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 Federation Internationale de Bobsledding et de Tobogganing (FIBT) 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 750 pounds (340 kilograms) with crew and equipment
- Four-man: minimum 463 pounds (210 kilograms) when empty, maximum 1,389 pounds (630 kilograms) with crew and equipment
Heavier sleds go faster, so teams that do not reach the maximum occupied weight may add ballast to make their bob heavier. Officials weigh the sleds at the end of the run to make sure they meet the weight requirement.
According to FIBT rules, bobsleds can have decorations and sponsor logos, much like race cars. The fiberglass hull cannot be transparent or fragile enough to break upon impact with part of the track. Hulls are typically made in two pieces, but steering comes from the front runners, not from movement in the hull.
The 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 FIBT 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 four degrees between the bob's runner and the reference runner results in disqualification.
Until the 1960s, bobsledders used a steering wheel to steer the bob. Now, drivers pull steering rings to change directions. These rings attach to a rope-and-pulley system that connect to the front runners, which can move about 3 inches (7.62 centimeters) to the left or right. The driver pulls the left ring to turn left and the right ring to pull right. 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.
Next, we'll look at how the athletes use the steering rings, handles and other parts of the bobsled when racing.