Project Nissan Sentra Spec-V part 5; Lessons in Geometry

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The Nissan rear suspension is very cool, for a wheelbarrow.  To keep the rear suspension from flexing sideways under load, Nissan uses a device called a Scott-Russell linkage.  However Scott and Russell must not have been very good suspension engineers.  The linkage does reduce flex but is hampered by the big soft gushy rubber bushings needed to keep it from binding up.  The linkage causes binding and uneven wheel rates from side to side.

Worse yet the Scott-Russell linkage has a very high rear roll center.  To eliminate these issues we have to get rid of the linkage entirely.  We replaced the linkage with a Panhard Rod.  The Panhard Rod keeps the suspension from flexing sideways at all and lowers the roll center by as much as 6” from stock. 

We designed the rods mounting points to be adjustable by inserting the pivots in different holes and sliding the mount so the roll center height can be adjusted to help control the amount of rear roll.  Ideally we want the rear to roll slightly less than the front.  With the Panhard rod in place, we have reduced this cars tendency to overload its front outside wheel.

The lower control arms front mount in our car hangs out in space unsupported.  This causes the lower control arms to move under hard cornering load causing steering inaccuracy and tire contact patch loss.