Typical mountainbikers ride in varying terrain; uphill, downhill, etc. a lighter weight bike will always allow for maximum comfort and forward efficiency. Also noteworthy is the fact that a light bike is more nimble and agile compared to a heavier model. Light weight bikes are virtually always preferable to heavy weight bikes, however, the light weight should never come at the expense of stability for any given riding condition. The overall goal of all bicycle gearbox manufacturers is to continuously develop and improve the bicycle gearboxx system and its transmission so that gearbox bicycles will be comparable in weight with their conventional derailleur based drivetrains.
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Q-11 · Why are derailleur based drivetrains maintenance heavy and prone to failure?
Since all components of a derailleur drivetrain are externally mounted, they are always exposed to full contact with the elements. Water, dust, dirt, debris, etc. will always find a way to infiltrate the mechanical parts of such a drivetrain. Constant maintenance in form of cleaning, washing, etc, is of great importance in order to maintain the overall efficiency of the system. Keeping all parts clean and properly adjusted is essential - yet, each time you ride the bike, most adjustments become undone and need to be attended to frequently. As a result, the total cost of ownership for any given bicycle is always increasing with use.
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Q-12 · What are the disadvantages to further frame attachments?
Adding frame attachments in form of a G-Boxx system typically add overall weight to the frame. Second, you loose mounting systems for other important items such as bottle holders, fender mounts, etc.
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Q-13 · Why is it an advantage to have less design restrictions at the bike frame?
Consumers typically like to have the most choices; putting any sort of constraint on bicycle designers and developers would essentially minimize the choice. Bikes would start looking similar versus allowing each individual frame manufacturer to implement their own design elements. The consumer therefore has the most choice in picking the frame he likes best.
Developing the G-CON-Standard was mainly required to allow a maximum number of different frame designs despite the standardization. The film in the following link ( rahmen.swf ) gives some examples. The fixing of the transmission box is only dependent on the fitting surfaces of the gearbox. These itself can be integrated differently in the frame corresponding to the design requirements.
The variety of constructions and designs in bicycle manufacturing is enormous. A three-figure number of manufacturers offers a wide range of different designs regarding city, trekking, competition, tour and mountainbiking. This is the reason why, developing the G-CON-standard, we put so much emphasis on creative freedom.
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Q-14 · What disadvantages do exposed chains have?
Externally mounted chains suffer from essentially the same problems as other externally mounted drivetrain components: they are exposed to the elements. Water, dirt, etc. will penetrate the chain and further reduce the efficiency of the system, resulting in an increase in overall maintenance.
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Q-15 · What are the advantages to using a solid rear hub?
Traditionally, the rear hub contains the free wheel as well as the cassette - moving all these parts to the G-Boxx, allows for a simple, stiff and maintenance free hub to be utilized (much like the front hub). Most importantly the unsprung weight can be dramatically reduced thereby allowing the suspension to work much more efficiently. More about this issue can be found under the button "special rear wheel hub".
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Q-16 · Why should you have the choice of utilizing a multitude of different components, even at Gearbox bikes?
Due to the fact that all drivetrain components are essentially compatible with one another, the consumer has the freedom to choose the components which suite his riding style best. A racer for example would go for ultra-light weight components, while a casual weekend rider would go for something more rugged and less prone to breaking. The cost factor is also to be considered; in the aforementioned example, a top end component costs several times more than a standard setup. Finally, a wide range in component choices allows for personal styling elements throughout the bike. For this reason the G-CON standard is designed with the basic subposition in mind not to restrict the use of multitude different components at the gearbox products itself. The G-CON standard is just defining the maximum size and connection points of the gearboxes to come in the futur.
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Q-17 · What is the efficiency of a transmission system?
