LAC: Wow! Tire Pressure!

[Mark R]

A few quick thoughts from an enthusiast, Tire Rack dealer, track instructor,
and all around car nut:

The tire rack article is a great starting point.  Always remember, it's your
HOT tire temperature that you're going for.  You check it cold for
consistency and ease.  The cold setting is there just to get you to a hot
setting.

Driving is nothing more than managing 4 contact patches.  Proper tire
maintenance is key.

Remember manufacturers set inflation pressures for a variety of concerns-
load capacity, ride, and handling is usually last on the criteria.  Load
capacity varies GREATLY with tire pressure.  When towing, my rear truck
tires go from a normal 35 PSI (cold) to 40 PSI (cold) because of this.
Cadillac recommends 30 PSI, but I've found 35/36 is fairly optimum for a
balance of ride versus handling.  As a rule of thumb, this is a good
starting point for most passenger tires driven by an enthusiast.

A good lesson is in the Firestone/Ford fiasco.  For a vehicle like the
Explorer, Firestone recommended a higher inflation pressure.  Ford ignored
it and went with a (too) low recommended pressure for ride quality.  Tire
industry magazines report that 25% of all tires are underinflated by 10% or
more.  Add to that people in the summertime who drive fast in VERY hot
conditions and overload their vehicles.  The sidewall flex and extreme heat
generated made for rapid failures.  IMHO, Ford had MUCH more blame than
Firestone in that situation, but they did a much better job spinning the
media.  Then again, Firestone could've stopped supplying Ford the tires when
it knew they were underinflated.

The tire is an air spring, so lowering pressures make the spring rate
softer, for a softer ride.

The higher the tire pressures, the less the sidewall flexes and therefore
rolling resistance and wind resistance go down.  This is why higher
pressures equate to slightly higher fuel economy.

For transitional response and "feel," you want a higher pressure.  For
ultimate handling (max footprint), you want a lower temperature.  In other
words, in a hard, steady state corner, you want the lowest hot temperature
that doesn't cause a loss of feel or the tire to roll onto it's sidewall.

Presuming a street car doesn't have a highly adjustable suspension, you can
help adjust the inadequacies of the suspension with some tire pressure
changes.  In other words, if the car understeers you go with whatever gets
you max grip in the front.  You lower the grip in the back so the car tends
more away from understeer and towards oversteer.  This is done by increasing
pressures (within reason) because lowering can cause excessive heat due to
sidewall flex (raising temps back up), and possible failure.  Obviously
adjusting tire pressures to give up grip isn't optimal, but you have to do
so to make the car handle and transition better.

Hopefully my quick thoughts make good sense to everyone,
Mark Rosenkrantz