Liners and liquids can keep drivers rolling in pressure situations

With tire failure on motorists' minds these days, we thought it might be instructive to talk about products that purport to fix or prevent flats; some that help deal with sudden loss of pressure; and run-flat tires and pressure-monitoring systems.

None of the products we're going to discuss even claims to deal with the kind of tread separation that brought on the Firestone recall. Such catastrophic failures remain rare.

Much more manageable are typical flats and blowouts. When either of these happen, it's critical to keep control and get to the side of the road. And remember that changing a flat on a busy road or freeway shoulder is always dangerous -- best to call your auto club or other assistance instead.

LIQUID SOLUTIONS

For those who believe in better motoring through chemistry, products include aerosol flat-repair products, liquid flat-proofing solutions and polyurethane coatings for the inside of the tire.

Unfortunately, these all have drawbacks.

Aerosol flat sealant and tire inflaters have been around for a long time, and some brands work quite well. Don't expect them to reinflate a tire completely, but they should put in enough pressure to get you to a service station. You'll need to drive slower because the underinflated tire will make handling squirrelly and it will get too hot if you go 70.

Eugene Petersen, an automotive engineer at Consumers Union, says the biggest problems with the aerosol products are that the fix isn't permanent and that some create such a mess inside the tire that it can make a permanent fix impossible. They can be used in a pinch to avoid being stranded; just be sure to get the tire properly repaired.

Next up, liquid flat-proofing. Basically, this employs a liquid containing an adhesive with a particle solid, usually plastic. As you drive, the stuff coats the inside of the tire. When a puncture occurs, air pressure pushes the liquid into the opening and seals it, provided that the hole isn't too large.

If you want to go this route, I recommend careful research. You'll want a product that stays liquid below freezing; has rust inhibitors to protect the wheels and steel tire belts; can be washed off the tire and wheel easily; and is nontoxic. It would be a good idea to warn the tire-shop technicians that you've used such a product before they break the bead and the stuff spills out on their equipment.

You'll also want something that isn't going to add a significant amount of weight.

Even following that advice, Petersen has his doubts.

"I wouldn't recommend buying these products for highway use," he says, because of how they might affect heat buildup and the potential for vibration-handling problems from weight or the material collecting more heavily in one spot.

LINERS

Another product that makes tires self-sealing is a liner made from very soft polyurethane. Again, weight is engineer Petersen's main concern because of its effects on ride and handling.

In addition, proper installation is critical so that the liner adheres evenly to the inside of the tire. This product seems to replicate what some manufacturers, such as Uniroyal, have built into certain tires.

Petersen says these have tested well and self-seal punctures up to about three-sixteenths of an inch. Anything larger than that, though, and you've got a good old-fashioned flat.

Overall, he says, "the best thing to do when you get a flat is to put the spare on."

SAFETY BANDS

Tyron Automotive Group of Britain has been making these since the late '70s and plans to bring them to the United States in December.

The steel-alloy bands are installed in the well of the rim after the tire is mounted. Filling this cavity, Tyron says, prevents the bead of a deflated tire from collapsing into the well. Such a collapse can cause the tire to shift on the wheel, resulting in loss of control, the company says. The resulting flailing can cause the tire to disintegrate and further damage the vehicle, including snapping the brake lines.

Rick Cole, who is in charge of U.S. distribution of the product, says the device allows a driver to continue at freeway speeds for about three or four miles, and farther than that at lower speeds. Each band weighs about 2 pounds and is supposed to last as long as the car. A set of four retails for about $300.

Consumers Union has not tested this product.