>>2011677As the other anon said CX bikes are UCI regulated. However the 33mm limit only applies to competition, I'd still call a CX frame with 35mms are CX bike. Chainring sizes aren't regulated but typically fall slightly below road sizes (~45 - 50) as opposed to Gravel bikes which have gear ratios much more in line with mtbs.
A gravel bike is essentially a casualized CX bike for the masses. More relaxed geometry, lower gearing, wider tires.
