Slingshot Rail Dragsters

May 03, 2010

RAY: This was from my 'Life Can Be a Drag' series and it was sent in by Kathy Sebastian.

'When I was a kid back in the 60s, my dad fell in love with drag racing. It seemed that every weekend he would drag me to see those things called Slingshot Rail Dragsters tear up the track.

Now, if you remember, these dragsters were weird looking, very long and open-framed cars, I guess, with a humungously powerful engine positioned just in front of the driver, who was seated in a cage in the very back of the vehicle. The front tires, which were way up front, were essentially bicycle tires and they were inflated to something like 80 PSI so as to minimize rolling resistance - nice skinny little tires, high pressure. While the rear tires were just the opposite -- the ones that were driven by the engine were huge racing slicks inflated to 10 PSI so as to maximize rolling resistance or traction. Even at that they would always manage to lose traction and start smoking before they could get out of the gate. It made for great theater and a lot of extra noise.

Well, when these cars started reaching quarter mile-speeds of 200 miles an hour and above, the crews noticed that after each run, the front tires came back with very low air pressure, in fact almost flat. This phenomenon was not observed on the rear tires. The question is, what caused the front tires to deflate? Where was the air going? And why?

RAY: Here's the answer. Centrifugal force was responsible, because what was happening is that as those front tires were turning at 200 miles an hour, the Schrader valve that's used to hold the air in was being pulled by centrifugal force and opening up.

TOM: No kidding.

RAY: No, that's what they said. I don't think kidding was exactly the word they used. The valve was opening up, and air pressure was being lost because it was just as if someone had stuck something in there to deflate the tire. But what was happening was the tire was spinning so fast that the Schrader valve was actually opening up due to centrifugal force, letting air out, and at the end of the run the tires would be flat. They solved the problem by putting O-rings in the little caps so that even though the valve opened the tires wouldn't lose pressure. Pretty cute, eh?

TOM: It's just cute but it doesn't seem like it's possible.

RAY: Doesn't seem possible? That's probably because it might be boh-oh-oh-oh-gus. Anyway, do we have a winner?

TOM: We certainly do. Our winner is Stan Wilman from Bettendorf, Iowa, and for having his answer selected at random from among all the correct answers that we got, Stan's going to get a $26 gift certificate to the Shameless Commerce Division at, with which Stan can get himself a set of Car Talk reusable shopping bags.

RAY: Congratulations, Stan!

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