Maintaining gas tank at 3/4

I just plotted the data for rolling resistance + aerodynamic drag; the blue line is a full tank (using Toyota's listed curb weight plus a 150 lb driver); the orange line is 3/4 tank, 18 lbs lighter. This is the difference in force that must be overcome for a given steady velocity:



It will make more difference in stop-and-go driving. But 18 lbs isn't much.

 

Wheels at 17” shouldn’t matter if your sustaining high speeds constantly when it comes to FE. If your driving stop and go on 17”s it’s the stationary-to-going forward work that the engine has to do which affects FE negatively

My JNCAIR stays home most of the time. The air compressor is great also.

 

Request for 70lbs reduction graph please, thanks.

 

My aviation training was that gasoline weighs about 6 pounds per gallon (less than water), so the weight savings of keeping the tank 3/4 full would be just 3x6=18 pounds.
I’ve opted to increase vehicle empty weight by carrying a full sized spare tire and rim , which cost me about 20 pounds more, plus emergency and survival equipment, which is a different focus for the obsession.

 

maybe my dude has water in his tank

 

My arithmetic training says that if Owner A fills the tank, while Owner B fills it only 3/4 full, and both refill at the same level, then Owner A's tank will contain exactly 1/8 of a tank more fuel on average, or about 9 pounds. "A" will waste less time buying fuel.

 

I know he rolls without a lot of the interior trim parts .

Who needs a backseat anyway.

 

Great plot. Thanks. I believe it. To me it shows the obvious - that MPG is highly dependent on speed, and comparing anything without factoring out that effect can easily lead to doubtful conclusions.

One possibly useful interpretation from this, just eyeballing the plot, is that at highway speeds, dropping 70 lbs gets you the same MPG gain as slowing down by about 1/2 mph. That may be a useful factor to consider while stripping your car to the bones.

Also, on the jump pack mentioned earlier, for something like that, I'd be more concerned with it becoming a dangerous projectile in a crash vs. any MPG effect.

 

My jump pack looks like somewhat bulky attache case, is stowed in the tray under the hatch floor. Still, good point, anything not secured atop the hatch floor could hit you in an accident. The rear seat back would help though.

 

There are actions of economy that I think reach ridiculous levels. This would be one of them.
Sure a 3/4ths tank is slightly lighter than a full tank...but come on? You own an operate a HYBRID with an HSD system. It's designed to be fuel efficient...period. Any minimal...and I mean MINIMAL gain one might have from the weight difference between an emptying full tank vs, an 3/4th full fuel tank isn't worth the effort. I would never do it.
First of all, with my full tank? I get the benefit of that much more driving range before I have to fill up again. And that weigh penalty? Is only going to exist for 1/4th the tank. Soon enough, I'll be at 3/4th and lessening. I would recommend filling and reaching a reasonable point of emptiness and repeating....but filling to try to maintain a constant state of 3/4th filled?

I've got much better things to do with my time.

 

Ok, spreadsheet time. Considering, full capacity is 45 liters, and you fill up when the tank is down to 1/4 full, then the average amount of gas you're toting is 5.625 liters less. Considering gas weighs slightly less than water (and a liter of water weighs a kilogram), on average the car weighs say 5.5 kilos less, or about 12 pounds.

 

Sumpthin' tells me that most of us would get a greater fuel economy improvement by going on a diet.

 

Seriously.
I've been researching tires, and depending on what tires you buy to replace you can impact levels of weight.
Pick up a load of groceries, carry a passenger...and that 1/4th a tank weight difference is eclipsed.

Sometimes I say...just drive and operate the vehicle.

Interesting to me, that if some people want a roof rack, or a bicycle hitch, they'll happily just install them and use them. Which is fine. But they will take an MPG hit when using them.
Meanwhile, some people obsess over the weight of a fully filled gas tank.

Also you have some people that have wished for a larger capacity tank...for further range.

I'm supportive of being supportive of efficiency, but some things just aren't worth it.

 

Gasoline is only about 75% as dense as water, so only about 9 pounds average difference, as I pointed out in an earlier post.

 

Yes but then I lose about 5% in fuel cost because I cannot take full advantage of my Harris Teeter fuel points.

Can't win.

 

Agree:

5.625 (kg, if water) * 0.72736 * 2.2 = 9.00108 (lbs, of gas)

 

yes...the HSD is designed to be efficient. However, weight obviously plays into it...as you well know, I'm sure. Heck Toyota removed a bunch of things on the Eco model to save 65 pounds or so ( curb weight of the Eco model is 3010lb vs 3075 lbs ). I can also *really* feel the difference between our Prius v wagon and our liftback ( 3274lb vs 3042lb ). And I can also really feel the difference when I remove the rear seats on the v wagon ( they are heavy )! The point is...the pairing of the drivetrain with the vehicle weight is a huge indicator of how said vehicle will perform ( or not ). And like you pointed out, I'm not sure folks think about how much of a hit they will take when installing accessories like roof racks, etc...

But yeah...the gas tank thing is overkill, for sure. However, you never know what these extreme hypermiler types will do to save weight.

 

pics or it didn't happen