I know that professional riders have to wear what they are given by sponsors, but I stumbled across three pictures in a row of the Giro Time Trial that was completed overnight that really caught my attention. This is especially related to the recent trend of short tail time trial helmets that are seemingly so popular now. There are many reasons for this, mainly because if you are a rider who moves / bobs / swings your head around, then the short tail might be faster for you. However, if you read the research by most aerodynamics gurus (which I am not, for the record) like Xavier Disley (find him on Twitter, he is a great follow) you will see that a long tail that sits in the right position is still normally the fastest option.
First picture is Jurgen Van den Broeck, His helmet 'choice' looks almost perfect. See how the long tail connects almost seamlessly with his flat back:
Second picture is Rigoberto Uran. He has a medium tail helmet, but as you can see from the picture, he often likes to put his head down, sticking the tail up into the air like an aero anchor. Far be it for me to criticize Rigoberto, but he needs to keep that head down, or get a short tail helmet:
Finally, Vasily Kiryienka (who won the stage). He tends to keep his head very steady in the position you can see. He has a short tail helmet here but doesn't need it. He would be better off with Jurgen's helmet or Rigaberto's:
The point of all this is that the same helmet that is perfect for you can be an aero brick for someone else. Do your research, work on your position and make an investment that will actually make you faster. The helmet is still one of the most economical ways to get some speed in a time trial.
