Better economy at the top of the tank?

^^^ here is an equation I stole from the Chevy Cruze chats.
My intent was to post this this on the spare tire thread but I will offer it here.
Think it says +50-lbs is -0.6 MPG at 50 MPG for 3165 car weight (PiP).
<:ASIDE>

...here's an equation that approximates the WT vs. MPG trade-off:​

​

(MPG2/MPG1) = (WT1/WT2)^0.72​

...where:​

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MPG1= prior fuel economy, mpg​

MPG2= new fuel economy, mpg​

WT1 = prior weight, lbs​

WT2 = new weight, lbs​

​

​

• addendum: equation is valid for vehicles in the 3,000± weight class (per GM engineer).​

​

​

Read more: http://priuschat.com/threads/relation-to-fuel-economy-vs-vehicle-resistance.116207/#ixzz2NwvAK3N7

 

Nope. All glide energy must be come from kinetic energy produced originally by the gasoline motor, more kinetic energy mean more gasoline. Unless one figures out a way to have the car only be heavier going down hill, weight will always negatively impact mileage.

I suppose you could always buy gas at the station at the top of the hill...

 

Interesting point about the weight of the gas, especially in a hybrid car this small.

While I have nothing but hearsay to reference, I've often been told my mechanics throughout my life that cars get better mileage on the "top half" of tank. Not that this was a true reading of fuel consumed, but rather a factor of how the gauge appeared to read.

My daily trips are rock-solid in their repetitiveness, at the most they might vary by a single lane change. I gotta get me a scangauge or somesuch so I can do the experiment.

 

...and depending on the car, those same mechanics may have been correct... as far as how the gauge "read"... but this can be vague. My 2001 Saturn SC2 would let me travel 110 miles on the first 1/4 of a tank if I filled it to the brim... but then would only get about 100 miles from 1/4 down to only 1/4 left... but I could go another 100 miles before my light would turn on. At that point I had another 70 miles. I avg'ed 350 miles per tank in that car.

Whereas the other end of the spectrum. The F-150 I borrowed from my cousin would get 150 miles on the first 1/2 of the tank but then another 250 on the bottom half.

So far, my perspective in this car isn't very happy with the gauge. The first bar can go well over 100 miles, but then the other 9 are no where near that... though, could you imagine if they were?

 

My first tank, dealer filled, got 162 MILES before the first bar went down. I did some quick math, nearly fainted, and then wondered how the rest of the tank would play out. It was barely 50 miles before the next bar disappeared. I think I have only twice let the fuel gauge get below the half-way mark, so I don't have a good perspective on how *my* car behaves in the bottom half of the tank.

 

The fuel level float has limited travel. After the fuel level float reaches that point, you continue to fill the tank
until it's full. The fuel above the floats limit will be used before the float can drop and register on the gauge.
My PC3 gets about 140 to 160 miles before the first bar drops and the next one drops off around 50 miles. For the first half of the tank, I can get about 400 + miles.

 

You get 400 when it initially shows half? Or when it no longer shows half? I've found that the minute the middle bar shows half is the only time the half bar is accurate. If you are getting 400 at the exact moment that is shows half, how far are you going on a tank? At that point you would be getting another ~200 miles before your light comes on and another ~75 miles after that (if you are pushing it). This would give you ~700 miles on a tank. Have you gotten this yet?

 

I'm not sure if it's exactly when it hits the 50% mark. I fill my tank to the top of the filler neck, so I'm getting two
extra gallons beyond the point when the pump kicks off. I usually refill at half a tank.
I'll run it down the next time and see what it says. I get an overall MPG of 55 using the refill info. That was during the
first 1100 miles of use. It should get better as it breaks-in. I run 42 PSI using the Kumho Ecowing 185/65/15 tire on a 15X6.5 alloy wheel and put them on before the last fill. I don't want to use that data because I had a 195/65/15 Mich. HydroEdge tire that killed my mileage. They were off my old Civic. I est. about a 7 MPG loss with them