The efficiency of a gearbox system (transmission system) is essentially the relationship between the amount of energy one exerts to move the gears vs. the amount of energy that is actually being converted into forward movement. A new and properly setup derailleur drivetrain has an efficiency of about %98; however, contamination by elements, etc. causes that number to drastically fall to between %80 and %95. We can therefore summarize that there is an immediate correlation between the efficiency of a drivetrain and the surrounding elements, which most of the time we can not change or positively impact (riding on a rainy day; under dusty conditions, etc.). Constant and continued exposure to these elements further reduces the overall efficiency dramatically. Therefore much of the energy is transformed into heat or friction and not into forward movement. G-Boxx has an efficiency factor of between %96 and %98. Due to all gear changing components being permanently sealed and encapsulated from the elements, this efficiency remains constant throughout the life of the bicycle.
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Q-18 · Why do we need the standard interface 'G-CON'?
This question can be answered most easily by following counterquestion: "Which problems do occur if there is no standard?" Each frame manufacturer would be forced to commit to a certain transmission and thus adjust his frame concept to it. For the brand, the manufacturer or even the customer it would not be possible to choose between (in near future greater number of) different transmission concepts and manufacturers the most adequate transmission, or change it later. Vice versa, the transmission designer cannot constantly react on alternating claims of the frame builder and adapt his transmission housing to these. Therefore,with the introduction of an open standard named G-CON which is defined independently, the connection between transmission and main frame is standardized. The standard represents an interface by which a transmission can be integrated into nearly every type of frame. It is also possible to adjust different types of transmission housings to a frame.
G-Con-Standard is characterized within the question 19.
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Q-19 · How is the G-Con-Standard defined?
In order to answers this question, we focus here on the gearbox housing only. Cause the gearbox replaces the classic bottom bracket shell, the housing needs certain connection points to the bicycle mainframe.
GCON-Master.jpg shows a transmission housing. It does not correspond to a certain manufacturer, it is chosen accidentally. There are four cylindrical interfaces at the middle part of the transmission housing. These, in the drawing red-marked interfaces, have a tight tolerance to be kept by the transmission manufacturer. Concentrical to each interface there is a 10mm (blue) and across to it two 7mm (yellow) drilled holes Pic 2.3. Exact dimensions are to be seen in the PDF-file GCON-coordinates_mounting_points.pdf , GCON-bolt_distances.pdf and GCON-bolt_angles.pdf . The mounting of the gearbox to the mainframe is shown within GCON-bolt-setup.jpg.
GCON-Master.jpg
GCON-bolt-setup.jpg
crosstapped-bolt.jpg
Weldin.jpg
A special crosstapped-bolt.jpg (yellow marked) can be put into the 10mm hole (blue marked). Tightening the M6 bolts pulls the interfaces (red) into the green-marked cylindrical groves of the main frame. The component of the frame which shows the green-marked areas is called ?Weldin.jpg " in the following.
The form-lock between the cylindrical interfaces of the transmission housing and the main frame results in an extraordinary strong connection ( GCON-Standard_weldin.pdf ) It is distinguished by following advantages:
- |
Frame and transmission housing can be made of different materials (e.g. aluminium/frame, magnesium/ transmission housing) |
- |
Easy-to-handle-service: transmission can be changed quickly by the mechanic if an transmission failure occurs |
- |
Every single supporting connection element is exchangeable. No threads in the transmission housing. If a thread is damaged the crosstapped-bolt can easily be exchanged. |
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The housing can be a "stress-member" of the frame ( question 21 ) |
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Various assembly opportunities are given |
a) with the use of the crosstapped-bolt
b) directly through stronger 10mm Bolt with a side connection ( double-downtube-GCON-frame.jpg)
double-downtube-GCON-frame.jpg
Additionally the gearbox housing need to have a connection to the rear swingarm. CON-Master.jpg shows on both sides a cylindrical boss (red marked) with the diameter of 45mm. Exact dimensions are to be seen in the PDF-file GCON-Coordinates_pivot_point_rear_swingarm.pdf. This Pivot point at the gearbox is design carry an 61809 2RS ball bearing ( 61809.jpg ). Location of this 7mm wide ballbearing is described within the GCON-bolt_distances.pdf.
Regarding more details about the connection of the rear swingarm please take a look at question 31.
More details about the chainstay connection of hardtail frames will be described within question 30.
Chainline related G-CON issues will be described within question 25.
