Shell develops custom race fuels for the Ferrari Formula 1 team. Their trackside laboratory helps them refine fuel for the race team and test formulas that could ultimately be transferred to the consumer market.

With the help of the Popular Science Buyer’s Guide to Cars, perhaps you’ve successfully scored your shiny new ride. That doesn’t mean you can stop thinking about it. Do you know what kind of gas you can put in? How often–really–should you change the oil? What kind of tire and wheel upgrades will improve your car’s performance, and which will degrade it? Although some might regard the assorted responsibilities of ownership as annoying hassles, paying close attention to them will ultimately pay dividends in performance, reliability, longevity and operating cost.

As a general rule, put in precisely the octane level that the manufacturer recommends–and nothing more. Some cars, particularly those with turbocharged engines or older models that are prone to knocking (higher-octane gases reduce premature detonation, which causes engine knock), require the higher octane levels found in premium gas. But most can be very safely run on medium-grade or even regular gas, saving those precious dimes at the pump. Increasing the octane level if the engine doesn’t require it has little advantage–in most cases it won’t make your engines any cleaner and it won’t increase your horsepower.

What will make a difference are detergent additives, and this is where gasoline products distinguish themselves. As miles add up, engines can accumulate deposits in the fuel injectors and on the engine valves, often in fewer than 5,000 miles. This can severely degrade engine performance, reducing power, making the engine run roughly, and increasing emissions. Off-brand gasoline sellers–local chains, national discount retailers and those operating independent stations–will include the minimum detergent quantities mandated by the government, but the major brands contend that the minimum is too little to keep engines clean. Certain automobile manufacturers agree with them, and Shell, Chevron and Conoco, among others, recently joined forces with Honda, BMW, GM and Toyota to create their own detergent-standard program, known as Top Tier. Gasolines from these retailers contain the highest detergent levels on the market, across all the octane levels offered.

An alternative to buying high-detergent gasolines all the time is to consider a fuel additive, such as Techron, which, when added every 5,000 miles or so, cleans deposits out of your fuel injector and off your engine valves. Because the inclusion of detergent additives to gas sold in the U.S. is entirely voluntary, such products might be a good idea if you tend to purchase off-brand gasoline from discount retailers.

The best thing you can possibly do for your new car is to change the oil regularly and reasonably frequently. Use the owner’s manual as a guide, particularly in terms of the viscosity ratings and the frequency of oil changes. Don’t pay too much attention when oil-change chains suggest that drivers need to change their oil, say, every 3,000 miles–many cars are designed to perform perfectly well with oil changes every 5,000 miles, or even more. Finally, synthetic oil is excellent, but it offers little real advantage over conventional oil except in extreme environments of cold, heat or prolonged aggressive driving, such as in a racecar.

Perhaps the most critical decisions drivers make after they purchase a new car concern their tires. You must balance price against performance, comfort and longevity. Below is our advice about this increasingly complex component of the driving experience.

  • The first thing you should do with your new car is determine what kind of tires it came with. Are they all-seasons with 60,000-mile warranties or performance tires that will be gone in 20? Some dealerships, particularly in the South, sell cars installed with summer tires, which are designed for long tread wear and a quiet ride but not at all for snow or ice. Such tires are fine for those climes and handle terrifically in the rain, but if you head North at all during the winter, beware.

  • When considering a tire upgrade along with a possible increase in wheel diameter, be cautious. Putting 22- or 24-inch wheels on your SUV, while flashy, adds up to 400 pounds of unsprung rotational weight, decreasing acceleration times and increasing stopping distance up to four car lengths. You should compensate for this with new brake pads and possibly larger rotors and calipers. When upgrading as a performance enhancement, increasing wheel diameter will increase your performance, but only up to a point. If you go from 15 to 16 inches, or 16 to 17, each step makes the car corner faster, since a shorter sidewall is stiffer than a taller one, and the driver can read the road much faster. Beyond 18 inches, the tire sidewall becomes too small for comfortable driving.

  • Driving on properly inflated tires is critical to fuel economy, vehicle performance and tread wear. In 2008, tire-pressure monitors will become mandatory for all cars sold in the U.S., but drivers must remember that the systems notify them only when the air pressure is too low by 25 percent. That 25 percent is critical–it’s where the real advantage in fuel economy and proper tire wear takes place. Furthermore, according to John Rastetter, director of product information at the Tire Rack, an online tire retailer that conducts extensive in-house testing of tire products, tire manufacturers, many of which oppose the legislation, are concerned that a 25 percent drop in tire pressure may be unsafe, because underinflated tires may not adequately support a fully loaded vehicle. “Even if you do have a tire-pressure-monitoring system in your car, don’t rely on it exclusively,” Rastetter advises. “Still check the tire pressure at least monthly to ensure that they aren’t riding even a few pounds low.”

  • If you get more than two or three substantial snowfalls a year, seriously consider snow tires, which are specially designed to grip snow on the pavement. “Traction in the snow is a partnership between the road and the tire, or the snow and the tire–or, in reality, the snow and the snow,” Rastetter says, explaining that snow-tire traction is achieved when the snow that is gripped and retained by the tire’s tread interacts with the snow on the pavement. Instead of buying snow tires and switching them onto your existing wheels every winter–and paying to have them mounted and rebalanced–consider buying a set of snow tires already mounted on inexpensive wheels. You can then put them on yourself and, in the process, spare your nice alloys the abuse of winter driving.

  • Rastetter also recommends rotating the tires front to back every 3,500 miles up to the 15,000-mile mark on your odometer. Thereafter, rotate every 6,000 miles up to 30,000 miles, and then every 4,000 miles up to 60,000 miles. Tires wear faster when they’re new and toward the end of their lives, so you want to rotate them more often during these periods.

  • Ultimately, your tire performance is mostly a function of what kind of roads you drive on–tire grip and tread wear are directly related to the quality of the local roads. Rastetter notes that asphalts vary from state to state because they’re all made from local materials. In Hawaii, for instance, where roads are made from abrasive volcanic pumice, tires have more grip, but they wear out faster.