A small frame refuses bags over edges, not over volume

Frame size is the first thing a bag listing asks for and the last thing that settles the answer. The engine checks every bag in the catalogue against three reference frames and records the dimension that decided each verdict. On the smallest of the three, the deciding dimension is almost never the one a size label describes.

7200 mlof usable in-frame volume on the small reference frame, 47 cm

Every bag, against the small frame

Read down the last column. The frame bags that are refused are refused on top tube length, which is an edge rather than a capacity. The seat packs are refused on exposed seatpost and on thru-axle mounts. The fork bag that is refused is refused on three-pack mounts, which asks what the fork has rather than how big the bike is. Nothing on this frame is refused for want of room, and the one frame bag that passes has in-frame volume named against it — the sweep records that verdict without saying what makes that bag different from the ones beside it.

Exposed seatpost is the number that moves

The two packs refused on the small frame for exposed seatpost both fit the large one, and the second column is the figure that changed underneath them. On the medium frame the constraint has already moved: one of those two fits with the post still named against it, and the other is Tight with tyre clearance named instead, so the post stopped being what limited it before the frame reached full size. The third pack ignores that line entirely. It is refused on the small and the medium frame for thru-axle mounts, and the frame it fits is the one whose own name says three-pack fork.

What a frame size does not decide

• The 9000 ml handlebar bag returns Fits on all three frames, limited each time by the same declared clearance, to the cables at full lock.
• The 15000 ml handlebar bag returns Tight on all three, limited each time by the same declared clearance, to the headlight bracket.
• The 3000 ml fork bag returns Tight on all three, limited each time by strap purchase on a rigid fork leg.
• The 4000 ml fork bag is the one that moves, and not for size: refused on the small and medium frames for three-pack mounts, and Fits on the large.

What this cannot tell you

By how much. The sweep records which dimension limited each verdict and not the millimetres of the gap, so a refusal here is a refusal without a margin — a frame a few millimetres either side of a reference frame could land the other way, and nothing above would show it. Nor is a reference frame your frame: these are three measured examples, and the answer that matters is the one your own geometry produces. Two rows in the first table are identical because the payload holds no maker and no model, deliberately, so bags that agree on every dimension shown here agree on the page as well. Nothing here was ridden, loaded or tested; every line is a rule applied to a measurement.