Regressive Revolution


Having first read about this two years ago… there is no breaking news here. At the time of first reading though, the concept of shock valving was only vaguely meaningful to me, and I didn’t fully understand what I was reading.

Car design is often about compromise. Want a great camber curve? Jack that roll center up. Want negative lift in the corners? Add some drag on the straight. Want 600hp out of 2.0L? Create a very narrow power band. Want minimal body roll in transition and cornering? Just add harshness over bumps.


Enter Penske’s regressive shock piston.

Don’t understand what you’re looking at? The vertical axis shows damping force, while damper piston speed is on the horizontal. Historically, shocks were linearly valved…. meaning the harder you hit them, the harder they pushed back. Since body roll, dive and squat act on dampers at much lower piston speeds than bumps and other impacts, racers needed horribly stiff shocks that barely worked at all over bumpers. Rally, and off road racers that needed dampers that worked in rough terrain, were forced to give up control of body roll and pitch.

And then digressive damping came to the “rescue”. Different piston design allowed fairly aggressive damping at lower piston speeds for high performance body control, while still allowing some compliance over rough terrain. Digressive pistons are found in basically every high performance racing shock these days.

…Except for Penske’s which recently introduced (and patented) a regressive piston. The curve is obviously not perfect (at mid speeds it is perhaps over damped) but it is certainly closer to the theoretical ideal, with the potential to provide a lot more roll and pitch control! Now two years since its release, regressive damping is become quite widely accepted… Originally it was accepted for use in rally and off road racing, but now road racers and even auto-xers seem to be using it.

Not sure how relevant it really is to auto-x, where roll and pitch control are basically the only concern… but for street and circuit where there are gutters and curbing…

Not that I can afford Penske products…

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