Option part for the R11 providing smoother power transfer to the wheels and improved on-power steering. 
ARC R100038 A10-25 Electric Touring Car Kit (Carbon Chassis)
Elceram Oxide 1/10 145A Brushless ESC with LCD Display
SRT BHMX2 i-BUS2 HV Ultra Low Profile Brushless Servo - 0.073s/18kg @7.4V
Fido 6500mAh 2S 7.4V 220C Super Low IR LCG Lipo Battery