How co-drivers prevent rally-car drivers from crashing

• Just like airplane pilots have their copilots, rally drivers have a co-driver sitting right next to them during each race.
• The codriver's main job is to read out loud a series of prewritten directions called "pacenotes" that the driver uses to navigate each stage.

• It's these notes that allow the driver to continue at full speed without hesitating at the courses' most dangerous sections in order to get the best possible time.

• Visit Business Insider's homepage for more stories.

Following is a transcript of the video.

Narrator: This man talking nonstop is what's known as a rally team's co-driver. He never touches the wheel, never touches a pedal, but he's just as important as the driver. And all those words he's saying — they're directions.

Rallying is hands down one of the most dangerous motorsports around. Drivers race down narrow public roads covered in everything from dirt and gravel to snow and ice at speeds of up to 100 miles per hour. Instead of drivers racing all at once, they go one by one around sharp blind corners and fly hundreds of feet off of sudden jumps.

Just like airplane pilots have their copilots, rally drivers have a co-driver sitting right next to them during each race. The codriver's main job is to read out loud a series of prewritten directions called "pacenotes" that the driver uses to navigate each stage. It's these notes that allow the driver to continue at full speed without hesitating at the courses' most dangerous sections in order to get the best possible time.

One of the codriver's most important jobs starts days before the race has even begun during an activity known as "recce."

Krista Skucas: During recce is when the driver and codriver will take a car out, and that is when they go out onto the stage roads and write the notes they'll be using while they are racing. So, this is done at low speeds, 35 mph is usually tops. The mental strain that it takes to just 100% focus on the road in front of you for sometimes 45 minutes to an hour of just paying attention to every deviation in the road and not missing anything.

Narrator: But while recce may seem time consuming and mind numbing, mistakes made or obstacles missed during it can lead to some of the biggest disasters. Nicolas Gilsoul, co-driver to one of the world's best rally drivers, Thierry Neuville, explained just how important recce is to a team's success — and safety.

Nicolas Gilsoul: We had last year a big accident with Thierry, but it was not due to misunderstanding. It was due to the fact that during the recce we did it in the fog, and the visibility was really bad. So we were driving quite slow, even slower than usually, and we underestimated the angle of a turn.

Narrator: Co-drivers have all kinds of strategies they use when writing pacenotes, and they'll have them written to read either horizontally or vertically. Krista gave us a look at how she does hers with an example she took with driver Sam Albert during their recce before Olympus Rally.

Kristas: So, a series of notes is right here. Always end in a distance (points to the 80 and 60) so you have time to circle back around and get to your next note. So this is "4++ left 80 hug 5 right 80. 5+ left into 5+ right tightens 4++ 60."

Narrator: While that series of numbers and symbols may sound like gibberish, it's actually fairly simple. The numbers one through six refer to the severity of an upcoming turn, one being the sharpest and six being the most gradual. The pluses and minuses are used as modifiers for turns that don't quite fit into being labeled just a full one or six.

Simple miscommunication with those notes, though, can have some of the worst consequences, like at 2018's Tour de Corse when codriver Paul Nagle called out a wrong pacenote to his driver, Kris Meeke, sending the pair flying off the track. By calling out "five left," Nagle instructed Meeke to keep the car in fifth gear for a gradual left turn but ended up sending the pair 30 mph into what ended up being a tight corner.

But codrivers need to be able to do more than simply read and write directions. Co-driver and driver need to be able to handle breakdowns and mechanical issues with the car by themselves with a limited supply of tools.

A famous example occurred in 2002's Acropolis Rally when codriver Phil Mills had to repair his driver Petter Solberg's loose steering wheel while they continued driving.

Nicolas: We have to sort out mechanical issues or damage on the car. And we only have a few tools on board, so sometimes we have to suddenly become MacGyver. For example, in 2014, I remember really well in Rally Mexico, we had a leak in the engine's cooling system. We had to refill the tank, but not with water because we didn't have any with us. We had a big bottle of Corona beer, and we were able to use the liquid to solve the situation.

Narrator: And then there are situations you just can't predict. At 2018's Rally Mexico, locals had set a trap for drivers by closing a large metal cattle gate, forcing co-driver Anders Jaeger to get out of the car and open it himself.

As expected, blindly following your co-driver's directions requires an intense level of trust between the two teammates. This method of driving leaves little to no room for error from either person.

Nicolas: Something which is really a key and you need to understand with our sport is we are working like what I call a mirror of confidence. Thierry needs to trust me and what I'm telling him while we're driving through the stage in the same way I need to trust him to be 100% confident about how he's driving, how he's approaching each turn through the stages.

Narrator: So while a rally team's success obviously depends on the talent and skills of its driver, just as much pressure sits on the shoulders of its co-driver. It's because of codrivers and all the duties that come with being one that the team's wheelman can focus on just one thing: driving. A co-driver at the top of their game can be the difference between a disastrous ending and standing at the top of the podium.