The farther forward (closer to front wheel) the center of mass of the combined bike and rider, the less the front wheel has to move laterally in order to maintain balance. Conversely, the further back (closer to the rear wheel) the center of mass is located, the more front wheel lateral movement or bike forward motion will be required to regain balance. This can be noticeable on long-wheelbase recumbents and choppers. It can also be an issue for touring bikes with a heavy load of gear over or even behind the rear wheel.[31] Mass over the rear wheel can be more easily controlled if it is lower than mass over the front wheel.[11] A bike is also an example of an inverted pendulum. Just as a broomstick is easier to balance than a pencil, a tall bike (with a high center of mass) can be easier to balance when ridden than a low one because its lean rate will be slower.[32] However, a rider can have the opposite impression of a bike when it is stationary. A top-heavy bike can require more effort to keep upright, when stopped in traffic for example, than a bike which is just as tall but with a lower center of mass. This is an example of a vertical second-class lever. A small force at the end of the lever, the seat or handlebars at the top of the bike, more easily moves a large mass if the mass is closer to the fulcrum, where the tires touch the ground. This is why touring cyclists are advised to carry loads low on a bike, and panniers hang down on either side of front and rear racks. While the term "chopper" is generally used to descri e a motorcycle or bicycle that has had some of its original parts replaced with custom parts, today's definition has grown to include custom motorcycles and bicycles that are low to the ground, usually with extended forks creating a long front end. Even as commercial interests are taking note of the popularity of choppers and expanding their lines,[1] most riders of choppers have hand built choppers and encourage others to make their own.[2] Arguably, a bought 'chopper' is not a 'chopper' at all, because no chopping was done—only a commercial transaction.[3] There are various cycling groups and clubs around the world that feature chopper bicycle riders such as the Choppercabras, Chopaderos, Freakbike Militia, SCUL, and C.h.u.n.k. 666, . Such groups encourage all chopper bicycle riders to join them on rides celebrating different events and holidays. Because the frame of a chopper bicycle and a chopper motorcycle can be strikingly similar, and of a high enough quality/durability, it is relatively common to have an empty space, or 'engine bay', in the frame, in which a motor can be inserted into the frame at a later date, among other tweaks and conversions. Depending on the quality of strength of the frame, and the engines size and output, this can result in blurring between the classifications of bicycle, moped, and/ or motorcycle. Legal laws and statutes may vary in your local state or territory. The designer who created the revolutionary Raleigh Chopper bicycle, which became a symbol of the 1970s, has died of cancer aged 85.