@AndRand: I'm not sure if you're actually understanding the graphs you're posting here, since if you did you'd immediately notice they're nonsense.
To give you a rough idea of what it should look like, let's for a moment forget about the longitudinal (slip ratio) grip curve. Just take the lateral one, put a pin at the 0-slip-angle point, grab it by its tail and spin it around 360°, leaving a 3D-trail while doing so. The shape you're left with is one of a rather simplisticly simulated tyre that behaves exactly the same no matter which direction it is being pushed. Now granted, just thinking about the tyre shape and its basic workings a little makes it clear that a real tyre doesn't work like this, but if used in a simulation it would result in a fairly drivable car, already several orders of magnitude better than what your magic fairy dust canyon curve would produce.
Now, that's only one curve which sucks, so lets make that a combination of two curves. But instead of spending ages tinkering with it and somehow ending up with the forces cancelling each other out, just morph the curve from the lateral to the longitudinal one as you do your 360° spin (so I guess you make a linear interpolation between both curves modulated by the current rotation angle or something). That's probably not quite how a real tyre works either, but by doing this really simple procedure you'd have already far surpassed everything you've brought up till now.
Sorry for putting this a bit bluntly, I just can't help myself sometimes :o