HPI Racing have new option parts for the HB D413 4WD off-road buggy available in the form of a +6mm main chassis, an Ackermann arm set and 15 degree caster blocks. Starting with the chassis, which was used by HB drivers such as Ty Tessmann during the recent IFMAR Worlds, the carbon fibre plate offers a 6mm longer wheelbase for increased stability and it must be used with the +3mm top front and rear top decks. Despite being longer the chassis is good for the use with the standard centre driveshafts. Other new parts include an optional steering Ackermann arm set made from carbon fibre as well as 15 degree caster blocks for the front of the buggy. The items help to fine-tune the steering characteristics for a variety of surfaces.