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20 · Which weight advantage offers G-CON?
Transmission bikes built-up without G-Con-Standard mostly have a welded connexion between transmission housing and frame. This includes that transmission housing and frame are made of the same material. Introducing the G-Con-Connection, it is assumable to reduce the total weight by using light materials like magnesium, carbon or special synthetic materials. Therefore it makes sense to chose different materials for transmission housing and frame. Non-weldable components (transmission housing) can be made, for example, of magnesium. The frame itself furtheron is produced using acknowledged technologies (welded part).
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21 · What are the different ways to fit a bicycle frame to a G-CON gearboxx?
The variety of constructions and designs in bicycle manufacturing is enormous. A three-figure number of manufacturers offers a wide range of different designs regarding city, trekking, competition, tour and mountainbiking. This is the reason why, developing the G-Con-standard, we put so much emphasis on creative freedom. Some two-dimensional examples can be seen in the following link ( rahmen.swf )
The three-dimensional illustrations 21-1.jpg , 21-2.jpg , 21-3.jpg and 21-4.jpg show different samples regarding G-CON-Connection. Illustration 21-1.jpg shows a frame in which the downtube is connected to the seat tube by a welded part. Picture 21-2.jpg shows a frame in which the downtube is connected to the seat tube through a further tube, and in Pic 21-3.jpg the G-CON Connection points are placed on two single milled parts without additional cross beams (Gearbox is a stress member here). However, the standard offers also the basis for further solutions, see Pic 21-4.jpg . Here, the front milled part is fitted to the two-folded downtube of the frame, and two-folded itself. The downtubes are connected at the side with screws to the front connection points of G-CON. These examples are only suggestions. There is a great number of other connections. From diecasted parts over titan- welded constructions to laminate carbon solutions. All in all, it is up to the manufacturer.
21-1.jpg
21-2.jpg
21-3.jpg
21-4.jpg
21-5.jpg
Apart from the parameters of the fitting surfaces the G-CON-Standard also defines an "maximum housing area" right around the transmission. This guarantees that components like damper , front frame and rear end do not collide with transmission parts.
In Pic 21-5.jpg the area in question, main frame and rear end are shown. Additionally informations of the maximum gearbox size can be downloaded in the CAD-DATA area at question 21. Certainly no manufacturer of gearboxes will use the whole maximum room for ther design. It would be ugly as hell. But in any case G-CON need to be clearly evident.
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22 · Which problems do occur if the gear box is welded directly to the frame?
If the transmission housing is welded to frame distortion occurs and, as a result, transmission and housing do not fit exactly. This prevents two independent lines of production. Manufacturers would be forced to demount the delivered transmission, weld the housing to the main frame and adapt the distortion to the housing. Then, all components and the frame would have to be mounted again. This effort is beyond reality and obstructs the rise of transmission bikes. Also a later change of the transmission (e.g. service) means bigger effort. A G-Con-connexion with screws solves this problem. The standard defines the connexion between the two components resulting in fitting accuracy. The manufacturers of transmissions and bicycles are able to work independently and design products which eventually can be connected because of the G-Con-Standard.
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23 · How can I build a hardtail frame with the G-CON standard?
At this moment in time there are no G-CON standards regarding hardtail frames; however here are some recommended solutions and there is likely to be more.
Currently it is possible to remove the swingarm bearings to make the rear of the frame rigid (below). The seatstays of the swingarm are merged with the top tube, and the swingarm clamp is removed. The clamp is now an individual part which is attached to the gearbox boss and bolted to the chainstays. It is important to separate the swingarm and clamp in order to allow the gearbox to be removed from the frame.
hardtail-solution-1-2.jpg
hardtail-solution-1-1.jpg
hardtail-solution-1-3.jpg
Another possible solution would be to have the chainstays and seat tube integrated into one part. The modified weldin would then be secured to the frame using 6 cross tapped bolts with the addition of two stud bolts.
hardtail-solution-2-1.jpg
hardtail-solution-2-2.jpg
hardtail-solution-2-3.jpg
As seen in this movie ( rahmen.swf ) there is the possibility to create connection points to the rear of the gearbox in order to attach chainstays, they could even be used for rear suspension pivot points. These points are not defined as of yet, in the future they may be developed so they are included in the G-CON standard. If you wish to integrate a gearbox into a hardtail frame now, please contact either the site editor (details can be found under the 'Contact' section) or transmission manufacturers (details of gearbox companies can be found under the 'Manufacturers' section).
