rec.autos.simulators

by **Haqsa** » Wed, 23 Apr 2003 00:09:22

Anybody know the motion ratios for a Winston Cup car suspension? I have
been playing around with setups in NR2003 and I am pretty sure that the roll
couple calculation shown in the setup screen is way wrong. They appear to
be using a front motion ratio of around 0.9 (spring motion / wheel motion)
and a rear ratio of around 0.5, but the pictures I have seen of NASCAR
suspensions seem to indicate that those two numbers should be reversed.
Thanks in advance for any information you can provide.

by **Doug Millike** » Wed, 23 Apr 2003 00:44:01

Reversed sounds about right (0.5 front, near 1.0 rear).

> Anybody know the motion ratios for a Winston Cup car suspension? I have
> been playing around with setups in NR2003 and I am pretty sure that the roll
> couple calculation shown in the setup screen is way wrong. They appear to
> be using a front motion ratio of around 0.9 (spring motion / wheel motion)
> and a rear ratio of around 0.5, but the pictures I have seen of NASCAR
> suspensions seem to indicate that those two numbers should be reversed.
> Thanks in advance for any information you can provide.

by **Haqsa** » Wed, 23 Apr 2003 02:29:43

Thanks. The reason I was looking into this is because the typical setup
included with the game shows a roll couple of about 91% in the garage
screen, and typical setups that I have downloaded show around 96%. I don't
believe a car would be driveable with that much front roll stiffness, but I
could be wrong. If I use motion ratios like the numbers you give they
appear to be more like around the 75% to 80% range, which makes a lot more
sense.

by **JTBur** » Wed, 23 Apr 2003 04:58:50

I motion that Jeff Gordon be suspended.

I motion that Jeff Gordon be suspended, but I don't know the ratio..

by **Doug Millike** » Wed, 23 Apr 2003 07:01:41

I'm pretty sure that the car would be drivable with 100% of the roll
torque taken on the front wheels, but depending on weight distribution and
other things it might push pretty badly... (and would be really tough to
set up for a long run).

Would be hard to get that configuration mechanically, the rear springs add
some roll stiffness no matter how soft they are. I don't think that
NASCAR would like to see anyone show up with just one rear spring over the
center of the axle<grin>. 100% front has been tried (with other
mechanical arrangements), in other kinds of race cars, sometimes quite
successfully. All the above discusses the spring & anti-roll bar
contributions ONLY (no discussion of roll-center height).

> Thanks. The reason I was looking into this is because the typical setup
> included with the game shows a roll couple of about 91% in the garage
> screen, and typical setups that I have downloaded show around 96%. I don't
> believe a car would be driveable with that much front roll stiffness, but I
> could be wrong. If I use motion ratios like the numbers you give they
> appear to be more like around the 75% to 80% range, which makes a lot more
> sense.

> > Reversed sounds about right (0.5 front, near 1.0 rear).

by **Ed Solhei** » Wed, 23 Apr 2003 23:34:04

Read - learn - fix - release.

--
ed_

"Haqsau" said:

> Thanks. The reason I was looking into this is because the typical setup
> included with the game shows a roll couple of about 91% in the garage
> screen, and typical setups that I have downloaded show around 96%. I
don't
> believe a car would be driveable with that much front roll stiffness, but
I
> could be wrong. If I use motion ratios like the numbers you give they
> appear to be more like around the 75% to 80% range, which makes a lot more
> sense.

> > Reversed sounds about right (0.5 front, near 1.0 rear).

>>> Anybody know the motion ratios for a Winston Cup car suspension? I have
>>> been playing around with setups in NR2003 and I am pretty sure that the
roll
>>> couple calculation shown in the setup screen is way wrong. They appear
to
>>> be using a front motion ratio of around 0.9 (spring motion / wheel
motion)
>>> and a rear ratio of around 0.5, but the pictures I have seen of NASCAR
>>> suspensions seem to indicate that those two numbers should be reversed.
>>> Thanks in advance for any information you can provide.

by **Eric Busc** » Thu, 24 Apr 2003 08:07:38

The display in the garage is really more of what should be called "front
roll stiffness distribution". Basically it's a measure of the
percentage of roll stiffness of your suspension (as determined by spring
and anti-roll bar selection) that comes from the front suspension.
Unlike a true "roll couple distribution" measurement, this value is
independent of roll center height (which in the game is fixed in the
front, and adjustable in the rear via the track bar).

