Austrian brand Simplon has had a Cirex carbon fibre ‘fully’ in its range for 15 years. This latest version pushes well beyond typical XC boundaries to create a confident, but still highly efficient, mile shrinking marathon and epic ride machine.
From the broad, bulged base to the tapered head tube and a box back section that leads into a very broad but flat kinked top tube, things are kept impressively tight in terms of tracking.
The steep, straight down tube kinks backwards well ahead of the bottom bracket to give room for down tube and seat tube bottle mounts. The square to round and subtly kinked seat tube also has an optional bolt-on front mech mount, with a pop off cover for a front pull Shimano Side Swing mech.
The main pivot covers also include really neat swivelling guides for the rear gear cable and brake hose. This stops either of them rubbing on the frame or potential for ghost shifting as the front and rear frame halves move.
The frame is Di2 compatible too with internal routing blanking plates to match, and the cable for the shock remote control can be tucked away internally too.
Simplon has also been savvy enough to make the Cirex internal dropper compatible, and my sample bike came with a KS Lev post as standard.
The sloping top tube splits ahead of the seat tube with the lower split running parallel to the high mounted, metric length Fox Float DPS shock. The upper split creates a higher bracing point for the seat tube and triangulates the upper pivot of the neat wraparound, shock driving linkage.
Sculpted rearstays with a skinny brace just over the top of the tyre are designed to flex to allow 110mm of rear wheel travel without a conventional rear pivot. Hollow carbon dropouts with alloy sandwich axle and rear mech sections keep the 148mm Boost back end stiff, light and durable/replaceable.
A hockey stick shaped drive side and S bend offside chainstay complete the chassis circuit back to the main pivot, which sits bang level and a hair behind top centre of the single chainring.
The unidirectional carbon frame uses a ‘Hot Melt’ pre-preg process to minimise excess resin content and the segmented build uses size specific tubes to tailor strength and weight to likely loads. Physical protection comes from a sump plate on the down tube and a chromed chain protection plate while chain slap is naturally reduced by the low slung drive side chain stay.
Simplon Cirex 120 X01 Eagle kit
Simplon prefers to build custom bikes to order from a massive selection of potential parts that could easily take this bike sub 10 kilos. I opted for the KS dropper and a wider riser bar than the 700mm carbon flat stick offered though and kept to alloy rather than carbon DT Swiss wheels.
My bike build still came with an inverted stem for a full XC stance, which I flipped upside and eventually swapped for a longer shaft to stabilise the steering. I also changed the featherweight but very fragile Schwalbe Lite Skin tyres as soon as I started to explore the Cirex’s off piste capabilities.
Simplon Cirex 120 X01 Eagle ride
With a weight around 11.5kg, even with tougher tyres, and a naturally tight suspension feel from the Performance rear shock the Cirex doesn’t waste any time showcasing its acceleration and climb crushing credentials.
Typically for a flex stay bike, power delivery is taut from sag point through the top of the stroke. There’s still enough movement to help keep the back wheel connected and fluid up and over small stutter bumps and roots. The 29er wheels obviously help with rollover too, with the long 450mm chainstays also boosting traction and back-end stability to keep you on line on climbs.
A relatively high for travel 340mm bottom bracket means plenty of crank clearance over lumps and ledges too. If you’re a hardtailer at heart and find the minimal shock movement distracting then a quick thumb flick of the handlebar remote will lock both the back end and fork out entirely.
There are a lot of lockable full suspension bikes designed primarily for powering up hills, but Simplon has designed the Cirex to gap them on the descents.
On paper that translates to a head angle that’s just the stable side of 70 degrees with a 120mm fork, plus that dropper post capability means lower body weight balance despite the high bottom bracket.
You can specify whatever cockpit dimensions you want for your preferred power steering level too. On the trail what really stands out is how tight it feels for a very light bike.
Assuming you’ve picked a front tyre that lets you show it, the mainframe is a lot stiffer than many carbon trail bikes I’ve ridden, let alone XC whips. As long as you’re not too heavy handed with the XT brakes you’ll likely be surprised with how controlled the Fox 32 fork feels.
It’s not over-stretched in terms of leverage at 120mm of travel and once you’ve got past a tight top-end the mid-stroke is very well controlled. The overall result is certainly more composed and capable of being pushed than the majority of hysterical handling hyper-light machines.
While frame length is definitely cramped by contemporary trail bike standards (reach on the large is only 435mm) that’s offset by longer stem suitability in terms of overall stretch. As I said, I actually moved to a longer stem during testing to suit the bike’s generally more athletic than aggro character.
The back end comes off the tight top into a lot more fluid mid-stroke that can swallow some serious slaps without choking too. While it’s definitely linear in stock form (you can obviously add spacers to tweak that) it’s not so baggy that you wallow offline in hard corners and it reins in rear movement before it gets dangerous to your rims.
There is a rebound sweet spot to work out, to keep the longer rear end reacting fast enough when things get really rattly. The reach to rear end balance also naturally keeps the nose down rather than easy to manual.
That kind of rearward handling ‘pivot point’ definitely suits the old-school push back, wheels on the ground riders who still dominate the marathon and XC demographic though.
Like I’ve said previously, it also helps keep the bike on line when you’re red lining pulse rate up a climb or flogging yourself towards the finish absolutely, err, fatigued.