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I'm fairly sure it's important to set a WRC car up also? When they can finish within seconds of each other after 4 days of competition, having a perfect set up would make the difference? I'm not sure codrivers are deciding what spring rates etc to run?
yes, it's important to set-up the car, but the way they do it is different, that's why I pointed out the part about what we see. They do testing (which we usually don't see) on a similar surface, altitude... to the rally they want to prepare. In this case, they go over a short piece of road over and over again and do a set-up work that reminds a bit of the F1 free practice. Here is when you'll get most of the pictures of the engineers.
But during a rally, the engineer can almost only work with what the driver tells him about the recce, the shakedown or, during service, about the stages. What I'm going to say it's an oversimplification, but during a rally what you have is a driver telling the engineer "I need a change in the diff", "I want it softer" and little more before going to have something to eat and prepare for the second loop of the day.
In short: in WRC, you will usually not see the engineer, plus they don't have the telemetry data you will find in F1, and the engineer will not tell a driver how to trace a certain curve (how to drive) because they have thousands of curves and they only take it once or twice. That all makes the driver/engineer couples much less visible in WRC, plus it's the co-driver who rally drivers need to have blind faith in.