Poseidon X Geometry & Bikepacking Bag Fit2026
The same page we read this geometry from. We don't hold live pricing or stock for frames, so check both there.
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What this frame gives a loaded bike
Chainstay length is the gap between the seat tube and the rear axle, which a rack, panniers and your heels all have to share. Bottom bracket drop is how far the cranks sit below the axles. Both are compared against the median across every current frame we hold.
425mm chainstays, 10mm shorter than the 435mm median across the 65 current frames here. Bottom bracket drop 65-67mm, 4mm less than the 70mm median. Poseidon publishes no fork cargo mounts, and the frame publishes up to 4 bottle or accessory positions. Poseidon publishes no rear rack answer, which is not the same as no — but it is not something to buy a rack on. Widest published tire 45mm on 700c / 29in.
Every figure above is the manufacturer's, computed against the rest of the database. It says what the frame allows, not how it feels — nobody here has ridden it.
What it can carry
Mount provision and clearance, as Poseidon publishes it.
Poseidon's wording: “It fits 700x40mm tires right out of the box, with the option to go up to 45mm* for even more cushion and stability. *700 x 45mm tire clearance can range based on tire and rim combinations.”
Geometry
All figures in millimeters except angles. Effective top tube and seat tube are the two that decide frame bag fit.
| Size | Eff. top tube | Seat tube | Standover | Head tube | Stack | Reach | Chainstay | Wheelbase | BB drop | Head angle | Seat angle |
|---|---|---|---|---|---|---|---|---|---|---|---|
| S | 520 | 490 | 774.7 | 120 | 552.6 | 370.6 | 425 | — | 67 | 69° | 75° |
| M | 535 | 510 | 793.75 | 140 | 579.4 | 373.8 | 425 | — | 67 | 71° | 74.5° |
| L | 550 | 530 | 812.8 | 160 | 596.4 | 372.7 | 425 | — | 65 | 71° | 73.5° |
| XL | 565 | 550 | 831.85 | 180 | 619.3 | 375.4 | 425 | — | 65 | 72° | 73° |
| XXL | 610 | 580 | 857.25 | 200 | 638.3 | 408.3 | 425 | — | 65 | 72° | 72.5° |
Bottom bracket height
Roughly 308–310mm off the ground. Poseidon doesn't publish this directly — we derive it from their BB drop and a typical 75cm tire diameter, so treat it as indicative rather than exact. It changes with the tire you fit. Lower means more stable and more pedal strikes; higher means the opposite.
Source — Poseidon's own geometry chart: https://www.poseidonbike.com/products/xgen3 — checked 2026-08-18. A dash means the figure isn't published; we leave it blank rather than estimate.
Note: Gen 3 X. Poseidon states it removed the fork mounts that earlier generations had, so forkMounts is null rather than the sentence saying so. Frame bottle mounts: 3 on S, 4 on M/L/XL. Wheelbase is not published in Poseidon’s chart. effectiveTopTube is the chart’s “Horizontal HT Top” row; the “Horizontal Center” row runs 26-45mm shorter. Poseidon wording: “Based on rider feedback, we’ve also removed the fork mounts for a sleeker, more efficient design.”
How the X compares
Against the frames people actually cross-shop it with — both charts held together, on the specs that decide what the bike carries.
Questions people ask about this frame
Answered from what Poseidon publish. Where they publish nothing, that is what it says.
Does the X take fork cargo cages?
Not published. Poseidon don't state any fork mount provision for this frame. That isn't the same as it having none, and we won't guess from a photo.
What is the widest tyre the X takes?
45mm on 700c / 29in. That is the frame figure rather than the fork's, and it is what limits a loaded bike.
Will a seat pack work on the X?
Not published. Poseidon don't state dropper compatibility for this frame, so we can't tell you whether a dropper would compete with a seat pack on it.
Which frame bags fit
Every frame bag we track, checked against this frame's published geometry. Pick your size.
Checking 16 frame bags against a 550mm effective top tube and 530mm seat tube. 16 fit.
Frame bag fit is calculated from Poseidon's published geometry, so it's as reliable as their chart. Seat packs and handlebar rolls depend on your exposed seatpost and bar width, which no geometry table lists — the bag finder covers those once you add your own measurements.