rec.autos.simulators

is it possible to drive in this view?

Actually, as slip angle is increased, the cornering force increases
to a peak, and then is approximately constant right out to 90 deg.
Once the slip angle is past the peak you can think of the tire as
just a slab of *** sliding on the road--changing the slip angle
doesn't have much effect on the side force.

So, the tread won't spring back as you suggest.  If the
the car has spun half-way-round and is moving backwards, the tread
will re-center when the slip angles are near zero (or 180, if you
prefer to think of it that way).

-- Doug
                Doug Milliken
                Milliken Research Associates Inc.

        (I'm referring to the Milliken who co-wrote "The Big,
Intimidating Book of Why Cars Go Fast")

Martin
Nigel Mansell RIP!

What he is saying is that the slip angle v. Coefficeint
of Friction chart looks something like this:

     |         ---
     |        /   \
     |       /     -------------
     |      /
cf   |     /
     |    /
     |   /
     |  /
     | /
     |/
     ---------------------------
        slip angle in degrees

When the tire passes the peak slip angle, the friction
force drops, but not as drastically as you suggest.
There will still be considerable force rolling the
tire sidewall, even while skidding at 90 degrees, so
the tire will not "snap back" in any visually
percievable amount.  In any event, the transition
is gradual.

--
Pat Dotson
IMPACT Motorsports
http://www.impactmotorsports.com/pd.html

Thank you

Steven

Pat's plot of lateral force (LF or Fy) vs slip angle (SA) (below) is good,
but I've changed the axis labels (to match standard terminology).
Sometimes there isn't any drop-off at the peak at all, the peak lateral
force stays about constant at the peak value.  The lateral force is
measured (defined) at the road surface, and lined up with the axle
(perpendicular to the center plane of the wheel, the "y" direction.)

Now to aligning torque (AT)--(another post in this thread).  AT vs slip
angle (SA) looks different than lateral force vs SA.  The AT rises to a
peak and then drops to near zero torque once the tire is at peak lateral
force.  The tire does get "twisted" at low slip angles because the front of
the print is just getting set onto the road, while the back of the print is
"stretched" sideways.  Once the whole print is sliding (above the peak LF)
then there isn't much difference between the sliding velocity (and force)
at the front and rear of the print.  Crudely like the plot below, where SA
is to the same scale as the plot above.

 AT     |     /\
 lb-ft  |    /  \
        |   /    \
        |  /      \
        | /        \
        |/          --\
         ---------------\====\---------======
           SA (degrees)        \------/

The figures and explanation that we put in Chapter 2, of "Race Car Vehicle
Dynamics" are much more complete.  Another shameless plug-- Get RCVD now
from Classic Motorbooks at the old price of $85 -- SAE just raised all the
prices at their in-house bookstore, RCVD is now $89 from SAE.

-- Doug

                Milliken Research Associates Inc.

My question is, does the peak aligning torque
occur at the leading edge of the peak lateral
force?  This would directly define what we
should feel in a force feedback wheel.  If the
two coincide, that would make driving on the
limit more intuitive.  Even if the two don't
coincide in reality, I think they should in
the simulation of FF effects   :)

BTW, I'm just learning this too - so if I
get something wrong, somone please correct me!

--
Pat Dotson
IMPACT Motorsports
http://www.impactmotorsports.com/pd.html

Does AT change depending on over/understeer?

--
Pat Dotson
IMPACT Motorsports
http://www.impactmotorsports.com/pd.html

Not as such...it's a tire property, so it changes with load, traction/
braking, camber, etc., and of course, slip angle.  Of course if your car is
wildly oversteer at the limit, you may have to spin out to get the front
tires to a high enough slip angle to be at their peak LF...!

I think I'm cutting into book sales by now...so I'd better quit this
thread.

-- Doug Milliken