•Q. I have a 2-year-old Camry, and I like to work on my cars. I live in northwestern Montana. Great place! But we have snow. I have a complete set of studded tires, and I am quite happy changing out all four tires twice a year. But I cannot get the wheels off the car myself — either set! I have changed wheels for 60 years, but I can’t seem to remove these. I had the dealer do it, and watched at the garage as they pounded on them with sledgehammers. I asked the service manager, and he told me that this is not an uncommon problem. What if my wife or I get a flat tire and need to remove a wheel? Did I mention I live in remote northwest Montana? The service manager told me that if that happens, I should loosen the lug nuts and drive it for a while, and the wheels will come loose. Is that really good advice?•

TOM: This is a pretty common problem, especially in parts of the country where snow, salt and rust are prevalent.

RAY: What happens is that there’s a protrusion on the hub, over which the hole at the center of the wheel slides. The wheel is then secured to the hub with the lug nuts.

TOM: That hole in the center of the wheel just barely fits around the hub’s protrusion. So if you have steel wheels, which I’m sure you do, and you have snow, salt and rust, which I know you do, the wheel and hub can become sort of fused with rust over time. That’s what makes the wheel hard to remove.

RAY: Brute force tends to be the tool of choice for this job. That’s why you saw the repair guys going at the wheels with sledgehammers.

TOM: My brother wasn’t paying attention when they taught this in mechanic school, so he also uses his sledgehammer for computer repair — less successfully.

RAY: But more satisfyingly.

TOM: What we do when we change a customer’s wheels in the snow belt is first take some sandpaper and clean off any rust or budding corrosion that we find on the inside of the hole in the wheel or on the outside of the hub protrusion.

RAY: You don’t have to worry if you end up making the hole a little bigger. The wheels are centered and held securely in place by the lug nuts.

TOM: Then we grease both surfaces before putting on the wheels. That usually helps a lot, at least for the six months or so until the next seasonal changeover.

RAY: And if you do have a flat tire and need to change a wheel in some remote area, the advice you got is almost good.

TOM: Yeah, almost. What you want to do is loosen the lug nuts a little bit — not a lot! Maybe a quarter of the way off. And then drive the car quickly for a very short distance (like 10 feet) and stop abruptly. Then put it in reverse and do the same thing going backward. That usually will jolt the stuck wheel free so you can remove it.

RAY: But don’t just loosen up the lug nuts and go driving around for a while. That usually doesn’t end well. Good luck.

•Q. I was shopping for spark plugs for my 2002 Dodge truck from a company that has a site on the Internet. They had spark plugs for carbureted engines and fuel-injected engines. I bought plugs for injected engines. Is there a difference?•

TOM: Every engine has its own unique requirements for spark plugs. It’s not really based on whether the engine is carbureted or fuel-injected; it’s based on the way the engine was designed.

RAY: For one thing, engines have different physical characteristics. For instance, some engines have thicker cylinder heads and require longer plugs with more threads to get the tip of the plug into the combustion chamber.

TOM: The amount of room on top of the cylinder head is another consideration. Older engines had only two valves per cylinder, so there was plenty of room for a nice, fat spark plug to stick its nose into the cylinder. But the majority of engines today are multivalve. You could have four or five valves cut into the top of each cylinder now, leaving much less room to fit a plug there. So most newer engines call for smaller, thinner plugs.

RAY: The other reason plugs are specific to engines is because the vehicle’s engineers designed the plug as part of a system needed to create a very specific pattern of combustion. They may want a spark plug with a hotter spark, or one that sits farther down in the combustion chamber to produce the precise shape, size and duration of flame they’re looking for in there. Those details affect an engine’s power, gas mileage and emissions.

TOM: For those reasons, there are hundreds of different spark plugs on the market. The only way to know which one you need is either by removing an old one and reading the number, or by looking up a car’s year, make, model and engine size in a parts locator, and getting the plug number that way.

RAY: Perhaps what you were seeing was a general “spark plugs for Dodge trucks” page on a website. Over time, there certainly have been both carbureted and fuel-injected engines used in those trucks.

TOM: But not in 2002. By then, every car and truck sold in the United States was fuel-injected. That means there’s only one correct spark-plug type for your truck. I hope you got that one.

Got a question about cars? Write to Click and Clack in care of this newspaper, or email them by visiting the Car Talk website at www.cartalk.com.