To fill or not to fill?
Discussion
Got to thinking about something that Top Gear did on the not too recent past, if you empty your boot, your car is lighter, fuel economy goes up... simple really..
Does this extend to filling your tank as well though. Fuel is luquid, which is heavy, but also moves around, making the vehicle move around. On this basis, (and possibly the way a car is aerodynamically designed and also the centre of gravity, is it better to keep the tank full (centre of gravity) or half / less than half empty (weight saving)
Thoughts?
Does this extend to filling your tank as well though. Fuel is luquid, which is heavy, but also moves around, making the vehicle move around. On this basis, (and possibly the way a car is aerodynamically designed and also the centre of gravity, is it better to keep the tank full (centre of gravity) or half / less than half empty (weight saving)
Thoughts?
thatone1967 said:
Got to thinking about something that Top Gear did on the not too recent past, if you empty your boot, your car is lighter, fuel economy goes up... simple really..
Does this extend to filling your tank as well though. Fuel is luquid, which is heavy, but also moves around, making the vehicle move around. On this basis, (and possibly the way a car is aerodynamically designed and also the centre of gravity, is it better to keep the tank full (centre of gravity) or half / less than half empty (weight saving)
Thoughts?
In the same way that folding your seats down makes your car faster?Does this extend to filling your tank as well though. Fuel is luquid, which is heavy, but also moves around, making the vehicle move around. On this basis, (and possibly the way a car is aerodynamically designed and also the centre of gravity, is it better to keep the tank full (centre of gravity) or half / less than half empty (weight saving)
Thoughts?
Yes, in theory you don't want fuel sloshing around when you're cornering hard - which is why race cars use baffled/foam filled tanks (along with surge/starvation issues). But I reckon if you're cornering hard enough to worry about the fuel unsettling the car - then you're driving too hard (on public roads).
Edited by Mattt on Monday 21st December 06:04
thatone1967 said:
Got to thinking about something that Top Gear did on the not too recent past, if you empty your boot, your car is lighter, fuel economy goes up... simple really..
Does this extend to filling your tank as well though. Fuel is luquid, which is heavy, but also moves around, making the vehicle move around. On this basis, (and possibly the way a car is aerodynamically designed and also the centre of gravity, is it better to keep the tank full (centre of gravity) or half / less than half empty (weight saving)
Thoughts?
On the road, in normal conditions. For best performance (e.g. getting away from the lights and improved MPG), carry as little fuel as you require.Does this extend to filling your tank as well though. Fuel is luquid, which is heavy, but also moves around, making the vehicle move around. On this basis, (and possibly the way a car is aerodynamically designed and also the centre of gravity, is it better to keep the tank full (centre of gravity) or half / less than half empty (weight saving)
Thoughts?
Munter said:
thatone1967 said:
Got to thinking about something that Top Gear did on the not too recent past, if you empty your boot, your car is lighter, fuel economy goes up... simple really..
Does this extend to filling your tank as well though. Fuel is luquid, which is heavy, but also moves around, making the vehicle move around. On this basis, (and possibly the way a car is aerodynamically designed and also the centre of gravity, is it better to keep the tank full (centre of gravity) or half / less than half empty (weight saving)
Thoughts?
On the road, in normal conditions. For best performance (e.g. getting away from the lights and improved MPG), carry as little fuel as you require.Does this extend to filling your tank as well though. Fuel is luquid, which is heavy, but also moves around, making the vehicle move around. On this basis, (and possibly the way a car is aerodynamically designed and also the centre of gravity, is it better to keep the tank full (centre of gravity) or half / less than half empty (weight saving)
Thoughts?
In reality it doesn't matter in the slightest whether you run a full tank or an empty one. It certainly doesn't feature in Roadcraft.
