I've been doing 30ish/f 35ish/r with tubes, mostly ok (had a couple of flats last year but otherwise have hit some rocks/roots without repercussions) but I'm starting to feel like it's costing me some time. Wonder if I can get away with like 25-30/f and 30r at 160lbs. It really is a compromise between high pressure/not flatting and lower and risk having a good race ruined. Would love to try tubulars this season, might have to see if someone will lend me some