Originally Posted by
bobones
Is it important for the riders to signal to each other the end of a turn, e.g. by guy in front flicking elbow or guy behind shouting "spell" or "spell up"? Seems to me that without communication, the guy behind is going to have to accelerate to get to the front and so disrupt the smooth flow and even pace. With communication the lead rider can ease off slightly to allow the drafter to come through at the same steady pace.
BTW, OP, I think you meant to say "concertina effect" as harmonicas don't move much!
I've never heard 'spell' before. If you are going hard enough then the lead rider won't hear anything.
All that 'communication' is unnecessary. Everything that transpires should be non-verbal.
The lead riders simply needs to slide over a bike width into the wind with a flick off the fingers on the leeward side as they ease off slightly on the pedals. The following rider holds the same pace and the lead rider slips in behind as the other rider moves past him.
As for duration, with two riders switching every 30 seconds is far too quick as it isn't enough time to recover and you'd spend a huge percentage of time changing leads. I would pull for a minute or two and then switch off. That gives time for recovery and the amount of time spent side by side is a much smaller portion of the overall time.