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24 · Can I build in a gearbox in a sloped position (backward or forward) to adapt it to my framedesign?
Yes, this is possible. The following 4 pictures ( 24-1.jpg , 24-2.jpg , 24-3.jpg and 24-4.jpg ) are showing the same frame with different angular orientations. It is just very important to insure that the chain to the rearwheel will not hit the crankarms or an other funktional element of the gearbox. The picture 24-5.jpg shows an impossible orientation. Clear to see here the chain is hitting the right crank at the lower end.
24-1.jpg
24-2.jpg
24-3.jpg
24-4.jpg
24-5.jpg
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25 · What is the chainline of a gearboxx bike?
At present, there are only a few transmission boxes available on the market (see manufacturers). The G-Con-Standard allows future manufacturers as most freedom in creativeness as possible. Regarding the 3-dimensional freedom of creativeness is exactly defined in the question 27.
The chainline is defined as the distance from the centerline of the bike to the middle of the chain that runs to the rear tyre.
GCON-chainline.jpg
G-CON is designed with the future in mind regarding smaller gearbox sizes. For this reason you find within the file GCON-chainline.jpg two different gearbox sizes with 2 different connection points of the rear swingarm. It is important to notice that the connect boss for the rear swingarm stays can be inside or outside of the rear-swingarm ball bearing. This leads into 4 different constellations:
1) |
GCON-OBK-wide (Outside-Bearing-Constellation wide) ; not used yet !! |
2) |
GCON-IBK-wide.pdf
(Inside-Bearing-Constellation wide) ; for example used on the Universal transmissions G-BOXX-2 ( www.g-boxx.com ) or on the SRSuntour Gearbox ( www.srsuntour-cycling.com) |
3) |
GCON-OBK-narrow (Outside-Bearing-Constellation narrow) ; not used yet !! |
4) |
GCON-IBK-narrow (Outside-Bearing-Constellation narrow) ; not used yet !! |
The radial distances are the same for all 4 Constallations according to question 19.
We draw your attention to the fact that the illustrations only show virtually chosen transmissions. Likely, each manufacturer designs his own transmission, with different sizes (number of teeth) of the output sprocket. The CON-Interface defines just the position of the output sprocket, the minimum and maximum package dimension of the transmission ( question 27 ) and the cranks ( question 28 ).
If these conditions are followed there are two possibilities of fixing suspended rear ends in bikes with G-Con-Standard:
1) |
a connection of the rear end to the main frame; these kind of frames have to be runned with chain adjuster in general |
|
2 a) |
a connection of the rear end to the transmission housing
centre of rotation of the rear end concentrical to the output shaft |
|
2 b) |
a connection of the rear end to the transmission housing
non-concentrical to the output shaft |
|
The G-Con-Standard defines positions for mounting the rear end bearing on cylindrical fitting surfaces by the restricted package dimension.
More information regarding the connection of the rear swingarm to the gearbox housing according to 2a will be given in question 31.
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26 · How can larger diameter down tubes be used with the G-CON standard?
As seen through images on the site, using a downtube with up to 50mm causes no problems. Anything larger requires the weldin to change its dimension as well as creating interferences with the connection points. The following demonstrate two solutions.
larger-down-tube-sol21.jpg
larger-down-tube-sol22.jpg
The above solution requires 6 cross tapped bolts and 2 stud bolts in comparison to the usual 8 cross tapped. Due to two of the connection points being covered, a section of the weldin is sheltered from the dowtube to allow two stud bolts and nuts to be used.
In addition the weld needs to be broadened in sections to accommodate the larger down tube.
larger-down-tube-sol12.jpg
larger-down-tube-sol11.jpg
The second solution above has the weld cutting through the downtube horizontally, this is to keep the holes free to accept the cross tapped bolts.
