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Little Spares, Lots of Problems

The Puzzler


RAY: It should be on someone else's car, but assuming it's going to be on your car, if you have a front wheel drive car you want to put it on the back. If you have a rear wheel drive car you want to put it on the front.

TOM: And if you have neither rear or front wheel drive car then it doesn't matter where you put it.

RAY: If you have a four wheel drive car --

TOM: You're done for.

RAY: -- they don't give you those little Mickey Mouse spares with four wheel drive cars but if you have a front wheel drive car the reason you want to put it on the back, and the reason you want to put it on the front if you have a rear wheel drive car, is you do not want it on the axle where the driving wheels are, in other words, the axle that has the differential, because when you have tires that are two different sizes it causes the side gears, or the spider gears, in the differential to actually turn, because when you're going along on a straight line those gears hardly turn at all. Every once in a while you make a little dip fake to the left or a little turn to the right and those little gears will --

TOM: A head fake, just a head fake.

RAY: Right, or you might think of passing somebody. Those gears will turn but very, very little. When you have tires that are two different sizes all the way across Canada those spider gears are turning like crazy and what will happen, because they're not designed to take that kind of abuse, is they will burn up.

TOM: And you will get the classic rear end hum.

RAY: Oh, yeah, you'll get it. You'll have it before you make Manitoba.

[ Car Talk Puzzler ]

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