Encore Puzzler Answer, 7/26/97: Little spares, lots of problems

RAY: Remember this Puzzler?

TOM: No.

RAY: No, I didn't think you did. Here you are about to embark on a very long trip --

TOM: You mean like to go home after the show.

RAY: You're driving the Trans Canadian expressway. No tolls on this expressway and you can't stop for more than a few minutes to like empty your coffee can or something. You know, so you have to just go right along --

TOM: Blast.

RAY: -- and you discover that you have a flat tire and you open the trunk only to discover that you have a space saver spare and it does have air in it. The question is, where do you place it? And the reason this is a Puzzler is because it is a different diameter. It is smaller in diameter than the other three tires and you have to put it someplace and you've got to drive the next three or four thousand miles with this thing on there. You can't drive to the next service station and get it replaced with a real tire. You're going to drive all across Canada and back again. So maybe you're going to drive -- depends which end you start at but you might drive three or four or five thousand miles with this littler tire on there.

TOM: So where should it be?

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 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. The winner this week was selected by Prime Minister Noboru Takeshita. No, Takeshita. I got it right, hunh?

TOM: Yeah.

[ Car Talk Puzzler ]