It totally depends on what you're using the bike for. Those tires have a huge range of acceptable pressures, starting with cold pressures around 24 rear, 29 front for track use up to 36 rear, 34 front for maximum load/mileage street touring. Lower pressures = more grip, higher pressures = more life / resistance to heavy load. I've always found about 29 rear, 32 front to be about right for general street/sport riding on the SP's. I even forgot to lower them on our demo V4S before riding it on the track a couple weeks ago and I never even noticed, the tires are that good.