Always air up your tires before every ride. Tires can loose up to 7 lbs. of pressure in 24 hrs. On the side wall of your tires you can find suggested psi info. You can safely add 10 lbs. to this number without any worry but, will give you a little harsher ride. I ride Continentals 4000 tire and always inflate my rear to 120, and front to 110. Having the correct psi will give you less rolling resistance while eliminating pinch flats from hitting something sharp and hard especially if you are a heavier rider.