A frame size is a name; these are the measurements that decide
My bike is a size M. Will this bag fit?
A rider with a size M frame wants to know whether a bag will fit it. No rule in this planner reads the size on the sticker. Every verdict comes out of measurements, so the checkable form of the question is which measurement decides — and that can be answered by holding one frame still and replacing one of its numbers at a time with the value another frame declares for the same thing.
0verdicts that move when this frame's in-frame volume is replaced by another frame's
The frame held still is the medium reference frame, The Mule. The whole seed catalogue — 13 bags — is classified against it, then classified again with one measurement swapped for the small frame's value, and again with the large frame's. Nothing here is invented: every value tried is read off one of the three reference frames. A bag counts as moved when its verdict changes, or when the dimension that limited it changes.
| Measurement | On this frame |
|---|---|
| Top tube edge | 540 mm |
| Down tube edge | 583 mm |
| Seat tube edge of the triangle | 534 mm |
| Head tube edge | 118 mm |
| Seat tube length of the frame | 470 mm |
| Exposed seatpost | 180 mm |
| Tyre clearance | 61 mm |
| In-frame volume | 10600 ml |
One measurement replaced, and what it moves
| Measurement | Small frame's value | Moves | Large frame's value | Moves |
|---|---|---|---|---|
| Top tube edge | 480 mm | 5 | 600 mm | 0 |
| Down tube edge | 520 mm | 4 | 640 mm | 0 |
| Seat tube edge of the triangle | 430 mm | 0 | 580 mm | 0 |
| Head tube edge | 95 mm | 0 | 155 mm | 0 |
| Seat tube length of the frame | 430 mm | 0 | 540 mm | 1 |
| Exposed seatpost | 120 mm | 2 | 220 mm | 1 |
| Tyre clearance | 45 mm | 2 | 70 mm | 1 |
| In-frame volume | 7200 ml | 0 | 13500 ml | 0 |
Two things in that table are worth a rider's attention. The direction is not symmetrical: the top tube and down tube edges refuse bags when they take the small frame's values and refuse nothing at the large frame's, so knowing a frame is bigger than the one that was measured tells you far less than knowing it is smaller. And several rows read nothing in both columns — the seat tube edge of the triangle, the head tube edge, and the in-frame volume. The last is the surprise, because the volume of the triangle is the figure a rider is most often handed, and neither of the other frames' values for it moves a single verdict in this catalogue. A measurement moves nothing here when no bag in this catalogue declares a requirement against it, which is a fact about these bags rather than a claim that the measurement never matters.
A verdict can hold while the reason for it changes
| Measurement replaced | Bag | Was | Becomes |
|---|---|---|---|
| Exposed seatpost, 180 mm to 220 mm | 11000 ml seat pack | fits, limited by exposed seatpost | fits, limited by tyre clearance |
| Top tube edge, 540 mm to 480 mm | 9000 ml frame bag | no-fit, limited by seat tube | no-fit, limited by top tube length |
| Seat tube length, 470 mm to 540 mm | 9000 ml frame bag | no-fit, limited by seat tube | fits, limited by top tube clearance |
The first two rows are the case against a single number standing in for a frame: the answer held still and what the answer was about did not. The third is the only row in the whole sweep where a no-fit becomes a fits, and the dimension limiting that bag afterwards is a different one again. A rider comparing two frames by one measurement can be right about the verdict and wrong about what would have to change to alter it.
What this cannot tell you
Whether your own frame fits any of this. These are reference frames, and the sweep only trades their declared values between them — it does not model a frame nobody has measured. Two of the things that decide a verdict are not measurements at all and so cannot be swapped one value at a time: the mount inventory, which is a list of bolt positions, and whether a dropper post is fitted, which is present or absent. The measurement tolerance was not varied either, because all three frames declare the same 8 mm and there is no other value to try. And nothing here holds a weight, a price or a maker, because none of those were ever measured.
Every claim above, and how it is known
- DERIVEDThe medium reference frame declares a top tube edge of 540 mm, a down tube edge of 583 mm, a seat tube edge of 534 mm, a head tube edge of 118 mm, a seat tube length of 470 mm, an exposed seatpost of 180 mm, a tyre clearance of 61 mm and an in-frame volume of 10600 ml.
- DERIVED13 bags in the seed catalogue are classified against the frame, before and after each measurement is replaced.
- DERIVEDReplacing the top tube edge with the small frame's 480 mm moves 5 verdicts; the large frame's 600 mm moves none.
- DERIVEDReplacing the down tube edge with the small frame's 520 mm moves 4 verdicts; the large frame's 640 mm moves none.
- DERIVEDReplacing the seat tube edge of the triangle with 430 mm or with 580 mm moves no verdict.
- DERIVEDReplacing the head tube edge with 95 mm or with 155 mm moves no verdict.
- DERIVEDReplacing the frame's seat tube length with the small frame's 430 mm moves no verdict; the large frame's 540 mm moves 1.
- DERIVEDReplacing the exposed seatpost with the small frame's 120 mm moves 2 verdicts; the large frame's 220 mm moves 1.
- DERIVEDReplacing the tyre clearance with the small frame's 45 mm moves 2 verdicts; the large frame's 70 mm moves 1.
- DERIVEDReplacing the in-frame volume with the small frame's 7200 ml or the large frame's 13500 ml moves no verdict.
- DERIVEDAt 180 mm and at 220 mm of exposed seatpost the 11000 ml seat pack fits, and the dimension limiting it moves from exposed seatpost to tyre clearance.
- DERIVEDAt a 540 mm and at a 480 mm top tube edge the 9000 ml frame bag returns no-fit, and the dimension limiting it moves from seat tube to top tube length.
- DERIVEDAt a 470 mm seat tube length the 9000 ml frame bag returns no-fit, limited by seat tube; at 540 mm it fits, limited by top tube clearance.
- DERIVEDAll three reference frames declare a measurement tolerance of 8 mm, so there is no other value to try.
Other notes worked the same way
- Two weeks asks for the same list a weekend does
Sweep the nights answer from one to ten: the list stays at twenty lines, one spec moves, and the food only grows once the shops are thin.
- Where the planner picks for you, and where it will not
Twelve of the twenty-six requirements offer a choice. The planner names one only when an answer makes another wrong, and in one it never does.
- Tight means two different boundaries, and only one is a measurement
The engine holds most clearances to 8 mm of measurement tolerance and the tyre gap to 15 mm, so a 12 mm gap can still come back Tight.
Every figure here came out of the same rules that answer the interview, so it moves when they do. Yours differ wherever your answers differ.