Q: In the 1970s, the shop I worked for had a tire truing machine that would rotate the tire while the blades slowly removed tread until the tire regained its round shape. Fast forward 50 years, and I, like many others with all-wheel drive vehicles, acquired a puncture that required the purchase of a new tire. Because the new tire had a different diameter than the other three, I had to replace all four tires. It seems to me that the purchase of one new tire and having tread removed so that it matches the other three would be a better choice. Your opinion?

A: I see your point, but I can't be of much help. The technique you mention is known as tire shaving. This is not only a rare technique, but the machines also are rare and they require a skill that very few have.

Skip the chip

Q: I have a 2007 Ford F-150 with a 5.4-liter engine that just turned 200,000 miles. It runs great. I am thinking of purchasing a superchip tuner with the idea of enhancing the performance. What are your thoughts on these tuners?

A: Keep in mind that some chips can disable some emissions systems. And some chips require the use of premium gas. I would think long and hard before I did this.

Negative goes first

Q: I am surprised that you did not comment about the person who disconnected his positive battery cable to fix his electrical system. You always remove the negative cable first.

A: Good point. I was focused on answering the reader's larger question when they stated that disconnecting the battery temporarily resolved their problem. Yes, always disconnect the negative cable first and reconnect it last. If your tool touches the car's metal while you are working on the positive connection, that contact will complete a circuit and create a spark. If the negative terminal tool contacts anything, nothing happens.

Bob Weber is a writer, mechanic and ASE-certified Master Automobile Technician. His writing has appeared in automotive trade publications, Consumer Guide and Consumers Digest. Send automotive questions along with name and town to motormouth.tribune@gmail.com.