I got these Club Roost Cross Terra 27 x 1 3/8 (630 x 37c) tires on my cyclogrinder whatever you want to call it bike. They're rated for 40-65 psi and I've run then down to 45 back/40 front but the ride is still a little harsh on mixed road/dirt conditions. I've considered going down to 30psi on them but a little concerned about pinch flats. I'm not a heavy guy at 150lbs, so is running that low a valid concern for 37c tires or should I go for it? They will be driven on fire roads, washboard and similar. Also, I've got some Mr. Tuffy tire liners in there - could those be the cause of the harsh ride? I didn't experience this with higher pressure Vittoria road tires on the same bike before I put the cross tires on and didn't have the liners in with the road tires. Thanks.