Mini choppers are scaled-down versions of custom-built motorcycles known as choppers

Chopper (motorcycle)

A chopper is a type of motorcycle that was either modified from an original motorcycle design or built from scratch to have a hand-crafted appearance. The main features of a chopper that make it stand out are its longer frame design accompanied by a stretch front end...

 and are generally constructed from 1" steel tubing or 3/4" steel black pipe. The tube or pipe is bent and then welded together to get the desired angles and shapes of the frame, which is usually custom made.

Engines and Transmission

Mini choppers use a variety of engines although the most typical would be a Briggs & Stratton

Briggs & Stratton

Briggs & Stratton is the world's largest manufacturer of air-cooled gasoline engines primarily for outdoor power equipment. Current production averages 11 million engines per year.-History:...

 or Tecumseh horizontal shaft industrial engine with a non-tapered shaft. Other engines include small motorcycle engines and power sport engines such as ATV and dirt bike engines. If an industrial engine is used,some sort of transmission also needs to be used to apply power to the rear wheel. Centrifugal clutch

Centrifugal clutch

A centrifugal clutch is a clutch that uses centrifugal force to connect two concentric shafts, with the driving shaft nested inside the driven shaft....

es, which allow the engine to idle without moving the chopper, are also used however they result in a fixed 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...

 for both low and higher speed operation. However, some people opt to make a jackshaft

Jackshaft

A jackshaft is a device for turning the wheels of a locomotive. It is essentially an axle with no wheels. Each end of the jackshaft has a crank pin and a counterweight. The driving wheels are then connected by side rods. The name may come from a combination of "jack," a slang term for a locomotive,...

, which allows the builder to change the gear ratio to his liking or to change which side the axle sprocket is on.
There is also a transmission called a torque converter

Torque converter

In modern usage, a torque converter is generally a type of hydrodynamic fluid coupling that is used to transfer rotating power from a prime mover, such as an internal combustion engine or electric motor, to a rotating driven load...

, or CVT (Continuously Variable Transmission

Continuously variable transmission

A continuously variable transmission is a transmission that can change steplessly through an infinite number of effective gear ratios between maximum and minimum values. This contrasts with other mechanical transmissions that offer a fixed number of gear ratios...

). The torque converter is essentially an automatic transmission

Automatic transmission

An automatic transmission is one type of motor vehicle transmission that can automatically change gear ratios as the vehicle moves, freeing the driver from having to shift gears manually...

 that changes gear ratios according to the speed of the engine. When the engine is at low RPMs, the gear ratio is at 1:x, depending on the ratio the torque converter has (This allows for more lower end torque). As the speed rises, the gear ratio changes to 1:1. As the higher end RPMs are reached, the gear ratio reaches X:1, which allows for a higher top speed.

Wheels

Mini choppers often use bicycle

Bicycle

A bicycle, also known as a bike, pushbike or cycle, is a human-powered, pedal-driven, single-track vehicle, having two wheels attached to a frame, one behind the other. A person who rides a bicycle is called a cyclist, or bicyclist....

 or moped

Moped

Mopeds are a type of low-powered motorcycle designed to provide economical and relatively safe transport with minimal licensing requirements.Mopeds were once all equipped with bicycle-like pedals , but moped has been increasingly applied by governments to vehicles without pedals, based on their...

 rims and tires on front and large pneumatic tires in the rear. Commonly golf cart wheels or 205/50-10 style tires are used in the back. The rear also needs something to let the wheel spin,and that's where that axle comes in. There are two different types of axle setups used, a live and a dead axle.

Axles

A live axle

Live axle

A live axle, sometimes called a solid axle, is a type of beam axle suspension system that uses the driveshafts that transmit power to the wheels to connect the wheels laterally so that they move together as a unit....

 is probably the most common axle setup used on mini choppers. The "live" term indicates that the axle spins along with the wheel, 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...

, and other pieces anchored to the axle. Since the axle spins, bearings are mounted to the swing arm frame. This is a very simple axle setup, and components are relatively easy to change. Each piece, such as wheel hub, disc brake rotor, sprocket, etc, are slid onto the axle and are held in place by set screw

Set screw

A set screw is a type of screw generally used to secure an object within or against another object. The most common examples are securing a pulley or gear to a shaft. Set screws are most often headless , meaning that the screw is fully threaded and has no head projecting past the major diameter of...

s or locking collars. The components can also be separated by bushings that are cut to the desired length. Since the axle spins, the wheel, brake, and sprocket components must be locked to the axle. This is accomplished by using a square key that fits into a groove on the axle and the components.

A dead axle (or hub and bearings) is much less common than the live axle setup used on most mini choppers. As opposed to a "live" axle, where the axle spins along with the wheel, this axle does not spin. The wheel or hub has built-in bearings

Bearing (mechanical)

A bearing is a device to allow constrained relative motion between two or more parts, typically rotation or linear movement. Bearings may be classified broadly according to the motions they allow and according to their principle of operation as well as by the directions of applied loads they can...

 to allow it to spin. Depending on the setup, all spinning components are attached to the hub or to the rim itself. The bearings and hub spin on the axle. This is the type of setup that is used on most motorcycles. Often, the axle is inserted into slotted dropouts

Dropout (bicycle part)

A bicycle dropout is a type of fork end that allows the rear wheel to be removed without first derailing the chain. The more inclusive term fork end refers to a slot in a frame or fork where the axle of the wheel is attached....

 and the chain is adjusted by moving the wheel forward or backward within the slots. This allows the engine to be mounted which makes the bike's drive train much more rigid and reliable. There are also other advantages to this type of axle, including the possibility of a cleaner and more attractive rear axle area, but this setup is often more expensive than a live axle and custom parts are much more difficult to locate.

Custom Parts

Custom parts are what make choppers art, whether it's coming up with a new frame design or thinking out of the box and using a car rim for the rear. Many builders build their own gas tanks that are similar to full-size motorcycle gas tanks, but scaled down to fit the bikes. Sheet metal

Sheet metal

Sheet metal is simply metal formed into thin and flat pieces. It is one of the fundamental forms used in metalworking, and can be cut and bent into a variety of different shapes. Countless everyday objects are constructed of the material...

 parts such as laser cut

Laser cutting

Laser cutting is a technology that uses a laser to cut materials, and is typically used for industrial manufacturing applications, but is also starting to be used by schools, small businesses and hobbyists. Laser cutting works by directing the output of a high-power laser, by computer, at the...

gussets are also used as accent pieces on the bike. The desire is to produce an individualized piece of mechanical art.