Kouki Kato explains long and short rear arms on the Team Associated B7.1 and B84

Photo: Kouki Kato RC Driver (source)

Japanese driver Kouki Kato has just posted a technical video devoted to a setup choice that many 1/10 buggy racers make without really understanding it: long versus short rear suspension arms. His demonstration is based on two Team Associated chassis, the 2WD B7.1 and the 4WD B84, both of which accept either length.

Long arms or short arms: two distinct behaviours

In his video, Kouki Kato details the characteristics specific to each configuration. Lengthening the rear arm changes the suspension’s travel angle and the way the wheel moves vertically: the motion becomes more linear, which generally translates into more stability and traction on rough tracks. Conversely, a short arm reacts more quickly and makes the car livelier, at the cost of a compromise on smoothness of travel.

The link with wheel offset

The most useful part of the demonstration concerns the relationship between arm length and wheel offset. Since changing the arm length moves the hub inwards or outwards, you have to compensate with wheel offset to keep the same rear track — otherwise you are changing two parameters at once and the test no longer means anything. Kouki Kato stresses this arm/offset pairing, which is the key to cleanly comparing two configurations on the Team Associated B7.1 as well as on the B84.

A useful reminder before the season resumes

This kind of technical clarification comes at a good time with the big end-of-season events approaching. For B7.1 and B84 owners, the video provides a clear working method: change one parameter at a time, and understand what the rear arm geometry actually does to the car’s behaviour before diving into blind testing.