• cortex khaki
  • cortex battleship
  • cortex grey
  • cortex brown
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    Cortex NX Eagle [Special Build]

    Short travel 29er


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    Select Accessories


    Our Sonder Product Manager, Neil, has put together this special build. It's the spec he'd choose to ride. A fast and agile short travel full suspension 29er mountain bike with SRAM NX Eagle 1x12 groupset, Rockshox Pike Ultimate fork and Deluxe Select+ rear shock.


    Select Options


    • Size
    • Colour
    • Size:

    • Colour:




    Every Sonder bike is built to order so tell us exactly how you want it. Make any changes you want from the standard build and when you're done, just hit “Add to Bag” at the bottom of the page.


    Sonder Aspect Riser [OEM]
    Sonder Aspect Riser 780mm


    Sonder Horizon Flat [OEM]
    Sonder Horizon Flat 720mm


    Sonder Confucius
    Sonder Confucius



    Sonder Abode [OEM]
    Sonder Abode Black / 138


    Sonder Kura [OEM]
    Sonder Kura


    Sonder Zone [OEM]
    Sonder Zone 152 / Black


    Brooks Cambium C17 Saddle [OEM] / All Weather / Black
    Brooks Cambium C17 Saddle / All Weather / Black


    Brooks B17 Saddle
    Brooks B17 Saddle Standard / Black



    X-Fusion Manic Drop Seatpost and Lever
    X-Fusion Manic Drop Seatpost and Lever 31.6mm / 170mm


    X-Fusion Manic Drop Seatpost and Lever
    X-Fusion Manic Drop Seatpost and Lever 31.6mm / 125mm


    X-Fusion Manic Drop Seatpost and Lever
    X-Fusion Manic Drop Seatpost and Lever 31.6mm / 150mm


    X-Fusion Manic Drop Seatpost and Lever
    X-Fusion Manic Drop Seatpost and Lever 31.6mm / 170mm


    RockShox Reverb / 150mm Drop / 31.6 x 440mm
    RockShox Reverb / 150mm Drop / 31.6 x 440mm


    RockShox Reverb / 125mm Drop / 31.6 x 390mm
    RockShox Reverb / 125mm Drop / 31.6 x 390mm



    RockShox Pike Ultimate RCT3 /
    RockShox Pike Ultimate RCT3 / 29er / 130mm


    RockShox Pike Ultimate RCT3 /
    RockShox Pike Ultimate RCT3 / 29er / 130mm


    Cane Creek Helm MK2 Air / 29 / 130mm
    Cane Creek Helm MK2 Air / 29 / 130mm 130mm



    Rockshox Deluxe Select+ / 190x45
    Rockshox Deluxe Select+ / 190x45


    Cane Creek DBair IL
    Cane Creek DBair IL 190 / 45



    Tubeless Tyre Upgrade and Setup
    Tubeless Tyre Upgrade and Setup



    Select Accessories


    Bottle Cages

    No Bottle Cages
    No Bottle Cages (none)


    Sonder Buzz Wire
    Sonder Buzz Wire Pair



    No Lights
    No Lights (none)


    Alpkit Phase 400 rechargeable bike light
    Phase 400


    Alpkit Boson rechargeable bike light and hand torch



    No Mudguards
    No Mudguards (none)


    sonder fender
    Sonder Fender Front MTB


    SKS Commuter Mudguard Set
    SKS Commuter Mudguard Set 28 / 45mm / Black



    No Pedals
    No Pedals (none)


    Sonder Torque
    Sonder Torque Black


    contact clipless road bike pedal
    Sonder Contact

    +€59,99 +€49,99

    reko clipless bike pedal
    Sonder Reko

    +€69,99 +€59,99

    sonder slingshot clipless pedal
    Sonder Slingshot Black


    Initial Price

    Cortex NX Eagle [Special Build] / Select a frame...



    Total Price



    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.

    Neil's take

    I find NX Eagle to be the sweet spot between performance and price. You're getting a lot of the benefits of GX Eagle mixed with some of the value of SX. It's a real Goldilocks groupset.

    Then, chuck in the excellent Pike forks, which give you great control over the rough stuff, and our lightweight, performance Alpha 29" wheels, that spin up quick and roll smoothly, and you've got a build that'll ride beautifully.

    At a glance

    • SRAM NX Eagle 12-speed groupset
    • Rockshox Pike Ultimate fork
    • Rockshox Deluxe Select+ shock
    • Sonder Alpha 29" wheelset

    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.


    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
    Frame:Cortex Frame | 6061 aluminium
    Fork:RockShox Pike Ultimate | 130mm (travel)
    Headset:FSA Orbit C-40-ACB
    Shifters:SRAM NX Eagle Trigger | 1x | 12-speed
    Brakes:SRAM Guide T | Hydraulic | Direct mount
    Rotors:Avid Centreline | 180mm (front), 160mm (rear) | 6-bolt
    Rear derailleur:SRAM NX Eagle | Long cage | 12-speed
    Chainset:SRAM NX Eagle DUB | 170mm | 32t
    Cassette:SRAM PG1230 | 11-50t | 12-speed
    Chain:SRAM NX Eagle | 12-speed
    Bottom bracket:SRAM DUB | BSA | 73mm
    Wheels:Sonder Alpha 29"
    Front tyre:Goodyear Newton MTF Trail Tubeless | 29 x 2.5" | Black
    Rear tyre:Goodyear Newton MTR Trail Tubeless | 29 x 2.4" | Black
    Tubes:WTB | 29 x 2.2-2.4"
    Finishing kit
    Handlebars:Sonder Aspect Riser | 78cm
    Stem:Sonder Piskie | 35mm
    Seatpost:X-Fusion Manic | 31.6mm | 150mm (drop)
    Saddle:Sonder Abode | 158mm | Black
    Grips:Sonder Clutch | Black
    Frame:S: 1.97kg; M: 2.0kg; L: 2.1kg; XL: 2.14kg
    Build:S: 12.4kg; M: 12.65kg; L: 13.8kg; XL: 13.9kg
    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:
    Small: Riders between 5ft 2in and 5ft 7in (157-170cm)
    Medium: Riders between 5ft 6in and 5ft 10in (167-177cm)
    Large: Riders between 5ft 9in and 6ft 2in (175-187cm)
    X-Large: Riders of 6ft 2in + (187cm)


    Size Small Medium Large X-Large
    ST - Seat tube 405 425 465 485
    TT - Top tube 575.6 597.3 625.6 649
    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 445 445 445 445
    BB - BB drop 52 52 52 52
    FO - Fork offset 46 46 46 46
    WB - Wheelbase 1169.1 1191.2 1220.2 1244.3
    SO - Stand over 749.7 768.4 782.6 796.6
    RE - Reach 420 440 465 485
    SK - Stack 601.7 606.3 615.4 624.6
    Frame Spec

    Alloy 29er short travel full suspension trail bike

    Weight: S: 2.8kg; M: 2.9kg; L: 3.0kg; XL: 3.08kg (without shock)
    Hydroformed and custom butted alloy frame tubing
    Internal cable routing
    Rear Shock: Rockshox Deluxe Select+ 190 x 45mm
    Horst link suspension layout
    120mm rear travel; 130mm fork travel
    Clearance for up to 29 x 2.6" wide tyres
    73mm BSA threaded bracket shell
    148 x 12mm rear thru-axle
    31.6mm seat tube, 34.9mm clamp
    Headset: IS42/28.6 | IS52/40

    • cortex khaki
    • cortex battleship
    • cortex grey
    • cortex brown