The average new car isn’t much more fuel-efficient than older ones. Still, to this day, the average vehicle has a range of between 20 and 30 miles per gallon, a stat which was very similar in the 1920s. How come with all the advances we’ve made in the last century is fuel efficiency the same?


The average new car isn’t much more fuel-efficient than older ones. Still, to this day, the average vehicle has a range of between 20 and 30 miles per gallon, a stat which was very similar in the 1920s. How come with all the advances we’ve made in the last century is fuel efficiency the same?

In: Technology

Can you provide the information for this? It depends on the vehicles that are counted. Averaging a large SUV with a Prius says nothing about them as individual vehicles.

Here is a chart that shows improvement.

This is a really complex question. Are we talking just four-door sedans? Because they have gotten more
Fuel efficient since 1920. But also, there are more variables than just fuel efficiency. For example, safety standards. A car built in 2021 and sold in the USA has to meet a tremendous number of safety standards. This means that fuel economy is sometimes sacrificed to meet these standards. Take a Honda Civic engine back to 1920 and slap it into a light crappy car and bam, there’s your efficiency gain. I mean you’ll be driving an unbalanced death trap, but you see what I mean.

A lot of modern cars are overbuilt compared to old ones: they have a large engine, more passenger seating, and usually some trunk space.

A prius, considered a fairly small modern car, weighs over 3000 pounds while the Model T (the stereotypical “old car” of the early 1900s) weighed up to 1500 pounds.

This means that a modern car can be twice the weight with the *same* fuel efficiency: definitely an improvement over the Model T!

If fuel efficiency hadn’t improved, you’d have horrible fuel efficiency in the range of 15mpg because vehicle weights have gone up significantly. Instead, fuel efficiency stayed the same (debatable, but ok) indicating that engines have absolutely improved

Most of the improvements in fuel efficiency have been reduced to nothing by things like increased speed, comfort and safety. A modern car is 3-4 times heavier then a 1920s car and have over ten times the power. However if you instead look at smaller slower cars there are several on the market which exceeds the 100 mpg mark.

While fuel efficiency doesn’t look like it’s gone up that much, it definitely has.

Also don’t forget that with the rise of electric cars, efficiency and emissions are on extreme ends, with MPGe almost an order of magnitude higher, while emissions are at 0. This doesn’t change the average fuel economy in gas cars, as they’re in a separate category of electric cars.

According to the EPA, since 2004, fuel economy is up 29%, power is up 16%, and emissions are down 23%. Compared to 1975, fuel economy has almost doubled while horsepower has increased over 75%.

When you only pay attention to fuel economy (and we’re not even talking about hybrids!), it’s easy to ignore things that also come into play, like innovations in safety, emissions, and power.

Just in the past 5 years, the average has increased almost 1 MPG while decreasing CO2 emissions, with some manufacturers like Kia increasing their MPG by almost 2.5

So it’s a few things. Fuel efficiency has been going up slowly but surely, but when you account for the power increase and emissions reductions, it’s a lot more substantial!

You can see all these stats [here](

For a lot of mechanical and chemical processes advancement is logarithmic and not exponential. Think of it like this: 1 mol of octane when combusted releases 5150 kJ of energy. If operating at 3000 rpm an engine is firing for 0.02 seconds so each piston discharges 103 kN per mole, which at 100% efficiency would accelerate a 4000 pound vehicle at 56.8 m/s^2. But keep in mind that it per mol. A liter of pure octane consists of 6.15 mols of octane. So if we had a vehicle that operated at 100% efficiency and we were somehow able to fuel it with 100 octane gasoline, it would exert 31,672.5 kJ of work and with the average weight of a vehicle being 4000 pounds (1814.37 kG) there is a theoretical maximum we can get based on mass.

Mainly because our vehicles are extraordinarily heavy compared to early cars. Most of that weight are in safety features, a minor accident that leaves you mildly shaken today would have killed you in the 1920s. Weight is the antithesis to fuel economy. Even then, my 5 star safety rated vehicle weighs 1645 Kg can go zero to 60 in less than six seconds averages 30 mpg while stopping from 60 in like 105 feet. These were sci fi numbers not that long ago. And no, I do not have an M, S, or AMG car, this is a standard vehicle. Shit, a new Honda Accord Touring has similar specs.

We’ve dramatically increased the speed and horsepower, added all sorts of safety features like roll cages and airbag systems, and increased creature comforts like air conditioning, additoinal insulated for weather and sound deadening, electronics/computers to provide entertainment, data, and control functions like ABS and AWD, power windows/locks, sunroofs, etc. which all add weight.

Like alot of people have said increases in weight, power, and other conveniences impaire it.

The biggest difference is your comparing a very small engine (I’ve seen 2 and even single piston drives in cars before 1930) that put out the power of my chainsaw.

With modern equipment I’m sure you could push 50mpg with em but your in a car that weighs in at 600lbs and top speeds of 15mpg. And your going to have no electronics, sheet steel/aluminum body, probably a lawn chair seat. Not worth it and the DOT will not let you sell em becuse its just not safe.

For the most part, cars have gotten a lot heavier and more powerful over time.

Fuel efficiency, especially recently, is improving. There are many factors at play, including what it means when you say average car.

Complete BS, new cars are way more efficient than old ones, and don’t give me that model T bull, they weighed fuck all and didn’t go fast. Ever drive a mid 70’s sedan with a V8 in it? Or an old pickup? Na, didn’t think so.

This is largely cultural and by design really. Cars have very much gotten more fuel-efficient but cars have also gotten much more luxurious and as a result, heavier. Which in turn negatively impacts fuel efficiency.

I say cultural but you’ll notice this much more with the enormous land boats that Americans favor.

European and Asian cars for instance are usually far more efficient because they’re built to be lighter and more compact. Many contemporary cars can manage double the range per gallon as their predecessors from 20 or 30 years ago for instance.