RE: Bumps, Suspension, Etc.

["Dave Dahlgren" <ddahlgren@snet.net>]

I have worked with the data quite a bit and tell you the following with a
few reservations. The first one being we have to find a way to log this data
both as down force and travel in inches. this will unfortunately for the
short term require using 8 channels rather than 4. The reason being that the
response curve in both down force and travel is not linear and is subject to
using only 6 data points to make it linear. Not ideal but better than a
straight line. Second is that the initial down force calibrations were done
with a couple of assumptions that proved incorrect. The largest one being we
were looking for lift and had more data points in the lift range than the
down force range or at least they are over a wider range. What we got was
down force over the entire run rather than lift so all the lift data points
in the calibration were wasted.

In places other than a gear change or other major input into the car the
travel is small at Bonneville. Approximately 0.10 inches as an average but
the car does move down with increased lift from the down force. So the
movement is superimposed on a curve that is progressively showing more down
force with the same chassis/wheel movement. There is some periodic movement
in the suspension That is fairly regular but does move up in frequency with
speed. I would suspect it is the natural frequency of the suspension or
shocks and is somewhat different front to rear which would further support
this thought as the rear suspension is much heavier.

During a gear change is when things get busy. You can watch the front unload
and drop as well as the rear go up. The when torque is applied you can see
the interaction of the RR tire vs. the LF tire and they move in very
predictable ways as well as the front come back up due to weight transfer.
Granted it is not as dramatic as a drag race car but the G forces are much
lower as well. The amplitude of these movements also decrease as you work
your up in gears just as you would suspect due to have less torque to apply
to the suspension. All of this data also matches up with the data from the
wheel speed sensors and the accelerometers as well. In my mind it make it
very believable. If any of it was noise I would assume the noise would be
present with the car sitting still and other than when the throttle is
snapped the traces are dead flat with changes in the 0.1 lb range. If you
snap the throttle there are some changes of about 10 lbs also believable.

I think there are a few things to learn here that are most important and
actually discount the actual suspension travel due to the salt condition as
that is something you can not change. I think you want to keep it to a small
amount, less than 0.1 to 0.2 inches and after that you are done with that
part. The two most important things to learn involve down force and lift
curves along with what is actually happening during a gear change. These are
things you can change. The down force while seemingly a good thing is still
drag. Knowing how much you have will tell you how much you have to either
add or get rid of to attain the desired speed. It will also indicate if you
are getting into lift and either losing traction or getting into a situation
that car will be uncontrollable. Some might say at this point to just add
ballast and that is fine if they want to do that, but if you still have the
lift that you are trying to counteract with ballast you still have the
associated drag from the lift so while you might go faster with the ballast
you will not go as fast as if you got rid of the lift in the first place.

The second most important thing to lean is what happens during a gear change
to unload the car. From what I can see a slow lazy shift is a great way to
unload the car and get into more problems than you going to fix by taking
your time and being gentle and smooth with the car. Having the luxury of
having 3 people drive the car while recording all this we do have the
profiles of what happens with 3 different driving styles. I can tell you
without a doubt that the slower the shift the more the rear unloads in down
force due to weight transfer, and the more suspension movement you get when
reapplying throttle. Personally I can now picture spinning a car with a slow
gear change rather than just hammering the gear change and not upsetting the
current weight balance. The other thing I think I can predict is that at
zero G input ,at least with this car and current springs and ride height
that the car will settle down in the nose and rise in the rear losing rear
down force and gaining it on the nose..

More later when there is more data.
The software package is the standard one that ships with the Edelbrock quick
data unit, and while not all that sophisticated is a fairly accurate
graphing program that does leave it up to the user to do the data
interpretation.

Dave Dahlgren