Z bars, T bars, sway bars?

[Flieger]

Is a normal torsion bar on a 911 front suspension a type of Z bar?

Z bars add springing force to one wheel independently, only in ride stiffness. There is no increase in roll stiffness. It is the opposite of an anti-roll/sway bar that ties the sides together resisting roll but does not contribute to ride stiffnes when both wheels are in bump.

I read somewhere (Fere or Ludvigson?) that one of the Porsche prototypes-906/910/909 used Z bars at one point.

Anyone have a picture of a Z bar?

Thanks

[Zeke]

This is a z-bar from a VW beetle. The orange parts. it's basically used as a load compensator.

[Flieger]

Thanks for the photo.

It looks like half of a through-chassis front sway bar on a 911 to me.

So there is a very short torsion bar (a few inches long) running perpendicular to the chassis and housed in the orange cover. This actualtes the lever arm which connects to the drop link and then the rear upright. Is this accurate?

[Zeke]

I think so.

[burgermeister]

Cool picture, milt!

If the bug Z bar has one arm pointed forward, and the other side's arm pointed rearward, it would add only ride rate I think. Vertical load would put the bar in torsion, rolling of the chassis would leave it unstressed. It appears to be a swing axle, so the roll center is quite high - right around the inside axle shaft joint height, so it probably doesn't need much additional roll stiffness ... but I have no idea why they put the Z bar in it. Help with jacking during cornering ? I could see it for an off-road application where the wheels need to maintain ground contact during big twist events.

In general, if it adds springing force to a wheel, it adds roll stiffness. Easy test: disconnect the sway bar and see if the car rolls over by itself.... Most of the roll stiffness comes from roll center height and the ride rate of the wheel, especially if you've upped the torsion bar sizes; the sway bars are more of a tuning element.

[Flieger]

Thanks, Burgermeister

Your comment about the opposite directions of the swing arm from the Z bar give me a clearer understanding.