Chain Drive

Chain Cleaning

Chain Lubrication

Chain Wear

Efficiency measurement of bicycle transmission

What I always wanted to know about working efficiency, but never trusted myself to ask!

Chain Drive

The gear chain is a wearable part and therefore the lifespan cannot be measured in riden kilometers, due to the applicated use, the shifting method of the rider and the condition of the chain itself, the lifespan of the gear chain can vary enormously. Naturally the starting quality of the chain plays a very important role.

In high performance use, the bicycle chain recieves up to 500kg of force. Therefore, an extremely high level of surface pressure of 300kg/mm2 is to be found here in the chain links. When the chainrings up front are smaller, the amount of force applied upon the chain is increased and with it, the amount of surface pressure in the links (e.g. on all MTBs with compact drive, microdrive, and hyperdrive C). The amount of surface pressure also rises when the chain is running at an angle so that the contact area is reduced.

Even though the Rohloff chain with its optimal patented linkage system that reduces the amount of wear caused by the surface pressure, it still needs to be lubricated just like any other type of bicycle chain. Without this lubricating film between the contact surfaces, an abrasive friction will occur within the linkage parts and this will lead to a quicker wear of the chain.

One of the essential wear factors is the amount of penetrated dirt within the chain linkages. Hard particles (e.g. sand) could enter the chain and lie on the above surface of the bearing collar, this sand then starts to work like sandpaper. Material from the pin surface will be slowly worn away, a little lubrication helps even if this occurs. Without this vital lubricative film, the lifespan of the chain can be drastically reduced. To fully understand this effect, we will turn back to the sandpaper example: Dry sandpaper is very abrasive. When however, it is used with a lubricant (e.g. water), the abrasive effect is conciderably reduced. With oil as a lubricant, the abrasiveness of the sandpaper has hardly any physical effect.

The manufacturers can increase the lifespan of the chain by designing an optimal linkage system, precise finishing and the use of an extremely hard pin surface.

The user can conciderably increase the lifespan of the chain simply by regularly cleaning and controlling the condition and lubrication of the chain.

Assembly of derailleur chains

In order to assemble the chain on the bike it has to be adjusted to the right length and then connected. All links of the chain are strained evenly. Therefore, a chain is only as strong as its weakest link.

One can distinguish four different methods of connecting a chain:

• Usage of a standard chain tool or plier with which one can open and close any pin of the chain
• Usage of a chain tool and a special pin with which the chain is ought to be connected
• Usage of a special connector which can be opened and closed without a tool (ie. superlink)
• Usage of the Rohloff Revolver 2 chain tool that can open, close and rivet any pin of the chain
  

Indeed, most chains do not have a special connector. The pin must be moved through the roller and pin link plate by using a tool. Whereas all other pins are riveted during the production process of the chain to improve its lateral stability, the connecting pin is only moved back in its fitting of the pin link plate by standard tools. This means that one side of the pins remains unriveted with the effect that the retention force of this pin will reach only about one third of the retention force of all other pins. The result is the same as with a connector: Where the chain is connected, it is by far less strong than at all other links. Therefore, standard chain tools and pliers should only be used for connecting chain provisionally (during trips, for example).

Shimano addressed this problem by introducing a special pin which is mushroomed on both sides in order to increase the retention force. In reality, however, this solution is not always satisfactory because the mushroomed pin can damage the pin link plate with the negative effect that the pin can move in the hole of the pin link plate.

Both the connector and the special black pin have a contructional disadvantage: for connecting the chain you need special parts which do not always work reliably.

Finally, the Rohloff Revolver 2 is easy to use and durable. Even in the bicycle factories it is used more and more often because the stringent product liablility laws force the manufacturers to make their bikes as save as technically possible. The same applies to the workshops of the dealers where the Rohloff Revolver 2 should not be missing.

In any case, a chain should only be assembled by trained personnel. After the assembly you should verify that the pin sticks out equally on both sides of the pin link plate.

There are two ways to correctly determine the length of the chain:

For the general practitioner:

This is the way that the majority of chains are measured. To start, take the chain by the end with the pertruding pin, add the number of teeth on the largest sprocket and the largest chain ring together, divide this number by two and finally add two to this number.

For example:

Largest chainring has 44 teeth, largest sprocket has 28 teeth

44 + 28 = 72 : 2 = 36

36 + 2 = 38

Now measure the length of the chainstay. The start end of the chain should be held at the centre of the quick release skewer and taken to the centre of the bottom bracket. This distance should be measured twice (if the ends of this measured distance are not able to be joined together, then add another link to this). Next, take this length of chain and add the number of links (that we calculated before) to it. This is the position where the chain should be shortened. The chain is now the correct length and has two different ends to allow it to be joined together, take care to follow the manufactures instructions when rejoining the chain together.

