Autos

According to the National Automobile Dealers Association (NADA), there are approximately 20,000 new car dealerships in the United States. These automobile dealerships employed more than one million people and together generated $576 billion in sales in 2008. That means that car dealerships accounted for approximately 14.6 percent of all retail sales in the United States for the calendar year.

New car dealers generate income through not only new car sales, but also through used car sales, vehicle service, financing and the sale of add-on products and services. In the United States and Canada, a new car dealership is generally a franchise, that is they usually sell only one manufacturer's products. Used car dealerships, conversely, may carry vehicles representing a variety of different manufacturers. Because of consolidation in the industry, however, it is not uncommon today for one owner to operate a chain of new car dealerships in a given area, representing several different manufacturers.

Dealerships generally consist of a showroom and a car lot, where inventory is displayed for sale. Often a new car dealership will also include service bays where they may perform maintenance and repairs on vehicles. Dealerships may also include a parts department where replacement and aftermarket items may be purchased.

In the United States, federal law requires that all new cars display a window sticker that lists the manufacturer's suggested retail price (MSRP)....

A helmet is a type of protective headgear used to shield the head from injury. Helmets are used in certain occupations and recreational activities that may put an individual at risk from falling objects or impact. Helmets are used by soldiers, construction workers and firefighters as well as in sports like football, hockey and baseball. Helmets are also used by race car drivers and motorcycle riders. Helmets can prevent or reduce head injuries, and may even save a rider's life.

It is believed that the first riding helmet was developed following a motorcycle crash that claimed the life of T. E. Lawrence – a.k.a. Lawrence of Arabia. Hugh Cairns was one of the doctors who treated Lawrence following his accident. He conducted a thorough study of motorcycle accident fatalities which led to the use of crash helmets by both military and civilian motorcyclists. Helmets have been found to greatly reduce injuries and fatalities in motorcycle accidents.

Because of this, many countries and most U.S. states have laws requiring helmet use while riding motorcycles and even while riding bicycles in many instances. Check with your local motor vehicle authority to see what type of helmet your state requires, if any.

Early motorcycle and auto racing helmets were little more than thinly-padded strips of leather. They didn't offer much protection in severe impacts. As our interest in safety has increased, helmets have evolved. Modern helmets provide considerable...

In the early 1930s, the Galvin brothers developed the first car radio. It was revolutionary, and cost the equivalent of $1,700 in today's dollars. Their company would later come to be known as Motorola, one of the leading manufacturers of auto stereo systems today. Decades later, auto stereo systems with tape players, cassette decks and 8-track machines would let us take our tunes on the road. Compact disc players came later, but we doubt the Galvins could have imagined the extent of auto stereo systems today.

The latest auto stereo systems can play DVDs packed with hours of music, and incorporate speakers by the dozen. Services like XM and Sirius beam hundreds of radio stations from satellites orbiting in outer space directly into our cars. Modern auto stereo systems have grown to incorporate video screens, gaming consoles and navigation systems. They can listen to voice commands, interact with iPods and MP3 players and even store music in computer hard drives.

As extensive as the options lists for auto stereo systems have become, the obsession with the loudest and clearest sound has lead to an entire underground scene of enthusiasts. While some aftermarket tuners turn their cars into high-performance racing machines, others go the opposite route, investing thousands to transform their cars into mobile theaters.

Mobile audio enthusiasts pack their rides with amplifiers and even electric capacitors to power speakers ranging from 8 inches up to...

There are a lot of things you can do to modify your car. Aftermarket tuners offer everything from turbochargers and exhaust systems to aero kits and custom interiors. But the first step in automotive customization almost invariably comes down to one thing: rims.

The popularity of upgrading a car's wheels has grown into an industry unto itself. Every new year brings bigger, lighter, flashier and more expensive rims. But when replacing a car's wheels with new ones, bigger isn't always better, and less can often be more.

While popular culture refers to wheels as "rims", wheels actually have several components. The rim of a wheel forms its circumference and holds the tire in place, and is joined to the hub by spokes. Many modern wheels are forged from a single piece of metal, so the rims and spokes are actually one unit. Racing-style modular wheels have spokes and rims fabricated separately and bolted together.

Performance enthusiasts look for lightweight rims to help cut down on "unsprung mass" (the combined weight of the wheels, tires, suspension and brakes), improving a car's performance more than cutting weight elsewhere on a vehicle. The most basic rims are made of steel, but are heavier than premium wheels made of aluminum alloy (known as "alloys") or magnesium ("mags"). Exotic materials like carbon fiber, meanwhile, are more complicated to manufacture and therefor more expensive.

Although bigger...