By Trevor Smith WHY RUN-FLAT TIRES ARE BULLET RESISTANT

EXPLANATION OF RUN-FLAT TIRES AND HOW THEY WORK 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 Armored vans such as Brinks Trucks. Cars available to the general public such as a Ford Mustang.

APPLICATIONS OF RUN-FLAT TIRES (CONTINUED) Military vehicles such as the Humvee.

APPLICATIONS OF RUN-FLAT TIRES (CONTINUED) The Presidential State Car, referred to as “The Beast” by the Secret Service.

THE PRESIDENTIAL STATE CAR AND USE OF RUN-FLAT TIRES 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 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 When Kevlar is spun, the resulting fiber has a tensile strength of about 3,620 Mpa, and a relative density of The polymer owes its high strength to the many inter-chain bonds. These inter-molecular hydrogen bonds form between the carbonyl groups and N H 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? 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. 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. 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.

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