Chase Elliott won, then lost the Snowball Derby last weekend. His car was disqualified for having tungsten ballast instead of the mandated lead ballast. Ballast is weight added to the car in strategic locations to help the car handle better.
A number of news reports have noted that ‘tungsten is heavier than lead’, which is only true when you’re comparing two pieces of metal the exact same volume. I learned this lesson when I was working on my book, The Physics of NASCAR.
It was 2007, I believe, when Kirk Almquist, then Elliott Sadler’s car chief, brought me two blocks of metal the same size. He held them out for me to see, but didn’t let me hold them. They were both a rather unimpressive dull grey.
“One of these”, he said, “is tungsten. The other is lead. Which is heavier?”
I made a quick mental recall of the periodic table (which was nowhere near as neat or organized as the one I’ve shown here from webelements.com, the best place on the web for periodic table information.)
Tungsten has the atomic symbol is W because the element was discovered as part of a mineral called Wolframite , which has a lot of tungsten in it. Lead is Pb, which comes from the Latin plumbum, meaning “liquid silver”. ‘
Tungsten is atomic number 74 and lead is atomic number 82. With a few exceptions, the larger the atomic number, the heavier the atom. The atomic weights (how much equal numbers of atoms of each substance weigh) are right there on the periodic table. A lead atom is about 1-1/8 times heavier than a tungsten atom. So I guessed lead.
Kirk got a big smile on his face and handed me the blocks. The tungsten block was a lot heavier than the lead block.
Why is a tungsten block heavier than the same sized lead block if lead atoms are heavier than tungsten atoms? It all has to do with how tightly the atoms are packed when they form a solid. The numbers on the periodic table just refer to the atoms, but the atoms pack themselves into regularly ordered patterns when they form solids. The more closely the atoms pack in, the higher the density of the solid.
The density of lead is 0.410 lb/in3, which means a cube of lead one inch on all sides weighs 0.41 pounds. Tungsten has a density of 0.70 lbs/in3, which means that a cube of tungsten one inch on all sides would weigh 0.70 lbs – 1.74 times more than the same sized cube of lead.
In ballast, we’re usually not talking about a pound at a time: we’re talking, say, 25 pounds. Ballast is usually installed into a car’s frame rails, so a typical cross-section for ballast is 2-5/8″ x 3-5/8″. Twenty-five pounds of tungsten would be 3.75″ long, while twenty-five pounds of lead would be 6.40″ long.
This is important because the weight distribution makes a huge difference in how a car handles. The weight pushing each tire into the track creates grip. The more weight pushing down on a tire, the more grip it has. Using a denser weight, like tungsten, allows you to more precisely place the weight. That allows you to do things like lower the center of gravity, or shift the weight from left to right and front to back in a way you can’t do with the physically larger piece of lead.
Elliott said that it was an oversight (and there’s no reason to believe it wasn’t), but rules and rules and they lost their win.
No Tungsten Allowed
Why is tungsten outlawed in many lower-level racing series?
Stock Car Steel and Aluminum Company (a typical supplier of race metal) will sell you a piece of tungsten 2-5/8″ x 3-5/8″ x 6″ long for $1876.88. A comparable lead weight would cost you somewhere around $100. Lower-level series don’t want to price the teams out of competition. When one team gets an advantage, all the others are going to have to do the same thing to keep up. It becomes a cost issue.
Tungsten is so expensive because it is more rare than lead and it is just harder to deal with. Tungsten has a very high melting point (6192 F vs. 621 F for lead), which means that shaping it into bars requires some heavy duty furnances.
Tungsten is also more difficult to machine because it is hard and brittle unless it is made very very pure (which is also expensive). Many machine tools are made from tungsten carbide (WC), one of the hardest carbides that exists.
There is even a trend now to make jewelry from tungsten and tungsten alloys, which raises a big problem: if your gold wedding ring gets stuck on your finger, you can cut it off. You can’t do that with tungsten. (The solution is that you have to take advantage of the brittle nature of the material and crush it without crushing the fingers.)