I tend to let my tank get to about a quarter full before I refuel. And when I refuel I fill to the top.
When at a quarter the car seems more responsive because it is considerably lighter.
What if I were to live close to the wire: i.e. let the car get to the last bar, and only refuel to one quarter or a half?
This would mean the car is always lighter (burns less fuel to move it’s weight) but I would be making more trips to the garage.
Most of the trips to the garage will be at the start or end of an intentional journey for some other purpose, so I’d be driving anyway.
It’s satisfying to have a full tank of fuel, but it’s also satisfying to have a more responsive car (and to know that I might be getting better fuel mileage)
I’ve never noticed this difference in my car, either in mileage or in responsiveness. According to WikiAnswers, gasoline weighs less than an equal volume of water at 60 degrees F. My car’s 15 gallon tank would, using the numbers on that site, hold about 92.25 lbs. of fuel when full. Having an extra adult in the car would make more difference weight-wise than having a full tank vs. a quarter full.
Comparing “fill-up to full & run down to empty” vs “fill to 1/2 & run down to 1/4” …
The fuel mileage difference for the lighter weight is so slight that driving 300 meters out of your way to get to the filling station would more than offset the gain from it. Depending on your car the turnover point might be closer to 100 meters.
Unless you have a tiny car with a relatively huge fuel tank, or one so underpowered it can barely get out of its own way, I’d be surprised if you could feel an obvious difference between a full & 1/4 tank.
I suspect some self-fulfilling thinking is underpinning your perception. You know the tank is full & therefore you expect the car to feel sluggsh, so it does feel that way. An actual measurement of performance under the same circumstances might show a non-zero, but still negligible difference, or it might well show zero depending on your instrument’s accuracy.