Today I purchased a new floor pump with a pressure gauge. The tires, Specialized 700x28, have a psi range of 115-125. I knew I needed more air in my tires, but had no idea I needed that much. Is there a rule of thumb for tire pressure regarding the low end or the high end of the psi range? I am still new at this and have replaced only two tubes due to a puncture and one new tire. Thanks in advance for your responses!