Q: I had my Honda Accord detailed, and when it was returned, I noticed significant water spots on my rear-view mirrors and the outside of the back window. I can only assume they were using hard water and did not wipe the windows fast enough. Although I'd like to hold them responsible, proving it was their fault is difficult. I have tried to remove the spots using a slightly diluted white vinegar solution, and also with a baking soda/vinegar mixture, with zero results. Is there any product to remedy this? Any suggestions, short of replacing the glass and mirrors?
— L.Q., Batavia, Ill.
A: We have a hunch the problem may have been caused by hydrofluoric acid (HF). It etches glass. Hydrofluoric acid is used in many automatic carwashes because it does an excellent job of removing brake dust, road grime and rust — and it is inexpensive. Diluted properly, it leaves cars sparking clean, but higher concentrations etch glass. We know of no way to remedy this. You may be able to feel the etching with your fingernail. The professional carwash industry generally decries HF, but some operators still insist on using it, especially to clean wheels. HF is insidiously dangerous, since it doesn't cause skin burns that you can feel as other acids do. Instead, it seeps through tissue, eats into bones and turns the calcium into calcium fluoride. It may take hours before the burn victim realizes it.
Q: Many answers given in papers on tire rotation are wrong. Do not cross-rotate tires; transfer them only front to back, back to front same side. As they roll, tires wear the leading edge of treads and leave the trailing edge in a raised following position. Run (the) palm of your hand in a reverse travel to rotation and it feels smooth. Now run your hand in the same direction as tire rotation and feel irregular bumping; I call it chirping. This raised condition, when a tire running in reverse travel abnormally meets the road, causes troubles — like poor steering, wheel tracking, bumpy ride, increased tire wear, etc. I have always done same-side rotation and have never experienced any problems and always have matched or exceeded manufacturer's tire mileage.
— P.S., Farmington, Conn.
A: Good for you. But I must disagree. The experts, including those who make tires, encourage routine tire rotation. It is not the leading and trailing edges of the tires, but the outer edges of the treads at the shoulders, that benefit. Because they handle the steering, front tires wear unevenly at the edges. The rear tires wear more evenly. Rotating the tires evens out the wear. Unless your vehicle demands that tires be rotated only front to back by design (directional tires) or the vehicle has different-size tires on the front and rear, here is the proper rotation sequence: For rear-wheel-drive cars, move the front tires to the rear, crossing them as you do so. Move the rear tires directly to the front without crossing them. For front-wheel-drive cars, move the front tires straight back and cross the rears to the front.