rec.autos.simulators

I didn't know that.  That would explain why I don't feel a drastic
difference between an 85-6 power side combo and a 45-6 power side combo.

[snip]

Yes. :)  Didn't bother me too much, though, since I'm more of a "pitch-
it-in-and-ride-the-throttoe-out" driver.  Probably goes part way
towards explaining why I'm having difficulty adapting to the more open
coast angles.

Nope.  I drive with the bias set at 56-57%.  I tried your 51% once
and I couldn't even keep the car from spinning while I was still
braking in a straight line.  You must be very good on the brakes. :)

Yes.  Here's why:

Discount the brakes for the moment.  It simplifies the conversation a
bit.  Let's say I'm coming up on a turn.  I let off the gas which
unloads the rear.  Since I'm coasting, the rear wheels are driving the
engine and supplying force to keep the engine spinning against its
compression.  While I'm in a straight line, both wheels supply the same
amount of torque back to the engine (more or less) since they're evenly
weighted.  When I begin my turn in, however, the inside rear unloads
further and becomes the least loaded of the two rear wheels.  This
unloading reduces the available traction at the inside rear and limits
the torque it can supply the engine for engine braking.  The engine
back-torque will remain split evenly between the two rear wheels unless
more torque is required than the available traction can supply (if I've
downshifted to aggressively, for instance).  The wheel that will loose
traction will be the inside rear under these circumstances, and once
that happens, the nearly open coast differential will send the majority
of the torque to the wheel with the least amount of grip (the inside
rear).  This will make the inside rear lock since the engine back-
torque has already overcome the available traction.

Adding brakes into the whole equation will cause the inside rear to
lock even sooner since there will now be mechanical braking as well as
engine braking trying to slow the wheel's rotation.

I'll agree with you to a certain extent.  Too abrupt a turn-in can
certainly cause the car to spin and, no doubt, contributes a bit to my
dilema.  It's not the only component, though, and what I've discribed
above remains valid under transient weight transfer conditions.

Eagerly awaiting your reply... :)

-Chris-

Sent via Deja.com http://www.racesimcentral.net/
Before you buy.

    -A

Okay now that tells me a lot. I'd be willing to bet you prefer to allow the
higher drag of a lower coast angle to provide you with a certain amount of
cornering stability. Which has led you to the mistaken belief that you're
getting some use out of engine braking.

<snipped from Ricardo's site>

"Since engine braking doesn't increase the size of the 'friction circle', it

can't slow you down faster."

You've lifted off the accelerator entirely at this point right??

Its not just the brakes, its brake and throttle together....to quote the
late
Denny Hulme "its all a question of balance" or...

<snipped from Ricardo's site>
Ricardo Nunnini:
"As your left foot comes up, your right foot goes down
you can even start getting your right foot down before your left has
finished
coming up."

See above qoute from Ricardo

Okay, this is where you're getting hung up....when you're using a smaller
ramp angle on the coast side (or more clutches on a higher ramp angle) the
wheels will be more closely locked together which as stated before will
create a certain amount of drag (or understeer) since the wheels are trying
to rotate at the same speed. With a more open coast side angle the wheels
are allowed to spin more independantly of one another allowing the car to
rotate more freely through its directional axis (greater tendency for
trailing throttle oversteer) which has nothing whatsoever to do with a wheel
locking. Since (what it sounds like from your description) you're trying to
coast your way to the apex, you've done 2 things:

1: By lifting off the throttle you've allowed the weight to transfer
forward, add brakes to the equation and you get more, (dependant to a
certain extent on ride height) which gives the front end even more bite.

2: if you're using an a higher coast side ramp angle, the rear wheels will
be less closely locked together, which means they will be able to rotate
more independantly of one another, which will make the rear end feel much
more loose (even in a straight line).

You see, the clutch pack differential functions on torque, its hard to
explain without a diagram, but I'll give you another qoute from "Drive to
Win":

"On the over-run and under neutral throttle conditions the unit is an open
differential - there is no differential caused understeer at the apex of
slow corners or during the transition from power off to power on."

"As soon as significant power is applied the spreading force of the spyder
and side gears applies a clamping force on the friction plates which is
proportional to the amount of torque being applied and the unit becomes a
very effective limited slip differential. Under full power the unit is
locked."

Do you see now? you can't lock a wheel if the ramp angle is set to 85 with
one clutch and you've got your foot off the throttle, the tendency for
trailing throttle oversteer is greater due to the fact that it will act like
an open diff. Its a matter of making the transition from power on to power
off and the smooth application of braking force all at the same time. Once
the car settles through your apex, (and you should be gently trailing off
the brake at this point) you smoothly apply the throttle through the exit
and send the diff back to full lock.

