(Copied from similar post on different thread, with editing):
I tour extensively, and ride ~17,000 miles/year. I'm riding a Triumph Thunderbird which just turned 3, w/ 52,000 miles on it. I ride it hard--I've been to the Dragon 3 times this year, and have worn flat spots on both silencers, as well as big flat spots on both side of my center stand. I commute on my bike, doing around 320 miles per week, usually at 75mph on the highways. I just got back from a 5,000 mile trip where, despite being fully loaded down for a 3-week tour and carrying my girlfriend, I still managed to get the chicken strips on a brand new pair of tires down to about half the width of my pinkie; I've discovered that I don't have chicken strips, I have 'scrape indicators' (ie, I can't possibly lean the bike over any farther without dragging at least three parts--silencer, center stand, footpeg--damn classic cruiser!). Hence the reason I'm now looking for a good sport tourer!

I do not claim to be a tire expert; however, I've done some research on my own, trying to figure out why my 2nd front tire (replaced by a Triumph dealer, who put a tire marked for Rear Use Only on the front because "it fit") never felt right. My impressions:

Tires obtain their maximal grip on a road surface when they reach a specified heat range. The ideal temperature for maximum grip is determined by the tire material. The degree to which they heat up is dependent on the material of the tire, the carrying load, and the cold tire pressure The higher the cold psi, the higher the tire temp will get as the pressure in the tire increases.

As it turned out, my rear-tire-on-the-front tire never felt right because it never got hot enough. Rear tires have much more material on them, have a wider contact patch, and are designed that way because rear tires sustain greater wear in pushing the bike. A rear tire on the front would never reach optimal operating temperature, resulting in a 'slippy' and 'squirrely' feel in the tire--exactly what I experienced.

I do not understand why manuals suggest a psi inflation less than the tire manufacturer prints on the side of the tire. Generally, most motorcycle tires (and all I've mounted on my bike) carry a "max load equals xxx lbs at 42 psi" statement on the sidewall. Generally, most motorcycle manufacturers suggest a rear tire pressure that matches the tire manufacturer's max load statement. I guess I can understand that in sustained, high-speed riding (though what defines high speed?) the motorcycle manufacturer would suggest a lower psi, because high speeds will require more accelleration and decelleration friction and would theoretically result in a hotter-than-optimal tire. This might lead to increased wear (and possibly a blowout?).

However, under touring conditions I was always taught to inflate the tires to the sidewall max; the tire manufacturer specifies that this is the greatest possible load the tire can handle, and tells you what psi to inflate the tire to so as to get this maximum load capacity. I can't imagine that high-speed riding creates more friction than when I (200 lbs) and my girlfriend (135 lbs) load up all our crap (probably close to 120 lbs of gear, including cases) and put it on a bike with several mods (probably another 30-40 lbs, given the windshield, Givi wingrack, and center stand) for a total weight of 485-500 lbs above wet bike weight (about 520 lbs). Under these conditions, I want the tires set to carry as much as they possibly can, and the tire manufacturer TELLS me how to set them thusly. Therefore, I always ride with my tires at the max pressure stated on the sidewall, and have never experienced cupping or abnormal wear. I usually get ~10,000-12,000 miles out of a rear tire, and ~16,000-18,000 miles out of a front tire.

A buddy of mine states he was taught in his MSF course to inflate the tires to the max sidewall pressure cold, then check the tires in the middle of the day. If the hot pressure is greater than 110% of the cold pressure, he states he was taught to let out enough air to make the pressure no greater than 110% of max cold (ie, 42psi cold, 46psi hot). I have never heard this, so I cannot speak to its validity. I can say that in my many years of touring and riding like a bat out of hell (many times both on the same trip!) I've never had any tire problems. I've used Pirelli's, Bridgestone, and Dunlop in the past, but by far my favorite brand is Avon--they have a reasonable wear life but feel really, really sticky, and let me open my bike up to its full potential. And they've always been at the max sidewall pressure, and I've never had any problems with cupping. :smokin