Glenn,
Don't feel too bad, I'm not sure that I understand the terms too well
either. I didn't even consider either until the car had spun at two
consecutive meets. After discussing our problem with a few more savvy
racers, I understood that the center if gravity is the weight balance
point front to rear. (As Jack has suggested, it is easy to find by
taking a couple of floor jacks and finding the point, fore & aft, where
the car will balance.) The center of mass is an aerodynamic
consideration. (the part of the vehicle that produces the most
resistance going through the air.) A bit more difficult to determine. I
understand that this point may even change as the car increases in
speed. Basically, it seems to be the biggest part of the car.
Considering a coupe/sedan, it would be at the windshield area, I would
think.
When we checked our car, the center of gravity was about six inches
behind the front of the door opening. We chose a location directly below
the bottom of the leading edge of the windshield, jacked the car up at
this point and added weight to the front of the car, roughly three feet
behind the front axle, until it balanced. It required 500 lbs. The car
weighs about 3000 lbs with the 500 lbs in place without the driver.
At the World finals in 1997, I took the first ride, and as I have
stated, the car literally freewheel for better than a mile on a very
loose course. The car moved, (drifted) from side to side on the course,
but without a hint of the rear wanting to get out to the side. I
considered the car cured.
At the previous meets, both spins had been snap spins, around once and
on down the course. We caught the spin at the World of Speed on video.
It took about two seconds from going straight down the course to
completing a spin and headed on down the course. (This spin is on my web
page if you would like to see it. www.bryantauto.com)
As has been mentioned already, how much a car is out of balance will
definitely affect the results of ill handling. After a couple of runs at
the World Finals, Jeff hit a hole on the turnout and broke a suspension
arm. I hadn't changed the front springs and the extra weight got us into
a coil bind situation. We fixed the damaged arm and took out about half
the weight. This put the car back into an unbalanced condition, but not
as sever as before the weight was added. However, this time when the car
got into trouble, it went into a long lazy spin, giving it more time to
dig in and get up side down. If I was able to choose, I would prefer the
quick spins.
Since all this, we have added a spoiler and taken out the weight. The
car has had no problems since. Of course, we have been running on better
courses and, since 2000, have been running gasoline instead of the
Alky/nitrous setup. When discussing this issue, I like Tom Burklands
comment. He said, "Think of the car as an arrow, you can add weight to
the front or feathers on the tail." At this point, the feathers seem to
be working.
Tom, Redding CA - #216 D/GCC
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