- Eric

by **Haqsa** » Thu, 24 Apr 2003 09:12:06

That image brings up a good point - the motion ratio for the rear springs is
not actually the same in roll as it is in vertical motion. In fact looking
at a model I have, I would guess the rear springs have about a 0.5 motion
ratio in roll, since they are mounted about halfway between the driveshaft
and the tire centerline in rear view. The example case I am trying to match
is with the front springs set to 700, rear to 300, and bars to 0. In the
NR2003 garage screen this gives me a front roll couple of 85%. So now if
the front motion ratio is 0.77 and the rear is 0.5 I get the same results as
Papy. I can accept 0.5 for the rear based on the above considerations, but
0.77 doesn't seem right for the front, that would require fairly long arms
and narrow tires, neither of which they have.

by **Haqsa** » Fri, 25 Apr 2003 02:05:58

That's what I thought front roll couple meant anyway. The thing I am trying
to figure out is this: it has been widely said, even in Papy manuals (N4
manual for example) and online help, that one normally wants a front roll
couple of 70% to 80%. Yet the Fast and Jasper setups are typically around
90% (according to the garage display), and some very fast setups that I have
downloaded are more like 96%. Further, when I try to get down to even 80% I
end up with spring and bar sizes that are very unrealistic. There is very
good documentation of what typical spring and bar sizes are, both online and
in the old N4 manual, and when I plug these in I am once again up in the 90%
range, according to the garage display. I'm just trying to figure out where
the disconnect is. I thought maybe it was due to motion ratios but now I'm
not so sure. One thing that does not appear to be accounted for is the roll
stiffness that is inherent to the rear suspension design. According to RCVD
the rear trailing arms are attached solidly to the axle, which means the
suspension assembly itself has some torsional stiffness in roll. Is this
accounted for in the garage roll couple calculation? Is it accounted for in
your handling model? If the answer to the first question is no and the
answer to the second question is yes then it all makes sense. If not, then
I think there is still a disconnect somewhere.

by **Eric Busc** » Fri, 25 Apr 2003 08:29:19

As I stated earlier, the real disconnect is that for NR2003 the value
displayed in the box really isn't a measure of front roll couple. Front
roll couple is dependent on roll stiffness, but it is also largely
dependent on the front and rear roll center heights. The value
displayed in NR2003's garage is not, and you can see this difference for
yourself in the game. As you change the anti-roll bars and springs
you'll see the displayed value change as expected, but if you change the
track bar height (the front roll center is fixed) you'll see that it
doesn't affect the displayed value at all. The recommended value is a
holdover from NR2002 (it simply was never updated for NR2003), so don't
worry too much that it doesn't match. For what it's measuring, it
matches up quite closely with a real Winston Cup car.

- Eric

by **Doug Millike** » Fri, 25 Apr 2003 11:06:25

We like "Total Lateral Load Transfer Distribution (TLLTD)" for
the combination of "springs/bars/aux-roll-stiffness" and "RCH effects".
See RCVD page 679 (bottom)--avoids a lot of confusion.

Auxillary roll stiffness might be, for example the windup of a NASCAR
rear axle (acting like an anti-roll bar).

-- Doug Milliken
www.millikenresearch.com/olley.html <-- new book here

> As I stated earlier, the real disconnect is that for NR2003 the value
> displayed in the box really isn't a measure of front roll couple. Front
> roll couple is dependent on roll stiffness, but it is also largely
> dependent on the front and rear roll center heights. The value
> displayed in NR2003's garage is not, and you can see this difference for
> yourself in the game. As you change the anti-roll bars and springs
> you'll see the displayed value change as expected, but if you change the
> track bar height (the front roll center is fixed) you'll see that it
> doesn't affect the displayed value at all. The recommended value is a
> holdover from NR2002 (it simply was never updated for NR2003), so don't
> worry too much that it doesn't match. For what it's measuring, it
> matches up quite closely with a real Winston Cup car.

