Bobsleigh is auto-racing on ice - fibreglass and steel vehicles fueled by muscle and gravity whip around ice-covered concrete tracks, reaching speeds in excess of 150km/h.
It's a discipline in which every hundredth of a second is crucial and difficult to shave off, even with the wide array of variables in equipment and track conditions.
Men's and women's Olympic bobsleigh events are made up of two runs per day for a total of four heats each in both the two-man and four-man divisions.
In each discipline, the lowest combined time over all the runs wins. In the event of a tie, both teams are awarded the same position. That seems an unlikely scenario after four runs, but that was exactly the case at the 1998 Nagano Games, when Canada and Italy split the two-man gold.
Teams must cross the finish line with their sled in all of their runs to remain in the competition.
The track
There are only 14 bobsleigh tracks in the world approved by the Federation Internationale de Bobsledding et de Toboganning (FIBT), bobsleigh's international governing organization.
Courses are standardized and must meet strict FIBT criteria for elements like width, length, the number and types of turns, and ice conditions.
However, not all tracks are cut from the same mould.
Newer courses, such as the 2006 Cesana Pariol in Torino, are designed for all three sliding sports - bobsleigh, luge and skeleton. These modern tracks are often much shorter, have fewer turns and are not as abrupt as some of the older European tracks originally built for bobsleigh events. Weather plays a major role in track conditions.
Courses often deteriorate as the competition goes on, depending on the humidity, temperature and precipitation. Dry air has a tendency to crack the track sooner, which can degrade track quality and add perilous fractions of a second to a crew's run.
Heavy snow and frosty ice can also cut into the speed generated in the start.
Dave MacEachern, CBC analyst and 1998 Olympic gold medallist, likens the track condition at the end of the event to the patchy, shredded ice at the end of the third period of a hockey game.
The sled - auto racing technology hits the ice
Technology is vital in bobsleigh. Inferior equipment can nullify the skills of the best pilot or pusher.
Top bobsleigh countries like the United States, Switzerland and Germany are dabbling in applying Formula One and NASCAR auto racing technology to the sleds. This type of experimentation is expensive, and not every national bobsleigh program can afford it.
A bobsleigh is one of the priciest pieces of Olympic sporting equipment, with top-flight fibreglass and steel constructions costing over $50,000 to build.
There are maximum weighting regulations to ensure that all sleds and crews are the same weight, since a heavier sled will pick more speed down a track.
The top sled weight in women's bobsleigh, crew and equipment combined, is 340kg. On the men's side, two-man teams and sleds are a maximum of 390kg, while the combined limit in four-man is 630kg.
Lighter crews are allowed to place ballasts, also called weight bars, in their sleds to make the maximum weight. While ballasts provide more bulk for the sled, it also keeps lighter teams at a disadvantage, since it is more difficult to push a heavier sled from a standing start than with heavier crews pushing lighter sleds.
Cool runnings
The steel runners on the base of the sled are the pod's only contact with the ice. Some runners work better in different types of weather, so athletes must work with their technicians to select the right equipment based on air temperature, the track and ice conditions.
There's a popular misconception that runners are sharp - they are actually blunt. Sleds hydroplane across the icy track; they do not cut into it. "You don't need a sharp edge to turn when you have that much weight, that much pressure and that much speed," says MacEachern.
Technicians and sliders sand their runners to a highly polished surface. Runner dimensions are strict and standardized. Teams whose runners fail to meet the FIBT rules risk disqualification, since smaller runners can increase sled speed.
It is also illegal for bob athletes to heat their runners, since warmer runners will make the ice slicker on contact. The temperature of a team's runners is taken before the race and is compared to a reference runner exposed to open air an hour before the competition. A crew's runners must be within four degrees above or below the reference runner.
FIBT rules also state that runners should be clean, bare steel, devoid of any agents that aid the runners' sliding ability or speed.
