Not to be confused with Crash Bandicoot’s large-headed nemesis, Sonder’s range-topping trail ripper, the Cortex GX AXS is a bike that combines solid trail-orientated geometry with ridiculous value for money. While there’s an awful lot to like about the bike and it’ll certainly please a lot of riders, a lack of refinement in a number of areas sadly holds it back from shining in the best full suspension mountain bikes segment
Sonder Cortex GX AXS - Technical details
The Cortex is Sonder’s 120mm traveled 29er that’s designed to fill the boots of downcountry, and all-mountain riding. That’s a mighty broad spectrum for one bike to fill.
Straight off the bat, the Cortex GX AXS offers, quite frankly, a silly bang for buck as bolted to its alloy frame is a RockShox Pike Ultimate providing 130mm of very well-damped suspension and loads of adjustability. The rear 120mm is handled by a RockShox Deluxe Select+, a noticeably less flashy bit of kit but one that does a good job, nonetheless.
The bike’s value gets even better as its shifting is provided by SRAM's GX AXS drivetrain. For those who don’t already know, it’s the brand's entry-level wireless 12-speed shifting and while it’s not the priciest of offerings (though still quite costly), its performance is nothing short of luxurious. Once you get accustomed to its customisable nature, almost instantaneous gear changes, and effortless lever throw, you’ll be reluctant to move back to cable-operated shifting.
That drivetrain is then accompanied by SRAM’s G2 R brakes, which slow a pair of Sonder’s own Alpha 29-inch wheels. They’re wrapped with the latest Goodyear Newton MTF 2.5in and MTR 2.4 tyres in the Trail casing. The rest of the kit comes from Sonder apart from the X-Fusion Manic dropper post which, on this particular bike, comes with 125mm of drop although Sonder's website says it should come equipped with a 150mm dropper.
On paper, Sonder has done a solid job with the Cortex’s geometry, outfitting it with common trail bike figures. We’ve got a large frame on test which utilises a 66-degree head angle and 74.5-degree seat tube and combines it with 465mm of reach. Those numbers are absolutely nothing to be sniffed at and they place this bike firmly within trail bike territory, promising a capable but versatile ride. It’s nothing terribly progressive but it’s far from conservative, which is fantastic to see.
The frame is internally cable routed, has clearance for up to a 2.6in tyre and a metric sized shock damps the Horst Link suspension platform. There’s also space for a bottle cage in the front triangle and an excellent touch is the threaded bottom bracket, which will make maintenance as simple as it gets, a must when the British weather seeps its way in.
Sonder Cortex GX AXS – Performance
I’ve been riding the Cortex for a good couple of months now over a range of terrains and I’ve found it to be something of a mixed bag. There’s an awful lot to like; it’s sorted geometry, and that awesome spec but a few niggles have cropped up that have, unfortunately, let it down. But let’s start off with the good stuff.
It’s a comfortable bike to sit over and pedal for the most part. The 74.5-degree seat tube angle is edging towards slack but it results in a spacious cockpit that’s especially comfortable to pedal over flatter ground. With the dropper post at full extension, the saddle sits quite far behind the crank, so when tackling steeper climbs I have felt folded over the bike but, because it isn’t hugely long, weight is evenly distributed, keeping the bike planted whatever the gradient.
In terms of comfort, the Cortex is well behaved on the pedals. Running the sag at 25%, pedal bob is present, but it’s minimal. The suspension platform balances efficiency with comfort well in this area of the stroke.
That very aggressive Goodyear MTR tyre at the rear pulls the reins on all-out pedaling efficiency, however. Its profile is tall and while it’s incredibly grippy where it’s needed, it’s miles from ‘downcountry’ and its drag is super noticeable when cranking away. Swap this for something lower profile, and you’ll have a bike that’ll be a monster when munching miles.
I found that there wasn't an awful lot of dropper post cable to play with. That meant that when raising the saddle to my preferred height, the cable pulled on the post's switch, meaning that the post would constantly drop whenever weighted. It took some fiddling with the cable to fix but there's not a lot of slack after the adjustment.
Considering that this is a large sized frame designed to accommodate folk from 5ft 9in up to 6ft 2in, it’s a surprise that a lot of seat post adjustment has been so limited. More cable please, Sonder. Speaking of which, the brake cables aren't particularly tidy either, with some pretty big twists as they reach the levers. This doesn't affect the bike at all, rather it hampers the bike's aesthetic merit.
Saddle height issues aside, the Cortex is easy to pedal with capable geometry. Thanks to a reasonable wheelbase the Cortex is stable at speed, leaving the Pike Ultimate fork to keep the front wheel tracking the ground as well as it does. The fork is excellently supported, too, firming up nicely in its midstroke as you push it into banked corners.
