Micro drive
Encyclopedia
Micro drive is a term used to describe the drivetrain
, mostly BMX
and MTB
, that use smaller than standard sized cogs
. The smallest rear sprocket
that fits on a freehub
body is an 11-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, can be used without affecting the gear ratio
, providing better ground clearance. For example, a bike using a 32t chainring with a 16t rear sprocket can change to a 18t chainring and a 9t sprocket, keeping the 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. Chain stretching and breaking can occur more easily. As the front and rear sprockets become smaller, the drive tension in the chain increases. Designers can overcome these issues by choosing materials with higher yield strengths, however usually at higher costs.
Bicycle drivetrain systems
Bicycle drivetrain systems are used to transmit power on bicycles, tricycles, quadracycles, unicycles, or other human-powered vehicles from the riders to the drive wheels. Most also include some type of a mechanism to convert speed and torque via gear ratios....
, mostly BMX
BMX
Bicycle motocross or BMX refers to the sport in which the main goal is extreme racing on bicycles in motocross style on tracks with inline start and expressive obstacles, and it is also the term that refers to the bicycle itself that is designed for dirt and motocross cycling.- History :BMX started...
and MTB
Mountain bike
A mountain bike or mountain bicycle is a bicycle created for off-road cycling. This activity includes traversing of rocks and washouts, and steep declines,...
, that use smaller than standard sized cogs
Gear
A gear is a rotating machine part having cut teeth, or cogs, which mesh with another toothed part in order to transmit torque. Two or more gears working in tandem are called a transmission and can produce a mechanical advantage through a gear ratio and thus may be considered a simple machine....
. The smallest rear sprocket
Sprocket
A sprocket or sprocket-wheel is a profiled wheel with teeth, cogs, or even sprockets that mesh with a chain, track or other perforated or indented material. The name 'sprocket' applies generally to any wheel upon which are radial projections that engage a chain passing over it...
that fits on a freehub
Freehub
A freehub is a type of bicycle hub that incorporates a ratcheting mechanism, and the name freehub is a registered trademark of Shimano. A set of sprockets are mounted onto a splined shaft of the freehub to engage the chain...
body is an 11-tooth, but with the use of a cassette hub, sometimes called a micro drive rear hub
Hub gear
A hub gear, internal-gear hub, or just gear hub is a gear ratio changing system commonly used on bicycles that is implemented with planetary or epicyclic gears. The gears and lubricants are sealed within the hub-shell of the bicycle's rear wheel, as opposed to derailleur gears, where the gears and...
, sprockets as small as 8 teeth may be used.
The advantage of micro drive is that it means a smaller front sprocket, or chainring, can be used without affecting the gear ratio
Gear ratio
The gear ratio of a gear train is the ratio of the angular velocity of the input gear to the angular velocity of the output gear, also known as the speed ratio of the gear train. The gear ratio can be computed directly from the numbers of teeth of the various gears that engage to form the gear...
, providing better ground clearance. For example, a bike using a 32t chainring with a 16t rear sprocket can change to a 18t chainring and a 9t sprocket, keeping the 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. Chain stretching and breaking can occur more easily. As the front and rear sprockets become smaller, the drive tension in the chain increases. Designers can overcome these issues by choosing materials with higher yield strengths, however usually at higher costs.