TECHNOLOGY – CONSULTANT
Mark Ortiz Automotive is a chassis consulting service primarily serving oval track and road racers. Here Mark answers your chassis set up and handling queries. If you have a question to put to him Email: markortizauto@
windstream.net Tel: +1 704-933-8876 Write: Mark Ortiz 155 Wankel Drive , Kannapolis NC 28083-8200, USA
Arm in arm? Q
In a double A arm suspension are the forces opposite for the upper A arm vs the lower A arm? Example: in a left-hand
turn is the force for the right front A arms inward on the lower and outward on the upper? I hope I made sense because I really want to
F
or this discussion, we will assume that the suspension is of a type that has an upper
control arm and a lower control arm, or can be approximated as such for modelling purposes. We will assume the lower control arm plane intersects the wheel plane below the wheel axis and the upper control arm plane intersects the wheel plane above
the wheel axis. We will also assume there are no drop gears in the uprights. If we are talking about the
forces on the control arms induced by ground plane forces (longitudinal and lateral forces at the contact patch, the forces that create geometric anti-roll and anti-pitch effects), for the most part the answer is yes, the forces induced in the upper and
Understanding the forces acting on A arms under load
know. I have watched Minding Your Anti [my video of a lecture I gave at UNC Charlotte in 2003, still available on DVD for US$50] a dozen times. It has helped me immensely. I just want to make sure I understand the forces correctly.
lower control arms are opposite in direction. The main exception would be the case of longitudinal forces from braking or propulsion, where the torque is applied to the wheel through a jointed shaft and only the thrust acts through the suspension linkage – that is, propulsion with a sprung final drive (independent or DeDion suspension) or braking with inboard brakes.
In terms of ground plane forces, generally speaking the forces induced in the upper and lower control arms are opposite in direction May 2012 •
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