The two above solutions are just recommendations of how to tackle a possible problem with a large diameter downtube, there are many other ways to solve the problem.
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27 · If I want to design a bicycle frame, what room do I have for composing the likes of rear shocks, tubing, linkages, etc?
As the movie ( rahmen.swf ) and question 31 illustrates, there are a great number of frame concepts that gearbox transmissions can be integrated into. However, when arranging the bearings, rear shock and tubes you have to bear in mind not to encroach on the area occupied by the G-CON maximum standards.
The G-CON standards can be found under the CAD DATA section of the website. The below images demonstrate various suspension designs which take into consideration the maximum G-CON measurements. Many frame and suspension designs can be accomplished when integrating a gearbox transmission as long as the designer/engineer observes the maximum G-CON dimensions, things such as, height, width, depth, bolt hole diameter and bolt hole positioning.
suspension_1_with_max_dim.jpg
suspension_2_with_max_dim.jpg
suspension_3_with_max_dim.jpg
For further information when designing your frame around a gearbox transmission, please see question 4, 6, 8 and 9.
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28 · Is the Q-factor in transmission bikes worse than in conventional bikes?
The Q-Factor is defined by the maximum distance between the outer edges of the crank arms
( Pic 28.1 ). The distance is measured at pedal height and is easiest when both crank arms are pointing in the same direction. An optimum Q-factor is relative, as it is dependent on the rider's physiology and the intended use of the bike (street, cross country, downhill). It is influenced by the shape of the cranks and the width of the inner bearing.
Pic 28.1
Current mountain bikes with derailleurs have a Q-factor range from 173mm to 176mm. Modern downhill and freeride bikes have Q-Factors between 188 - 192mm, this is due to wider tyres and the rigidity required in the rear swingarm resulting in a larger width. Recent gearbox concepts create similar values as mentioned. To prevent collisions from the chain line it is important to pay attention to the width of the Q-Factor, the chain line is explained further in question 25.
Chainline attention is even more relavent when sloping the gearbox forwards or backwards, this is explained further in question 24. A lower Q-factor has a positive effect on the rider`s aerodynamics by improving the streamline, higher values result in high exposure at the knee-joints.
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29 · What are the differences between manufacturing a gearbox and conventional frame?
This question is asked because of the worry that manufacturing a gearbox frame would take much more time and effort to produce in comparison to a conventional gear hanger frame. The first difference of manufacturing a frame with a gearbox in comparison to a frame with a conventional gear hanger is the area around the bottom bracket. In comparison the mounting points between the frame and bottom Weldin/bracket on the gearbox frame are higher along the tubes. Responding to this the Weldin is simply a different shape to accommodate the mounting points and gearbox. Therefore the manufacturing processes equate to the same time and effort.
When an aluminium-made frame is manufactured, first, the bottom bracket housing without thread is welded to the tubes of the frame. The drilled hole of the bottom bracket housing is smaller than the final diameter. This is to prevent the welding from destroying the bottom bracket housing thread. Therefore, only after the following heat treatment, the housing is reamed to the acquired thread-inside-diameter and the bottom bracket is threaded afterwards. Finally, the bottom bracket housing's side surface is bevelled so that the desired width (normally 68mm) is reached.
Frames with gearboxes are manufactured in a similar way. The Weldin illustrated in 4.1 is designed by the manufacturer and its dimensions adapted to the frame (see question 2 ).
Pic 4.1
We have learnt that different applications require different solutions from the Weldin. Therefore the Weldin needs to change to accommodate these applications; applications such as, larger downtubes ( question 26 ) and hardtail frames ( question 23 ); the following are examples of this.
q291.jpg
q292.jpg
q293.jpg
This movie ( bohrschablone.swf ) demonstrates one possible solution how to create precise fixing points between the Weldin and the gearbox. Firstly the fitting surface on the Weldin has a final standardized diameter of 18mm; this before the stages left at 17mm (Pic 13.1). The Weldin is then welded to the tubes of the frame (Pic 13.2). The frame is secured to a jig, which is sandwiched between two plates. Within the plates are holes to guide the drill for reaming. The radiuses are then reamed to produce the precise standardised dimension of 18mm (Pic 13.3).
