Wild Bill does have a point. Running right at the Max in not a good idea. I should have included that 10% under that is about right, but it slipped my mind. My apologies.
I got this directly off the Michelin site he recommended;
"Too much pressure and the contact patch shrinks, the grip is reduced and you can expect a harsh ride. ... Low air pressure causes the contact patch to increase causing unsafe handling, an unstable sidewall and damage to the tire casing. Riding on tires with improper inflation, especially under-inflated, is dangerous and a serious safety issue."
I found with Avon Venom tires, that if you ran at the Kawasaki factory recommendations, they would squirm, flex, slip, and the tread would cup. However, at about 10% under the Max on the sidewall they felt like the bike was glued to the road. the ride wasn't as cushy, but not harsh. and even after slight cupping I was able to get over 10K from the rear and 14K out of the front. (exceptional mileage for an Avon Venom)
If your tire says 40 on the side, I would start at about 36. if it feels soft & squirms, go up a pound or two. if it feels harsh, go down a pound or two.
1 psi goes a long way in a bike tire!
I currently am running Michelin Commander II's and the sidewalls say 44 for the rear, and 42 for the front. ..... I'm running 39 and 36 respectively and they seem to be doing very well. The grip is excellent, and the tread-wear is phenomenal, and the ride is firm but not harsh.
(I am hoping to get better than 20K out of these Michelins)
Hope this helped a little
J.