Trying to remember every little crest, kink, camber, junction and corner over 400km of competitive rallying, while flying along at up to 200km/h, is not possible on your own.
Without a co-driver, a rally will unravel faster than a woolly jumper caught on a nail. They hold the key to surviving each stage, or making a mess of an expensive race car, among other things.
Nine-time world rally champion Sebastien Loeb recognises the need for a supremely accomplished co-driver and once said: "He [Daniel Elena] is an important part, of course. We have started together, we have won everything together."
New Zealand's only World Rally Championship driver, Hayden Paddon, has one of the best in the business in the passenger seat. The Herald on Sunday put a few questions to John Kennard.
How do you cope with writing down notes while being flung around some of the goat tracks that make up rally stages?
Sometimes it's pretty hard, and Argentina was a perfect example. It was like driving up and down riverbeds. Some of the stages, I had to rewrite completely and it was hard to decipher what I had written down on recce. Sometimes I had to erase 70 per cent of it and do it all again. Just trying to write anything down on bad roads is crazy difficult as you're bouncing around so much in the car. On a smooth rally like Whangarei, 99.9 per cent of what I write during the day I won't have to tidy up, or do anything to the original notes.
What happens when you try to read stuff back to Hayden at race speed?
On the rough stuff at high speed, you're hitting things so hard, it's difficult to read what's on the page as it's moving around so much. You get into the habit of looking at two notes or more during a smooth bit, absorbing them into your head and then speaking them.
What happens if you sneeze or cough and you get behind where Hayden is on the road?
Knowing Hayden and the car so well now, I can just keep reading [constantly without looking up] unless the distances [to corners] are over 100m, then I might pause and look up. Dust and stuff inside the car can cause a bit of a problem, but you've got so much adrenalin and you're concentrating so hard, you don't tend to cough or sneeze. It must have happened somewhere, though, but not to me.
A lot of people suffer from motion sickness. What's it like being thrown around like a ball bearing in a can on a paint-mixer machine?
Until about four years ago, I used to take something on rallies all the time. Do you know the Paihia Bomb? It got to the stage I didn't need them on recce, just during the rally because you get so hot and wound up. Now there's no time to think about anything else but the information during the stages, so I don't have time to think about being sick. The WRC cars are so fast now, you don't really get a chance to look up.
On a full shakedown or recce, how long do you spend in the car?
On some rallies, we'll leave the hotel at 5am and not get back until sometimes more than 12 hours later. Then we have to sit down and go back through all the notes to make sure everything is OK.
Does Hayden ever let you drive between rally events?
No. He wants to drive all the time. There was one time, though, when he said he was so tired, he had to pull over and I had to drive. But you couldn't say it was by choice.