The importance of a clean rear

[Javert]

Last year we saw how cleaner rear design (RB & Ferrari) worked better with EBD, while McLaren seem have suffered their complex rear

Also this year Red Bull have more space in the rear than McLaren, and they seem to have more downforce.

Is this equation valid ? Can you always manage flows in a better way if you have a cleaner rear ?

Williams seems cleaner than other cars but they struggle to find decent downforce.

[Just_a_fan]

It's dangerous to try to pick one aspect of a car and say "this is important and key to performance". The car has to be looked at as a whole because the air reaching the rear has already been worked by the rest of the car. The front wing has a huge effect on the flow to the rear for example.

This year we've seen McLaren going a different route to rear end airflow and it appears to be working well. Williams have a tiny rear end but are struggling. Ferrari have basically developed last year's car (with a rear end similar to McLaren's this year) and are struggling compared to RBR and McLaren.

Of course, this year the RBR's clean rear end design has led to compromises with KERS. Whether they can get a reliable KERS with the current aero design is the key question of the season I think. If they can do it soon then they can run away from the rest. If not, I think we'll see a closer season as McLaren/Ferrari/Renault/Mercedes all develop aer-related speed from their designs which already incorporate KERS.

[l4mbch0ps]

Its often very difficult, as a mere observer, to determine exactly what makes a particular car faster than another - especially in a comparison like Mclaren vs. Red Bull. The teams are all approaching the same problem - clawing back down force lost from the ban of double diffusers - they are just approaching it in different ways. The Red Bull focuses on the tight coke bottle rear end because they are feeding their diffuser and their beam wing with air coming AROUND the side pods. The Mclaren, on the other hand, while also focusing on increasing rear downforce, are feeding their diffuser and beam wing with air coming OVER the side pods.
One of the big differences in these approaches is the impact on packaging. Mclaren have obviously had to get creative with their cooling solution, and Red Bull is having difficulties with KERS - rumored to be due to their distributed packaging of the system.
As a layman, or even a fairly knowledgeable enthusiast, it's extremely difficult to visually evaluate the two solutions. We can't see down force, unfortunately.

I think the generalization you are looking for could be something like this:

Removing impediments to airflow will often have positive impacts on downforce.

By the way... I'm not an aerodynamicist in real life, but I do play one on the interwebs.