Old mpg v modern mpg
Discussion
Why could my 1983 R5 GTL easily pull 45+ mpg on a gentle motoray run....and yet the modern small ICE car doesn't do hugely better (with exceptions, of course).
My 2014 Lancia Ypsilon 1.2 might do 50/55 mpg but where's the real advance?
I appreciate that a modern supermini is safer/bigger/heavier/emissions restricted and many other things but why are these cars not doing 150 mpg 40 years later?
Have we reached the finite point of the efficiency/development for petrol/diesel or is the investment now going to electric as that is viwed as the future and ICE will be destined for the bin?
My 2014 Lancia Ypsilon 1.2 might do 50/55 mpg but where's the real advance?
I appreciate that a modern supermini is safer/bigger/heavier/emissions restricted and many other things but why are these cars not doing 150 mpg 40 years later?
Have we reached the finite point of the efficiency/development for petrol/diesel or is the investment now going to electric as that is viwed as the future and ICE will be destined for the bin?
There was a statistic around 2000 that suggested global average mpg hadn't much changed since ~1920. We'd traded the potential for economy for performance and vehicle size.
Honestly, I think that worm turned in the all-turbo era; I know plenty of people who get 60mpg from dinky 3-pot petrol engines, whereas a 1lt Fiesta from the 1980s, for all its lightness and simplicity, wouldn’t have got close to that.
Honestly, I think that worm turned in the all-turbo era; I know plenty of people who get 60mpg from dinky 3-pot petrol engines, whereas a 1lt Fiesta from the 1980s, for all its lightness and simplicity, wouldn’t have got close to that.
bloomen said:
Weightweightweight.
And because of the weight more grunt is needed.
Spot on. And because of the weight more grunt is needed.
I was very grateful that BMW switched to turbos from natural aspiration in that regard too. Their naturally aspirated cars were woeful on fuel because of the weight of them in my experience. Whereas with turbos, not only do you get better mpg, but you also get more torque/performance too.
Mass is half the story, the other half is drag.
The effect of mass does not change the fuel consumption per mile with regard to speed, it is only really defined by the mass of the car and the coefficient of rolling resistance of the tyres.
The same cannot be said for drag which increases with the square of speed in terms of energy (fuel) per mile.
Over about 50 mph the fuel consumed to overcome drag is usually higher than what is being used to overcome rolling resistance.
Drag is determined by the frontal area of the car, the drag coefficient and the temperature (density) of the outside air.
Which is partly why range drops in winter.
Fuel is also consumed to accelerate the car, which if then converted to heat in the brakes, increases consumption again.
If that kinetic energy is used to overcome drag and rolling resistance by coasting instead of heating the brakes, that essentially means the fuel used to accelerate the car has been put to use to displace fuel that would have been required to overcome drag/friction.
Aircon also consumes fuel.
No, it's not all about 'weight'.
The effect of mass does not change the fuel consumption per mile with regard to speed, it is only really defined by the mass of the car and the coefficient of rolling resistance of the tyres.
The same cannot be said for drag which increases with the square of speed in terms of energy (fuel) per mile.
Over about 50 mph the fuel consumed to overcome drag is usually higher than what is being used to overcome rolling resistance.
Drag is determined by the frontal area of the car, the drag coefficient and the temperature (density) of the outside air.
Which is partly why range drops in winter.
Fuel is also consumed to accelerate the car, which if then converted to heat in the brakes, increases consumption again.
If that kinetic energy is used to overcome drag and rolling resistance by coasting instead of heating the brakes, that essentially means the fuel used to accelerate the car has been put to use to displace fuel that would have been required to overcome drag/friction.
Aircon also consumes fuel.
No, it's not all about 'weight'.
GT9 said:
Aircon also consumes fuel.
I always thought that was a bit of a myth really, well I did until I drove an EV for the first time anyway. I decided to switch the A/C on in it...and it shaved 30 miles off the range immediately! 
That normally wouldn't be a problem I'd imagine, but I only had 50 miles on the range in the first place. So it gave me range anxiety straight away, so I decided to open the windows instead to clear the steamed up windscreen rather than have the A/C on.
Sid123 said:
Why could my 1983 R5 GTL easily pull 45+ mpg on a gentle motoray run....and yet the modern small ICE car doesn't do hugely better (with exceptions, of course).
My 2014 Lancia Ypsilon 1.2 might do 50/55 mpg but where's the real advance?
