Want 125+ MPG Cars? Be Prepared For Change

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Toyota FT-Bh Concept

Toyota FT-Bh Concept

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What aspects of modern motoring would you be prepared to give up to achieve 125 mpg fuel efficiency?

Carmakers have made huge strides in recent years to improve fuel efficiency, but they've had to balance these economy needs with the demand for ever increasing equipment and safety levels, and higher performance too.

So what would it take for cars to reach a real-world 125 mpg on the highway?


Air resistance is one of the biggest factors in highway economy, and surprisingly it's one area where we might not see a great deal of change.

A decade ago, it took compromised shapes like the original Honda Insight to achieve low-drag figures, but today's aerodynamic shapes are surprisingly normal. The Toyota Prius is most distinctive, but cars like the 2013 Hyundai Sonata Hybrid return a similar 0.25 coefficient of drag figure.

The biggest aerodynamic change could be reserved for small cars, which have a limited surface area over which it's difficult to tailor a wind-cheating shape. That could call for more extreme styling, like that of the Toyota FT-Bh concept, with its 0.235 Cd.


We've discussed the benefits of low weight more than once, but reaching the targets needed to make big strides in efficiency might call for more obvious changes than clever use of materials under the skin.

2011 Renault Captur Concept

2011 Renault Captur Concept

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That includes more minimalist interiors than we're used to. We've seen them on concept cars for years, but an effective way of really shedding the pounds is reducing large, heavy expanses of dashboard to a minimum, and simplifying seats.

If this sounds like bad news to fans of cosseting, luxurious interiors, then perhaps some of the benefits might draw you in. Not only will economy improve everywhere, with less mass to move around, but so will performance, braking and handling. Not only that, but with less interior trim and narrower seats, interior space would improve.

You might have to take a slight hit on equipment levels, but it's likely that much of the equipment that remains will be controlled by something like a smartphone, reducing the need for a complicated dashboard full of electronics.


There's no getting away from it--engines will have to change, and it's unlikely they'll be getting bigger and more powerful. In fact, power figures are likely to remain fairly static, while capacity decreases. Turbochargers and hybrid systems are likely to become more prevalent, as both can be used to prop up the power of downsized engines.

Paired with both reduced weight and better aerodynamics, the smaller engines will be able to deliver better economy, without struggling against the large, heavyweight bodies of modern cars.

We're also likely to see fewer cylinders, already a bone of contention for muscle car fans. That said, muscle cars are never likely to get 125mpg anyway, so it's really the smallest cars where cylinders will decrease.

Volkswagen Polo Blue GT

Volkswagen Polo Blue GT

Enlarge Photo
Some will also take inspiration from those large V-8s, as cylinder deactivation becomes more prevalent. Volkswagen has recently introduced just that on its Polo Blue GT, sold in Europe. That car gets up to 52 mpg, not a bad figure for an otherwise standard, 140bhp gasoline subcompact.

Small-capacity diesel engines are another option, but diesel is becoming scarce in small cars even in Europe, as they cost more to manufacture and the profit margins are becoming too slim.

Large strides

One thing is for sure: Creating a 125 mpg car won't be easy, and it will require compromise. It goes without saying that some of the changes above may well add to the cost of a vehicle, particularly if a car is to achieve that sort of economy in the near future.

It's very likely that electricity will play a large part in hitting high figures. Theoretically, it's possible for cars like the 2012 Toyota Prius Plug-In and the 2012 Chevrolet Volt to hit 125 mpg on some journeys, by combining zero-emissions electric running with small amounts of fuel.

However, to sustain 125 mpg over longer distances, cars will need more than a token 40-odd miles of electric running, so some of the other factors above will play a major part.

And in the long term, it could all be academic, as battery electric vehicles make "miles per gallon" figures a moot point...


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Comments (12)
  1. I agree, EVs make the pursuit of 125 mpg look like a huge waste of time. Still we do need to achieve high fuel milage so we can be weaned off oil while EV technology is still being refined.

  2. Until there is an "outside authority" checking cd measures any values reported simply by the manufacturers should be taken as questionable. There is no really standard protocol for this measurement that EVERYONE follows at this time, so producer reports are at best relative only to other cars from the same company.

  3. I easily get somewhere around 4 miles per KWh. 1 gal of gas is about 33KWh to 36KWh in energy. That is already 122-144 mpg equivalent. It will be hard for the gas engine to match that of the electric motors...

  4. I doubt any real world ICE powered vehicle that people would actually buy in any serious numbers will ever get anywhere near 125 MPG but I do agree that any steps in that direction will require compromise: less car, less performance, more complexity/cost.

    So I guess the choice is increasingly going to be between ever more costly and compromised ICE vehicles and ever cheaper and more practical battery powered vehicles. I think I know who will win that race....

  5. The problem is that ICE are inefficient to start with. The only way to get 100+mpg is to reduce the weight of the vehicle to "NOTHING". A motorcyle barely get that MPG. Imagine a car with all the comfortable and safetly features...

    The only way you can do 100+ mpg is by going fuel cell... (without doing plugins).

  6. Plenty of 125cc motorcycles and scooters get well into the 100s on mpg, and for their size they're relatively aerodynamically inefficient.

    A sleek, light-weight production car with a small, perhaps hybrid-assisted engine, should be able to get over 100mpg by now. A modern take on the original Insight would be fascinating, given that some owners of that car already get figures in the 100s.

  7. Your spot on Antony and the car was out there from 2000 to 2006. Trouble was it was before its time,not promoted,and not an earner for Honda.I could regularly pull over a hundred to the gallon for a tank average of 84mpg. For max efficiency using an ICE or hybrid unit the car needs to be redefined and reconfigured. This would take the form of an enclosed tilting four wheeled, tandem seated pod like 2 seater. We can already see manufacturers touting these devices on the show circuits but again to far ahead for most to accept.Traditionalists can only think car as we know it today forgetting just how different todays cars are from say, the fifties.Looking at this evolution its inevitable these non cars will eventually be accepted.

  8. Well, will those "seated pod" pass US crash test? Will it have A/C and radio with comfort?

    Solar car "worked" too (I was in the sun race team). But let us NOT kid ourselves that we can power cars with solar.

    It is similar thing here. UNLESS you give up all "car" comfort, safety, performance and stability, it won't get EPA rated 100mpg in real world with today's requirement.

  9. You are correct. My bike regurly give me mileage of 55 Km Per Liter, and my scooter goes approx 45-50 Km per liter. My bike is 150 cc/14 BHP naked bike. There are other 100cc bikes which goes to approx 80 Km per Liter as well.

  10. "A sleek, light-weight production car" that will also pass crash test and comes with A/C, radio, comfortable seats...etc.

    Sure, you can design a covered up "scooter" for 100mpg. But it doesn't have any of the "comfort" features that people need. I guess if you make pure MPG goal by comprising safety and comfort, then it is doable. But that is NOT going to sell...

  11. "A sleek, light-weight production car" that will also pass crash test and comes with A/C, radio, comfortable seats...etc.
    Yes I owned one eight years ago probably while you were still in college, it was the gen 1 Insight.
    It met all these requirements so it can be done without compromising safety and comfort.

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