Surly

Surly Pack RatGeometry & Bikepacking Bag Fit

Discontinued. Surly no longer lists the Pack Rat. It's here because these frames stay in circulation second-hand and the geometry is still what you need to pick bags — but you won't find one new.

Frame
4130 chromoly steel
Sizes
8

Surly Pack Rat frame geometry, drawn to scale

Every tube angle and length below is from the published chart, not an illustration. The front triangle area is the number that decides which frame bags fit — and it changes a lot across sizes.

Surly Pack Rat — 38cm. Front triangle ≈ 910 cm² · effective top tube 495mm · seat tube 380mm
Surly Pack Rat in size 38cm, drawn to scale from Surly's published geometry. The shaded area is the front triangle — roughly 910 cm² of space for a frame bag. Wheels are indicative; frame lines are accurate.
Surly Pack Rat — 42cm. Front triangle ≈ 1024 cm² · effective top tube 505mm · seat tube 420mm
Surly Pack Rat in size 42cm, drawn to scale from Surly's published geometry. The shaded area is the front triangle — roughly 1024 cm² of space for a frame bag. Wheels are indicative; frame lines are accurate.
Surly Pack Rat — 46cm. Front triangle ≈ 1152 cm² · effective top tube 520mm · seat tube 460mm
Surly Pack Rat in size 46cm, drawn to scale from Surly's published geometry. The shaded area is the front triangle — roughly 1152 cm² of space for a frame bag. Wheels are indicative; frame lines are accurate.
Surly Pack Rat — 50cm. Front triangle ≈ 1286 cm² · effective top tube 535mm · seat tube 500mm
Surly Pack Rat in size 50cm, drawn to scale from Surly's published geometry. The shaded area is the front triangle — roughly 1286 cm² of space for a frame bag. Wheels are indicative; frame lines are accurate.
Surly Pack Rat — 52cm. Front triangle ≈ 1372 cm² · effective top tube 550mm · seat tube 520mm
Surly Pack Rat in size 52cm, drawn to scale from Surly's published geometry. The shaded area is the front triangle — roughly 1372 cm² of space for a frame bag. Wheels are indicative; frame lines are accurate.
Surly Pack Rat — 54cm. Front triangle ≈ 1459 cm² · effective top tube 565mm · seat tube 540mm
Surly Pack Rat in size 54cm, drawn to scale from Surly's published geometry. The shaded area is the front triangle — roughly 1459 cm² of space for a frame bag. Wheels are indicative; frame lines are accurate.
Surly Pack Rat — 56cm. Front triangle ≈ 1548 cm² · effective top tube 580mm · seat tube 560mm
Surly Pack Rat in size 56cm, drawn to scale from Surly's published geometry. The shaded area is the front triangle — roughly 1548 cm² of space for a frame bag. Wheels are indicative; frame lines are accurate.
Surly Pack Rat — 58cm. Front triangle ≈ 1642 cm² · effective top tube 595mm · seat tube 580mm
Surly Pack Rat in size 58cm, drawn to scale from Surly's published geometry. The shaded area is the front triangle — roughly 1642 cm² of space for a frame bag. Wheels are indicative; frame lines are accurate.

What it can carry

Mount provision and clearance, as Surly publishes it.

Fork mounts
Yes — fork cargo mounts (count not published)
Bottle mounts
3
Rack & fender
Rack mounts published

Geometry

All figures in millimetres except angles. Effective top tube and seat tube are the two that decide frame bag fit.

SizeEff. top tubeSeat tubeStandoverHead tubeStackReachChainstayWheelbaseBB dropHead angleSeat angle
38cm495380698904793714109624572.5°75.5°
42cm5054207251054953724109634573°75°
46cm5204607511205123784109654574°74.5°
50cm5355007771355273844109754574°74°
52cm5505208051305513874159865574°73.5°
54cm5655408211455663924159965574°73°
56cm58056083716058039741510055574°72.5°
58cm59558085417559540241510145574°72°

Bottom bracket height

Roughly 320–330mm off the ground. Surlydoesn't publish this directly — we derive it from their BB drop and a typical 75cm tyre diameter, so treat it as indicative rather than exact. It changes with the tyre you fit. Lower means more stable and more pedal strikes; higher means the opposite.

Source — Surly's own geometry chart: https://surlybikes.com/products/pack-rat — checked 2026-08-16. A dash means the figure isn't published; we leave it blank rather than estimate.

Which frame bags fit

Every frame bag we track, checked against this frame's published geometry. Pick your size.

Checking 12 frame bags against a 550mm effective top tube and 520mm seat tube. 12 fit.

Excellent fit
Salsa EXP Series Anything Cradle

Plenty of room in frame triangle

$75
200g
Excellent fit
Oveja Negra Super Wedgie Half Frame Bag

Plenty of room in frame triangle

$110
170g
Excellent fit
Rockgeist Half Frame Bag

Plenty of room in frame triangle

$130
170g
Good fit
Moosetreks Full Frame Bag

Good fit within frame triangle

$60
300g
Good fit
Topeak Midloader Frame Bag

Good fit within frame triangle

$65
220g
Good fit
Blackburn Outpost Frame Bag Medium

Good fit within frame triangle

$80
280g
Good fit
Apidura Racing Frame Pack

Good fit within frame triangle

$130
145g
Good fit
Ortlieb Frame-Pack RC

Good fit within frame triangle

$150
250g
Good fit
Revelate Designs Ranger Frame Bag

Good fit within frame triangle

$155
230g
Good fit
Bedrock Bags Entrada Frame Bag

Good fit within frame triangle

$185
210g
Good fit
Porcelain Rocket Mr. Fusion Frame Bag

Good fit within frame triangle

$195
190g
Tight
Apidura Expedition Full Frame Pack

Tight fit against top tube length

$175
310g

Frame bag fit is calculated from Surly'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.