Pic 13.1
Pic 13.2
Pic 13.3
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30 · What do I have to take into consideration if I build a bicycle frame with the G-CON standard?
When manufacturing a frame in compliance with the G-CON standard, the following steps may be useful.
Step 1.a CAD DATA
When designing a G-CON frame it is a good idea to first understand existing G-CON designs. Under the CAD DATA section of this website the following 3D parts are available to create an assembly of a G-CON frame (Pic 1.1, 1.2, 1.3, 1.4) in your chosen 3D package.
- Public-domain_axle_plate_left
- Public-domain_axle_plate_right
- Public-domain_bearing_clamp
- Public-domain_dropout_left
- Public-domain_dropout_right
- Public-domain_left_rocker_arm
- Public-domain_right_rocker_arm
- Public-domain_mainframe
- Public-domain_weldin
Also included in the assembly is the 3D model, Max_Dim. This model does not represent a gearbox but the maximum dimensions of the G-CON geometry.
Pic 1.1
Pic 1.2
Pic 1.3
Pic 1.4
Step 1.b The Weldin
The interface between the frame and gearbox is the Weldin (Pic 1.5), this part is welded to the frame and has connection points for the gearbox. This part is initally very important to the frame but also for when modifiying the frame to meet certain requirements, for these requirements the Weldin may change, for example if a larger downtube ( question 26 ) is wanted (Pic 1.6 and 1.7) or you would like to produce a hardtail ( question 23 ) frame (Pic 1.8).
Pic 1.5
Pic 1.6
Pic 1.7
Pic 1.8
For information on the Weldin please refer to question 19 and 24.
Pic 1.9
Pic 2.0
Pic 2.1
Step 1.d Chain interference
It is very important that the frame design does not make the chain interfer with any other parts. The chain line runs between the output sprocket of the gearbox and the rear hub. To understand the chain line more please read question 25, 7, 8, 9 and 14.
Step 2 The G-CON Dummy Tool
In order to aid manufacturers with the production of G-CON standard frames we produced the G-CON Dummy Tool. The tool is not a replica gearbox but a physical model to provide the maximum measurements of G-CON standards such as, mounting points and bottom bracket position. As well as providing measurements the G-CON Dummy Tool also conducts four more functions which are detailed below.
More in depth information surrounding the G-CON standards can be found under question 19.
DSC04380.JPG
DSC04352.JPG
DSC04347.JPG
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Checking chain line
Important in the design of the frame is the chain line, the G-CON dummy tool enables the designer/engineer to check this element against their frame designs to find any discrepancy's. The G-CON dummy tool has two sprockets coloured green and red; these represent the sprockets of the OBK wide and IBK wide respectively and can be used in conjunction with the rear hub to illustrate the chain line of your frame design.
Some have asked why the OBK and IBK wide differ with the positioning of their sprockets, this configuration is not due to any design principles but physical constraints, outside and inside bearing constellations. Rohloff technology is used inside the 14 speed OBK wide, this results in the chain running between the outside placed bearings to the swingarm (outside - bearing - constellation OBK). In comparison the 9 speed IBK wide which utilises UT - Technology ( http://www.g-boxx.com ) allowing a wider chain line setup. This in turn locates the rear swingarm bearings inside of the output sprocket (inside - bearing - constellation IBK).
To read further into the G-CON chain line please read question 25.
Also relevant to the G-CON chain line is the following query located on the G-CON blog page :
http://g-boxx.blogspot.com/2006/03/135mm-vs-150mm-hub.html
Checking for crank collision
The cranks on the G-CON dummy tool are designed to independantly rotate, when mounted to your frame design it is simple to pin point any frame collisions by turning the crank arms. For further information on mounting your gearbox to frames please read question 21 and 24 and view this movie ( rahmen.swf ).