The athletes: Speed and power
Bobsleigh crews are made up of either two or four athletes depending on the event.
A two-man team is comprised of a driver and a brakeman. Both the driver and brakeman are responsible for pushing the sled down the track at the start.
During the run, the brakeman is bent over to reduce wind resistance as he rides along with the driver, who uses steering handles to guide the sled.
Two pushmen join the driver and brakeman in a four-man crew. Their role is similar to that of the brakeman in the two-man - get the sled moving as fast as possible off the start and do as little as possible during the run so as to not knock the sled off line or increase wind resistance.
The brakeman's only duty beyond the explosive start is applying the sled brakes at the end of the run.
Both the driver and brakeman need to be in exceptional physical condition, combining speed and strength. Bob athletes often come from a track and field or football background.
"Physiologically speaking, the best athletes on the team are the brakemen on every team," says MacEachern. "They're quicker, faster and much more explosive than the drivers typically are. They're there because they're world-class sprinters. They're also very strong. They do a lot of Olympic lifting for training."
A brakeman on a two-man podium typically weighs in the 100kg-110kg range. In years past, drivers were much smaller than brakemen, but this is changing. The body-type and athletic ability of drivers and brakemen are edging closer together.
The start is the most important phase in a bobsleigh run. Sliders push the sled down an icy straightaway and load into the sled before the descent. Aside from gravity, the push is the sled's only fuel source. The first key to a strong start is having crew members with the speed and strength to accelerate a 250-kg sled to 50km/h over 65m in about five seconds.
Crews also work on timing their starts, ensuring every team member is in sync. Drivers hold onto a retractable push-bar, while brakemen have immobile handles at the rear of the sled. In the four-man event, pushmen use non-retractable bars at the start.
"Most teams use a static start where their driver actually runs at the bar," says MacEachern. "That driver typically wants to hit his bar after the sled has moved three or four inches so the inertia has been broken for him, and that helps the brakeman break inertia faster with the driver plowing into the driver bar."
Common mistakes
Bobsleigh drivers are always hunting for ways to shave fractions of seconds off their times, but inevitably things go wrong. The slightest error can wreck a run and put a team out of medal contention.
Any wall contact near the top of the track is a momentum killer. Even a one-kilometre-per-hour difference affects a sled's overall speed and momentum.
"The thing to look for is why it's happening," says MacEachern. "Typically people are hitting the walls because of the exits of the corners they just came out of. So if they're hitting way down on a right-hand corner, if they hit the wall down the left-hand side at the exit of that corner, it's because they were on that corner for too long. If they're hitting right-hand wall, it's like releasing pressure too much in a race car. If you come out of the corner too early your pressure is going to be pushing you to the right. If you come out late, eventually you'll twist left or slam into the wall left."
Gravitational forces
Bobsleigh isn't for the faint of heart - literally. Athletes reach up to six Gs of force in some corners, making them feel six times heavier than their already-bulky selves.
"I've had heart monitors on in Cortina, Italy, where I've had 230 [beats per minute] on my heartbeat. It's pretty routine," says MacEachern. "You get the snot beat out of you on some of the older tracks, and if you crash, guaranteed, it's the worst experience of your life. Going 140km/h, getting your skin burnt off. If you're lucky, you're not concussed or getting your shoulder dislocated or burned or broken."
Athletes are often out of breath at the end of the run, especially the brakemen, since they push a sled at world-class sprint speeds and get no time to recover while riding in a bent-over position.
Driving: Two-man vs. four-man
A four-man sled is easier for a driver to control, but harder to extricate from difficult situations since the increased weight makes it less responsive than a two-man sled. If a four-man sled hits a skid, its own weight, coupled with that of the 630-kg crew, makes it hard for the sled to react as quickly to the driver's actions.
Conversely, the odds of skidding, hitting walls or veering off line increases in two-man sleds, but the lighter combination of crew and sled make it easier to drive out of such mistakes.
