Why do small cars get better gas mileage?

Question

i have already asked this question but i messed up one part I think it is because they weigh less therefor they require less energy, but my husband says that bigger cars have bigger motors that should make up the difference. I still say it doesnt matter what the size of the motor is it doesnt change the fact that it takes more eneregy to move a bigger car. Please help us end this debate

he compares it this a 4 year old boy would use more energy to pick up a 50 pound box than a 30 year old man so shouldnt a 6 cyl motor use less energy to move a big car and that if you put a 6 cly motor into a small car its gas mileage would go down ......i say although that is true it still doesnt equal out you cant say that a bigger motor should make up for the increase in weight and thats its both bigger motors use more gas (which I again say is b/c they are bigger lol) but the main reason is because they weigh more

I again say they do burn gas faster bc they are bigger and heavier!

Answer 1

I'm not totally sure about this one but smaller cars - they tend to be more aerodynamically built.

Answer 2

you win, they're lighter.

try pushing a wagon down the street.

then pushing a car down the street.

which took more energy?

larger engines use more gas.

they often to accelerate faster.

but that uses gas.

smaller engines have to work harder, and produce less power, but waste less gas.

HOWEVER, if you put a small engine in a big heavy car, it would get terrible mileage because it just didn't have enough power to push the car and you'd always be stressing it -- wasting gas.

as for the big man, small boy argument, consider, if you had a small wagon to move, who would expend more energy moving it?  a kid?  or Arnold Schwarzenegger?  i maintain the kid, because he could do it an not have to drag Arnold's body around at the same time.  you get better efficiency when you match the motor to the load.

finally, big heavy cars do not get better highway mileage.

a heavy Cadillac or Hummer maybe gets 18 / 22 mpg, and

a prius gets 45 / 43 mpg.  far better.

a little ordinary Civic gets something like 29 / 35.

lighter is better / cheaper.

EDIT:  concerning why big engines use more fuel.

i think it's because people don't use them as well.

however, if you put 'em in neutral, and rev both up to 3000 rpm, the larger engine will use more fuel.

it has a larger displacement, and will just eat more gasoline.

(and air.)

now when driving, you don't have to rev the larger engine as much, but having the extra power makes it tempting.

one might argue that the larger engine will weigh more, and thus use more gas, but i doubt this is a big factor.

Answer 3

Well you are kind of both right. Gas mileage is a combination of things. If a car weighs less then it is easier to move (better gas mileage). Also, the wind resistance all affects it. A boxy car will get worse gasemileage then a streamlined car. At the same time, having a smaller engine improves gas mileage. Cars generally only need closer to 100hp to get the job done but cars usually have 200hp. So when you have an engine that outputs more work then is required, you're just wasting that energy and thus, wasting gas. Check out the diagram in that link. It'll show you where all the energy in the gas goes. Without an explanation, having a bigger engine would result in similar losses of gas mileage as having a bigger, heavier vehicle. So you both are right. What do ya know? time for make up s*x

Answer 4

Small cars get better gas mileage in town, since they are light and mostly in the low rev range. Small cars have less inertia to overcome to get going than big cars and so use less gas on pull off.

Small cars get horrible gas mileage on motorways etc, because they are in the very high end of the rev range to maintain the 70mph speed limit. My Corsa is begging for another gear for efficient cruising....

Big cars get horrible mileage in town because although they are in low revs most of the time, they burn more gas per rev because the engine is bigger. Overcoming bigger inertia also burns gas.

Big cars get better gas mileage on motorways because they are in mid-range of the revs and so use less gas.

Regarding the 4 vs 6 cylinder, it depends on the power output of the engines and the efficiency to which they are built. I'd expect the fuel used to generate say 100hp to be the same. The 6cy does it by having more cylinders and thus lower revs for the same power. The 4 cy does it by revving higher. In practical use, most drivers waste the power of the 6cy engine, resulting in less fuel efficiency. Also, in a city it would be terrible compared to the 4cy.

Answer 5

mostly because they have smaller engines

Answer 6

You are arguing about something as silly and basic as this? Don't you have a bedroom to go to?

Try this,...

small cars weigh much less and therefore have much smaller engines which require less fuel to operate. Because the car is small, wind resistence is much less than larger cars. They can go the same speed as large cars because of the gear ratios in the transmissions.

large cars weigh much more and need bigger engines to move them & keep them moving. Air resistence is a bigger factor because the car is larger. Naturally, these bigger engines gulp more fuel because they need more to operate. Six cylinders take more gas than 4 cylinders do because they have 2 more cylinders to fill.

Answer 7

The weight (mass) of the car definitely makes a difference during acceleration. The greater the mass, the greater the force needed to produce a given acceleration. Put a larger engine in a given car and acceleration might be greater at the price of burning more fuel per second.

    During highway driving at constant speed, the air resistance of a larger car is probably the greatest factor affecting mileage.

   Even at constant speed a car with an engine of greater displacement will probably burn more fuel to to maintain that speed. That's why some cars now come equipped with engines where one or more cylinders shut down when not needed or the displacement of the pistons in all the cylinders can be reduced.

Answer 8

mainly because they are bigger thus they need bigger engines so technically ur both rite :)

Answer 9

its both, engine size and vehicle weight both determine what kind of fuel mileage your vehicle gets, a small car w/ a big engine gets worse gas mileage than a small car w/ a small engine

Answer 10

smaller engine