Liners and Liquids to Fix Tires in Pressure Situations
This week we’re going to talk about inflation pressures.
No, not the kind Alan Greenspan worries about, unless the Fed chairman is driving a certain SUV with a certain brand of recalled tires.
The pressure here is what keeps your tires up and your motoring as carefree as possible.
So 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.
We start our product tour with Eugene Petersen, an automotive engineer at Consumers Union.
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 so that you can get to a service station. You’ll need to drive slower because the under-inflated tire will make handling squirrelly and it will get too hot if you go 70.
Petersen 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. For a radial, that means having the shop remove the tire and patch it from the inside. A push-through plug is faster and cheaper, but it can do additional damage.
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 it 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.
His concerns center on tire balance. If the substance puddles and then congeals while a vehicle is parked, the tire will be out of balance until the stuff becomes evenly distributed.
On the other hand, Steve Mazor, chief automotive engineer for the Automobile Club of Southern California, says his team has tested one such product, a green gooey liquid that’s added to the tire. (The club doesn’t endorse products, so he wouldn’t name names.)
All the air has to be out of the tire, Mazor notes, so you would need a compressor. The maker claims the fix is permanent, and the club found that to be true in the tire it tested. The stuff was left in for the tire’s remaining life, about 12,000 miles, and didn’t cause any ill handling, Mazor says.
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 3/16 of an inch. But they are not run-flat tires, so having a hole that’s larger than the tire can seal means 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. These are yet another bit of technology designed to deal with punctures and blowouts. Tyron Automotive Group of Britain has been making them since the late ‘70s and plans to bring them to the U.S. 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 runs 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, but Petersen says its primary advantage would seem to be the ability it gives motorists to limp off the freeway. In short, it adds some run-flat capability.
Run-flat tires. That brings us to today’s run-flat tires: passenger car successors to models used for years by some commercial vehicles and other modes of transport--such as presidential limos--for which tire failure is, shall we say, not an option.
Run-flats have extra-stiff sidewalls so that they can bear the load of the vehicle without air. Depending on brand and model, they can be driven 65 to 200 miles deflated without sustaining damage. These tires require a pressure-monitoring system so the driver is alerted when air is lost.
Run-flats have two drawbacks because of their stiff sidewalls: Rolling resistance is higher, which makes them less fuel-efficient; and they don’t ride or handle quite as well as an equivalent normal pneumatic tire.
A few cars come with run-flats as original equipment, or you can have aftermarket versions fitted with the obligatory monitoring system. (And now manufacturers are coming forward, in the wake of the Firestone mess, to offer pressure- and heat-monitoring systems for non-run-flat tires.)
The pressure monitors use wireless sensors, one on each wheel, that report back to a dash-mounted display. Many units tell how much above or below ideal pressure the tires are, and some output a temperature reading.
The latter may be interesting information, but Petersen says it’s difficult to say how that would relate to actual tire temperature. Like other engineers, he doubts that the temperature readings would be delivered quickly enough to warn of a catastrophic failure.
Another type of pressure warning system that’s available on some General Motors models uses the anti-lock brake system, he says. Because ABS monitors the wheels’ rotation, it can detect the slight change in speed that a deflating tire would cause.
On the horizon is a Michelin system called PAX that promises run-flat capability of 55 mph for 125 miles, higher load-handling capability (allowing its use on SUVs) and lower rolling resistance than with current-generation run-flats.
PAX uses an asymmetrical rim, one that has a different diameter for the outside tire bead from the diameter for the inside bead. And those beads are quite different from what we have today. They do not require air to remain seated to the rim. The tire also has far less sidewall than the current design. Added to this are an internal support band and wireless sensor, which alerts the driver of a loss of pressure.
The lower-profile tire-wheel combination saves space, which can be used for more room for the engine or trunk or for the passenger compartment, or even for larger brakes.
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Meanwhile, as most of us are driving on standard-design tires, Petersen of Consumers Union and the Auto Club’s Mazor both say the basic routine you should follow is to check the pressure at least monthly (after investing $10 to $20 for a decent dial gauge), inspect the tread and sidewalls for damage, look at how evenly the tread is being worn, check tread depth and rotate your tires. Uneven wear can indicate worn suspension parts, but it can also be caused by improper inflation.
This stuff is pretty basic, but it can pay off in longer tire life, better gas mileage and safer, better handling. And you don’t have to be Fed chairman to see the economics of that.
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Robert Beamesderfer is Highway 1’s news editor. He can be reached at bob.beamesderfer@latimes.com.
