The rear tire on my Bike Friday is also rated at 85 psi (Primo Comet), but I regularly inflate it to about 110 psi when the bike is loaded with my camping gear. It's never caused any problem. I've heard that tires are supposed to be able to handle up to twice their rated pressure - but that assumes that the rim can handle it without any deformation or undue stress so I wouldn't recommend going that high.