Those are the option parts i used in my XRAY XB2 on carpet all the time and most of them on dirt as well.

#323351 Alu Rear Upright
This option part gives you more adjustability for wheelbase and makes the car more stable.

#323041 Alu Rear Roll-Center Holder
This parts will be necessary when using more then 3mm shims underneath the ball stud, to keep the strength of the car.

#365471-O Alu Drive Shaft Safety Collar - Orange
This part just replaces the original plastic part and you never need to worry about a drive pin coming loose; Also it is a nice fashion part to give the car a nice orange touch.

#323110-G/323120-G & 322110-G Comp. Susp.
Arm rear L/R & front made from the very durable and strong XRAY Graphite Composite makes the car more precise to drive and makes the car land perfect.

#329701 XB2 Body Light Weight
Taking away extra weight makes the car react quicker with wanting it to traction-roll less

#322041 Alu Front Roll-Center Holder
This part adds a little weight to the very front of the car and makes it more precise to drive.

#322312 Brass Front Lower Arm Mount 26°
Maybe this is my favorite option part of all - It adds extra weight to the front of your car to give it more steering on power, which everybody is looking for when racing on high bite.