Roll play with a Rotax racer

The curious Novalink that is a feature of US F500 cars is the subject of a fascinating dialogue in this month’s suspension master-class

- MARK ORTIZ

Q Soon I will be designing an F500 car, and I have questions regarding their suspension. Above is a picture of a typical rear-end; it seems to show two Panhard-like rods attached to a pivoting frame. The frame is hinged on both sides. At first I thought this set-up does not seem to allow any roll, other than that given by flexing of that frame. This may be part of the design intent, as the rules prohibit anti-roll bars. How do you determine the roll centre for this design? For F500 racecars, would there be an advantage to a low rear roll centre as found with the Mumford link?

Also, after studying the picture some more, I began to think that it looks like the axle can roll, if it is displaced sideways, per a four-bar linkage. But it would then roll in the wrong direction, causing the car to roll outwards in turn. I am confused.

THE CONSULTANT

A You’re right, it can roll, and it has geometric pro-roll: roll centre below ground. The roll centre is essentially where the centerlines of the silver links meet, as it would be with a Mumford system. I’ve seen F500 cars occasionally but never had a client running one. It looks to me like they wouldn’t be particularly tail-heavy since the engines are light. I would think that they’d have a tendency toward locked axle understeer, and that you’d want to have the inside rear relatively lightly loaded to combat that. Would that be correct?