First Principles

Mark Ortiz Automotive is 3

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 Cmail: [email protected] Tel: +1 704-933-8876 Write: Mark Ortiz 155 Wankel Drive, Kannapolis NC 28083-8200, USA

THIS MONTH: B Is it possible to have a suspension with zero camber change in both ride and roll?

Many semi-independent designs can be configured to have a little camber change and scrub in both ride and roll and lower roll centres than are commonplace with pure beam axles.


independent suspension a In your June 2008 Chassis Newsletter, you stated, 'With a passive independent suspension, it is impossible to have zero camber change in both ride and roll/ but I recently ran across an interesting article on a camber compensating suspension that was first published in Racecar Engineering in 2001 ( dax/) that shows a system that looks like it does a good job of keeping camber very constant in both modes. I was therefore interested to hear your take on it.

I've started looking into ideas for building a car for the track. I basically want an FSA6 car, stretched for the higher speeds of a road course, with more power. My target is 8001b, 175bhp with a Hayabusa engine. I'm looking to keep it simple and easy to fabricate and repair, and am leaning towards a monoshock on the front, with a torsion bar for anti-roll, but I'm not sure if that will be up to the task on the rear. I look forward to hearing your feedback.

A As may be seen from the linked article, this system superficially resembles a conventional short-long-arm (SLA) suspension. Unlike the SLA system, however, it mechanically interconnects the upper control arms in a manner that, in cornering, pulls the top of the outside wheel inboard and pushes the top of the nside wheel outboard, providing more camber recovery than the SLA. Indeed, it can have 100 per cent camber recovery in roll, just like a beam axle does (ignoring the component of roll due to tyre deflection), or even more than that if desired. I: can, at the same time, also have no camber change at all in ride - again like a beam axle - or some moderate amount of camber change in ride.

This suspension is one of a family of layouts that look like what we traditionally call independent suspensions, but are not independent in the usual sense. That is, they share two characteristics we associate with beam axles, and not with independent suspensions.

First, they do not have the same camber properties with respect to the sprung mass in both ride and roll. Second, when there is vertical displacement of only one wheel of the pair, and not the sprung mass, the wheel not displaced vertically undergoes camber change, and usually some lateral displacement or scrub at the contact patch.

There is no generally agreed convention regarding how such

February 2011 *

The suspension system in question from the Dax Rush kit car appeared in RE V11N6. The upper wishbone pivots are mounted on a link hanging from the chassis mounts

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