> - Eric

> > That's what I thought front roll couple meant anyway. The thing I am
> trying
> > to figure out is this: it has been widely said, even in Papy manuals
> (N4
> > manual for example) and online help, that one normally wants a front
> roll
> > couple of 70% to 80%. Yet the Fast and Jasper setups are typically
> around
> > 90% (according to the garage display), and some very fast setups that
> I have
> > downloaded are more like 96%. Further, when I try to get down to even
> 80% I
> > end up with spring and bar sizes that are very unrealistic. There is
> very
> > good documentation of what typical spring and bar sizes are, both
> online and
> > in the old N4 manual, and when I plug these in I am once again up in
> the 90%
> > range, according to the garage display. I'm just trying to figure out
> where
> > the disconnect is. I thought maybe it was due to motion ratios but
> now I'm
> > not so sure. One thing that does not appear to be accounted for is
> the roll
> > stiffness that is inherent to the rear suspension design. According
> to RCVD
> > the rear trailing arms are attached solidly to the axle, which means
> the
> > suspension assembly itself has some torsional stiffness in roll. Is
> this
> > accounted for in the garage roll couple calculation? Is it accounted
> for in
> > your handling model? If the answer to the first question is no and
> the
> > answer to the second question is yes then it all makes sense. If not,
> then
> > I think there is still a disconnect somewhere.

by **Eric Busc** » Fri, 25 Apr 2003 12:41:37

Manuel Daskalos of Jasper Motorsports had suggested displaying the
arguably more useful front LLTD percentage, but unfortunately it was
never implemented for NR2003.

- Eric

by **JazzyJ** » Tue, 20 May 2003 15:43:37

I would say it depends on your driving style and what the rest of your
set-up is. I can tell you that some drivers in Winston Cup run big
front bars and some run smaller front bars. I would say as a rule of
thumb a roll gradient between .9 and 1.2 degrees is a resonable range.
RSD numbers typically range from 82% on the softside and 88% on the
highside. Alot of your FARB selection depends on you spring
selection. Your spring selection depends on several factors such as
track surface, aerodynamic pitch attitude and some but to a much
lesser extent RSD, and fore/aft and squash wedging concerns.

by **JazzyJ** » Tue, 20 May 2003 15:56:03

To add to my earlier comments, the rear truck arms add to the
effective roll stiffness of the rear of the car. The only data I have
seems to suggest it is about 20 percent of the rears total roll
resistance. This changes depending on what style of connection you
use for your truck arm bushings (monoballs, small *** bushings or
big *** bushings).

It is true that LLTD is a more encompassing element of the cars
handling. WC stock cars being panhard bar solid axle rear end cars
have the distinction to having a large percentage on their roll
stiffness distribution being to the front. This is of course is due
to the high roll center position in the rear. In other words, most of
the weight transfer across the front end is across bars and springs
where as most of the weight transfer across the rear is across the
solid geometry of the rear panhard bar.

Therefor, RSD is not a tell tale sign of overall LLTD. In fact, it
goes to show you why large bar changes often result in a very little
change in actual balance of the car(although they do offer transient
handling and driver feel changes).

In my experience, typical dynamic LLTD values occure around -1% to +3
percent of the nose weight percentage value.

by **JazzyJ** » Tue, 20 May 2003 16:07:38

Typical motion ratios vary depend on how a given team decides to mount
their spring buckets and shock mounts in the front. But in general
these are the numbers that I see commonly on different cars that have
been roamed.

In ride:
LF spring .54, RF spring .51, Rear springs .85
Front shocks .75
Rear shocks 1.05

In roll:
front sway bar .785
rear springs (35" spread)
front springs (IFS calcs)
rear shocks .585

These can vary depend on different styles of cars, car parts and
geometry styles.

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