The same can’t quite be said for the rear suspension, however. It is supportive around the sag point, as mentioned before, but push the bike beyond that area of its travel and it’s eager to give up those valuable millimeters. This is great in some respects, as it makes the meager 120mm of travel feel like much more but I expect a lot more support from this amount of suspension.
If you like a trail-munching rear end, that's the Cortex all over as its travel is free to soak up all kinds of bumps but it ramps up very late in the shock's stroke - meaning harsh bottom outs are rare. This kinematic does result in quite a vague feeling rear, however, and it can feel sluggish in the corners as the suspension tends to bog down. Adding some bottomless tokens into the shock should fix this, boosting support earlier in the travel.
But the Cortex is more about its well-balanced geometry as it offers a ride that’ll please a lot of riders - it’s a well-rounded bike in terms of geometry. It’s taken steep moments, flat-and-twisty sections, and flow trails all well within its stride. In fact, the Cortex is nothing short of fun once you’ve got the suspension set up properly and it’s capable of a surprising amount of riding. While at first, I was skeptical of the downcountry/all-mountain claims, the bike certainly lives up to them.
In the corners, while the downfalls of the rear suspension are clear, the agility nestled within that geometry is incredibly welcomed. Short but fast changes in direction are more than possible, creating a fun and exciting ride, despite the energy-sucking suspension platform. And of course, that Goodyear MTR at the rear simply bites, giving that rear-end all of the grip it could ever need. When leaned over during more sustained corners, the bike does require some supervision due to the Goodyear MTF’s less than ideal shoulder knobs at the front, but generally, grip management isn’t something to worry about.
The dropper post travel on this bike is a bit of a weird one. As I touched on before, this test bike came with 125mm of drop whereas it should come with 150mm. With this dropper installed, the saddle was very much in the way and I felt as if I had to ride around it. However, this would quickly be solved if it came with the 150mm dropper as promised on the website. Getting the saddle well and truly out of the way would seriously open this bike up to rowdier trails.
While the geometry encourages silly line choice, can absolutely cope with more demanding trails, and stay composed at respectable speeds, the SRAM G2 brakes, paired with 180- and 160mm rotors are quick to slap a ruler on the Cortex’s knuckles.
The brakes are built with four-piston calipers, which is great, but having them grab onto miniature rotors isn’t so confident-inspiring when you do tip into something a little spicy. The combination isn’t the most powerful which can get pretty scary when you begin to push the bike. For general trail centre jaunts, the power on offer is just about enough but when I’ve shown the bike something a bit steeper, or more natural, I’ve had to hang on the brakes to avoid pinging myself over the lip of a berm. The G2 brakes aren’t the most powerful on the market either, which can result in some serious arm pump (the least of your worries during technical sections) but larger rotors would increase this bike’s capabilities.
On the subject of internally routed cockpit accessories, hurtling through some of my favourite downhill trails was audibly accompanied by an awful lot of rattle. While the internal cable routing gives the Cortex its sleek aesthetic, the cables aren’t internally guided or tied down in the frame, so they’re free to whip about as if they’re windmilling through a Slipknot mosh pit. Sadly, there’s little that can be done about this.
It’s a similar story at the chainstay, too. There’s no form of protection or noise damping here, so chain slap is regular occurrence. It’s not too much to ask for stock chainstay protection on any bike these days, let alone a bike costing north of £2,000.
Sonder Cortex GX AXS – Verdict
While it is flawed in a number of respects, the Cortex's excellence shines thanks to its geometry but its saving grace is just how much bike you’re getting for the cash. These issues, for the most part, are curable aftermarket, too.
But for £300 less, you could get Canyon’s Spectral 125 CF 7. The build kit isn’t quite as flashy but it comes with a carbon frame and, during testing, the Spectral 125 CF8 seriously impressed with its supportive suspension platform and lightning fast geometry. It gets SRAM Code RS brakes, too, so it’ll definitely be able to dump the anchor.
You could even pick up a Cotic FlareMAX for £200 less. That’s a steel-framed downcountry rig with a more progressive geometry, featuring a 490mm reach on a large frame. Though, you’re not getting anywhere near the price/performance ratio as it comes with a RockShox Revelation fork and a Shimano SLX groupset. We’ve tested the FlareMAX Gold G4 XT and praised it for its huge capability and hooligan characteristic.
Though with builds starting at just £1,700 there’s a Cortex for almost every budget. Even then, you’ll be incredibly lucky to find a bike specced with a Pike Ultimate and GX AXS for south of £4k, unless it’s on sale. Hence, the bike’s mind blowing value.
Even with a clear need for refinement, the Sonder Cortex GX AXS is a bike that can appeal to a lot of people. If you’re after a capable bike that can cover a lot of miles comfortably, while being confident, fast and a proper laugh downhill, and you don’t mind a bit of tinkering and suspension fettling, the Cortex GX AXS provides excellent value for money that’ll get any trail rider tempted.