Billy said:
I love a hard tyre as it gives excellent roll and speed, but also it gives
you a rough ride.
Anyhow, my tyres say max is 120, but some of my friends run theirs at 140
they say.
My 2c - presuusre is only a minor consideration.
In the first sense, safety is relative. If you've only ever run a tyre
over clean hot mix, then old age is your greatest danger, but if you
regularly ride over glass slivers then a cut could set it off at
anytime. Watch for a sudden bumpy ride as groups of fibres are cut then
the tyre starts to bulge in spots.
A skinny road tyre doesn't have a lot of volume to blow off, but a 2.25"
fatties at 140psi has a lot of air to flip/turn/push the wheel sideways.
Of course you might be fast enough to react and nothing might happen
straight away.
To me, the real problem with fatties is when they are dead flat, they
just roll anyways and you have absolutely no directional control. I
could never walk my mtb home with a flat tyre as I would be exhausted
trying to keep it up.
Keep em fresh, watch for crazing/cracking in the tyre and watch for
sudden bumps the bumbs and you should be okay.
The one blowout I ever had was from being skint student and using free
old tyres.