In my experience, overinflating mtn tires is more likely to break the sidewall of the rim, than to hurt the tire. I was running a set of 2" tires rated for 70psi, when after cracking the *second* new Mavic rim, I came to realize the rims could not take it. For those who may be unaware, as the tire width increases, the force against the bead also increases at the *same* pressure.