rec.autos.simulators

I downloaded Leonoardo Grandis' setup for Monza at Schubi's site. He
has his brake bias at 51. How the hell is it possible to brake in a
straight line with the bb at 51?? I have to set it at least to 53 to
brake in a straight line, and I have to be -really- carefull then,
especially with his setup.

Any tips?

Andre

The reason Leonoardo can handle it is severe trail-braking.  Try a tiny bit
of accelerator while gradually easing off the brake into the corner
         Its F$$$&&&G difficult  :-)     Dan Leach

On Mon, 3 Jul 2000 15:57:06 +0100, "Dan Leach"

It's not the trailbraking I think. For example, when I brake for the
Parabolica at Monza,  first I brake without giving gas. As soon as the
tires start screeching lightly (normally a very good braking point)
the car becomes unstable as hell and I have to fight heavily to keep
it under control. While fighting against the spin, I don't brake
optimal, resulting in a nice juicy crash at the end of the straight.

When I watch Leonardo's replay, his tires screech even more than mine
do, he brakes even more, and the car seems to be very stable.
Can't image how he does it... but I like the bias at 51 for all the
other corners, it's great for CG, and perfect for trailbraking at the
Lesmo's. I would love to be able to brake at the Para with the bias at
51....

PS 1) Leonardo drove the current record at Monza with this setup,
1:26.49...

PS 2) I just got a very bright idea: I also mailed the question to the
master himself :) I'll let you know if and what his answer is.

Andre

One way the car can become unstable in yaw under braking
is the rear tires starting to lock up, losing their capability
to contribute sideforce. The rear tires sideforce acts like the
fletching (feathers, etc.) on the back of an arrow or the tail surfaces
of an airplane. Just through geometry, when the car rotates,
the rear tires give torques that tend to straighten the car back
again while the front tires (assuming they aren't also locking)
give increasingly large torques with increasing angle that tend to
make the car rotate even faster. Front tires destabilize while the
rear tires are stabilizing.

If you lock the rears before the fronts lock, the car
becomes unstable in yaw. (A small angle tends to become very great
very fast until it quickly exceeds where the spin can be caught
and corrected.)

If you use some throttle you are (in effect) increasing the brake bias
back toward the fronts because the drive torque cancels some
of the rear brake torques. So you can use throttle to compensate
for brake bias too far aft, but it seems like an advanced technique ;)

Presumably, the rears aren't locking.

Another possibility is superhuman ability. It isn't impossible to
drive an unstable car, just very hard because you have to be so
quick and so precise. ;)

Also, if there aren't any yaw disturbances then the instability
doesn't come into play, ... much. ;)    I spin my GPL
car under braking even with safe brake bias settings because I get
into situations where I have to brake hard when the car isn't properly
settled. The weight transfer changes cause yaw disturbances I'm too
slow to correct.

- Matt

Very well said, only one point missed, while braking and applying the gas,
the torque applied to the rear wheels also pulls the car lower to the ground
making it more stable. (Lower CG). I personally use 46-48% brake bias and
use heavy trail braking.....

Ken