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Re: Torsen Tunnel Visions
In a message dated 98-03-07 00:18:12 EST, you write:
<< but you've just said that the 'cf' *isn't* constant, because you've got
> front or rear...
>orin's point is that 50:50 does not occur with slip and a locked centre.
For KISS, let's not get into the braking part.
Again, Dave, you are missing the key to the whole issue. In your scenario, a
wider tire travelling sideways in a turn, can't have more "traction" than a
narrow tire in a turn, or vice versa. Specifically, doesn't a wider tire with
a higher cf have more 'traction' (forward rotation ability) and a narrow tire
have with a lower cf (snow FI) have more 'traction' (forward rotation
ability), EVEN if they are sliding sideways? What does that tell you about
the difference between Slip Angle and Traction? IN a straight line you have
absolute traction. IN a turn you have two forces, Slip Angle and Traction.
The very definition of a turn. If they are interpreted as one force (as a
Torsen Center does), and exactly the opposite to reality, don't you see a
problem with that in terms of chassis dynamics?
Dave, take your car on a wet road, 50mph throw it sideways, steer with the
skid, clutch in. The back tires will stop rotatating, while the fronts still
do... Why? Slip Angle rear is higher than Slip Angle front. Get that Slip
Angle high enough, you can have the rears traveling backwards and the fronts
Now, since you are correctly speaking of Torque Sensing, understand that we
don't need Slip Angle to be that high. Why? Because a Center Diff reacts to
Slip Angle, before the driveshafts actually spin at different speeds. So,
extrapolating that, the Slip Angle Center Torsens will "react to" on dry
pavement is "somewhere" between straight ahead, and 90 degrees. Add to that,
your point that the 'significance' depends on how "tight" a turn might be,
>no, in this case, if you're steering with a slide around the apex
>oversteering), the front is travelling *less* distance around the corner than
>the rear, by definition.
>because it is travelling less, then the torsen sees a better torque reaction
>and feeds the power to the *correct* [front] axle. this is what you want.
UP TO a 'significant' slip angle. So, initially the fronts will travel slower
around a turn, mild throttle, we have mild understeer. Why? Because of the
above. What does that mean to the torsen? That the rears are "spinning"
(since they are travelling faster), so torque to front. So initially the
fronts get the torque. As Slip Angle increases, you get the rears slowing in
relation to the fronts. Why? Because you can steer. Torsen: Rears slower
than fronts, fronts "spinning", rears get torque. Torsen Centers don't care
what the actual chassis dynamics are Dave. That's not it's job. It's dumb,
it controls ALL chassis dynamics in an absolute traction world. Either the
front and rear driveshaft spin at the same speed, or distribute torque. Don't
make the mistake of making it smarter than it is. In the above scenario, it
has things backwards to reality. The backs travel "faster" around a corner
than the fronts. That is an absolute traction equation to the torsen,
specifically, the rears are "spinning" in relation to the fronts. A Torsen
center can't interpret inputs ANY other way.
When Slip Angle is a constant, fwd/rwd, what happens between tires can be
measured in an absolute traction world. That is the design. You put that
torsen in the center, a whole 'nother set of variables comes aboard, and can
ONLY be looked at thru that same absolute traction window. It's beauty to
some, can be costly to others. My exact point. A torsen should behave
consistently in the real world in which we drive. And interpret "variables"
correctly, so that the driver can predict outcomes of inputs. When it is an
absolute traction device all the time, that interpretation of actual events,
can become exactly opposite Torsen design, and your expectations. My argument
is, that is exactly why it can bite the best of drivers.
The most often heard quote by those bitten (including myself): "I wasn't even
driving that hard!!" By the definition of a Center Torsen. At the very edge
(wheel up) it works correctly, per Dave E.'s and Jeff and my posts. So, drive
up to 7/10ths OR drive 10/10> and watch your cf? Ok....