At 03:13 PM 3/15/2009, Rob wrote:
>manufacture know what the tire is designed for. If you put a tire on
>that calls for a max of 60 psi and you are running it at 40 psi it
>has 30% less pressure than it should, that adds up to heat.

I have to disagree there, Rob.  It only creates excessive heat if
there's excessive sidewall flex, and that depends on the vehicle
running on those tires.  The tire manufacturer specifies the maximum
cold inflation pressure, and the maximum load at that pressure.  The
vehicle manufacturer specifies the minimum tire specs, and specifies
an inflation pressure which is sufficient to sustain the vehicle load
with (usually) a 10-20% fudge factor; and is otherwise a compromise
among tire life, ride comfort, handling, fuel economy, phase of the
moon etc. for the particular vehicle.  That includes differential
pressures between front and rear in our case.  If you're willing to
sacrifice a bit of comfort, I believe adding a few psi to the
recommended pressures will help all the other qualities.
*Over*inflation -- for the particular vehicle, not for the tire --
will cause accelerated tread wear in the middle as well as a nasty
ride and perhaps other difficulties.  Changing the front/rear
differential pressure will change the handling.

If y'all really want to get into the meat of this stuff, here's a
place to start, with a guy (tireman9) who designs tires for a living...
http://www.eng-tips.com/viewthread.cfm?qid=15003&page=1
http://www.eng-tips.com/faqs.cfm?fid=1148

  --
David Beierl - Providence RI USA -- http://pws.prserv.net/synergy/Vanagon/
'89 Po' White Star "Scamp"