Many manufacturers have begun to produce the chainrings with alternating tooth profiles. There are chainrings for any taste and color: red and blue, elegant and not very. Beautiful engraving is also a great thing (but this doesn't enhance the chainring's performance).

      How big is the difference between the models? When try to choose one, what should you pay attention to? Consider this problem from the technical point of view.There are a few fundamental differences between single chainrings and ordinary ones, to which we got accustomed for a long time. They are as follows:

 

- narrow/wide teeth;


- modified shape of a tooth profile;


- tooth height;

 

 

      Each item above directly ensures ultimate chain retention.

 

 

Wide tooth

      It seems, this item is more or less clear.

      Links of a chain have altering width. But ordinary chainrings have equal width for all teeth. If the chain engages by its narrow link, all goes well, if it engages by wide link, an extra degree of freedom appears due to appearing of a gap. Because of that during shaking and vibration a chain moves more freely from side to side and can easily drop off. The chainring with alternating tooth thickness restricts lateral movement of a chain and reduce the possibility of dropping off.

 

 

Tooth profile

      The teeth of the single chainring should hold a chain on the chainring without additional accessories (frames, chain guides etc.). This is a main feature of a single system. Standard teeth, compatible to GOST, ISO, or DIN, poorly conform to this task. They have very wide destination as they work on different mechanisms in very different conditions, besides at high speeds and loads. In order "general technical" chain gears become all-purpose, large geometric allowances are provided. Large allowances provide a clearance (gap) between a teeth and a chain. Gaps weaken the contact of the chainring with a chain and increase backlashes. This is not our way.

      Proper tooth profile should provide maximum contact between the chainring and a chain and repeat the trajectory of links' movement. However, there is a nuance. The tooth profile must have an allowance taking into account the chain wear, i. e. gradual lengthening of a chain.

      Variation appears. Design engineers have different imagination, experience and qualification and each manufacturer has solved this problem in their own way. For clarity Fig. 1 includes the exaggerated scheme for not very successful profile (A) and "right" profile (B) of a tooth. It is easy to understand that a chain can easier drop off more "sloping" tooth, than "steep" tooth.

      For unknown reasons some famous companies use almost standard teeth. There is some doubt that they firmly hold a chain (Fig. 2)

 

      Some manufacturers have changed the tooth, but use the same tooth height (Fig. 3)

 

 

Tooth height

      To our opinion, the height is the most important thing that distinguishes a reliable single chainring from ordinary one. Let us remember the functions of a chainring (besides power transmission). A chainring should properly receive the chain links (due to vibration they come to a chainring along a broken line), as well as quench the transverse oscillations of the chain. During shaking on each chainring only a few teeth engaged participate in this action.

      Fig. 4 shows the scheme of acting of the chainring 30T. The chainring with high tooth profile is shown on the right. The transverse oscillations of the chain are prevented by last three teeth. The first tooth has fully engaged, the second — almost completely (the chain cannot drop off it). The third tooth is just beginning to engage, but already holds the chain.

      Ordinary chainring (Fig. 4, left) holds the chain by only two teeth. First tooth has engaged. The second has engaged only by half and can "lose" a chain after heavy shock. The third tooth is just approaching to a chain. But the tooth doesn't hold it. So the reliability of such design is at least one third less.

      Some companies have ventured to abandon teeth Narrow Wide in favor of more or less ordinary, but high teeth. For example, Shimano and FSA used in prototypes of their single chainrings a high tooth with modified profile (Fig. 5). We tested this solution and tests hint that chainrings of this type operate in fact well and reliably. But tests are continuing so it is early to draw a conclusion for now. Perhaps, this will be a subject of the next article.

 

 

      For illustration in Fig. 6 the comparative diagram of tooth heights of different manufacturers is shown. These are our measurements, accuracy is +/- 0.1 mm.

 

Dust resistance

      Anyone who used Narrow Wide chainrings could notice that they easier get dirty than ordinary chainrings with narrow teeth. This is a true problem. The tighter the chain fits to a chainring, the better it is held by the latter. But tight seating prevents operation when there is adhesion of mud. So a compromise is needed.

 

 

 

      Sram goes to the heart of the issue in most deep way. The teeth on its prototypes near their "roots" have a form preventing mud from adhering and accumulation (Fig. 7).

 

 

      In fact, this innovation is not so great: Sram used a method for mud removal applying in motocross (Fig. 8). But one can notice, that Sram simplified the structure of serial samples depending on the model. Perhapse, this was done for lowing cost.

 

 

       Our tests have demonstrated, that for a good removal of mud it is requires wide mud clearance. On (Fig. 9, A) the classic recession of the chainring Narrow Wide is shown. Recession is equidistant from tooth’s outline. Due to such a design (Fig. 10) the mud cannot fall off and as a result it does not allow for the chain to "sit" on its place. The chain can drop off.

 

      The mud can be drained out in a proper way, when the recession outline goes below (Fig. 9, B). Clearance increases and the mud falls through the zone of engagement. The chamfer is more enhanced version of recession (Fig. 11, B; Fig. 12). In such a case the mud is much easier drawn aside and doesn't obstruct a chainring.

Fig 12 

      We encountered such niceties and nuances while designing of our chainrings. We tested, modified, altered, tested again, improved again... And decided to share obtained practical experience with you.

 

      Certainly, knowing all these nuances, we have implemented them in our chainrings. And every manufacturer proclaims its chainrings as the best. It is their duty, so to speak. Therefore, we can only say that we tried to make them such.

 

 

Sincerely yours, Garbaruk Team

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Garbaruk