So it can bring your trip or race to a complete standstill, and you walk up the hills pushing your bike. It can also damage both frame and drive-train components.
And, surprisingly, it can occur with new equipment, and also in clean conditions. The reasons why are also clarified in this article.
Because it usually occurs unexpectedly during forceful pedalling, the chain can be permanently twisted, teeth can be damaged, and chain-stays of aluminium or carbon-fibre can also be damaged by the chain being wedged hard against them.
It occurs most frequently with small chain-rings (granny-rings) of triple-ring MOUNTAIN BIKES, but does also occur with larger rings, and on ROAD BIKES. There are two main forms of chain suck :
For a chain to disengage easily from a chain-ring :
Small chain-rings have high chain loads due to the pedal arm's high leverage ratio. They also have fewer teeth to carry the load ; thus each individual tooth carries a high load and there is a tendency for some load to be carried even by the bottom teeth. High tooth loading also leads to higher tooth wear. For these reasons, small granny-rings are more vulnerable to chain-suck than larger rings.
There are some obvious issues which can cause chain-suck such as damage to chain-rings, teeth, or the chain. Tight chain links caused by damage, or by poorly maintained chains packed with dried mud, can also cause chain-suck. Clearly, these problems can directly cause snagging of the chain. But common chain-suck detailed below is the most frequent, and can affect any bike without obvious cause.
When Tooth-Wear, and Low-Stretch (New) Chains, and High Friction (eg Mud) are present in various combinations, they cause the chain-ring's bottom teeth to be loaded or overloaded, and also resist disengagement of the chain. The chain does not have enough weight to disengage itself from the bottom teeth of the chain-ring in these circumstances, nor can the rear-derailleur spring provide enough tension after the chain starts being dragged up. The links are carried around and up the rear of the chain-ring under continuing load ...the chain sucks !!
So how does any chain load get transferred to the bottom teeth in the first place ?
Tooth wear results in hooking / indentation / pockets in the pressure faces of the teeth. This is the MAIN CAUSE of CHAIN-SUCK. Wear has two consequences both of which cause chain-suck to get worse, namely :
"Wear" can also cause burrs or ridges on the tooth sides and thickened teeth, particularly with softer chain-ring materials ; but despite popular belief this, in itself, does not normally cause chain-suck, although it might contribute to a much lesser degree. As already stated, it is "wear" to the tooth pressure faces which shapes them adversely, then allowing the following factors to initiate chain-suck.
A New (or low-stretch) chain has its contact against the tooth pressure-faces extended or transferred farther towards the bottom of the chain-ring. As a result chain load is increasingly transferred towards the bottom teeth where it increases both frictional and mechanical resistance to disengagement. And ....chain-suck becomes likely. By contrast, the links of more highly stretched chains mesh tightly with one or two upper teeth on the chain-ring, and their slack accumulates to move the rollers away from contact with the pressure-faces of both mid-height and bottom teeth; this may avoid chain-suck in the short term, but it overloads the upper teeth causing greater metal failure and abrasion, ultimately increasing the potential for chain-suck especially when a new chain is installed.
High friction occurs mainly when the chain gets muddy, or wet and gritty, but it can also occur with inadequate lubrication and dry dusty conditions. Frictional resistance to disengagement becomes increasingly activated as the chain loading on the bottom teeth increases, and also if there is an adverse friction angle due to tooth wear/indentation. Load gets transferred to the bottom teeth as described above. Loaded friction then binds the chain both internally at its rotating pins/bushings, and at the contact between its rollers and the tooth pressure-faces. Mud or grit can have an additional effect probably of lesser magnitude ; it can contribute both to decreasing the effective chain pitch and to directly elevating the chain rollers by packing, respectively into the internal spaces within the chain and between the rollers and tooth roots ; both these effects contribute to an adverse mismatch in pitch, and so increase the transfer of load to the bottom teeth. Not all muds are equal ; different mud, grit, sand, clay, etc, can have very different frictional characteristics and packing characteristics, so some will precipitate chain-suck readily while others may not cause problems. In all cases, it is the in-line loading and friction of the chain on tooth pressure-faces which is the main issue, NOT friction on tooth sides or wedging of mud/grit across teeth. Finally, cohesion/adhesion can be high for some clays if they remain stiff in consistency, but this is likely to be a rare situation insofar as it influences chain-suck ; wet splashed mud is usually soft.
Forceful pedalling on steeper gradients is usually the action which finally precipitates chain-suck. It should, perhaps, be called the CHAIN-SUCK-PYRAMID with high-pedalling-force bringing the underlying CHAIN-SUCK-TRIANGLE into play, namely tooth-wear, low-stretch-chain, and high-friction.