Smoothness is the key

Thomas

: "Since engine braking doesn't increase the size of the 'friction circle', it

: can't slow you down faster."

  Actually this is erroneous - or rather it's true only in a "static"
case.  Engine braking _could_ slow you down faster if you had a reason
to want more braking at the rear at any point.  The weight distribution
of the car is bound to change from front to rear under braking.  A very
precise driver might be able to get more "stopping force" by using
engine braking to put extra braking force on the rears when the weight
shifts more "rearward" (I imagine this would be as you start to turn).

  So engine braking could help you brake by acting as a "dynamic" brake
balance.  I doubt anyone's actually good enough to make use of this in
practice - but I've been wrong before and I plan to be wrong again.

--
Richard G. Clegg       Only the mind is waving
    Networks and Non-Linear Dynamics Group
      Dept. of Mathematics, Uni. of York
    www:  http://manor.york.ac.uk/top.html

Bingo! :) I use it and I've observed many other drivers using it
too. And yes, dynamic brake balance is what we're after. The place
were I've noticed I'm using it most is when braking into T1 at
Brands Hatch. This braking zone is so weird that even with 52%
braking balance the fronts always lock before the rears. This
place actually makes you feel like you have infinite rear wheel
traction. Atleast in the Lotus. The problem is that using anything
like 52% balance or below is going to make you go tail first
into all the other corners on that track. So the solution is to
use 53-54% balance, and shift down like you're shooting aliens
with that downshifting button when coming into T1.

Regards,
  Casper

:>: "Since engine braking doesn't increase the size of the 'friction
:>: circle', it  can't slow you down faster."

:> Actually this is erroneous - or rather it's true only in a "static"
:> case.

: The sentence is correct in that you probably cannot increase the
: SIZE of the friction circle with engine braking, but! it can
: make you slow down faster :) The explanation is like you say below,
: and in 'friction circle terms' the explanation is that engine
: braking can get you closer to the edge of the friction circle,
: instead of staying way inside it.

  Well - I meant the "it can't slow you down faster" bit is erroneous.

:>  So engine braking could help you brake by acting as a "dynamic" brake
:>balance.  I doubt anyone's actually good enough to make use of this in
:>practice - but I've been wrong before and I plan to be wrong again.

: Bingo! :) I use it and I've observed many other drivers using it
: too. And yes, dynamic brake balance is what we're after. The place
: were I've noticed I'm using it most is when braking into T1 at
: Brands Hatch. This braking zone is so weird that even with 52%
: braking balance the fronts always lock before the rears. This
: place actually makes you feel like you have infinite rear wheel
: traction.

  OK - colour me impressed.  I really thought this was of
"academic interest only"  (as an academic I hate that phrase -
I mean the implication that academic == irrelevant)...  Is there
anywhere apart from Brands where this trick is helpful?  It could
be some quirk of the coding of Brands which may not be done to the
same standard as the other tracks (for example with sharp graduations in
grip levels).  I can believe this kind of thing could really make a
difference if (say) brands was coded in such a way as to have sharp and
sudden grip transitions and you found yourself in a situation where for
a car's length the rear of the car had plenty more grip than the front.

  Incidentally, does anyone know how GPL codes friction on surface.  It
would explain some of the peculiarities of the physics model if it were
coded as having a particular value exactly specified for different parts
of the track (as opposed to some kind of distribution specification
on different parts of the track).

: Atleast in the Lotus. The problem is that using anything
: like 52% balance or below is going to make you go tail first
: into all the other corners on that track. So the solution is to
: use 53-54% balance, and shift down like you're shooting aliens
: with that downshifting button when coming into T1.

  (Grin) Gaining the extra braking from the engine in places where the
rears have more grip....  I have to say tho that this seems a funny way
for things to work and may be a peculiarity of the brands coding.  By
the way, I would have thought that it would be the most effective way to
brake by waiting until after the car has settled from it's initial
"dive" when you first press the brakes before using the engine braking.
(Because there's more weight on the rears then).  Am I right or is the
effect too subtle to notice?

--
Richard G. Clegg       Only the mind is waving
    Networks and Non-Linear Dynamics Group
      Dept. of Mathematics, Uni. of York
    www:  http://manor.york.ac.uk/top.html

The previous times I've written about engine braking were used for
illustrative purposes and don't necessarily apply to my driving style.
Some of the comments do and some of the comments don't.

Sure, but it can bring you closer to the edge of the friction circle if
your setup and driving style weren't allowing you to get there
previously.

Yes.  Completely.  And fully on the brakes in a straight line way
before the turn-in point has been reached.

True, but I was referring to complete, straight-line, full honk braking
for the parabolica.  After turn-in, well that's another matter, but
during completely straight-line braking 51% is just too far rearward
for my tastes and abilities.

