ABS and Chains May Be a Risky Combination on Icy Winter Roads

Tire chains are supposed to be essential winter safety equipment, but there’s a big unknown about their use.

Neither auto makers nor government safety regulators have examined whether the chains are compatible with modern anti-lock braking systems.

Moreover, experts disagree about proper driving practices on snow and ice when using the chains on vehicles equipped with anti-lock brakes.

The National Highway Traffic Safety Administration can offer little help. It does not set standards for tire chains and has not done any testing on them, according to an agency spokesman. The NHTSA Web site makes no mention of chains.

Tire chains get little attention from auto makers and government safety regulators, despite the fact that police and highway patrol agencies around the nation consider them essential safety equipment in heavy snow and icy conditions.

In many regions, including the formidable mountain areas of California, chains are often required equipment when a winter storm hits. There are times in California when they are needed just to get across the mountain passes that separate the Los Angeles area from the rest of the state.

Tire chains are intended to improve traction, enabling vehicles to climb steep grades, to handle turns and, most important, to stop on roads blanketed in slippery ice and snow.

Few motorists would think twice about slapping a set of chains on a car or truck equipped with an anti-lock braking system, or ABS--especially with a burly highway patrol officer standing at the side of the road in blowing snow and insisting that chains are a condition of further travel.

But one of the nation’s largest chain makers says they may disable anti-lock brakes. “ABS really becomes incapacitated when the tire chains are on because the computers that control the system don’t pick up the correct sensing,” said Rick Schmunck, president of Quality Tire Chain Corp. of Hillsboro, Ore. Herecommends that drivers manually pump the brakes when stopping in snow. Schmunck said that when the chains dig in, snow builds up in front of the chains. Only by manually pumping the brakes can that buildup be released.

That contradicts the advice from auto makers and brake manufacturers: Never pump the brake pedal on cars equipped with ABS, because the system does it better. Anti-lock systems modulate the pressure on a brake 15 to 25 times per second, vastly faster than it can be done by humans.

“The tire chain is only as good as the person who is behind the wheel,” Schmunck said.

Auto makers and brake system manufacturers are not sure what to make of that. Some see merit in his analysis, but others are hesitant to change their recommendation that motorists should never pump anti-lock brakes.

Experts at Robert Bosch Corp., a major ABS supplier, recommend that, even with chains, motorists apply steady, firm pressure. They said ABS works well with chains.

But Bob Lange, General Motors’ executive director for safety integration, says “the application of a chain would change the nature of the tire patch on the roadway.”

North Hollywood brake mechanic and author Karen Valenti agrees that tire chains could affect ABS performance. “Chains take the tire off the ground,” she said.

For Californians, ABS is a particular conundrum. Motorists here don’t have a lot of day-to-day experience with ABS and when they do experience the pulsing sensation that indicates the system is working, they tend to “freak out,” Valenti said. “They lose control and don’t pay attention to what they are doing. All it takes is a split second and you could go over the edge at Big Bear,” she said.

But Sam Memmolo, a spokesman for the ABS industry, said his faith in ABS is unshaken--with or without tire chains.

Memmolo is not a huge fan of chains in the first place. He says he used to carry them when he made frequent trips over Donner Pass, near Lake Tahoe, putting them on the rear tires of his front-wheel-drive Saab just to mollify the CHP.

“I don’t think chains render ABS ineffective,” he said, but added: “That’s first blush and I haven’t given it much thought.”

Neither, it seems, have many others.

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Wright and Vartabedian cannot answer mail personally but respond in this column to automotive questions of general interest. Write to Your Wheels, Business Section, Los Angeles Times, 202 W. 1st St., Los Angeles, CA 90012. Vartabedian can be e-mailed at ralph.vartabedianlatimes.com.