Rear roll center

[jonnyo89]

After reading about front roll-center correction, it got me thinking about the effects of lowering on the rear beam angle of these cars. I'm no suspension guru - I have a rudimentary understanding of front roll-center geometry but nothing that relates to rear torsion beams.

I've been pondering what a raising of the beam mounting point would do, i.e. bringing the angle of beam 'droop' back towards OE. Fire away.

 

[Steven103]

Not a lot.

Large changes in the trailing arm angle make very small differences in RC height because the IC (instantaneous centre, of the arc described by the wheel in bump, ish) is relatively close to the vehicle centreline. On a typical McPherson or double wishbone the IC is somewhere well outside the track width.

Because of that, and again unlike the front, there’s not enough travel in the rear suspension to make the RC go anywhere weird e.g. below the ground.

Then remember that the important point is the vehicle’s Roll Axis, rather than an individual roll centre. Because a Clio is something like 65:35 weight distribution, the RA height at the CofG is effected nearly twice as much by the front RC than the rear RC.

You can estimate the RC of a trailing arm with twist/torsion beam by starting with the RC of a trailing arm, and moving the inboard pickups onto the vehicle centre line.

 

[Kev@KAM]

With the limitations of a twist beam in play then rear roll centre is not really an area that can be improved significantly to actually make any difference.
I always prefer to work a different way. Find the problem first. What do you want to achieve? Better grip, tyre wear, the chassis dynamics at a certain part of the corner?