Fuel fill up to max?

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Drago

Legendary Member
[QUOTE 5329218, member: 9609"]but that is exactly what I am saying with a real world rule of thumb used for the figures - if you increase a vehicles weight by 2.5% then its fuel consumption is likely to go up by 1% - if you increase a vehicles weight by 50% then its fuel consumption is likely to increase around 20% (based on average driving on average roads))[/QUOTE]

I'm not so sure...? Once moving at any real speed aerodynamic loads become significant, and that's going to remain the same regardless of to load on board (leaving out considerations about suspension compression that might affect the cars physical attitude/orientation). A full tank of fuel may add mass and will undoubtedly make a difference, but my gut call is that the percentages being touted are a little high. Indeed, the increase inertia can be exploited at the other end of the scale, to travel further when lifting off the throttle.
 

derrick

The Glue that binds us together.
I always try and keep half a tank in my motor, only because my old mum lives in Clacton, if i get a phone call in the middle of the night, i know i can jump in the motor and drive straight there.
 

johnnyb47

Guru
Location
Wales
I always fill my car to the brim and never let run below 1/4 of a tank. I only do this because its got an over complicated fuel tank system. It's got three fuel pumps and two tanks. When it gets below 1/4 on the gauge ,one of the scavenger pumps moves the diesel over to the other tank and are notoriously unreliable. Keeping it full lessens the chance of dam thing breaking down. It's even got a small radiator that cools the unused fuel on the return feed back to the tank.

.
 

SpokeyDokey

67, & my GP says I will officially be old at 70!
Moderator
[QUOTE 5330062, member: 9609"]there is a speed where wind resistance becomes the greater user of fuel than rolling resistance, in a lorry that is mid 50s mph, and they reckon at this speed rolling resistance=40%, wind resistance=40% and other losses =20%

and in reality this works out really well - take a fully loaded bulker running at 44t, it is likely to be returning between 8 and 9 mpg on flattish roads. If it runs back empty (18t) it is very likely to return just over 13mpg.
44t is 145% heavier than 18t
40% of 145 is 58%
add 58% on to 8.5 mpg and you get 13.43 mpg
wind resistance has not changed and speeds will be similar.
these numbers work out very well for wagons.


obviously cars are considerably more aerodynamic so if anything rolling resistance will be more likely be a bigger factor than wind resistance, so if anything weight will play a bigger part.[/QUOTE]

Good answer - and extra points for hitting 00.00 as your posting time. :smile:
 

sight-pin

Veteran
The pickup is in the same place regardless of how much fuel is in the tank.

True, it's something from my mechanic days years ago when garage tanks wasn't always the cleanest, all sorts of crap could be mixed / floating in petrol years ago was my experience. Filters used to be full of rubbish.
 

Tin Pot

Guru
All electric. I’m hoping my next vehicle will be. 0-100kph in 3.5s. Charging plate on the drive, always ready to rock and roll.
 
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