Could installing directional tires backwards cause an accident in the snow?

Dear Car Talk

Dear Car Talk | May 01, 2003

Dear Tom and Ray:

On a snowy morning this past winter, my work buddy crashed into a guardrail. When he took the car to the body shop, he was told that his tires were installed backward. Is this possible, and can improper tire installation reduce traction in snow? -- Frank

RAY: OK, Frank. We'll answer your question. But just between you and me, we know your buddy was just driving too fast in the snow, like a lot of people do. And now he's looking for someone to blame, right? The American way.

TOM: I guess suing the guardrail manufacturer didn't pan out, so he's moving on to the tire store.

RAY: Well, here's the story. It IS possible to put SOME tires on backward. Some higher-performance tires are "directional." That means they're optimized with a single rotational direction in mind. If the tire manufacturer knows in advance in which direction the tire will rotate, it can optimize each individual groove and tread block for that direction.

TOM: In other words, the manufacturer doesn't have to make any compromises just to make sure the tire is equally good in both directions. So, for instance, it can often improve the way water is channeled, or how the sipes (little cuts) in the tire are arranged.

RAY: So, does running a directional tire backward have any effect on its traction? Sure -- but not much. According to the tire engineers we spoke to, running a directional tire backward would not make it radically unsafe to drive on. In fact, you'd probably never even notice it. Come to think of it, your buddy never DID notice it! You just wouldn't be getting the optimal performance out of the tire.

TOM: It's possible that the water-channeling ability of a "backward" tire could be slightly diminished, and the same could be true for slush, I suppose. But the word we got is that "it's worse than removing the 'do not remove' tag from your mattress, but not a lot worse."

RAY: So tell your buddy to take his lumps for driving like a knucklehead, and slow down when it snows. And he can simply have his tires turned around so that they rotate in the right direction. No damage has been done to them by running them backward.

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