Welding with the G-CON dummy tool
The G-CON dummy tool has a bottom bracket shell width of 68mm allowing it to be mounted on to exsisting welding jigs. The tool acts as an adaptor to common botttom bracket holders, this allows the production of a G-CON standard frame. The G-CON dummy tool is very heavy and rigid, this provides the strength needed to withstand the welding process keeping the tool true without any warping.
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Frame alignment with the G-CON dummy tool
The G-CON dummy tool can also be used in jigs when undertaking the frame alignment process, the bottom bracket shell is used here similar to the welding stage. Once again the tool acts as an adaptor to common botttom bracket holders; this allows you to align your G-CON standard frame design.
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Step 3 Long term durability and testing
G-boxx.org provides suggestions and experiences to help companies design and manufacture a G-CON frame. The long term durability of each company's own frame is their responsibilty. It is suggested the frames undergo exstensive testing conducted by companies such as Velotech.de and EFBE.de.
Products produced which are not in compliance to the specifications contained within the CAD data section will be considered incompatible with standardized design. The drawings are not product drawings; they are to be used as reference documents for the determination of final product specifications. These final specifications are the responsibility of the manufacturer who intends to comply with this geometry.
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31 · How does the rear swingarm of a full suspension bike work in detail?
The G-CON standard is not a rule but more an interface between frame and gearbox designers. There are many rear end designs which can be used with G-CON, and also as many ways to adapt certain points of the design to produce different solutions, for example a four bar linkage gearbox frame or even a VPP frame utilising a gearbox.
The pivot point of the rear swingarm can be located around the gearbox to create the result you desire, concentric, behind, above or in front. All various suspension designs can be accommodated with a gearbox, the pivot point does not have to be attached to the gearbox but can be mounted in front, behind or above.
The pivot design concentric to the output sprocket (image below) is the most developed and also the CAD data for these are public domain and downloadable through the CAD DATA section. The G-CON pivot points are on both sides of the gearbox, both 45mm diameter bosses located 120mm above, and 5- 7° clockwise the bottom bracket center point.
The horizontal position of the two bosses are not symmetric to the center line of the bike, the left boss is 4.5mm further along the z axis than the right, this is due to space claimed by the drive sprocket on the right. Placed on this boss is a ball bearing 61809-2RSR-Y (brown part). It is recommended to use this industrial ball bearing due to it's quality, also in stainless steel to improve durability. The ball bearing is held in place by the rear swing arm and clamp (green part). The clamp and swingarm are placed around the bearing and boss, these are then held in position by two cross tapped bolts (red and yellow parts). This clamping secures the bearing around its perimeter 360°, in addition manufactured into the swingarm is a flange which then sandwiches the bearing with the gearbox housing. This is purely a suggested position and method to secure the rear swingarm position point, many other designs can be applied to your frame to achieve your own solution. More examples of swingarm designs can be seen below and in this movie ( rahmen.swf ).
- Single pivot design frame
- Swingarm pivot point mounted in front of the gearbox
- Due to pivot point an extra chain tensioner would be required.
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- Swing arm with seat stays removed
- Pivoted concentric to the output sprocket
- Concentric swing arm pivot point results in constant chain tension.
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- Multi linkage suspension design
- Pivots concentrically to the output sprocket
- Due to pivoting position no chain tensioning is required.
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possible-linkage-2-front.jpg
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The most developed frame design with swing arm pivoting concentrically to the output sprocket.
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original-linkage-assem-side.jpg
original-linkage-assem-front.jpg
original-linkage-assem-rear.jpg
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32 · Is the a "free to use" design for a G-CON-gearbox bike available somewhere?
Yes, the company Universal transmission offers a bikeframe design free for everybody who wants to learn and play around with some 2D and 3D drawings. We have put these into the CAD-DATA area of this webpage.
It is a design for a plain enduro MTB-frame for 6 inch forks and with 7 inch travel in the back.
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Please do notice that the drawings within this webpage are not product drawings. They are to be used as reference documents for the determination of final product specifications. These final specifications are responsibility of the manufacturer who intends to comply with the G-CON geometry.
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