Years ago,at the International Human-Powered Vehicle Speed Trials,at Battle Mountain,Georgi,who'd designed the VARNA Diablo,fastest bike,told us that the 1/4-inch gap between the wheels and wheel fairings was responsible for half the drag of the bike; which has around Cd 0.11.
I' don't have much data on exposed-wheel rigs,so I'm not much help to you.
