The Mugen Seiki X7R/X7TR Chassis Weight can be mounted to the back of the front gear box, or to the front of the rear gear box. This weight can be used to increase the steering and traction in low grip conditions and also to adjust the front to rear balance of the car when cornering. You can mount this weight both front and rear for nitro kit, but only front for ECO kit.
To further tuning options, Mugen offers this weight in 40 grams (MUGE2420). 3x8mm button head mounting screws (not included)