surely it is better to push through a rad than it is to pull through performance wise?
Numerous people have done trials and reviews, most notably Linus Tech Tips.
Generally they find that there is no discernible difference between Push and Pull, performance-wise.
Using Push-Pull, however, does improve performance.
the fan has to pull the air through the resistance of the rad.
Yup.
the fan has to push air into the rad. no resistance from the rad for getting the air.
Q: If there's no resistance, then why do we use Static Pressure fans?
A: Because there *is* resistance - The same resistance that a Pull fan must overcome.
The air must go through the radiator fins. That is it.
How it does this is the exact same for Push and Pull.
It's actually the restricted space between the fins causing the resistance.
Basically, unless your fan is absolutely *perfect*, the airflow will not go in a dead straight line, so will bounce off the fins' surfaces in a zig-zag pattern.
We're talking perfect on a very small scale here, though, so pretty much every fan has the same hurdle. Many SP fans have a more focussed flow, which better directs the airflow, but that's about the best you can get unless you want to pay thousands per fan.
Normal Air-Flow fans tend to move lots of air, so you get the air slowing down as it bounces around between the fins, while lots of faster air is coming in. This faster air backs up and pushes, both against the slower air in front and back against the fan blades, which forcibly slows the fan down. This causes compression and if the pressure is high enough it stalls the fan blades - Thus compression stall and why it's often better to use SP fans through restrictions like radiators, grilles, meshes and HDD cages.
Static Pressure fans move comparatively less air, but move it with more force so that it blasts through the fins and doesn't bounce around so much. In order to push this air with force, it still needs to pull it in from behind (because that's how fans work, surprisingly) so unless there is a compressor that can compress the airflow incoming and blast it out the exhaust with more force, all hidden away in that 25mm of fan thickness, the value it pulls through a rad will be the same as what it can push.
EDIT - what stat would you look at for pulling air? and why?
mm/H2O
Because Push and Pull both require high static pressure and that's what it's most commonly measured in.
That, or just look at the temperatures you're getting with Push vs Pull.
Most fans perform in one within a few degrees of the other.
