eli5: why does a car get 35mpg, but a lawn mower 2?

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A car can take a vehicle that weighs 2000lbs 35 miles on gallon of gas, but a lawn mower that weights 35lbs and has one spinning blade only goes 2 or 3 miles before needing a refill.

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9 Answers

Anonymous 0 Comments

Even a car moving at ~3-4mph for a long time will result in very poor fuel efficiency.

Equipment like farm equipment isn’t designed to be efficient over distance, it’s primary goal is to deliver a lot of power to an attached tool(s)

Anonymous 0 Comments

If you drove the same distance at the same speed with the same load, it would be alot closer. But your lawnmower is also spinning blades and cutting grass. This is a tremendous load for such a small engine. The equivalent to the car would be hard to make but it would be like driving at full throttle all the time. The mileage would be going down tremendously at that load setting as well.

Cars are also fuel injected and optimized for fuel economy. Your lawn mower is basically the same since the 60s. Technology has not changed much during that time for a standard lawnmower.

Anonymous 0 Comments

because the motor is more efficient in a car. This efficiency cost a lot to research and a lot to build motors in such a way. Measured against the price of a car and 5he amount of cars sold ajd the amount of fuel the owner buys in the lifetime of thr car, this is a reasonable investment. Not so much with cheap, relatively sparsely used lawnmowers. Also Mowers should be simpler in construction in order to be more resilient and easy to (self) repair

Anonymous 0 Comments

Cars are designed to travel long distances down the road efficiently, whereas lawnmowers are designed to cut grass. You could just as well note that cars make very poor lawnmowers, despite being much more expensive.

Lawnmowers use most of the energy from burning gasoline to spin the blade and cut the grass. They could be far more efficient at traveling if you dispensed with the blade and used them only on a paved road.

Anonymous 0 Comments

What speed are we talking? A car is fairly streamlined, which means it uses a lot less fuel to push through the air at a higher speed.

A lawnmower has very grippy, knobby tires, which also make for poor fuel mileage on a car. Put hardcore mud tires on a car, and its mileage will drop too.

A lawnmower isn’t geared for speed. It’s at high revs when going maybe 10 mph. Car has better gearing, letting the engine barely pur along at 50 mph.

And overall, every system has its waste energy. Gas engines aren’t very efficient, and you waste the majority of your energy every second that it’s running. A car at 50 mph spends 1/5th the time driving as the lawnmower at 10 mph, so that’s a lot less time it’s wasting fuel.

In case you take that last part wrong, no there is a point where wind resistance causes far more fuel use than you can save by running for less time since velocity gets squared in the drag equation. But drive a car along at a pokey 10 mph, and your mileage will drop too.

Anonymous 0 Comments

Cars and lawn-mowers are designed to serve different purposes. Cars are a means of conveyance. Lawn-mowers cut grass.

Cars may consume a gallon of gasoline every 35 miles traveled, but how many blades of grass do they cut for that same gallon of gasoline? (hint: it’s zero) Thus, even though a car may be several orders of magnitude more efficient than a lawn mower at getting you from one place to another (assuming the lawn-mower is self-propelled and you ride on top of it), in terms of cutting grass, a lawn-mower is infinitely more efficient than a car.

Anonymous 0 Comments

Distance is not the most useful comparison here, time would be better.

A small car rated for 35mpg could idle for an hour and use a quarter of a gallon (getting 0mpg) or it could drive for an hour at 70mph using two gallons (getting 35mpg).

A push mower probably uses a quarter to a half a gallon an hour no matter what it’s doing.

Take the same engine and stick it in a scooter that only goes 25mph, if it used a third of a gallon for that hour, that would still be 75mpg, which in isolation would make the lawn mower engine seem “better.”

That said there’s a lot more going on with this comparison. The lawn mower is likely a 2 cycle engine with a carburator and basically one operating RPM. All cars now are 4 cycle engines with fuel injection and now variable timing, so it is definitely true that they can get more rotational work from the same unit of fuel, it’s just not quite as drastic as the example sounds.

Anonymous 0 Comments

Because lawnmowers are wildly inefficient. Just s simple 1 cylinder carbureted engine. No ecu, no direct injection, no variable valve timing, no egr system, no variable spark timing. just suck squeeze bang and blow.

Also low pressure tires over grass vs higher pressure tires over pavement.

Anonymous 0 Comments

Unless you have a reel style mower, the engine in a lawn mower runs at maximum governed speed while mowing. Your vehicle wouldn’t get 35mpg if you floored the accelerator and kept it there.