The following formula can be used to calculate the precise length of the bicycle chain:

LK = 0,157a + 1/2 Z1 + 1/2 Z2 + 2

LK = chain length in links (number of pins)
a = chainstay length in mm (quick release skewer to bottom bracket center)
Z1 = number of teeth on the largest chainring
Z2 = number of teeth on the largest sprocket

Example:

Chainstay length a=420mm, Z1=44 teeth, Z2=28 teeth
LK=0,157 x 420 + 44/2 + 28/2 + 2

LK = 108,94 which means 108 links

IMPORTANT:

The result is always rounded up or down to the next even number. This is due to the fact that one end of the chain has to have the opposite type of link to the that of the first link in order to allow the chain to be rejoined.

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Chain Cleaning

Particles already in the link can hardly be removed by any cleaning method (not even with ultrasonic waves). In order to prevent particles being transported into the link in the first place, the chain should be kept dry and clean on the outside by being wiped from time to time with an oily cloth. Additionally, sprockets, pulleys and chainrings should be kept clean as well because these parts are in direct contact with the rollers of the chain.

Only a very dirty chain should be cleaned intensively. We do not recommend any of the currently available chain cleaning devices because the liquids used normally have a very negative effect in the chain links. The links will not be free from particles after the application but the cleaning liquid will mix with the lubricant which in most cases destroys its lubricating feature. Therefore, before using a cleaning liquid, test it by mixing it with the lubricant you use.

We recommend cleaning liquids which do not have 100% degreasing effect, such as diesel or paraffin. Environmently more friendly are products based on modern washing-up liquids. They work quite well and can be easily washed out of the link with water.

Please make sure that the chain is lubricated correctly after an intensive cleaning!

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Chain Lubrication

A constant lubricating film in the link can improve the durability of the chain substantially. However, this is not easily achieved because the link movements are small while the pressures are very high which makes difficult sustaining the lubricant film.

Only special lubricants will be able to cope with the unique conditions to be found in the link of a chain. Firstly, the lubricant must be able to creep into the link and between the moving parts. Secondly, the lubricant must be able to withstand the high pressures in the link. A lubricant without this extremely important property will be displaced by the pressure with the effect that metal rubs on metal as if there were no lubricant at all.

Our tests have shown that most available lubricants do not fulfill these requirements. Most products do prevent rust and are better than no lubrication at all, but are not suitable for the hard conditions in the link of a chain. These lubes are in particular the popular silicon and teflon products, but also all very liquid oils. Unsuitable for correct lubrication are also all products which claim to have a cleaning and/or rust removing effects.

In order to give the user a secure alternative in terms of lubricating the chain, we have developed the automatic chain lubrication system Rohloff LUBMATIC and the biodegradable, pressure resistant Rohloff special chain lubricant Oil of Rohloff. This high performance lubricant creeps under water and has a stable viscosity over a wide temperature range.

For off road trips and riding in the cold period you can additionally protect your chain by using a wax spray. However, the wax does not lube your chain, therefore it should only be used after lubrication. The wax film reduces the amount of dirt sticking on the chain and partly protects the link against dirt and water. Please only use thick products which leave a noticeable white wax film.

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Technical Information about the Wear and the Replacement of Standard Chains 1/2" x 3/32"
Any chain becomes longer due to wear. Because of constructional reasons, this only effects the pitch of the pin link plate so that the pitch of the chain changes due to wear: the originally identical distances between the rollers change into the so called S-O-S pitch, long-short-long-short.

The stretching of the chain and the inhomogenous pitch result in increased wear of the sprockets and chainrings. In principle, one can use a chain as long as the chain does not spring. Normally, chains are replaced before that moment because a worn chain does not shift very well.

In case of relatively cheap sprockets and chain rings and normal riding conditions one can use the chain as long as it words well. If you replace the chain you then replace sprockets and chain rings as well.

If expensive sprockets and chain rings are used, the chain should be replaced before it starts to damage the sprockets and chain rings due to excessive wear. Furthermore, we recommend to use a Rohloff S-L-T 99 chain because it wears sprockets and chain rings less due to its constructional advantages.

How can you check when your chain should be replaced? The standard formula is that your chain should be replaced when it has been stretched more than 0,1mm per link. With the chain wear indicator Rohloff Caliber 2 you can check with one glance whether it is time to replace the chain by hooking it between the rollers of the chain. With two different gauges you can adjust your checking to the type of sprockets you use. If you use aluminium sprockets, you should replace the chain even before the stretching of 0,1mm per link. Problems of the power transmission are not always caused by the chain. Modern sprockets with low and thin teeth and mass production of low quality material are just two reasons, why sprockets can be damaged even before the chains in worn.

