OK driver education is always tops... but here's the reason this is significant... on a stock car, not too much... when you start adding power, forward traction becomes the primary limitation, and once you start increasing the power more and more, it very significantly becomes the limitation in a very obvious way.
You can ignore that, fine, for people really looking to improve, hope they think beyond what everyone else says. Motorsports of all sorts there's usually reason to add weight in certain areas. The Fiesta ST does AX as well or better depending on the course, with a full tank of fuel... there's a reason for that. On a stock suspension car, the weight transfer and the performance curve of the tire can be optimized with a full tank compared to empty tank, so if there's only 300-600lbs of transient pressure on the contact patch of the rear tire, it's probably well on the left side of the curve... when it's off the ground it's zero lbs of course... but then is it the performance limitation? It's a problem solving excercise, what can we do within a given ruleset.
You can ignore that, fine, for people really looking to improve, hope they think beyond what everyone else says. Motorsports of all sorts there's usually reason to add weight in certain areas. The Fiesta ST does AX as well or better depending on the course, with a full tank of fuel... there's a reason for that. On a stock suspension car, the weight transfer and the performance curve of the tire can be optimized with a full tank compared to empty tank, so if there's only 300-600lbs of transient pressure on the contact patch of the rear tire, it's probably well on the left side of the curve... when it's off the ground it's zero lbs of course... but then is it the performance limitation? It's a problem solving excercise, what can we do within a given ruleset.
[ As to the "full" tank of gas - that's ~11 gallons, which weigh 66 pounds (6 lbs per 1 gal); it also does not behave as a solid body (in a non-round tank), generating a non-trivial roll moment of inertia. So, yeah, when superimposed with the rotation of the rear of the car, it produces a synergestic effect - something that a rigid roll bar can't. ]