IIRC, a gallon of water weighs ~8# and gasoline is lighter, but a quick web search failed to yield a number. I’ve carried gas cans before, let’s estimate 6#. Car tanks run, generally, from about 10 to 20 gallons. So, with a large tank, you’ve got about 120# sitting just behind the rear end that’s not there when you’re near empty.
I know when I drove a smaller car I could definitely feel a difference in handling (more at speed than edging into a parking space) when I had a person (let’s say average 150# for a person) with me than when alone.
Considering that most people are alone in their car most of the time they’re driving it (not known if this is true for you), I’d guess you might be able to feel some difference in handling dependent on the state of the fuel tank.
Yeah of course your car handles differently with a full tank, but what ARG was saying was that his handles better with a full tank. FWIW, mine does too, but I drive a Mustang, and they’re notoriously light in the rear end.
WAG time: I think any car would feel more stable with extra weight in the back (maybe this only applies to rear-wheel drive cars).
Don’t ask me to prove it tho
my car is front wheel drive and it runs significantly better with a full gas tank. of course, it wouldn’t surprise me if this was because of a fuel pump problem or something. my car is a piece of crap.
As Beatle pointed out, you’re noticing a lower power/weight ratio. In my experience, an “average” person can notice a difference of 50lb or 10 HP. Apparently, you prefer this lower ratio (personally, I prefer a ratio of .1 or higher). It’s just a matter of personal preference.
Also, FWD “understeer” (it’s not really, people just got used to RWD oversteer) becomes more noticeable with less weight behind you.
Do try to keep at least 1/4 tank of gas in cars w/ electric fuel pumps. The pump uses the fuel for cooling.
And Beatle, good guess. Gasoline is about (depending on additives) 6.2lb/gal.
Cars are engineered to facilitate a wide range of loads, from a single driver to a fully occupied passenger compartment pulling a heavy trailer. That being said, most cars will handle better with a load of some sort placed on the suspension. Springs, shocks and struts will feel “tighter” when compressed somewhat. A full gas tank may only add 120 pounds, but that weight is enough to take some of the travel out of the suspension, providing crisper handling.
Race cars are set up for different scenarios (qualifying: near empty tank, higher speed and racing: full tank, optimal acceleration) by tuning suspension components. You can modify your car’s handling by replacing factory components with specialized parts (some are adjustable) or by placing a sandbag or two (or your mother-in-law) in your trunk.