Modern bobsled races are competitions between two-person or four-person teams. Bobsleds have the same basic components whether they are built to hold two or four athletes. Each bob has:
- A steel frame
- A fiberglass hull that's closed in the front and open in the back, also called a cowling
- A movable set of front runners
- A fixed set of rear runners
- Collapsible push-bars for driver and crewmen
- Fixed push-bars for brakemen
- A jagged metal brake on a lever, used only after the bob crosses the finish line
- A steering system
The International Bobsleigh & Skeleton Federation (IBSF) sets rules for the composition and dimensions of each of these components, as well as the total weight of bobsleds. Bobsled manufacturers work closely with bobsled teams and designers to make the best sled design.
Each type of bob has a minimum weight when empty and a maximum weight with bobsledders and their equipment. Weight limits for bobsleds are:
- Two-man: minimum 384 pounds (170 kilograms) when empty, maximum 860 pounds (390 kilograms) with crew and equipment.
- Two-woman: minimum 284 pounds (129 kilograms) when empty, maximum 715 pounds (325 kilograms) with crew and equipment
- Four-man: minimum 463 pounds (210 kilograms) when empty, maximum 1,390 pounds (630 kilograms) with crew and equipment [source: IBSF].
Heavier sleds go faster, so teams that do not reach the maximum occupied weight may add ballasts to make their bob heavier. Officials weigh the sleds at the end of the run to make sure they meet the weight requirement. The hull, which is also known as a cowling, is constructed of fiberglass. It is closed in the front and open in the back so bobsledders can hop in and out. The hull cannot be transparent or so flimsy that it breaks apart in crashes. Hulls are typically made in two pieces, but steering comes from the front runners, not from movement in the hull [source: IBSF].
The steel runners themselves are blunt. They're polished until very smooth, minimizing the friction between them and the ice. Since narrow runners further reduce friction and are faster, the IBSF has rules covering runner width. Applying plating, coating or lubricant to the runners is illegal, as is heating them. Race officials electronically measure the temperature of the runners before the race and compare it to a reference runner that has been exposed to air for at least an hour. A temperature difference of more than 4 degrees Celsius (7 degrees Fahrenheit) between the bob's runner and the reference runner results in disqualification [source: IBSF].
Until the 1960s, bobsledders used a steering wheel to steer the bob. Now, drivers use a steering mechanism that consists of two pieces of rope attached to a steering bolt that turns the front frame of the bobsled. The driver can pull on the rope with his or her right hand to steer the sled to the right, and with the left hand to steer to the left. The brake, located at the end of a lever between the brakeman's knees, stays in place until after the bob crosses the finish line [source: IBSF].
Next, we'll look at how the athletes use the steering rings, handles and other parts of the bobsled when racing.