Trek and Specialized are giants in the mountain bike world, and both of these new XC bikes weigh in under 10kg and have five figure price tags. And that’s not all they have in common. Dynamic geometry and component choice of the Trek Supercaliber SLR 9.9 XX AXS Gen 2 and Specialized S-Works Epic World Cup are closely matched too. They feel surprisingly different on the trail though. So what are the details that affect the dynamic performance, and which one – if either – should you pick for ultimate cross-country speed? That’s the question this head-to-head test will answer.

• Read the full review of the Specialized S-Works Epic World Cup
• Read the full review of the Trek Supercaliber SLR 9.9 XX AXS Gen 2

Now, if you’ve not been following World Cup XC racing recently, you will have missed out on some excellent competition from insanely skilled and fit athletes. You also won’t know that most courses now feature sections that you’d assume were designed for 16kg, sticky tyre enduro bikes, not sub 10kg, semi-slick tyre-shod whippets. It’s why the best XC race bikes now look like lightened versions of trail bikes, with conventional linkage-driven shocks giving 100-120mm of travel. And both Trek (Top Fuel) and Specialized (Epic Evo) have bikes in that category too.

Suspension and frame layout

Trek and Specialized both used integrated shock designs to boost stiffness and give a hardtail look

That’s not what we’re looking at here, however. Both the Supercaliber SLR 9.9 XX AXS Gen 2 (£10,800) and Specialized S-Works Epic World Cup ($11,000) use a proprietary top tube embedded shock giving 80mm and 75mm of travel respectively. This gives them a traditional hardtail-style frame layout, rather than a distinctly separate front triangle and swingarm. Where the increased triangulation and more firmly anchored shocks open up potential for greater stiffness without adding extra weight. Both brands trade on that too, claiming hardtail-style power delivery, but with suspension when you need it. And it’s true, both the Trek and Specialized feel stiffer than conventional XC full-suspension bikes. But for different reasons. On the Trek Supercaliber it’s a structural thing, while the Specialized Epic WC creates the illusion of stiffness with its suspension set up.

Specialized’s Brain equipped RockShox SID fork is marginally heavier than the stock SID

Thankfully things are a lot simpler up front, where the latest RockShox SID SL Ultralight 110mm travel fork is hardwired to the same TwistLoc two position remote as the rear shock on the Trek. Specialized has transferred its long running Brain inertia valve to the latest 110mm travel SID SL fork. This reactive lockout has preset ‘Brian fade’ sensitivity, using a preloaded spring on the inertia valve. There’s no handlebar remote, but you can reach down and move the ‘fade’ lever on-the-fly with your hand if the trail is smooth enough. The latest version has had the spike valve removed for a more open feel, and even when ‘locked out’ you still get 15mm of cushion for traction. All-in, the Brian system adds 183g over the standard SID fork.

Left: Trek has a twist grip remote for the fork and Shock. Right: Specialized relies on smart suspension tech

On the scales

Claimed frame weights are different for both bikes. Specialized suggests a near 250g advantage over the Trek, but the sub 10kg build weights for each bike are very close when we checked them in the workshop. The Trek weighs 9.72kg (21.43lb), the Specialized a smidge heavier at 9.75kg (21.5lb). And that’s because the Epic WC has a heavier Brain version of RockShox’s SID SL fork and a power meter chainset too. That said, both add less to the overall weight of the Specialized than the Fox Transfer SL dropper does on the Trek. Yup that’s right,  Specialized fits a rigid post. All of which suggests that the claimed weights are a little off. 

Geometry side-by-side

If you take a quick glance at the geometry chart, the head angle on the Specialized is a lot slacker than the Trek. But the static geometry does not tell the whole story. The Specialized is designed to run very little shock sag, so the dynamic head angle with the rider on board is actually very close to the Trek. And it’s a similar story with the BB heights. The Trek appears to be a lot higher, but once you factor in the increased shock sag, it’s pretty close to the Specialized. On the trail then, the dynamic geometry of both bikes is much closer than it appears in the chart below (using our own measurements, not the manufacturers claimed figures).  

Build kits

Trek’s top end Supercaliber has Level Ultimate 4-piston brakes, a XX AXS drivetrain and a one-piece Bontrager cockpit

As the model name suggests, there’s a full SRAM XX AXS drivetrain on the Trek, complete with carbon rear derailleur cage and hollow carbon crankarms. While the new XX transmission isn’t as fast to shift as older AXS systems, you don’t have to ease up on effort while changing, so everything is literally geared towards going faster. Unlike the Specialized Epic WC, there’s no power meter chainset here though. Bontrager’s top Race Series Limited kit provides the one piece bar/stem (750/80mm equivalent) and the carbon rail saddle. The ultralight (but lifetime warrantied) carbon Kovee wheels have a 108 point engagement rear hub, which joins in the fast and furious fun with near immediate reaction to pedal inputs.

