Transcript Why run-flat tires are bullet resistant - mixon13-14

WHY RUN-FLAT TIRES ARE BULLET
RESISTANT
By Trevor Smith
EXPLANATION OF RUN-FLAT TIRES AND HOW
THEY WORK
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What are run flat tires?
A run-flat tire is a pneumatic tire that is designed to resist the effects of deflation when
punctured, and to enable the vehicle to continue to be driven at reduced speeds (up to 55 mph)
and for limited distances of up to 100 mi, or even 200 mi depending on the type of tire.
How do run flat tires work?
The diagram below shows the Dunlop DSST run flat system. These tires can be placed on any
rim - the sidewall is reinforced allowing the tire to support the vehicle's weight. The tire is
constructed with new rubber compounds that prevent tire destruction with excessive flexing.
Run Flat tires allow a vehicle with complete loss of tire pressure to handle effectively. Braking,
acceleration, and steering behavior remain unchanged. Mobility is also maintained even after a
puncture, but you must refer to each individual tire’s guidelines from the Manufacturer.
APPLICATIONS OF RUN-FLAT TIRES
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Armored vans such as Brinks Trucks.
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Cars available to the general public such as a Ford Mustang.
APPLICATIONS OF RUN-FLAT TIRES
(CONTINUED)
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Military vehicles such as the Humvee.
APPLICATIONS OF RUN-FLAT TIRES
(CONTINUED)
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The Presidential State Car, referred to as “The Beast” by the Secret Service.
THE PRESIDENTIAL STATE CAR AND USE OF
RUN-FLAT TIRES
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The Secret Service refers to the heavily armored vehicle as The Beast. Most details of the
car are classified for security reasons. A special night vision system is in a secret location.
Special loops replace the stock door handles; agents hold on to them when running
alongside the car. Goodyear run-flat tires fit into extra-large wheel wells. The car is
sealed against biochemical attacks. Kept in the trunk is a blood bank of the President's
blood type. It also has its own oxygen supply.
EXTRA PROTECTION ON RUN-FLAT TIRES
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For extra bullet resistance, such as run-flat tires found on Brinks trucks and other armored
vans, you may want to use Kevlar. Kevlar is found in Bulletproof vests, gloves, helmets,
etc. Most run-flat tires on armored vans are layered with Kevlar in the sidewalls of the
tires for extra protection against bullet penetration.
Kevlar Fiber
WHAT KEVLAR IS MADE OF
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When Kevlar is spun, the resulting fiber has a tensile strength of about 3,620 Mpa, and a
relative density of 1.44. The polymer owes its high strength to the many inter-chain bonds.
These inter-molecular hydrogen bonds form between the carbonyl groups and NH
centers. Additional strength is derived from aromatic stacking interactions between
adjacent strands. These interactions have a greater influence on Kevlar than the van der
Waals interactions and chain length that typically influence the properties of other
synthetic polymers and fibers such as Dyneema. The presence of salts and certain other
impurities, especially calcium, could interfere with the strand interactions and caution is
used to avoid inclusion in its production. Kevlar's structure consists of relatively rigid
molecules which tend to form mostly planar sheet-like structures rather like silk protein.
Kevlar Chemical Composition
WHAT DETERIORATES KEVLAR OR DESTROYS
IT?
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From the previous slide, we looked at what Kevlar was made of. The previous slide
states: “The presence of salts and certain other impurities, especially calcium, could
interfere with the strand interactions and caution is used to avoid inclusion in its
production.” This statement shows that Kevlar can be destroyed by various salts and
calcium.
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If you were to drive run-flat tires coated with Kevlar in the winter in the Midwest, your
Kevlar protection would be ruined, because of all the road salt. There are obviously ways
to stop this, but if someone tries to do this without stopping road salt getting to the Kevlar,
it would be ruined.
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Armored vans have already stopped that problem, by putting a separator inside the tire,
stopping the salt from getting to the sidewalls filled with Kevlar.
SOURCES
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https://customerservice.blackcircles.com/entries/21233098-Run-Flat-tyres-explained
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http://en.wikipedia.org/wiki/Kevlar
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http://en.wikipedia.org/wiki/Run-flat_tire
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