I don't see where Ricardo's quote is valid while under steady-state
straight-line braking.

I think we're gonna just have to agree to disagree.  I see what you're
saying and don't disagree with that, but I also still believe that what
I've been saying is applicable in addition to the things you're saying.

-Chris-

Sent via Deja.com http://www.deja.com/
Before you buy.

Been using 45 coast side, and 5 or 6 clutches usually, but I'm gonna
experiment with a more open diff and more rearward brake balance next chance
I get.

I imagine some sway bar adjustments will be neccessary to reduce the
oversteer.  Or would that just defeat the purpose?

    -A

        > > My own personal observations:
        > >
        > > --I originally used a 30 coast ramp with six clutches.  This
        > > combination gave me stability under trail-braking and trailing
        > > throttle situations.  The car exhibits little to no trailing-
        > > throttle oversteer with this combination.
        >
        > But bags of mid corner understeer.... Right?
        Yes. :)  Didn't bother me too much, though, since I'm more of a
"pitch-
        it-in-and-ride-the-throttoe-out" driver.  Probably goes part way
        towards explaining why I'm having difficulty adapting to the more
open
        coast angles.

    Okay now that tells me a lot. I'd be willing to bet you prefer to allow
the higher drag of a lower coast angle to provide you with a certain amount
of cornering stability. Which has led you to the mistaken belief that you're
getting some use out of engine braking.
    <snipped from Ricardo's site>

    "Since engine braking doesn't increase the size of the 'friction
circle', it
    can't slow you down faster."

        > The only way your argument makes any sense is if you've got your
        > brake bias set too far rearward.
        Nope.  I drive with the bias set at 56-57%.  I tried your 51% once
        and I couldn't even keep the car from spinning while I was still
        braking in a straight line.  You must be very good on the brakes. :)

    You've lifted off the accelerator entirely at this point right??
    Its not just the brakes, its brake and throttle together....to quote the
late
    Denny Hulme "its all a question of balance" or...

    <snipped from Ricardo's site>
    Ricardo Nunnini:
    "As your left foot comes up, your right foot goes down
    you can even start getting your right foot down before your left has
finished
    coming up."

        > Think about it for a second, you're claiming that less locking
        > is more likely to lock a wheel....
        Yes.  Here's why:

        Discount the brakes for the moment.  It simplifies the conversation
a
        bit.  Let's say I'm coming up on a turn.  I let off the gas which
        unloads the rear.  Since I'm coasting, the rear wheels are driving
the
        engine and supplying force to keep the engine spinning against its
        compression.

    See above qoute from Ricardo
        While I'm in a straight line, both wheels supply the same
        amount of torque back to the engine (more or less) since they're
evenly
        weighted.  When I begin my turn in, however, the inside rear unloads
        further and becomes the least loaded of the two rear wheels.  This
        unloading reduces the available traction at the inside rear and
limits
        the torque it can supply the engine for engine braking.  The engine
        back-torque will remain split evenly between the two rear wheels
unless
        more torque is required than the available traction can supply (if
I've
        downshifted to aggressively, for instance).  The wheel that will
loose
        traction will be the inside rear under these circumstances, and once
        that happens, the nearly open coast differential will send the
majority
        of the torque to the wheel with the least amount of grip (the inside
        rear).  This will make the inside rear lock since the engine back-
        torque has already overcome the available traction.
    Okay, this is where you're getting hung up....when you're using a
smaller ramp angle on the coast side (or more clutches on a higher ramp
angle) the wheels will be more closely locked together which as stated
before will create a certain amount of drag (or understeer) since the wheels
are trying to rotate at the same speed. With a more open coast side angle
the wheels are allowed to spin more independantly of one another allowing
the car to rotate more freely through its directional axis (greater tendency
for trailing throttle oversteer) which has nothing whatsoever to do with a
wheel locking. Since (what it sounds like from your description) you're
trying to coast your way to the apex, you've done 2 things:
    1: By lifting off the throttle you've allowed the weight to transfer
forward, add brakes to the equation and you get more, (dependant to a
certain extent on ride height) which gives the front end even more bite.

    2: if you're using an a higher coast side ramp angle, the rear wheels
will be less closely locked together, which means they will be able to
rotate more independantly of one another, which will make the rear end feel
much more loose (even in a straight line).

    You see, the clutch pack differential functions on torque, its hard to
explain without a diagram, but I'll give you another qoute from "Drive to
Win":

    "On the over-run and under neutral throttle conditions the unit is an
open differential - there is no differential caused understeer at the apex
of slow corners or during the transition from power off to power on."

