Micro drive is a type of bicycle drivetrain, mostly

BMX BMX, an abbreviation for bicycle motocross or bike motocross, is a cycle sport performed on BMX bikes, either in competitive BMX racing or freestyle BMX, or else in general street or off-road recreation. History BMX began during the earl ...

and MTB, that uses smaller than standard-sized

sprocket A sprocket, sprocket-wheel or chainwheel is a profiled wheel with teeth that mesh with a chain, track or other perforated or indented material. The name 'sprocket' applies generally to any wheel upon which radial projections engage a chain pass ...

s. The smallest rear

that fits on a

freehub A freehub is a type of bicycle hub that incorporates a ratcheting mechanism. A set of sprockets (called a " cassette") is mounted onto a splined shaft of the freehub to engage the chain. The ratcheting mechanism is a part of the hub, in contr ...

body is an 10-tooth, but with the use of a cassette hub, sometimes called a micro drive rear hub, sprockets as small as 8 teeth may be used. The advantage of micro drive is that it means a smaller front sprocket, or

chainring The crankset (in the US) or chainset (in the UK), is the component of a bicycle drivetrain that converts the reciprocating motion of the rider's legs into rotational motion used to drive the chain or belt, which in turn drives the rear wheel. ...

, can be used without affecting the

gear ratio A gear train is a mechanical system formed by mounting gears on a frame so the teeth of the gears engage. Gear teeth are designed to ensure the pitch circles of engaging gears roll on each other without slipping, providing a smooth transmission ...

, providing better ground clearance. For example, a bike using a 32-tooth chainring with a 16-tooth rear sprocket can switch to using an 18-tooth chainring and a 9-tooth sprocket, and still have a 2:1 ratio. Another advantage is the reduction in weight with the reduction in size of all the parts. The disadvantage is increased stresses on the drive train, leading to increased wear and even premature failure. As the front and rear sprockets become smaller, the tension in the

Chain A chain is a wikt:series#Noun, serial assembly of connected pieces, called links, typically made of metal, with an overall character similar to that of a rope in that it is flexible and curved in compression (physics), compression but line (g ...

increases, and

stretching Stretching is a form of physical exercise in which a specific muscle or tendon (or muscle group) is deliberately flexed or stretched in order to improve the muscle's felt elasticity and achieve comfortable muscle tone. The result is a feelin ...

and breaking can occur more easily. Designers can overcome these issues by choosing materials with higher

yield strength In materials science and engineering, the yield point is the point on a stress-strain curve that indicates the limit of Elasticity (physics), elastic behavior and the beginning of Plasticity (physics), plastic behavior. Below the yield point, ...

s, however usually at higher costs.

References

{{DEFAULTSORT:Micro Drive Bicycle drivetrains