Nohachi's suspension ramblings thread

[Ozone]

Roll Centre came up in another thread so I thought I'd add to it here.

Rather than a CAD model, I have calculated the Roll Centre height using Excel spreadsheet. This might sound difficult, but in fact it is very easy, you just need to use simple trigonometry. The hardest thing is accurately measuring the suspension.

I have measured my car the best I can, it had the following parts that effect geometry:
Ride height: -65mm front, -55mm rear (compared with ref values in manual)
RCAs on front, 45mm height.

My output is as follows:
Front Roll Centre height = 90mm
Rear Roll Centre height = 265mm

You usually want the front Roll Centre height to be lower than the rear.

I have recently changed to 30mm lowering springs and Bilstein dampers (GReddy is too harsh for UK roads IMO).
I've calculated the following for this condition:
Front Roll Centre height = 190mm (with RCA), 70mm (without RCA)
Rear Roll Centre height = 280mm

I actually removed the RCAs and experience the sensation of "front of the vehicle rolling" when cornering. Having spoken to engineers at work more experienced than me at Handling, this is most likely due to the front Roll Centre being too low in comparison with the rear and the fact that the vehicle is actually rolling - the new springs are less than half the stiffness of the GReddy setup! I'm now planning to re-install the RCAs and see what effect it has.

If I had more money I would fit stiffer front and rear roll bars and lower the rear Roll Centre like Lotus did with the Cortina by using an A-frame link instead of a panhard rod (picture on the left)
http://www.pixelmatic.com.au/cortina/mk1...arends.gif

or on the Caterham 7 (also a Lotus design)
http://www.scalereplica.com/images/stori...CN3161.jpg

My thinking is you can use the existing body mounting points used by the lower trailing arms and add a mounting point on the bottom of the axle housing/diff. You would also need some lateral bracing of the body mounting points but otherwise I do not forsee an issue with this setup. This would give a rear Roll Centre height in the region of 120~140mm...