Being 300+; the narrowest tires I have are Terry (made by Panaracer) 28-571 on my SR; and at 110 psi are marginal. My commuter has 32-630, running 120psi in a Specialized Allroad Armadillo on the rear and 100psi in a Bell Kevlar on the front. On the tandem, we have Kenda Kwest 37-622 running 100 psi; which give a very smooth ride.