For those that don't know much about the techo stuff but would like to improve their understanding before the race, a visit to Mulsanne Corner website is well worthwhile.
its a great source for understanding all the little, subtle aero differences between different cars and will give you some good ideas on what to look at during a pit walk.
There also some interesting techo stuff on historical Le Mans cars, including a good article on why the Mercedes became airborne in 1999 and explanation of the subtle differences between the 2001 - 2003 Bentley's.
http://www.mulsannescorner.com/