Originally Posted by CdCf
I've seen that number as well, but always in the context of drafting a single rider. A whole pack should provide an even greater reduction in effort for the same speed.
The measured drag goes as 1st rider, 100%; 2nd, 71%; 3rd, 64.1%; 4th, 64.0.
http://www.midweekclub.ca/articles/broker98.pdf So it looks like the reduction asymptotes after the third rider and being in the pack isn't likely to drop drag more. The pack will expand the region of low drag compared to a single line, though.