Thread: MPG vs L/100k

JDNSW, it's completely acceptable to remove common factors on both sides of the division equation. For example, with my around-town gas usage approximating 25l/100km, I tend to simplify that to 1l/4km.

I could, of course, express this as 4km/l and mean the same thing, and then I COULD go through the exercise of converting to MPG to tell me that it's really bad fuel economy...

Does improving your fuel consumption from 14 mpg to 15 mpg save you as much money as improving from 28 mpg to 29 mpg?
Even though both are a 1 mpg improvement, the answer is No.
Would it be the same if you improved from 28 mpg to 30 mpg? No.
What improvement on 28 mpg would be needed to save the same amount of money?
The answer is 32.3 mpg.
In other words if you are getting 28 mpg, you need to get an extra 4.2 mpg to save as much money as someone on 14 mpg getting just 1 extra mile per gallon.
(10.7 L/100km to 8.7 L/100km versus 20.1 L/100km to 18.8 L/100km) (Numbers rounded to 2 decimal places to try to avoid making this look like a complicated issue)
Because mpg numbers are so big,the benefits of improvements for economical vehicles are exaggerated. The same problem applies to a lesser extent to km/L The more economical the vehicle, the greater the apparent benefit.
The mpg figures for a thirsty vehicle are quite small, so worthwhile savings are made to look insignificant.
If you work with L/100km, the problem disappears. An improvement of 1 litre/100km saves exactly the same amomut of money regardless of whether you are driving a Kenworth or a Prius.
Doesn't that make L/100km look more logical and less misleading than mpg or km/L?

Originally Posted by vnx205

Does improving your fuel consumption from 14 mpg to 15 mpg save you as much money as improving from 28 mpg to 29 mpg?
Even though both are a 1 mpg improvement, the answer is No.
Would it be the same if you improved from 28 mpg to 30 mpg? No.
What improvement on 28 mpg would be needed to save the same amount of money?
The answer is 32.3 mpg.
In other words if you are getting 28 mpg, you need to get an extra 4.2 mpg to save as much money as someone on 14 mpg getting just 1 extra mile per gallon.
(10.7 L/100km to 8.7 L/100km versus 20.1 L/100km to 18.8 L/100km) (Numbers rounded to 2 decimal places to try to avoid making this look like a complicated issue)
Because mpg numbers are so big,the benefits of improvements for economical vehicles are exaggerated. The same problem applies to a lesser extent to km/L The more economical the vehicle, the greater the apparent benefit.
The mpg figures for a thirsty vehicle are quite small, so worthwhile savings are made to look insignificant.
If you work with L/100km, the problem disappears. An improvement of 1 litre/100km saves exactly the same amomut of money regardless of whether you are driving a Kenworth or a Prius.
Doesn't that make L/100km look more logical and less misleading than mpg or km/L?

It is not a problem - you can simply put the argument the other way - the number you get simply depends on which way up you put the fraction - to use your argument, the same amount of money is far less significant to the Kenworth driver than the Prius driver. And there is no reason to use litres/100km instead of litres/km. Neither way of putting it is misleading to anyone with elementary numeracy, and the change from distance/fuel quantity to fuel quantity/100*distance was an unnecessary change that is used nowhere outside Australia as far as I am aware, so your view of what is more logical and less misleading is not shared by the vast majority of motorists worldwide both today and for the last hundred plus years. But as I said, it doesn't make a significant difference which method you use, the most important is to use what you are familiar with.

John

I agree that people tend to work with the system that they have become accustomed to. However I don't think it hurts to have people aware of the fact that the sytem they are using can be misleading.
The fact that the majority of the world's population uses a particular system does not mean it is logical or sensible or efficient or anything else. It usually means it is the one that has become entrenched through years, decades or centuries of use.
I think it is generally accepted that Beta video was technically better than VHS, but VHS won out through sheer weight of numbers.
The qwerty keyboard is used almost universally even though more efficient keyboard layouts such as the Dvorak keyboard exist. The qwerty layout was designed to be inefficient. It helped stop mechanical problems with early manual typewriters. We are stuck with the inefficient qwerty because so many people are familiar with it.
I think we may have to put up with some people using mpg or km/l not because they are logical but because people are familiar with them.

Originally Posted by vnx205

I agree that people tend to work with the system that they have become accustomed to. However I don't think it hurts to have people aware of the fact that the sytem they are using can be misleading.
The fact that the majority of the world's population uses a particular system does not mean it is logical or sensible or efficient or anything else. It usually means it is the one that has become entrenched through years, decades or centuries of use.
I think it is generally accepted that Beta video was technically better than VHS, but VHS won out through sheer weight of numbers.
The qwerty keyboard is used almost universally even though more efficient keyboard layouts such as the Dvorak keyboard exist. The qwerty layout was designed to be inefficient. It helped stop mechanical problems with early manual typewriters. We are stuck with the inefficient qwerty because so many people are familiar with it.
I think we may have to put up with some people using mpg or km/l not because they are logical but because people are familiar with them.

I have to agree that just because most people do something does not make it logical or sensible or efficient or anything else - look at wearing clothes for example.

I have seen recently (in discussions on Blu-ray vs HD-DVD) that the reason Beta lost out was that VHS was cheaper to duplicate tapes, but I suspect that the main reason may have been that Sony tried to keep Beta to themselves.

I agree entirely about Qwerty - but having learnt to type on this keyboard I am not about to change!

But I don't think you can say that distance/quantity is either more or less logical than quantity/distance - it is simply the inverse - although it may be more logical than quantity/distance*100, but even here it is only the same as comparing a fraction to a percentage.

Which way round you prefer your fraction, apart from habit, simply depends on whether (at the time) you are more interested in how far you can go for a given amount of fuel, or how much fuel you will need to go a fixed distance. If you are looking at how significant is a change in fuel consumption (or a comparison) in both cases you have to use a fraction or a percentage - e.g. 33mpg vs 30mpg is a 10% improvement, 9l/100km vs 10l/100km is a 10% improvement.

(of course, going the other way is a trap for the unwary - going from 33mpg down to 30mpg is only 9% worse, and you have to bear in mind that in the other cases one is a 10% increase in the distance you can go, where the other is a 10% decrease in the fuel used for a fixed distance).

John

mmm don't really6 care about mpg or l/100K. But being a pom i am new to ther l/100k. more on Mpg. But i know my truck's L/100 because i had to work it out going round aus because a toyota owner at every camp i stayed at would ask me what i was getting out of my deffender. So i found out and then took the **** out of them for the amount their diesel was doing

Yes, the main reason was that Sony tried to keep Beta to itself - and bomed out badly. But the format is still alive and well as Betacam Digital (or was the last time I looked). The tape runs eight times faster than the old domestic variety.

As I don't have a working fuel gauge I'm safe in my 5 kms to the litre calculation.

GQ

My daughter has a degree in film & television production. She assures me Beta is better and is still used by professionals. Apparently the simpler tape path is one reason, fewer tapes get munched in the machines.