Extreme tooth wear combined with a low stretch chain can be enough for chain-suck to occur without raised friction. On the other hand, even with a much lesser degree of tooth wear, chain-suck can occur, provided that the low stretch chain is accompanied by high friction.
adverse rotational alignment of teeth on adjacent rings is more usually the MAIN CAUSE of 2-RING-Suck. This is an alternative source of mismatch in pitch between the chain links and the teeth of chain-rings. This time it is across chain-rings, instead of just on a single ring. It occurs when the distance between teeth on adjacent rings is not well matched to the length of transferring chain. In a manner similar to 1-ring suck, when the cross-over length of chain is shorter than the corresponding distance between dispatching and receiving teeth, then the pressure-face of the dispatching tooth (which leads in the pedalling cycle) never gets unloaded because the receiving tooth isn't able to take up the load and remove it from the dispatching tooth. The pressure-face of the dispatching tooth then remains overloaded until reaching the bottom of the ring where it needs to both disengage from the chain, and allow final dispatch of the chain to the receiving ring. Dispatch is difficult while loaded ; frictional & mechanical resistance to disengagement (ie mud/grit & tooth indentation/hooking) will worsen the problem if present ...and 2-ring suck becomes likely.
Tooth wear is the combination of two main contributors :
Abrasive wear by grit and mud, on the other hand, takes more time, even if tooth loading is high. Also, it does not cause tooth widening or side-burrs on its own (unless accompanied by indentation failure of softer tooth material). Instead the tooth face becomes eroded to the familiar shape of concave / hooked teeth. This hooking is also a key cause of chain-suck.
Material used for many chain-rings is not strong, hard, or tough enough for the smaller rings. Even special heat-treated alloys of aluminium, die-pressed powder-alloys, and many steels used for chain-rings are notoriously soft for the high stress environment of granny-ring teeth. Only special types of hard tough alloyed or stainless steel, or titanium, are really adequate for these small rings.
Manufacture of chain-rings by common die-stamping methods is inaccurate. This gives rise to increased stress concentrations where chain-rollers contact the teeth, and increases the opportunity for localised metal failure & wear, and indentations.
Total wear does not need to be very great for chain-suck to start when high friction circumstances are present ; the wear may be noticeable only as a slight steepening (or alternatively indentation) of the pressure faces of the teeth.
Chain-suck is also known to occur with new or almost new drive-trains, or components thereof. For 1-ring suck, the problem is usually caused by soft chain-ring material (and sometimes by manufacturer's errors not easily detected by the unaided eye). 2-ring suck can also occur when new where the rotational alignment of adjacent rings is poor (actually more common on new than worn rings).
Any of the above problems should be cause for rejecting components as manufacturer errors, with the components unsuitable for purpose, or faulty !
2-ring suck : follow these procedures and measures to achieve the same aim of unloading bottom teeth ; this time it is across chain-rings instead of a single ring.
Damaged components (teeth:bent, rings:bent, chain:twisted or tight-links) can cause chain-suck. Obviously, these must always be investigated first and resolved. Chain-suck itself can cause such damage - so even if other underlying causes are resolved, parts thus damaged must also be dealt with to prevent recurrence.
Other ways of avoiding chain-suck and even methods for alleviating it on-the-trail (eg filing tooth profiles), are also described in "the OVERALL picture".
Anti chain-suck plates in a wide variety of commercial and home-made designs claim to prevent the consequences of chain-suck. These plates can be effective when they work, but often don't work well, then causing worse damage to chain-stays than if they were absent - therefore not recommended as a general solution.
Extra spring tensioning devices for the rear derailleur, mostly of home-made design, are claimed to work but at the expense of more sluggish gear changes. For strong chain-suck conditions, high spring tension would be required which is not advisable for the sensitive mechanism of rear derailleurs.
Maintenance : Clean and Lube your chain regularly ; generally this will not alleviate chain-suck directly (see below), but it does help to prevent abrasive wear to teeth and chain over the longer term, which helps indirectly. Not to mention preventing sonic ear pain. Replace your chain at or before the stretch limit ; this will prevent undue wear to the chain-rings (causing chain-suck), and to the rear sprockets.
Manufacturers make untenable claims about their lubricants' abilities in the presence of mud. Actual field testing and the slightest understanding of both the flow dynamics and the scouring abilities of a mud slurry within a chain's interior, debunk such claims for any of the lubricants commonly used. In fact, a good way to clean a chain really thoroughly is to go for a muddy ride and head for all mud and water puddles ; thereafter use detergent and a hose ; the chain will be clean and free of lubricant both inside and out ; even the old caked gunk will be gone.
Chain-rings must have both design and materials which are suitable for resisting wear and providing a long component life free of chain-suck, even at those times when lubrication is absent and mud scours everything.
Even without mud, lubrication will not necessarily prevent chain-suck. This depends on how badly the teeth are worn, and whether they are subject to the additional resistance to disengagement arising from a new unstretched chain.
Cleaning and lubrication always remain essential to reduce tooth and chain wear.
Cross-country racers or those planning long rides with mud should weigh the modest cost of a suitable new chain-ring against the risk of having their ride spoiled by chain-suck.
|For the related articles, follow the links below ...|
|Chain-Suck : in a NUTSHELL ...comprehensive summary and solutions|
|Chain-Suck : the OVERALL picture ...details of mechanisms & solutions|
|Chain-Suck : the DETAILED Investigations ...field & workshop testing|
|Chain-Suck : the FIELD TEST ...a field testing method for identifying causes|
|Chain-Suck : Restoring Worn Tooth Pressure-Faces ...by filing them|
|Chain-Stretch : Norms and Measurement ...when to get rid of your chain|
|LINKS ...to other interesting websites|
|LINK to YOUR SITE ...how to place a link from your website to this site|
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