Dear Car Talk:
I have a 2013 Volkswagen Jetta Hybrid, and I am considering getting lighter alloy wheels that are about 10 pounds lighter than the factory wheels. Would reducing 40 pounds of weight improve my mileage significantly, reduce my stopping distance and improve the handling enough to justify such an upgrade? -- Jesada
I don't know how much these new wheels would cost you, Jesada, but unless you're stealing them, I don't see you making back your money in improved gas mileage during your natural lifetime.
You'd be reducing the weight of the car by about 1 percent. And while the relationship between weight and mileage isn't direct, even if you got a 1 percent increase in mpg, you're talking about half a mile per gallon. According to my math, if you drive 15,000 miles a year with these new wheels, you'd save $11.
In theory, the answer to all of your questions is "yes": Reducing weight does improve fuel economy, reduce stopping distances and improve handling. But would it be enough for you to notice?
You might notice that the handling feels a little spryer. And if you really wanted to believe it, you probably could convince yourself that you were sensing the other benefits as well. But I think most people would not notice much, if any, difference off the racetrack.
If your primary interest is increasing your mileage -- and boosting your bragging rights on the Jetta Hybrid blogs, which I bet you frequent -- you'd be better off adding a few pounds of air to each of your tires. If, for instance, your tires call for 32 pounds of air per square inch (psi), fill them to 35 or 36.
In most cases, overfilling your tires by 10 percent over the car manufacturer's recommended inflation pressure is safe (whereas underinflating them is not safe). And overinflating your tires will reduce rolling friction and improve your mileage a bit. It also can improve steering response and cornering.
The downside is that it will make your ride stiffer, degrading your ride quality and comfort a bit. But you can make up for that by taking all that money you saved on those alloy wheels and buying yourself a padded bicycle helmet. That'll keep you from getting lumps on your head if you bounce up and hit the roof while driving around on your overinflated tires, Jesada. Good luck.