Bert
Depends on typical use cycle / weekly mileage etc, but especially if you drive an economical diesel there's really not much real point in filling it right up and carrying around a half tank of fuel ( dead weight, not to mention the cost) that won't be used for the first 250-300 miles... Even on a very long journey, it's not a bad idea to have a stop along the way, to stretch legs etc so why not refuel at the same time.
It always makes me smile when I hear people talk about the 'extra weight of a diesel engine causing understeer' (?!) when in most cases it's more than balanced by the extra weight of half a tank of (unnecessary) fuel being carried around in the back of the car...
I've also been thinking about this, in terms of rear tyre wear.
My job requires me to travel (almost) anywhere in the country at a moments notice, so I fill up at the start of every day.
On an average (say 200-mile) day, I probably use about 1/3 a tank. 80-litre fuel tank means, I'm usually carrying about 50-litres unnecessarily, but I just don't find it reassuring to be driving around with the tank less than a third full.
My job requires me to travel (almost) anywhere in the country at a moments notice, so I fill up at the start of every day.
On an average (say 200-mile) day, I probably use about 1/3 a tank. 80-litre fuel tank means, I'm usually carrying about 50-litres unnecessarily, but I just don't find it reassuring to be driving around with the tank less than a third full.
BertBert said:
Munter said:
thatone1967 said:
Got to thinking about something that Top Gear did on the not too recent past, if you empty your boot, your car is lighter, fuel economy goes up... simple really..
Does this extend to filling your tank as well though. Fuel is luquid, which is heavy, but also moves around, making the vehicle move around. On this basis, (and possibly the way a car is aerodynamically designed and also the centre of gravity, is it better to keep the tank full (centre of gravity) or half / less than half empty (weight saving)
Thoughts?
On the road, in normal conditions. For best performance (e.g. getting away from the lights and improved MPG), carry as little fuel as you require.Does this extend to filling your tank as well though. Fuel is luquid, which is heavy, but also moves around, making the vehicle move around. On this basis, (and possibly the way a car is aerodynamically designed and also the centre of gravity, is it better to keep the tank full (centre of gravity) or half / less than half empty (weight saving)
Thoughts?
Generally speaking I run with about 1/4 to 1/2 a tank in and around the local roads, and only ever fill the car up if I intend to drive a long distance. Plus fuel tends to go off and I don't drive much, so one fill up might last a month in my car...
RobM77 said:
Mattt said:
Rob, IIRC on the Z$ with a full tank it gives better weight distribution - near 50/50 I was told.
Thanks 
The Elise is 67:30 to start with though, so I don't fancy making it worse 
Munter said:
RobM77 said:
Mattt said:
Rob, IIRC on the Z$ with a full tank it gives better weight distribution - near 50/50 I was told.
Thanks The Elise is 67:30 to start with though, so I don't fancy making it worse Maybe the other three are in an extra dimension?... 
It's about 70:30 actually RobM77 said:
Munter said:
RobM77 said:
Mattt said:
Rob, IIRC on the Z$ with a full tank it gives better weight distribution - near 50/50 I was told.
Thanks The Elise is 67:30 to start with though, so I don't fancy making it worse Maybe the other three are in an extra dimension?... It's about 70:30 actually Anyhow, while we're about it, I must say that the old Pug 406 produces much better traction in snow than does the (much heralded here) Mazda MX-5. I discovered that yesterday afternoon.
When I eventually managed to escape from the car park in Eileen's MX-5 it was fun with the RWD on snow
but traction was really not good.Best wishes all,
Dave.
I only get 250ish miles to a tank, and that equates to roughly a week's driving, so I fill up once a week and have done with it. I tried (for several weeks) just filling half a tank and it made absolutely zero difference to my indicated mpg, so I've gone back to brimming it each time.
RobM77 said:
No doubt the most economic strategy would be a balance between the two. I never fill my tank for this reason; I can feel the performance difference with a 50kg person in my car, so why would I want to load 50kg of fuel into it?
