Why don't subcompacts get better mileage?

Question

If a Honda Civic can weigh 2600 pounds and have 140hp and get 30/40 mpg (city/hwy), why do all of the subcompacts (Aerio, Fit, Versa, Yaris, Scion, etc.) which weigh several hundred pounds less, have smaller engines and around 100 hp not get better mileage? Is it so hard to make a tiny, light, underpowered car that gets 40+ mpg?

Answer 1

The answer on the surface is that, no it's not hard to make a subcompact that gets 40 + MPG. It is difficult to make one that satisfies the Federal Motor Vehicle Safety Standards (the minimum safety requirements imposed on manufacturers in the U.S.) and is marketable to the general public (i.e. in demand). All cars are a compromise of hunderds of design elements, all of which effect mileage. design elements include things like intended use, number of occupants, amount of cargo to be carried, etc. Small engines alone, forgetting horsepower for a moment, do not automatically equate to higher mileage. For example my rotary engined Mazda RX2 has a 1.186 Liter engine, is a small car with decent aerodynamics and has never gotten better than 15 MPG in stock configuation. A small engine is not necessarily efficient just because it is small. The Cd, coefficient of drag, of a vehicle is a huge gas mileage variable. To explain this compare your Honda Accord, a vehicle with a low roof height, a highly laid back windshield, and a very smooth, aerodynamically shaped nose to the Scion Xb which, by comparison, is a barn door going through the air. It has a tall roof height, a more upright, flatter windshield, and an almost flat front end all of which contribute to higher wind resistance and/or drag which greatly reduce gas mileage. to build a car that gets 60-80MPG is not at all impossible with todays technology. The problem is that such a car would have so many design compromises aimed at better fuel economy that creature comforts, useability, and even drivability would suffer to the point that most people would not buy it, especially spoiled Americans. And if a car company doesn't think it can sell such a car, it will not produce it.

Answer 2

good question, another example, i have a 2004 hyundai accent, i drove it off the showroom flor, it gets about 28 mpg hwy, i also have a '92 cadillac deville, 4.8 liter v8, if i run cruise control i get normally 31-34 mpg.
but to answer your question, apparently it is so hard to do that or they would have done it by now.

Answer 3

More weight per horsepower. And I'd think they'd weigh more cause of other features than the older small cars had. Like navigation, and countless airbags, and other safety features.

Answer 4

That is odd.
It's the engine design and maybe the amount of drag that can affect the mpg