The frame bag and the bottles want the same triangle
If I fit a frame bag, where does my water go?
The frame triangle is the best cargo space on a bicycle: low, central, and shaped for dense weight. That is why a frame bag goes there, and it is also why the bottle cages were already there. Fit the bag and the water has to go somewhere. How sharp that trade is depends on two numbers the planner already holds — how much water your ride needs, and how much triangle your frame has.
7500 mlof water capacity asked for at the longest dry-gap answer
What the planner asks you to carry
| Longest stretch without water | Water capacity asked for |
|---|---|
| 20 km | 2500 ml |
| 60 km | 4500 ml |
| 120 km | 7500 ml |
Those millilitres have to ride somewhere, and the default answer is bottles at the bosses inside the triangle — the same bosses a frame bag sits over.
What the three reference frames offer
| Frame | Usable triangle | Mounts |
|---|---|---|
| Small · 47 cm | 7200 ml | 2 bottle |
| Medium · The Mule | 10600 ml | 2 bottle, 1 rear rack |
| Large · 58 cm, three-pack fork | 13500 ml | 3 bottle, 1 rear rack, 2 three-pack, 1 thru-axle |
What the measured frame bags take
| Frame bag capacity | Clearance left at the bosses |
|---|---|
| 5500 ml | not stated |
| 6000 ml | 18 mm |
| 6000 ml | 24 mm |
| 6500 ml | 3 mm |
| 7000 ml | 11 mm |
| 9000 ml | not stated |
Put the tables side by side and the shape of the trade appears. On the small frame, a 6000 ml bag is most of a 7200 ml triangle, and that frame has exactly 2 bottle mounts and nothing else — no rack, no fork mounts to move the water to. On the large frame, the same bag sits in a 13500 ml triangle alongside 3 bottle mounts, 2 three-pack mounts and a rear rack mount, so the water has places to go. And capacity alone does not decide it: the two 6000 ml bags leave 18 mm and 24 mm at the bosses — identical volume, different room left underneath.
What these numbers cannot tell you
This page works from three reference frames and six measured bags; your triangle is none of them, and a clearance measured at one frame's bosses does not transfer to yours. Whether a particular bottle and cage still fit under a particular bag at 18 mm or at 3 mm is exactly the comparison the fit check makes against your own frame's measurements — this page cannot make it for you. And the water figures assume the dry gap you tell the planner: answer that question carelessly and every millilitre downstream of it is carefully wrong.
Every claim above, and how it is known
- DERIVEDAt a longest dry gap of 20 km the planner asks for 2500 ml of water capacity.
- DERIVEDAt a longest dry gap of 60 km the planner asks for 4500 ml of water capacity.
- DERIVEDAt a longest dry gap of 120 km the planner asks for 7500 ml of water capacity.
- DERIVEDThe small reference frame (47 cm) has a usable triangle of 7200 ml and 2 bottle mounts.
- DERIVEDThe medium reference frame (The Mule) has a usable triangle of 10600 ml, 2 bottle mounts and 1 rear rack mount.
- DERIVEDThe large reference frame (58 cm, three-pack fork) has a usable triangle of 13500 ml, 3 bottle mounts, 1 rear rack mount, 2 three-pack mounts and 1 thru-axle mount.
- DERIVEDThe measured frame bags hold 5500 ml, 6000 ml, 6000 ml, 6500 ml, 7000 ml and 9000 ml.
- DERIVEDWhere boss clearance was measured, the frame bags leave 3 mm, 11 mm, 18 mm and 24 mm at the bottle bosses; for two bags it is not stated.
- DERIVEDTwo measured bags of identical 6000 ml capacity leave different boss clearances: 18 mm and 24 mm.
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.
- A frame size is a name; these are the measurements that decide
Swap one measurement of a medium frame for another frame's value: the top and down tube edges move verdicts, and the triangle's volume moves none.
- 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.
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.