Specialized’s Epic WC gets less powerful 2-piston brakes

It’s a similar blend of parts on the Specialized. The transmission is SRAM’s top line XX SL AXS wireless kit including a full Quarq power meter on the narrow stance 168mm Q-Factor chainset. Specialized’s partner-brand Roval provides the Control SL Integrated cockpit, which mimics a 760mm bar in a 70mm stem, and the superlight Control SL wheels. Our only gripe with the build is that the two-piston SRAM Level Ultimate brakes are both less powerful and 10g heavier than the four-piston versions. Lever feel is great though, and you get a 180mm front rotor for power compensation.

Performance

We struggled to get to grips with the suspension on the Specialized Epic WC

We literally spent months setting and re-setting sag levels, tweaking the compression and rebound damping on the Specialized Epic World Cup, and riding it in as many different situations as possible. In the process we figured out that there are some things the Epic WC does very well. The ‘take no prisoners’ vibe is a psychological gift for flat-out attacks. The split personality suspension works very well in firmer modes when powering from smooth surfaces to stutter bumps (or vice versa). Fixed seat post aside, the spec is pretty much perfect premium race gear, and its clean looks were universally praised. 

For an XC bike, the Specialized Epic WC isn’t as firm under foot as we expected

Now for the negatives. The topped out, sat ‘on’ not ‘connected to’ the trail suspension response undermines control and traction significantly on descents, and you get tired really quickly on technical trails. The (relatively) soggy pedalling action also saps energy and morale, and being unable to change that feeling when riding inevitably means compromise, rather than customised, performance for each section of track too. 

Once the shock bushing loosened up, the Trek Supercaliber took off like a rocket

Contrast that with the Trek Supercaliber. Sure it took a couple of rides for the ZEB bushing on the IsoStrut shock to free up, and the skinny Bontrager tyres needed switching out too, but the Supercaliber just felt ‘right’ from the start, especially from a race point of view. The combination of the structural stiffness and the very positive pedalling feel from the higher-than-average anti-squat, and extra low speed compression damping, gives a noticeably different character to most conventional XC bikes. And even though the suspension response is firm, the fact it’s progressive makes it more predictable than the reversed stiff-to-soft action of the Specialized. 

The Gen 2 Trek Supercaliber is born for speed

There’s none of the harsh, hammering topped-out staccato of the Epic World Cup either, and the standard SID SL fork is a lot less spikey than Specialized’s Brain equipped unit. As a result, fatigue levels were dramatically reduced, even on rougher descents when testing the bikes back-to-back. In fact, the only time the Trek felt at a disadvantage to the Epic World Cup was on smooth climbs, where the increased sag felt less efficient than the topped out Epic. That’s immediately remedied with a twist of the lockout though, and overall the Trek Supercaliber just felt a lot more sorted, connected and intuitive for racing and flat out XC/Trail riding.

Conclusion

And the clear winner here is the Trek Supercaliber SLR 9.9 XX AXS Gen 2

Having said that, neither bike is as fast on descents/technical sections as most longer-travel XC bikes, and therefore they aren’t as versatile either. They don’t offer any weight advantage either, and with a remote multi-mode suspension, rather than binary lockouts, most 120mm bikes are faster on a lot of climbs and more tuneable for different sections of track. 

So if there’s no real weight advantage, and both bikes have less travel for bigger hits and the extra complications of proprietary shocks, why would you want to consider either of them over a conventional full-suspension race bike? The answer potentially lies in their very different ride vibes. You can read the full test of the Trek Supercaliber SLR 9.9 XX AXS Gen 2 here and the Specialized S-Works Epic World Cup here. 

Also we’re already seeing both the Supercaliber and Specialized’s Epic Evo using RockShox Flight Attendant electronic suspension adjustment on the World Cup race circuit too. That makes investing £10k in a proprietary suspension system and frame potentially less appetising when Ai might be end up doing a better job on a more versatile frame in the not-too-distant future.

Test Winner’s Stablemates – alternatives for different budgets 

SRAM or Shimano? You get to choose as Trek also has the Supercaliber SLR 9.9 XTR Gen 2

Trek Supercaliber SLR 9.9 XTR Gen 2 £10,350

Sit squarely in the blue Shimano camp but want all the benefits of the Gen 2 Supercaliber SLR 9.9 frame? Well Trek also has a full Shimano XTR equipped bike. It gets a Fox 34 Step-Cast fork with 110mm travel paired with the IsoStrut, RockShox SIDLuxe shock and a twin lock out remote. You also get higher volume 2.4in tyres for more traction and control. Bonus. 

Trek’s Supercaliber SL 9.6 Gen 2 has all the latest XC tech, without the sky-high pricing

Trek Supercaliber SL 9.6 Gen 2 £3,780

XC race full suspension bikes are usually prohibitively expensive, not the Supercaliber SL 9.6 Gen 2. It shares the same frame layout and suspension tech as our test winner, but uses a heavier OCLV carbon lay-up and a RockShox Recon Gold RL fork to reduce costs and achieve a more competitive price point. You also get a 12-speed Shimano SLX drivetrain and a dropper post, so it’s ready to rock and roll.