Chain Tensioners

... Or wheel positioners. It really depends on your purpose for putting them on. You may want them to maintain a consistent chain tension, like my tail-whip fiending friend, so the pedals will stay in position when your feet leave them. Or perhaps your wheel moves on you when you don't have it slammed in the dropouts, but slammed, the chain is too loose. A positioner will allow you to give extra support to prevent the wheel from moving. This post will analyze the various types of possitioners available and weigh their pros and cons against one another.


Pull-Type
The original tensioner design consists of a washer around the axle, with either a stud and nut, or bolt. The bolt/nut tightens against a plate on the end of the dropout
Some pull-type tensioners have issues with shorter dropouts. But as of late, slimmed down designs (such as the Poverty Short Stop shown above) have almost done away with that problem.

A variation on the design is the Premium SS Tesnioner, which uses the bolt to push directly against the dropout. With the proper bolt size, this tensioner can work with any size dropout. Unfortunately with only a bolt in contact with the curved end of the dropout, it can move around pretty easily.


Push-type
These tensioners have appeared in recent years in two variations:

1. Integrated tensioners into the dropout use a set screw or bolt through the dropout to push the wheel back and into possition. The pressure on the axle threads may compact them slightly. This may cause some issues on hubs with threaded collars, and may allow the wheel to slip forward slightly as the threads compact. (ex: Sunday wave dropouts)



2. Bolt-on tensioners use a bolt-on tab similar to gyro tabs and cable guides. They push on the hub collar rather than the axle itself. In some cases there can be interference with the chain and/or driver. (ex: Fly Tierra)



Spacer type
In the past, riders have jammed various items between their axle and dropout to allow their wheel to be "slammed". I used aluminum cable ends crushed down and carefully inserted, but they would continue to compact, and were difficult to work with. Simple BMX has come out with specially cut spacers in 0.1mm variations. With the availability of half-links (albeit current designs are rather flawed in that they stretch easily), a wheel only needs up to 13mm of adjustment as the chain is 12.7mm pin-to-pin. Unfortunately there are reports of these compacting down (or more likely compacting into the threads of the axle)





Drive vs. Non-drive
With the chain on the drive side, tensioners only need to work in one direction (the chain works in the other). As such, tensioners have been designed to work only moving the wheel out of the dropouts. The problem arises when working with the non-drive side, especially with pegs. When a load is taken pushing the drive side axle out of the dropouts (such as an ice pick or tail tap), the tensioner does not support the wheel, and thus it can move out of position. To fix this problem, we may want to start looking into a hybrid push-pull tensioner. I have done some work integrating this into a hub collar and/or guard. I'll post up more info when I get some prototypes done...