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Wow, lots has been said about Obama's technically correct response to a question, to paraphrase, asked, "What can we ordinary people do?".  The McCain campaign has been brutal, and ignorantly so.

Nothing is more important, other than the drive train, in making any land vehicle "go" than the instruments that actually touch the road.  Those instruments are tires, or as the Brits say, tyres.

Tires are the agent that converts the energy produces by the engine (for fuel powered vehicles) or the motor (for others) from the source of the motive power to the ground, in most cases a lane, street, road, highway, or Interstate highway.

Tires work because they have friction between the tire and the surface on which they impinge.  If there were no friction, there would be no motive force, like trying to drive on glare ice (some call it black ice).

With no friction, no motive force.  Tires have undergone a very substantial evolution in the past century or so.  For instance, the tires on the Model "T" Ford were embossed with "FORD" over and over.  Better traction than slicks.

The first tires were solid rubber, like the ones on children's wagons.  They rode hard, were not very durable, and no one really liked them.  Then a fellow named Goodyear had an idea to inflate a rubber bladder inside of a thick sheath to absorb some of the shock.  That was the genesis of the pneumatic tire.

Back in the old days, the tires and the inner tube were natural rubber, modified with additives and vulcanization processes to make both more useful.  They were made by hand, with only crude molds to shape them.  Then they were welded with a failure prone joint.  At speeds of 20 mph, on a wheel of 20+ inches, not much of a problem.

Later, it was discovered that if cotton could be integrated into the rubber matrix, a more tough tire could be had.  That went further, and others examined the tread pattern.  By the start of World War II, tires were not simple rubber balloons, but complex structures of rubber, fiber, and advanced (for the time) tread design.

The upshot of those developments was the bias ply tire, which up until recently (the 1970's) was the standard.  In that design, one or more plies of fabric (at the time nylon or other strong synthetic fabrics) were bonded to rubber to form the sidewall of the tire, and more layers were bonded with the tread to make a stronger interface with the road.

Bias ply tires are still in use in some limited areas, like extremely large truck tires, because that design is very strong.  It is not economical insofar as rolling resistance goes, though.

The next breakthrough was the reinforcement of the tread with either steel thread or a synthetic material, like Kevlar just being developed then).  This advancement reduced blowouts by a large factor.  But there was a price to pay, because steel belts tended to be through out of the tread because of centrifugal force.

Another fast forward to now.  Radial tires are the norm, and the means that instead of the fibers that connect the rubber together in an angled fashion are instead in an arrangement from the center of the tire to the reinforcing belts, and to the center again.  There are cross links to provide stability, but the bulk of the connections are from center to outside to center.

This reduces the rolling resistance of tires tremendously.  Instead of pulling every fiber of the tire to keep it round, radial tires allow a spot to go flat, for an instant, without compromising the rest of the tire, and the flat spot recovers immediately, unless temperature limits have been exceeded.

Most of the failures a few years ago had to do with a specific brand of tires, but almost all of those had to do with underinflation of those tires.  A low tire causes more contact with the road, and that caused more friction.  In a addition, the sidewall of a tire is not designed to make contact with anything but the air.

When a tire is low in inflation, the treat softens and the sidewall tends to impact the road.  The combination of those can be extremely bad, but usually is not, but it does always cause excessive wear on parts of a tire not intended to contact the road, and greater rolling resistance to the tread that is intended to contact the road.

The bottom line is that there is a greater risk of tire failure with an underinflated tire, and a certain increase in rolling resistance.  That is not to say that every tire manufactured has a "best" pressure.

Look in the driver's door in any car made after around 1990, and you will see a recommendation for tire pressure, front and back.  There is a reason for it, and it has to do with the combination of ride and fuel economy.  Better economy usually means a more harsh ride, but not always.

NEVER exceed the pressure stamped on the tire itself, for fear of explosion whilst driving.

I know that this a bit nonsensical, but I have been up since 6 this morning getting ready to drive to Arkansas to watch Eldest Son march in his Commencement Friday.  I will hang around a bit to clarify, but not too long tonight.  Warmest regards, Doc.

Warmest regards, Doc.

Originally posted to Translator on Tue Aug 05, 2008 at 07:36 PM PDT.

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