XRAY - Model racing cars

Hi,
A tire question to the pro drivers...
I'm using Bruno Coelho setup, from Germany EOS (xform/index.php?act=view&ID=103&setup=xb4_2016), and tried several combinations of tires.
Our track is Astroturf, with high grip and small bumps, mostly smooth.

It seems that when i use rear mini spikes (Y) and front wide staggers (Y), the car loose the rear traction in every corner, there is way too much front traction.
When i used narrow front tires (cutting the wheel...) from Schumacher front 2WD, or Jconcepts SWAGGERS, the car is very balanced and controlled.

The weird thing is, that most, if not all the pro drivers, are using the front schumacher wide staggers, which makes me feel that i'm wrong here, and the setup is not working.
Should i use more grip tires in the back? tried the mini pins, with the same behavior...

WDYT?
Thanks
Guy

If you are fast then everything is ok.
Try to get more grip at rear.

Tires
More toe in
softer swaybar