In terms of drag caused by a bicycle rider, the biggest loss is caused by the rider themselves followed by the wheels and frame.
The drag caused by wheels is significant because of two fundamental reasons. The first is they hit the air first as they are the most forward part of the bike and second because they are rotating. The effective air speed at the top of a wheel/tyre is double the indicated speed of the bike.
In the bike industry, wheel aerodynamic testing has generally been conducted by two groups of people - Wheel manufacturers and journalists. Wheel manufacturers will usually adjust tests to make their particular wheels look more favourable than their competitors in testing. This is usually achieved by a combination of adjusting speeds and angles. The reality is this type of test is not impartial.
Journalists on the other hand tend to visit their local university and ask some clever boffin to conduct their testing for them and give them the