How Choppers Work

Chopper Transmissions

This motorcycle’s transmission connects to the rear wheel with a belt drive system.

In a similar vein, chopper transmissions need to be flashy as well. Many companies sell transmissions designed to match specific engines. Transmissions sit behind the engine and come in four-, five- and six-speed varieties. Most modern choppers use either five- or six-speed transmissions -- only older choppers or bikes designed to look like vintage models use a four-speed transmission.

Most companies design frames to hold a particular kind of transmission, though many companies sell special cases that give you more choices. For example, you might need a special transmission case to mount a five-speed transmission on a frame that normally would carry a four-speed transmission. The case mounts to the frame, and you mount the transmission to the case. Otherwise, the transmission and frame wouldn't match up, and you'd be stuck with a bike and a transmission that don't fit together.



The transmission powers the drive system for the chopper, which is either a chain system or a belt system. Chains and belts connect one side of the drive system, the transmission, to the other side, the rear tire. Transmissions only provide power to the rear tire; the front wheels aren't powered. A small sprocket in the drive system turns the chain or belt at the transmission end, which then turns a larger sprocket at the tire end, making the tire move. Most choppers use an open primary system, meaning the belt or chain isn't covered by housing or casing -- it's left out in the open for all to admire. It also means that you need to pay attention when riding one because you don't want to get caught in the chopper's drive system.

A recent trend in chopper design is to use wide tires in the rear. In order to provide power to a wheel with a wide tire, builders have to offset the transmission to one side, particularly if it's a belt system. Without offsetting the transmission, the belt would not have enough clearance from the rear tire. By offsetting the transmission, a builder can make sure there's plenty of clearance. Unfortunately, offsetting the transmission too much can hurt a bike's stability and, perhaps worse in the eyes of a chopper designer, make it look less impressive.

In the next section, we'll look at the other components of a chopper and how they set these bikes apart from other motorcycles.