The stock a-arms have 12-degrees of castor. They have a tendency to make the car oversteer when off-throttle but understeer when on-throttle.
You may want to try the "optional" a-arms which have 6 degrees of castor.
It should say on the arm which it is, between the shock joint and inside front pivot ball, it'll say 6, 12, or not have anything at all (which is the rear upper a-arms which have zero degrees of castor).
http://www.teamxray.com/xshop/produc...?kategoria=744
Here they have the 6-degree a-arms and also the adjustable tie-rods, which are also very helpful if you don't already have those.
Atomic also makes a-arms for the M18, but unfortunately I found that they were unusable because they had way too much friction in the ball joints.