Cortex GX Eagle

Photos for illustration purposes. Please check the bike spec for detailed component listings.

Cortex GX Eagle

Short travel 29er full suspension mountian bike


Fast and agile short travel full sus 29er mountain bike with SRAM GX Eagle drivetrain, Rockshox Pike Ultimate fork and Deluxe rear shock

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Orderbook opens November for delivery in April.


Fast and agile, Cortex is a trail riding, down-country, all terrain mountain bike for seriously epic days out. It comes alive on long technical descents with 120 mm rear travel, big wheels and a stiff responsive frame.

With bang up to date geometry, Cortex is confidence inspiring with a playful character. Stand up and mash on the pedals out of turns, manual sections of trail and pop off tree stumps, rocks and roots. Smash out short and loose technical climbs, flat out descents and tight techy singletrack sections. The harder you push the bigger you grin.

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  • Fast and agile short travel full sus 29er; perfect for mixed terrain and day long epics
  • Frame: Sonder Cortex 120 mm travel, hand-welded 6061 double butted aluminium
  • Fork: RockShox Pike Ultimate RCT3 / 29 / 130mm
  • Rockshox Deluxe Select+ / 190x45
  • Groupset: SRAM GX Eagle, 1x12, 10-50
  • Brakes: SRAM Guide R
  • Seat Post: X-Fusion Manic Drop Seatpost and Lever / 31.8mm / 125mm
  • Wheelset: Love Mud Hobo 29er Wheelset / XD
  • Up to date geometry for trail bike agility and enduro bike stability

Cortex frameset is hand-welded from 6061 double butted aluminium with a tapered ovalised top-tube and large section down-tube for a stiff chassis with just enough compliance to get you out of trouble. 66 head angle, 74.5 seat tube angle, 40 mm bottom bracket drop and a 465 mm reach (size large). Cortex’s dialed in geometry and 2.6" tyre clearance offers a comfortable and efficient climbing position for big miles and a stable, spirited platform for smashing up descents.

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Up to Date Trail Bike Geometry

Trail bike Agility with Enduro bike stability, the Cortex has a confidence inspiring, stable and forgiving ride.

Metric Shock Standard

Designed around metric shock sizing standard, with lengthened shocks and shorter strokes that increase bushing overlap for more smooth, supple, sensitive and reactive suspension action.​

Horst link suspension design

The tried and tested Horst link suspension design allows the suspension to stay active when braking.​

Tyre Clearance

​Clearance for up to 29 x 2.6in tyres.

Internal Cable Routing

​Internal routing in the front triangle for clean lines.

Build Spec
BuildCortex GX Eagle
Frame:Sonder Cortex Frame
Fork:Cane Creek Helm MK2 Air / 29 / 130mm
Shock:Rockshox Deluxe Select+ / 190x45
Headset:Love Mud Rumour / ZS44-ZS56
Seat Clamp:Love Mud Gromit / 34.9mm
Group Set
Brake Front:SRAM Guide R / 950mm
Brake Rear:SRAM Guide R / 1800mm
Rotor Front:Avid Centreline Rotor / 180mm
Rotor Rear:Avid Centreline Rotor / 160mm
Rear Mech:SRAM GX Eagle Rear Derailleur / 12 / Long
Rear Shifter:SRAM GX Eagle Trigger Shifter
Chainset:SRAM GX Eagle Crankset DUB / 170mm / 32
Bottom Bracket:SRAM Bottom Bracket / DUB
Chain:SRAM GX Eagle Chain / 120 Links
Cassette:SRAM XG1275 Eagle Cassette / 12 / 10-50
Finishing Kit
Stem:Love Mud Piskie Stem / 31.8mm / 35mm
Seatpost:X-Fusion Manic Drop Seatpost and Lever / 31.6mm / 125mm
Saddle:Sonder Abode / Black
Tape/Grips:Sonder Clutch / Black
Handlebar:Sonder Aspect Riser
Wheels:Sonder Alpha 29 / XD
Front Tyre:WTB Vigilante / Light High Grip / 29 / 2.5
Rear Tyre:WTB Trail Boss / Tough Fast Rolling / 29 / 2.4
Tubes:WTB Inner Tube / 29 / 1.9-2.3
Frame:S: 1.97 kg; M: 2.0 kg; L: 2.1 kg; XL: 2.14 kg
Built:S: 12.4 kg; M: 12.65 kg; L: 13.8 kg; XL: 13.9 kg
Pedals not included with full builds
Geometry and Sizing


It is important to get the right size bike, if the bike fits it will be faster, more comfortable, and easier to handle. You can also take into consideration the standover height to ensure you pick a bike that will be a good fit. If you measure your inside leg and ensure there is a minimum of an inch from the toptube to your crotch this will give you enough seatpost adjustment to find your optimum saddle height. Generally we recommend:
Riders between 5ft 2in and 5ft 7in
Riders between 5ft 6in and 5ft 10in
Riders between 5ft 9in and 6ft 2in
Riders of 6ft 2in +


Size Small Medium Large X-Large
ST - Seat tube 400 425 465 485
TT - Top tube 587 608 636 658
HT - Head tube 100 105 115 125
HA - Head angle 66 66 66 66
SA - Seat angle 74.5 74.5 74.5 74.5
CS - Chainstay 442 445 447 450
BB - BB drop 40 40 40 40
FO - Fork offset 51 51 51 51
WB - Wheelbase 1169 1191 1220 1244
SO - Stand over TBC TBC TBC TBC
RE - Reach 420 440 465 485
SK - Stack 602 606 615 625
Tyre Diameter 755 755 755 755
Fork Axle to Crown 540 540 540 540
Frame Spec
Alloy 29er short travel full suspension trail bike
Weight: S: 2.73kg; M: 2.91kg; L: 3.05kg; XL: 3.11kg
Hydroformed and custom butted alloy frame tubing
Internal cable routing
Rear Shock: Rockshox Deluxe Select+ 190 x 45 mm
Horst link suspension layout
120 mm rear travel; 130 mm fork travel
Clearance for up to 29” x 2.6 in wide tyres
73 mm BSA threaded bracket shell
148 x 12 mm rear thru-axle
31.6mm seat tube, 34.9mm clamp
ZS44/28.6| ZS56/40 headset (frame and rear shock does not come with headset)
Bike Radar Reviews Sonder Cortex

Bike Radar have their eyes set on the new Sonder Cortex

"Sonder has added to its bicycle range with the Cortex trail bike — a 120mm travel full suspension 29er that starts at £1,500 and is designed, it seems, to do just about anything."

Read the full review here.

Guy Kesteven at Bike Perfect Reviews the Sonder Cortex

We handed the Cortex over to Guy Kesteven for some real trail testing.

Cortex is a light, well-shaped frame that balances instant familiarity with extra confidence on faster, rowdier trails. Add an easy to set up fork, decent stop, go and finishing kit rolling on sturdy wheels with a properly surefooted front tyre and you’ve got a great package for the price.

Read the full review here.

Sonder Cortex: Singletrack First Ride Review

Andi at Singletrack gets an exclusive first ride review of the latest 120mm travel full-suspension bike from Sonder. Meet the 2020 Sonder Cortex.

"While riding the Sonder it felt just as fast as my big bike but sharper to corner, easier to hop and overall a hell of a lot of fun to ride, and I cannot wait to get on it again."

Read the full first ride review over on Singletrack.

Author: Andi Sykes