Well, your car is poorly balanced, being a WWD car. It probably does help the balance to leave the spare in the trunk. As for the gas, it would depend on your car. My cavalier used to starve if it had less than a 1/4 tank. My Miata can run on or below "E", but it has a baffeled tank. At most events I don't care how much gas I have. At the PCA event, I had over 3/4 tank.