    "As soon as significant power is applied the spreading force of the
spyder and side gears applies a clamping force on the friction plates which
is proportional to the amount of torque being applied and the unit becomes a
very effective limited slip differential. Under full power the unit is
locked."

    Do you see now? you can't lock a wheel if the ramp angle is set to 85
with one clutch and you've got your foot off the throttle, the tendency for
trailing throttle oversteer is greater due to the fact that it will act like
an open diff. Its a matter of making the transition from power on to power
off and the smooth application of braking force all at the same time. Once
the car settles through your apex, (and you should be gently trailing off
the brake at this point) you smoothly apply the throttle through the exit
and send the diff back to full lock.

    Smoothness is the key

    Thomas

Thomas

You can indeed make straight line braking more stable by using more clutches
or lower ramp angles, but it just might be better to do it by adjusting the
brake balance.

Unfortunately, I have no idea how Thomas is getting away with 51%.

    -A

Having said that, even if you don't plan to use this kind of setup in
competition its an excellent way to improve your sensitivity and also learn
something about the operation of the limited slip differential. Chances are that
people will still stick to the 85/30 (on a low slung chassis....but thats a
whole 'nuther can 'o worms) due to the fact that it's more tolerant of throttle
and brake transitions, although I wouldn't be surprised if a Lake or Woeger type
could brake some records with 45/85.

Thomas

PS I'd be glad to send you some replays/setups if you're interested...drop me a
note.

Well it depends very much on driving style and preference. I'd
say its used in varying degrees on different tracks. At
Monza for example where all the braking zones are similar
to each other (no elevation change and pretty straight braking),
I use a braking balance of 53% (if I remember correctly). With
this balance its strictly forbidden to use engine braking, since
it immidiately throws the car around. This is a kind of
counter-example to engine braking, but I just wanted to point
out that how rapidly you downshift when braking does have
an effect on car stability and stopping power. I could use
55% balance at Monza, but I'd have to downshift like mad at
every corner, and I'd still not get the same stopping power
as with 53%.

No, I don't think this is the case. The braking zone for T1 at Brands
is just plain evil. First it's an uphill jump over the finish line,
which obviously reduces your grip to close to zero, then as you come
down from your short flight the springs compress and you gain
additional grip from the car settling back onto the track, and then
finally the road dips away from underneath the car going downhill
and turning to the right at the same time.

Now, you don't need no sharp graduations in grip level coded into
the track. You get those sharp changes in grip level just because
of the roller coaster ride provided by the natural elevation
changes of the track.

Well if I'd have to guess I'd guess the grip level is coded
as an overall grip level for a particular track. With no
section specific levels. This isn't a rallycross sim after
all ;) But I might be wrong...

As I said above I think this is just as it is supposed to work. It
might seem strange at first, but if you think how the car is
being thrown around the grip levels of individual wheels
is bound to change just because of the physics involved, not
because of anything coded into the track.

You're right. And hitting the brakes to soon and too hard locks up
everything. But you can begin downshifting quite early still (about
the same time as you start to apply the brakes), since it takes a
little bit of time for the computer guy in the car to get his hand
on the stick, press the clutch (?), blip the throttle, and move the
stick down a gear.

You can check out my Brands lap at Schubi's if your interested in how
its done :) I STILL manage to lock up a front wheel though...

Regards,
  Casper

<much snippage>

Ok, let's hear it from the professionals:

http://www.itv-f1.com/pitpass/4604.2html

In that transcript, Damon Hill and his engineer seem to be curing
oversteer by increasing diff loading. This is more to do with
traction, but it might offer some insight.

-joe-

I always presumed that if you let the wheels rotate more as they wish
they won't scrub as much and so more grip is obtained, hence less diff
locking gives more drive-wheel grip.

I have another question here, somewhat theoretical as I'm interested
in the ideas rather than the practice (I don't have GPL as I'm without
a system to run it on). When diff locking is increased, the drive
wheels cannot turn as indepentantly through a corner. When cornering,
weight shifts to the outside wheel and so it has more grip. The
natural tendency of the outside wheel is to turn faster than the
inside, but with more locking it must turn at a more similar speed to
the inside.

Does the outside wheel drag the inside wheel up to its speed, or does
the inside slow the outside wheel down to its speed? I'm guessing the
former as the outside has more grip.

-joe-

I don't know if you're right about grip, but moving the brake balance
rearward would help take advantage of the extra grip if there is any.  The
catch is, that if you go too far rearward, the rears will lock up because
you don't have any "ABS".

I've been experimenting with a more open diff, and moving the brake balance
just one or two clicks back, and it seems to work pretty well.  It does seem
like I can brake a tiny bit harder now.  I chalked this up to less friction
from the diff, but it could be more grip just like you say.

    -A