[EricH]

Mybe you should say it this way: No pre-arranged coaching (over airwaves or otherwise) allowed, other than from the designated coach. If the drivers choose to listen to yelled instructions from the sidelines, then that is their choice. This is assuming that they can hear them over the music, other teams, their coach, the other coaches, and any other noise.

I have been in at least one situation where I did not hear someone cheering for me in a competition and only knew about it later. The same could apply here; the drivers may just zone out everything except needed information. In fact, it is quite probable that even if you do try to communicate with them, they will ignore you to do what they need to do.