The Road Packs are typically best suited to more traditional road and touring geometries. If your bike doesn’t have tons of standover clearance and is pretty square (equal seat tube and top tube lengths) these are likely to be the best fit. The safest bet is to grab a tape measure and consult this sheet. Small, Medium and Large carry 3L, 4.5L and 6L respectively.
Three velcro straps attach these bags to your top tube, then 3 or 4 locking cam straps tighten them securely in place on the head tube, down tube and seat tube.