In order to check the wear of sprockets, Rohloff has developed the HG-IG-sprocket wear indicator Rohloff HG-IG-Check. Without a tool it is nearly impossible to spot the wear of HG and IG sprockets so that very often the sprockets are replaced with the chain. With the Rohloff HG-IG-Check it becomes possible to check the sprockets which gives a clear answer whether it is necessary to replace them or not. Therefore, this inexpensive tool should be found in all workshops.

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Efficiency measurement of bicycle transmission

1. Introduction

The power produced by the cyclist consists of a relatively constant speed and widely variable torque due to the crank kinematics. Measurements show that while there are at different power inputs speed variations of about 5% are typical, the torque variations can be over 90% throughout a single crank revolution. Table 4 shows the results at different power inputs.

table 2

The power characteristics are largely governed by the torque component.

figure 1

The cyclical torque of a cyclist produces an alternating load situation on all power transmitting parts, chainlinks, chainrings, bearings, gears, etc, which is very important to keep in mind when evaluating the mechanical losses which effect the efficiency.

A precise simulation of the cyclical torque is not easy to produce in the laboratory and from measuring point of view excessively costly. For this reason, when measuring mechanical efficiency electric motors with a constant power input are used. This brings up the question of how to choose the appropriate power input when using a constant torque so that the efficiency measurement correlates to the efficiency that would be measured with the cyclical load actually applied in the real world. We encountered a similar problem when designing our chain and chainring wear test, which is operated at constant torque. Extensive comparison between components used in real world and components worn out on the test bench show the following: If the field tested components were used at an average of 150W with an average cyclic torque between 5Nm and 30Nm, this correlated to a chain tested at a constant torque of 30Nm in our laboratory.

It can be assumed that the reasons that cause the wear of components are the same ones that are responsible for the efficiency. Therefore you can deduce from the comparisons that a in a lab test, a constant power input using the maximum value of the cyclic load produces results that are closer to reality than choosing a constant power input using the average load.

For example, an average cycling power 80W in real life should be simulated by a test bench power of 160W at the same speed.


2. Interpretation of the measurements

In order to give a correct interpretation of the results it is important to establish what the losses are composed of.

Losses are created by friction. The value is determined by the type of friction (rolling or sliding), the size of surfaces in contact, type of surface finish, material hardness, lubrication, combination of the rubbing parts. Two separate types of losses exist in bicycle transmissions:

a) Power dependent losses. These are created by friction of parts that are moving under a driving load, i.e. chainlinks, gears, bearings, etc. The quantity of the loss grows proportional to the transmitted power.

b) Power independent losses. These losses are created by friction of moving parts and are not changed by the driving load, in other words these losses are constant regardless of the load applied, i.e. gaskets, shims, lubricants, the quantity of loss depends on speed, temperature, and lubricant viscosity.

In the following example, two bicycle transmission systems are compared. Both have a 91% efficiency at 50W input. They have two different power dependent and power independent losses.

System A

table 3

In system A, seven percent of the input power is lost due to power dependent friction plus one Watt of power independent friction for each value of input power. The values shown in Table 5 are input powers from 50W to 500W with their respective efficiency ranging from 91%-92.8%.

System B

table 4

In system B, only three percent of the input power is lost due to power dependent friction that exists in the chain, gears, etc. An additional 3W of power are lost due to power independent friction that exists due to tight and good sealing seals.

At 50W power input the efficiency of system B is at 91%, the same as system A. At higher power inputs, the overall efficiency increases until it reaches 96.4% the efficiency is significantly higher than the efficiency of system A. This is due to the fact that the power dependent losses become dominant over the power independent losses at higher power inputs.

figure2

In addition to curves for systems A and B, Figure 2 also shows curves for systems C and D. The curve for system C describes how the power independent losses increase from one to two Watts due to temperature or lubricating film changes at the seal of system A. The curve for system D describes the efficiency changes of system B with a reduction from three to two Watts of the power independent loss for the same reason. The examples show that for power input of less than 200W that even small changes of +/- 1W of power independent losses play a large role in the overall efficiency. Since power independent losses are the result of a complex relationship between speed changes, temperature changes (created by own friction heating), and lubrication. These variations can occur in the test situation. If power input is less than 200W, it must be confirmed that the influence of those variations are verified by repeated tests. Over 200W the influence of power independent losses can be neglected.

Knowing that, all measurement values shouldn t be absolute values, but rather represented as a range of values showing the corresponding upper and lower boundaries.

3. Reason for efficiency measurements

The reason for efficiency measurements is to find out which one of the different bicycle transmissions converts the most of the bicyclist s power into forward motion. To propel the rider forward in the most efficient manner, it is important that the rider be able to choose an appropriate gear for the given load or riding situation, a gear that is suitable to the rider s fitness level

The development of power in the muscles is subject to a grade of efficiency. This efficiency is the ratio of metabolic capacity and the delivered mechanical power, i.e. the power at the crank. The efficiency depends on the muscle power combined with the speed of movement, if both variables reach their optimum, the muscle efficiency can increase by 25%.