I appreciate that a modern supermini is safer/bigger/heavier/emissions restricted and many other things but why are these cars not doing 150 mpg 40 years later?
Have we reached the finite point of the efficiency/development for petrol/diesel or is the investment now going to electric as that is viwed as the future and ICE will be destined for the bin?
Maybe my perspective is out, but my 208 GTi with 240bhp, will happily sit at 70/80 on a run and average a real world (not the cars computer) 45mpg ive had 48 out of it before too . And I'm not a economic driver at all. Id say that's pretty impressive, as it's significantly heavier and probably has 3 or 4 times the BHP. My 2014 Lancia Ypsilon 1.2 might do 50/55 mpg but where's the real advance?
I appreciate that a modern supermini is safer/bigger/heavier/emissions restricted and many other things but why are these cars not doing 150 mpg 40 years later?
Have we reached the finite point of the efficiency/development for petrol/diesel or is the investment now going to electric as that is viwed as the future and ICE will be destined for the bin?
cerb4.5lee said:
GT9 said:
Aircon also consumes fuel.
I always thought that was a bit of a myth really, well I did until I drove an EV for the first time anyway. I decided to switch the A/C on in it...and it shaved 30 miles off the range immediately! That normally wouldn't be a problem I'd imagine, but I only had 50 miles on the range in the first place. So it gave me range anxiety straight away, so I decided to open the windows instead to clear the steamed up windscreen rather than have the A/C on.
I've been thinking it has improved significantly since the 1980s!
I had a couple of 4 speed Capri 2.8is back then and they both averaged about 27mpg producing a claimed 160bhp.
I've had two 3 litre BMW Z4 Coupes and they averaged between 32 and 34mpg with a claimed 261bhp. Even my Z4M with 338bhp manages 27mpg.
They're heavier than the Capris, but are way more efficient and produce far more power with 24V twin-cam engines and variable valve timing. Although as a result I probably don't cane them quite as much because I'm older and wiser, they get to licence losing speeds much quicker and there are cameras everywhere now!
I had a couple of 4 speed Capri 2.8is back then and they both averaged about 27mpg producing a claimed 160bhp.
I've had two 3 litre BMW Z4 Coupes and they averaged between 32 and 34mpg with a claimed 261bhp. Even my Z4M with 338bhp manages 27mpg.
They're heavier than the Capris, but are way more efficient and produce far more power with 24V twin-cam engines and variable valve timing. Although as a result I probably don't cane them quite as much because I'm older and wiser, they get to licence losing speeds much quicker and there are cameras everywhere now!
jonathan_roberts said:
cerb4.5lee said:
GT9 said:
Aircon also consumes fuel.
I always thought that was a bit of a myth really, well I did until I drove an EV for the first time anyway. I decided to switch the A/C on in it...and it shaved 30 miles off the range immediately! That normally wouldn't be a problem I'd imagine, but I only had 50 miles on the range in the first place. So it gave me range anxiety straight away, so I decided to open the windows instead to clear the steamed up windscreen rather than have the A/C on.
t! 
AmyRichardson said:
There was a statistic around 2000 that suggested global average mpg hadn't much changed since ~1920. We'd traded the potential for economy for performance and vehicle size.
Honestly, I think that worm turned in the all-turbo era; I know plenty of people who get 60mpg from dinky 3-pot petrol engines, whereas a 1lt Fiesta from the 1980s, for all its lightness and simplicity, wouldn’t have got close to that.
That is my experience too.Honestly, I think that worm turned in the all-turbo era; I know plenty of people who get 60mpg from dinky 3-pot petrol engines, whereas a 1lt Fiesta from the 1980s, for all its lightness and simplicity, wouldn’t have got close to that.
My daily has averaged 51mpg over the last 8,000 miles (Jaguar XF 2.2 diesel). Yet the cars with half the capacity I drove 30-40 years ago averaged mid 30's mpg.
That my diesel V90 CC on a 4,000 continental trip in the winter, loaded and with a roof box, returned a genuine 42mpg (trip computer 45) is impressive, I reckon.
What would have been the 1980’s version of that trip and how efficient would it have been?
And the relative comfort of new cars is off the scale. We’ve come a long way.
What would have been the 1980’s version of that trip and how efficient would it have been?
And the relative comfort of new cars is off the scale. We’ve come a long way.
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