Something like you get with an old style locked hub when driven on dry pavement?

sometimes the AWD fights itself in certain conditions under close to full lock. like an audi quattro. I have experienced it before. if they are concerned have a dealer look at it.

At close to full lock most (all?) cars totally loose ackerman steering and one wheel will slide or skip depending on avail grip. Skinny high profile tires can hide the effect due to tread squirm. Not so much w/ wide low profiles like on the panamera.

If it has viscous coupling diffs then those shouldn't be a factor at slow speed.

When you guys say full lock, are you talking in terms of steering wheel or differential?

Steering wheel.

Stephen, can you explain? I think I get what you were meaning to say, but wanted to make sure I follow. Ackerman is a fundamental aspect to the steering geometry and is present regardless of vehicle speed. In fact, the effects of Ackerman are most apparent during low-speed turns. It's even common for race cars to run Reverse Ackerman, to allow the outside wheel to turn in more than the inside wheel. Most production cars do not run much Ackerman, given that it causes tire wear issues at higher speeds and can upset the car during higher speed turns. Fortunately, for the reasons you specified re: tread squirm, the need for Ackerman is not very high.


Sorry to derail!

To the OP: what happens when the driver makes a very tight turn and feeds in the power quickly but evenly? If it is dynamic toe change, the effects should not be all that noticeable (unless your friend has the butt of Schumi himself). Have you ridden with him? +1 to the loose nuts theory.

Ackerman is not fundamental. You either achieve it (get close enough) or you don't. You have to design the rack location and tie rod geometry to achieve it. Im not aware of any race cars that go out of their way to do the opposite, so thats news to me if it is. You technically need more steering angle on an inside unloaded wheel as it needs a higher slip angle to be optimal (due to lower normal forces) so achieving ackerman should still be desired.

Race cars steer at fairly small angles and don't HAVE to acheive perfect ackerman esp if some other constraint causes bigger problems (like engine vs steering rack location.) I think it was Chapman who once said suspension geometry doesn't matter if its stiff enough (insinuating over very small bump distances even lousy geometries don't change enough to matter.)

My old jetta3 *SUCKED BALLS* w/ respect to ackerman. Don't know if it had too much or too little. 5mph in a concrete parking garage sounded like 50mph. Some cars are dead quiet so they're getting it right. While the dub had some mechanical trail, Im pretty sure it achieved positive caster at the limits too. That suspension geo sucked...

I'm with you now -- gotcha. You can think of Ackerman as an element of suspension geometry akin to caster, camber, or toe. I.e., it's designed/dialed into the geometry just like you would an alignment. What you were referring to is the very symptoms Ackerman was attempting to address. Basically a semantics discussion, really. Thanks :)


There's a nice discussion of Ackerman vs Reverse Ackerman in Race Car Vehicle Dynamics by Milliken. Again, sorry to derail. Also please don't take my reply for being attacking or negative; I just enjoy a friendly engineering discussion where ever I can get it (don't get to do it for my day job anymore...) and I'm typing on a phone! :)

'Nuff said. Argh. That one has been on my 'to get' list forever. Even used it costs a fortune (yeah, yeah, I know cheap for what you get;))

Back to your scheduled programming...