What’s the Difference Between All-Wheel Drive and Four-Wheel Drive?

iStock/PeopleImages
iStock/PeopleImages

As the weather turns nasty, you may start to think more about your car’s transmission—particularly, its ability to get you up and down muddy, snowy, or icy roads. While you may know that two-wheel drive isn’t the best option for driving in harsh weather, other terms are more confusing. Like, for instance, all-wheel drive versus four-wheel drive. Don’t all cars have four wheels (at least when it comes to sedans, SUVs, and other consumer vehicles)? As Jalopnik explains, the difference between all-wheel drive (AWD) and four-wheel drive (4WD) is more than just semantics—and which type you need depends heavily on the kind of driving you do on a regular basis.

When a car manufacturer specifies something as two-, four-, or all-wheel drive, the company is referring to the tires that receive power from the engine. With two-wheel drive, the engine powers either the front axle or the back axle of the car, meaning that the engine is moving only the front tires or the back tires. The other axle is just rolling along. When four-wheel drive (sometimes referred to as 4x4) is engaged, meanwhile, the engine rotates all four wheels. This helps give the car extra traction on slippery surfaces like sand, ice, and gravel—so that even if one set of wheels can’t get traction on a slippery surface, the other wheels might be able to.

The key word there is “engaged.” Traditionally, four-wheel drive means that your car can drive with all four wheels, but you have to manually choose that option. The rest of the time, you’re in two-wheel drive mode. As Ray Magliozzi of NPR’s "Car Talk" once explained to a listener, four-wheel drive is “designed to be engaged when you're already stuck, or in a specific situation where you know you might get stuck—like in snow, sand, or mud. It’s not designed for normal road use, and must be disengaged before you drive on dry, paved roads.”

In all-wheel drive, meanwhile, the car figures out what kind of traction you need all on its own. It has sensors that figure out how much power should go to each wheel to give you the best traction without any input on your part. This is a useful feature for driving in a variety of different conditions, while a dedicated four-wheel drive mode might be better for serious off-roading.

Be warned: There are downsides to all that extra traction. A car’s engine has to work harder to power all four wheels. Those engines are also heavier, which itself takes more power to move. As a result, four-wheel or all-wheel drive cars usually use significantly more fuel than your typical two-wheel drive model.

There are other caveats to this explanation: Full-time four-wheel drive cars do exist, but they differ slightly from all-wheel drive vehicles because of how the two axles of the car move in relation to each other. In four-wheel drive, the front and rear wheels are locked together so they spin at the same rate; in all-wheel drive, the wheels aren’t locked like this—different amounts of power go to the different wheels as needed.

All this said, even if you live somewhere with snowy winters, it doesn’t necessarily mean you should spring for all-wheel drive. If you’re driving a lot in inclement weather—say, if you live in South Dakota or Wyoming rather than sunny Southern California—winter tires may actually be a lot more important than which wheels the engine is powering. Need proof? Watch the video comparison here.

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What Is the Shelf Life of Donated Eyes?

iStock.com/Pedro_Turrini
iStock.com/Pedro_Turrini

Zoe-Anne Barcellos:

I can only answer for cornea and eye donation.

The FDA does all oversight (no pun intended) of organ disposition.

The main organs—heart, liver, pancreas, lungs, etc.—are transplanted within hours. They are just not viable if they are not being perfused constantly.

The other tissues—like bone, skin, tendons, etc.—do not need to be transplanted immediately. But I am not sure on the regulations of when they need to be transplanted.

With the eyes, there are four tissues that can be recovered.

We recover whole eyes for research and education purposes. These usually go much faster, but we can hold them up to a year.

Conjunctiva can also be recovered; conjunctiva is a clear covering over most of the eye (it is what gets irritated when you have pink eye). I have been working as a recovery tech for five years, and our office has not had a request for "conj" in all that time. I believe it is mostly used for research, but I could be wrong.

Sclera is the white area of your eye. It is fairly thick and flexible. If you have ever touched a reptile egg, that is what it reminds me of. We recover sclera for transplant. They use it for several things, but mainly to patch punctures. Similar to if you pop the inner tube of your bike and repair it. Sclera can also be used to repair ear drums. We can hold on to this for up to a year.

The main thing we recover is corneas. In the U.S., we must transplant these within seven days of recovery. (Recovery is usually within hours of death, but we can push it up to 20 hours after if needed.) Sometimes we have more corneas than we need, and then they are shipped overseas and transplanted up to 14 days after recovery. There is no real different outcome with the later transplant time, but the FDA in the U.S. made the rules. (You can sign up to be an organ, tissue, and eye donor here.)

This post originally appeared on Quora. Click here to view.

Why Are There No Snakes in Ireland?

iStock
iStock

Legend tells of St. Patrick using the power of his faith to drive all of Ireland’s snakes into the sea. It’s an impressive image, but there’s no way it could have happened.

There never were any snakes in Ireland, partly for the same reason that there are no snakes in Hawaii, Iceland, New Zealand, Greenland, or Antarctica: the Emerald Isle is, well, an island.

Eightofnine via Wikimedia Commons // Public Domain

Once upon a time, Ireland was connected to a larger landmass. But that time was an ice age that kept the land far too chilly for cold-blooded reptiles. As the ice age ended around 10,000 years ago, glaciers melted, pouring even more cold water into the now-impassable expanse between Ireland and its neighbors.

Other animals, like wild boars, lynx, and brown bears, managed to make it across—as did a single reptile: the common lizard. Snakes, however, missed their chance.

The country’s serpent-free reputation has, somewhat perversely, turned snake ownership into a status symbol. There have been numerous reports of large pet snakes escaping or being released. As of yet, no species has managed to take hold in the wild—a small miracle in itself.

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