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.

H. Honigl

Source: H. Honigl