Tires and Steering

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Inspect your tires and check the air pressure once a month. Tires are where the rubber meets the road, so to speak, and no place to cheap out. A blowout at high speed will provide convincing proof if you need it.

There should be 3/32 inch of tread to be legal and safe. Place a penny in the tread. If the top of Abe’s head isn’t covered, replace the tire. While it’s true that the performance of a tire with a lot of miles and a thin, but legal tread is just as good as a brand new tire on dry pavement, wet pavement is another story. Thin treads can’t shed water as rapidly so slow down or you might just hydroplane into the next life.

Tire wear should be even across the tread:

• More wear on one edge indicates misalignment,
• More wear on both edges indicates under-inflation,
• More wear in the center than the edges indicates over-inflation.
• Stripes across the width of the tread indicates the tire is worn out and must be replaced.
  This wear indicator is molded right into the tire.

It’s impossible to tell whether a radial tire is properly inflated by looking at it. It’s tough to tell what they’re thinking by their appearance, too. The air pressure should be measured with a gauge and should be seasonally adjusted like a variable rate mortgage. (Don’t use the indicator on the air pump at the filling station to measure pressure. These are often inaccurate.) As the weather gets colder, the pressure will go down considerably, and the opposite happens when it gets warmer. Measure the pressure when the tires are cold. That is, you shouldn’t have driven more than a mile or two before measuring.

Tire rotation should be done every 7,000 miles or so. The current wisdom is to cross rotate radial tires as was done years ago with old-fashioned bias-ply tires. That is, the front-right should be swapped with the rear-left, and the front-left with the rear-right tire. (Dr. Dipstick refuses to add the complication of a full-sized spare tire to this problem.) If the tire rotation interval is a lot greater than 7,000 miles, this method can result in tread separation. In this case swap tires front to rear on the same side.

The economics of tire rotation are mysterious and puzzling. It pays to rotate tires in the sense that the overall wear will be averaged out and the number of miles out of the tires will be greater. However, if you have to pay someone to do the job, it’s not at all clear that rotating tires leads to lower total cost over the life of the tires. The best suggestion is that if you drive the US average of 15,000 miles per year, have them rotated when you get your brakes inspected. If you do this at the recommended six month intervals, you will have driven about 7,500 miles. Simply instruct the mechanic - since the wheels will be off anyway - to put the front-right on the back-left, etc., after the inspection. Maybe you can get him to not charge extra for the service that way.

You may find the wheel balance to be off right after a tire rotation. This is a likely cause of a vibration noticed in the steering wheel that occurs at a particular speed. The rear tires may simply have worn irregularly, and that may not have been noticeable until they were moved to the front. It may not be that, however. Have the steering system checked immediately, and also have the wheels balanced.

Inflate the tires to the level indicated in the owner’s manual - not to the values marked on the sidewalls of the tires. Those are maximums and you want the value that is appropriate for the car, it’s suspension and load. The correct pressures are shown in your owner’s manual, and also usually on the car itself in the glove compartment, door jamb or gas filler cover. Record the correct pressures in your log.

The steering alignment and wheel balance should be checked about every 30,000 miles, or if you ever notice peculiar tire wear as described above.

The level of the power steering fluid should be checked once a month. It need never be changed.

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