BRITISH DESIGN | tested and ridden on the trails of planet earth

Sirius 4G 27.5+


“Muscular steering, full-featured steel hardtail…rock-shrugging fun.” – MBUK

Includes rear axle and FUNN Descend headset and Frodon seat collar.



Evolution geometry applies what we’ve learned over the years from the previous generations of award-winning Sirius and takes it to the next level in our 4th generation, long-travel, semi-skimmed*, slack and low frame that’s ready to rail and riot for “rock-shrugging fun.”

Sliding dropouts give alternative gear options, facilitating the use of an internal gear hub or singlespeed set-up and a custom chainstay yoke will happily accommodate tyres up to 27.5×2.8″ or 29×2.4″, depending on your preference.

* not recommended for full-fat tyres >2.9″


Sizes available: 15.5″, 17.0″,18.5″ & 20.0″

Geometry data indicates a 515mm (axle to crown) suspension fork. Each additional 10mm of fork length will slacken/reduce the head angle by approximately 0.5-1.0 degree.

Small Medium Large X-Large
A: Head Angle 67 67 67 67
B: Seat Angle 73 74 74 74
C: ST C-T 394 432 470 508
D: TT Length (effective) 580 600 620 640
E: HT Length 100 105 115 130
F: BB Drop 64 64 64 64
G: Chainstays 430+ 430+ 430+ 430+
H: Wheelbase 1102+ 1133+ 1154+ 1176+
X: Reach 393 422 439 455
Y: Stack 622 626 636 649
Fork Length (min/max) 515-555mm Max Tyre Size 27.5×2.8″/29×2.4″
BB Width 73 mm Headset 44mm (internal)
Seat Post 30.9mm Seat Clamp 34.9mm
Stem Length (min/max) 35-70mm
27.5+ Set-up
Effective Wheel Radius, 27.5×2.8″ 726mm
BB Height, 515mm Fork 299mm (726/2)-F i.e. effective wheel radius/2, minus BB Drop
BB Height, 552 mm Fork* 311mm *DVO Diamond, 140mm Travel
29er Set-up
Effective Wheel Radius, 29er 744mm
BB Height, 515mm Fork 308mm (744/2)-F i.e. effective wheel radius/2, minus BB Drop



For information on Reach & Stack, click here.


Featured builds using a DVO Diamond fork set at 140mm have a head angle of between 64.5-65.5 degrees and a BB height of 311mm (using Maxxis Rekon 2.8″ tyres).


  • CrMo 4130 heat treated tubing throughout – read about it here
  • DT custom butted and bent for added strength and to eliminate gussets
  • DT horizontally ovalised at BB for greater stiffness
  • Custom CS/BB yoke for strength and huge tyre clearance
  • 44mm (internal) head tube
  • Sliding/replaceable dropouts: supplied with 142mm bolt-through axle.
  • Cable routing for externally or internally activated dropper post
  • 1 set of bottle bosses
  • Matte paint and decals
  • Metal headbadge


Specification of frame is subject to change without prior notice.


15.5″, 17.0″, 18.5″, 20.0″


Charcoal (Matte), Toxic Lemon (Matte)


142mm x M12 rear axle (M12 x P1.75), FUNN Frodon seat collar (black/polished), FUNN Descend headset combo (black) ZS44/28.6 + EC44/40

Fork Info'

The bike in the photos is using a DVO Diamond Boost fork set at 140mm, giving a head angle of between 64.5-65.5 degrees. This is the same fork we’re offering as an option with the frame bundle. The DVO Diamond can also be adjusted (internally) between 130-160mm of travel.

NOTE: each additional 10mm of fork length will slacken (reduce) the head angle by approximately 0.5-1.0 degree and will also raise the bottom bracket.

For specifications or more information, please refer to the DVO Suspension website.

Custom Tubing

The Sirius 4G frame uses custom, triple butted, heat treated, CrMo 4130. This super-alloy is drawn and butted in the same factory that our frames are fabricated in which allows us to not only keep everything in-house, but to also draw on their technical expertise as leaders in this field.

The strength of the tubeset is comparable to branded tubesets like Reynolds (725 & 853) or True Temper (Versus HT), for example.