Jalmar, I love your 2 cents!! My book say's 32 psi and my tire itself says 40psi. What do I do?
I expect to get at least 10K km out of a rear tire. If I get more, I see it as a bonus. If I get less, I look for errors... I got 6K km out of the factory rear tire. I changed it because I didn't like it so much. I changed it for a Metzler Feel Free. I think the factory tire could have lasted maybe 8K. Now I have 3K on the Metzler, and it is doing good
On the factory tire I used 36 psi pressure. Thats 10% up from what is recommended. On the Metzler I use 39 psi. I have never experienced any change in roadholding with 39 psi, so I think that's OK. After 3K km in all kind of traffic, it holds the profile nice and round.
This is what I do. I am no tire specialist. I just do what Metzler recommended on my touring bikes long ago. And I have used that trick for many years with no problems.
Another thing that often is overlooked is the gauge. Is your pressure gauge correct? I am so lucky that I can get my gauge measured every now and then, so I know that it is correct. I have tested many different gauges, and found that there are many bad ones out there. Up to 25-30% wrong readings on the cheap ones. So maybe you think you have the right pressure, but have to low because of a bad gauge?
Tire shops should have correct gauges, so you can check your own if you check the pressure with your gauge right after they have filled the tire. Gas station gauges are not that good usually. At least here in Norway.
Another thing I do when I get on new tires, is that I measure the tread depth in several places around the tire. I measure where the tread wear indicators are so I'm sure to remember where I measured. After 1K km I measure again in the same places. Then I know how much tread wear it has been in 1K km, and I can calculate how long the tire is going to last. And it is surprising how accurate that has been for my tires. Actually I do this for every 1K km on a tire just for the fun of it. But I am an old geek and love to keep track of things
(This method is not a scientific correct method. Just for fun.)