A hybrid car’s battery should long outlast its warranty Dear Car Talk: In 2014, I bought a new Toyota Camry XLE Hybrid. It’s the best car I’ve ever owned. It’s got about 72,000 miles on it. Everything is working great. But the 10-year warranty on the “bi

Dear Car Talk: Can you explain the physics and engineering for the concept of “unsprung weight?” I see people who drive cars like mine (a 2006 BMW Z4) talking about how to “reduce unsprung weight.” What are they looking to do? Thanks. — Russ

In the simplest terms, “unsprung” is everything below the car’s springs. So, it’s things like wheels, tires, axles, and brakes.

If you want to get picky, there is some weight that’s considered partially sprung weight. There are some suspension parts that attach both above and below the springs. But for the purposes of explaining the concept, think of it as mostly wheels and tires.

Why do people want to lose unsprung weight? People with performance cars want less unsprung weight because it improves the car’s handling.

When you drive over bumps, the tires and wheels get bounced up in the air. The lighter they are, the quicker the springs can force them back down on to the pavement and keep them there. The more time the tires spend in full contact with the road, the better the car’s handling.

Heavier wheels and tires react more slowly, and when they hit the ground, they’re more likely to bounce up again. It’s more weight for the springs and shocks to manage.

So, to reduce unsprung weight, manufacturers (or car owners) replace steel wheels with lighter, aluminum alloy wheels. That’s probably the most cost-effective change you can make. And for people who drive on the streets (as opposed to the track), doing more than that is probably not worth the money.

Still, some zealots will look for narrower wheels that can be fitted with narrower, lighter tires. And they might even replace steel brake calipers with alloy calipers and use carbon ceramic rotors. You can go nuts with this stuff and even try to save a few ounces with lighterweight lug nuts. But by then, your family will have left you, Russ.

Got a question about cars? Write to Ray in care of King Features, 628 Virginia Drive, Orlando, FL 32803, or email by visiting the Car Talk website at www.cartalk.com.