I posted this question awhile ago and got some crazy responses. This seems to be the most reasonable explanation I've read.
Q. "Where Does Tread Rubber Go?" by Peggy J. Fisher
For years that was a mystery, but people are a lot smarter today and a lot more allergic so we now know without a doubt what happens to tread rubber that wears off tires.
I'm not talking about the "roadgators" that litter the highways as a result of tires running underinflated, but rather the rubber that disappears from tires in normal operation. Since the highways are not discolored with blackened tread bits, you have to wonder if perhaps the tire tread disappears along with our socks that never seem to make it out of the dryer.
Well, the transportation and tire industries have been concerned about this problem for a long time. It is estimated that more than 600,000 metric tons of tire tread are worn off American vehicles every year. Instead of leaving black smudges on the highways, tiny particles of tread are worn off tires and are released into the air. The concern was that all of this material might remain in the air, in suspended particles that could be dangerous to humans.
In tests made near highways it was found that virtually no rubber stayed on the road due to wind, rain, and movement of the surrounding traffic. Instead the microscopic tread particles that become airborne are heavy enough to fall to the ground. In fact, most of the particle debris found along roadsides accounted for at least 50 percent of the total missing tire tread and possibly much more. The most plentiful tire debris is in the form of styrene butadiene rubber (SBR), the most common rubber hydrocarbon in tire treads.
It is estimated that the rest of the worn tread rubber is dissolved through oxidation and devulcanization. One estimate speculated that devulcanization accounted for 30 percent of the disappearing SBR. Wind, water runoff, oxygen and microbial attack all act to help degrade tread particulates which degenerate faster than the tread rubber on tires.
Since tire tread rubber is essentially an inert material, it doesn't contribute to acid rain or soil pollution and since it is microscopic it doesn't bother most of us. However, if you are a latex allergy victim, it's a different story.
Latex is the basis of natural rubber. At least 70-75 percent of the natural rubber produced today is used to make tires. (The rest apparently goes to making latex gloves and protection for other smaller body parts, as well as paint and adhesives.)
In passenger tires the tread cap is a blend of natural rubber, butyl and SBR and the tread is almost exclusively SBR. In commercial truck tires, varying amounts of natural rubber are mixed with SBR to make the tread, depending upon the performance characteristics of the tire. Therefore, some latex particles can be found in natural rubber tread particles along the side of the road.
Ground rubber from recycled tires is also mixed with asphalt in some paving processes. Natural rubber, SBR and butyl rubber are added to improve the temperature sensitivity of asphalt at both low and high temperature extremes. In the U.S. recycled rubber has been used to reinforce asphalt since the early 1960s. When asphalt is being mixed or sprayed, natural rubber latex particles are almost certainly being aerosolized. As a result, latex allergens have been found in tire dust, roadside dust and air sample. That's why you may experience a reaction around streets that are being paved, or asphalt that is being added to roof structures, or if you live near highways.
New research has found that there is something else to worry about in tire road dust. Millions of people spend hours each day stuck in traffic. This traffic nightmare is not just costing us time and money but perhaps even our health.
Asthma rates have been steadily increasing and are now up to 75 per cent over the last 20 years. Surveys show the closer to busy, congested roads you live, the higher the asthma rates. In the past we have blamed it on pollution and diesel exhaust, but new research finds that road dust may be what's making you wheeze. When the road dust particles were analyzed, researchers found latex from tires and asphalt as expected. But they were totally surprised to find large amounts of allergenic pollen grains and mold far from their origins.
Apparently tires can grind pollen particles so fine that they remain airborne for miles and can be easily inhaled to trigger an allergic reaction. It was also found that even minute particles of pollen could trigger an attack rather than whole pollen grains. Yet few would suspect it came from road dust.
This article originally appeared in a slightly different form in TIRE BUSINESS and is used with permission.
Peggy J. Fisher is President of Fleet Tire Consulting, Rochester Hills, MI
Q. "Where Does Tread Rubber Go?" by Peggy J. Fisher
For years that was a mystery, but people are a lot smarter today and a lot more allergic so we now know without a doubt what happens to tread rubber that wears off tires.
I'm not talking about the "roadgators" that litter the highways as a result of tires running underinflated, but rather the rubber that disappears from tires in normal operation. Since the highways are not discolored with blackened tread bits, you have to wonder if perhaps the tire tread disappears along with our socks that never seem to make it out of the dryer.
Well, the transportation and tire industries have been concerned about this problem for a long time. It is estimated that more than 600,000 metric tons of tire tread are worn off American vehicles every year. Instead of leaving black smudges on the highways, tiny particles of tread are worn off tires and are released into the air. The concern was that all of this material might remain in the air, in suspended particles that could be dangerous to humans.
In tests made near highways it was found that virtually no rubber stayed on the road due to wind, rain, and movement of the surrounding traffic. Instead the microscopic tread particles that become airborne are heavy enough to fall to the ground. In fact, most of the particle debris found along roadsides accounted for at least 50 percent of the total missing tire tread and possibly much more. The most plentiful tire debris is in the form of styrene butadiene rubber (SBR), the most common rubber hydrocarbon in tire treads.
It is estimated that the rest of the worn tread rubber is dissolved through oxidation and devulcanization. One estimate speculated that devulcanization accounted for 30 percent of the disappearing SBR. Wind, water runoff, oxygen and microbial attack all act to help degrade tread particulates which degenerate faster than the tread rubber on tires.
Since tire tread rubber is essentially an inert material, it doesn't contribute to acid rain or soil pollution and since it is microscopic it doesn't bother most of us. However, if you are a latex allergy victim, it's a different story.
Latex is the basis of natural rubber. At least 70-75 percent of the natural rubber produced today is used to make tires. (The rest apparently goes to making latex gloves and protection for other smaller body parts, as well as paint and adhesives.)
In passenger tires the tread cap is a blend of natural rubber, butyl and SBR and the tread is almost exclusively SBR. In commercial truck tires, varying amounts of natural rubber are mixed with SBR to make the tread, depending upon the performance characteristics of the tire. Therefore, some latex particles can be found in natural rubber tread particles along the side of the road.
Ground rubber from recycled tires is also mixed with asphalt in some paving processes. Natural rubber, SBR and butyl rubber are added to improve the temperature sensitivity of asphalt at both low and high temperature extremes. In the U.S. recycled rubber has been used to reinforce asphalt since the early 1960s. When asphalt is being mixed or sprayed, natural rubber latex particles are almost certainly being aerosolized. As a result, latex allergens have been found in tire dust, roadside dust and air sample. That's why you may experience a reaction around streets that are being paved, or asphalt that is being added to roof structures, or if you live near highways.
New research has found that there is something else to worry about in tire road dust. Millions of people spend hours each day stuck in traffic. This traffic nightmare is not just costing us time and money but perhaps even our health.
Asthma rates have been steadily increasing and are now up to 75 per cent over the last 20 years. Surveys show the closer to busy, congested roads you live, the higher the asthma rates. In the past we have blamed it on pollution and diesel exhaust, but new research finds that road dust may be what's making you wheeze. When the road dust particles were analyzed, researchers found latex from tires and asphalt as expected. But they were totally surprised to find large amounts of allergenic pollen grains and mold far from their origins.
Apparently tires can grind pollen particles so fine that they remain airborne for miles and can be easily inhaled to trigger an allergic reaction. It was also found that even minute particles of pollen could trigger an attack rather than whole pollen grains. Yet few would suspect it came from road dust.
This article originally appeared in a slightly different form in TIRE BUSINESS and is used with permission.
Peggy J. Fisher is President of Fleet Tire Consulting, Rochester Hills, MI