The differences in muscle efficiency between positive and negative fatigue ratios (bodily stress/developed power) can easily vary by 10%. This is of much larger value than the variation of mechanical efficiencies of various bicycle transmissions systems.

table 5

Rider A is using a perfect gear ratio for the situation and his muscle efficiency is 24%. His bicycle transmission is moving in a gear with relatively poor mechanical efficiency of 93%. Rider B is using an unfavorable gear with a high efficiency of 97%., however, because of the unfavorable speed, his muscles work at 22% efficiency. The overall efficiency shows taking into consideration muscle and transmission losses that rider A is riding more efficiently even though his transmission efficiency is lower than rider B s.

In order to use the rider as a bicycle engine most effectively, the ratio increments between the gears are as important as a good mechanical efficiency. The most efficient energy conversion is very limited using transmissions with only a few gears. A larger selection of gears with smaller increments make a favorable energy conversion possible in a wider range of riding situations, but only if the correct gear is used. Sport medical research shows that the increments between gears must be smaller than 15% to benefit the rider s efficiency.

Under this point of view it does not make sense to compare transmissions with only a few gears, large gaps, and small overall range, with transmissions with many gears, small increments, and a large range of gears. A comparison of different transmission systems should always take into consideration its application.


4. Conclusions

A) All measurements below 200W need to be evaluated cautiously because the influence of the variations of the power independent losses are very high.

B) From a practical point of view changes of efficiency play a major role only when riding above the recreational level i.e. greater than 100W. **Consider the influence of the cyclic torque curve on the efficiency test runs below 200W and at constant torque curve don t make sense from a practical point of view.

C) When comparing transmission systems range of gears and number of gears should be taken into consideration in addition to the efficiency. Only by doing that the practical effect can be described.


5. Rohloff measurement results

1. We would like to point out that the points represented here should be a stimulus for a discussion since there are so many open questions in the field of practical efficiency measurements regarding bicycle transmission systems. As a comparison to Kyle and Berfo s results, our results in figure 3 and figure 4 show our efficiency measurements of a 24-speed derailleur system with 46-36-26 toothed chainrings and Shimano XT 11-28 toothed cassette, and the Rohloff SPEEDHUB 500/14 with a primary gearing of 46 tooth chainring and 16 tooth hub cog. Both systems had been broken in for 100km.

The measurements include the losses of the complete transmission, bottom bracket, chain, hubs, etc. In order to simulate a strong rider who applies about 160W and produces a maximum torque of 50Nm (285N @ pedal), the measurements were taken at a power of 314W with constant torque.

* Crank speed: 60min-1
* Brake power: (constant) 314W
* Torque: 50Nm


The reproducibility of the results and their precision was verified by repeated test runs. Figure 3 shows the efficiency of the derailleur system plotted vs. distance per crank revolution. Note the gear ratios are not consistently spaced as can be seen on the plot.

figure 5

Figure 5 shows the efficiency ranges of figures 3 and 4 on the same plot for comparison.

The efficiency of internally geared hubs drops when the number of working planetary sets increases. This fact must be shown in the efficiency results of the gear hubs tested. In the SPEEDHUB 500/14 there are three planetary gear sets that can be used in series. The unique gear ratios are created by engaging different combinations gears within these planetary sets. Table 9 shows the number of the active (working) planetary gear sets per gear.

Active gearsets in the Rohloff SPEEDHUB 500/14 for each gear

table 6

figure 6

Figure 6 shows the range of efficiency of the SPEEDHUB 500/14 plotted vs. gear number. The efficiency plots confirms the number of the active planetary sets as represented in Table 9. Gear 11 has the highest efficiency because it is the direct drive gear, no planetary gearsets are activated. The curve between gears 1 and 7 corresponds with the curve between gears 8 and 14. This is due to the fact that the first two planetary gear sets are shifted between gears 1 and 7 in the same way as they are between gears 8 and 14, however gears 1 to 7 have an extra planetary gearset activated providing a compound low gear. The efficiency between gears 1 and 7 is about 2% lower due to the use of the third planetary gear set. In order to show this fact more clearly the curve between gears 8 and 14 has been copied and shifted to the left so that it can be compared with the curve representing the efficiencies of gears 1 to 7. The results correspond to the gear combination or respectively to the number of active planetary gears inside the hub.


6. Conclusion

The explanations show that efficiency of bicycle transmissions depends on many factors whose research may require prohibitive cost. In order to measure real-life values, factors such as contamination, lubrication, wear, and production tolerances should be included as well as sports medical research. We think that there is still a lot of room for tests and discussions.

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© by Rohloff AG -- Technical specification are subject to changes without notice.