Today: Click and Clack weigh in on lead weights.

Dear Car Talk

Dear Car Talk | Feb 01, 2010

Dear Tom and Ray:

It turns out that lead wheel weights are the biggest source of lead in California's waterways. There is a bill that would ban them in favor of safer alternatives, especially stainless steel. My question is, Exactly what do wheel weights do? I know they are used to balance the wheels, but what exactly does that mean?

-- Ang

RAY: Wheel and tire combinations are not born balanced, Ang. In that way, they're like my brother.

TOM: Right. But unlike me, wheels and tires can be balanced fairly easily. When we say "balanced," we mean that the weight of the wheel-tire combination is evenly distributed so the wheel won't wobble.

RAY: When a steel wheel or a rubber tire comes off the assembly line, it doesn't always come out perfectly. Oh, it's close. So close that if you drove on it at speeds up to 30 or 35 mph, it would seem perfect, and you'd never know the difference.

TOM: But once you get up to 40 mph or so, those small imperfections in weight balance will make your car shake like a half-prepared fruit smoothie still whirling around in the blender.

RAY: Why are these products not perfect? The metal or rubber poured into the mold might not be entirely homogeneous -- meaning the materials used might not be blended perfectly. Think about pancake batter and the occasional pocket of flour you come across. It's not that extreme in wheel and tire production, but it doesn't take much of an imperfection to be noticeable at high speeds.

TOM: And rather than perfect the production process of every tire and wheel made on the planet, it's a lot cheaper to balance the tires after the fact with a few cents' worth of lead weights.

RAY: Right. If you were manufacturing wheels for gyroscopes to be used in space lasers, and the future of life on Earth depended on them, then sure, you'd use much more expensive equipment and make the parts come out perfectly. But wheels and tires for cars don't need to rise to that standard.

TOM: But there's absolutely no reason why tire dealers and repair shops can't use stainless or "powdered" steel weights instead of lead weights. They work just as well, they don't leach lead into our drinking water and they cost almost the same, maybe a few pennies more.

RAY: A number of states have already banned lead weights, and I suspect the rest, including California, will soon follow. We're all for it.

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