Generally speaking I run with about 1/4 to 1/2 a tank in and around the local roads, and only ever fill the car up if I intend to drive a long distance. Plus fuel tends to go off and I don't drive much, so one fill up might last a month in my car...
Petrol weighs 737g/litre. My car's tank is about 70 litres, so a full tank weighs about 52kg. Half a tank weighs 26kg. So the difference between 1/2 and full is 26kg (rather than 50kg). My car weighs about 1450kg, so the weight difference is less than 2% of the vehicle weight. I'd challenge almost anyone to feel a 2% change in power-to-weight through the seat of their pants...Generally speaking I run with about 1/4 to 1/2 a tank in and around the local roads, and only ever fill the car up if I intend to drive a long distance. Plus fuel tends to go off and I don't drive much, so one fill up might last a month in my car...
GW65 said:
a full tank weighs about 52kg. Half a tank weighs 26kg. So the difference between 1/2 and full is 26kg (rather than 50kg). My car weighs about 1450kg, so the weight difference is less than 2% of the vehicle weight. I'd challenge almost anyone to feel a 2% change in power-to-weight through the seat of their pants...
Challenge accepted :-) Granted that my car is half the weight of yours though, so the percentages are doubled. In my Elise (800kg) I can feel a 20kg bag in the boot. Plus the difference between a 60kg passenger and an 80kg one is huge. Edited to say: where the weight is makes a significant difference. 10kg hung out the back of the car (a Caterham spare wheel for instance) makes more of a difference than 10kg in the passenger footwell. Equally, fuel is stored low down in most cars in relation to the roll centre, so it makes less of a difference than, for instance, a hard top added to a convertible.Edited by RobM77 on Saturday 26th December 15:14
RobM77 said:
GW65 said:
a full tank weighs about 52kg. Half a tank weighs 26kg. So the difference between 1/2 and full is 26kg (rather than 50kg). My car weighs about 1450kg, so the weight difference is less than 2% of the vehicle weight. I'd challenge almost anyone to feel a 2% change in power-to-weight through the seat of their pants...
Challenge accepted :-) Granted that my car is half the weight of yours though, so the percentages are doubled. In my Elise (800kg) I can feel a 20kg bag in the boot. Plus the difference between a 60kg passenger and an 80kg one is huge. Edited to say: where the weight is makes a significant difference. 10kg hung out the back of the car (a Caterham spare wheel for instance) makes more of a difference than 10kg in the passenger footwell. Equally, fuel is stored low down in most cars in relation to the roll centre, so it makes less of a difference than, for instance, a hard top added to a convertible.Edited by RobM77 on Saturday 26th December 15:14
Bert
BertBert said:
RobM77 said:
GW65 said:
a full tank weighs about 52kg. Half a tank weighs 26kg. So the difference between 1/2 and full is 26kg (rather than 50kg). My car weighs about 1450kg, so the weight difference is less than 2% of the vehicle weight. I'd challenge almost anyone to feel a 2% change in power-to-weight through the seat of their pants...
Challenge accepted :-) Granted that my car is half the weight of yours though, so the percentages are doubled. In my Elise (800kg) I can feel a 20kg bag in the boot. Plus the difference between a 60kg passenger and an 80kg one is huge. Edited to say: where the weight is makes a significant difference. 10kg hung out the back of the car (a Caterham spare wheel for instance) makes more of a difference than 10kg in the passenger footwell. Equally, fuel is stored low down in most cars in relation to the roll centre, so it makes less of a difference than, for instance, a hard top added to a convertible.Bert
Have you driven an Elise? The difference between an 8/9 stone person and a 12/13 stone person is massive. For starters I'm barely strong enough to turn the steering wheel at anything less than about 10mph! Plus when you brake you've got to push the pedal noticeably harder. In a Caterham the effect is massive, with any passenger much over 10 stone causing monumental understeer.I really don't like taking passengers around who weigh more than 10 stone.
What I would bet on is that I can guess a passenger's weight to within 1½ stone in a Caterham.
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