RAY MAGLIOZZI

Dear Car Talk: Back in the days of bias ply tires, there was a standard X-plus rotation pattern that also involved the spare. When radials came along, we were told they were directional and should only be switched between front and rear, and had to be kept on the same side of the car. Now, when pros do tire rotation on our cars, they’ve reverted to the old X-plus method.

What changed? — David

More experience and better tire construction. When radials first came into common use in the 1960s and 1970s, manufacturers believed that those tires developed a “memory” for what direction they turned.

I don’t think they believed tires had a literal memory (“Remember the time David bashed me into that curbstone after Fred’s bachelor party?”). But they were concerned that the adhesives that held the internal belts together could fail if the forces at work on the tire switched to the opposite direction. And when you switch a tire from the right side of your car to the left side, you change its rolling direction and change the direction of those forces.

As better adhesives were developed, and we had more real-life experience with radial tires, the manufacturers eventually concluded that this was really not an issue, and it was perfectly safe to switch the tires’ direction. Sadly, they missed the opportunity to call this “tire amnesia.”

Not only is it safe to use the X pattern, but it’s highly desirable. The X pattern you refer to is where you take the right rear and move it to the left front, and the left rear to the right front. So, you’re switching both the rolling direction and the front/rear position of all tires. If you have a full-size spare (that’s the “plus”), it usually goes on the right rear, and the left front becomes the spare.

That rotation evens out the way all the tires wear down. Front tires wear faster than rear tires, since they carry a heavier load of steering and braking. And the individual chunks of tread tend to wear down more at their trailing end than their leading end. Reversing the rolling direction evens that out and makes the tires less noisy and longer lasting.

So, the X pattern, or X-plus, is the way to go now if you opt to rotate your tires. And unless your tires are specifically designed to be directional (some are), you can forget all about that issue, just like your tires have.

Got a question about cars? Write to Ray in care of King Features, 300 W. 57th St., 41st Floor, New York, NY 10019, or email by visiting the Car Talk website at www.cartalk.com.