Trek has struck gold with it's latest flagship XC race bike, the Supercaliber gen 2.

Product Overview

Overall rating:

Score 9

Trek Supercaliber SLR 9.9 XX AXS Gen 2


  • Conventional, predictable, race-ready package. Dropper post as standard.


  • Press Fit BB servicing sucks. No power meter as standard.


Trek Supercaliber SLR 9.9 XX AXS Gen 2 review


Price as reviewed:


Trek’s new Supercaliber is very much an evolution of the original ‘revolutionary’ design. As a result, it feels like a very sorted, balanced and predictable XC bike, its eagerness for speed clear from the first pedal stroke, and that makes it one of the best XC bikes we’ve tested.

Trek Supercaliber SLR 9.9 XX AXS Gen 2

Trek’s Supercaliber SLR 9.9 XX AXS Gen 2 builds on a winning formula.

And it’s by design. Because apart from a significantly slacker head angle (67.5º down from 69º) the Gen 2 Supercaliber doesn’t look dramatically different to Gen 1. 

Trek Supercaliber SLR 9.9 XX AXS Gen 2

IsoStrut suspension needs 10 hours riding to start feeling smooth rather than stubborn.

Frame and geometry

Trek even made a conscious decision not to alter the rest of the geometry much (reach and seat angle are slightly increased) so as not to disturb the riding position for their finely tuned pro athletes.

Scrape away the multiple paintwork options though (three alone on the flagship SLR 9.9 XX AXS model) and there’s a completely new set of tube profiles. The SLR frame uses a more exotic carbon fibre construct than before and the internal ‘trunking’ for the frame routed brake hose and dropper cable have been removed. Also seeing as Trek’s pro racers generally removed the Knock-Block steering limiter puck from the top tube, that’s no longer fitted either. 

Trek Supercaliber SLR 9.9 XX AXS Gen 2

Press fit BB saves weight but is a mechanic’s nightmare, and no power meter as standard.

Taken together, these updates give an average weight saving of 200g (depending on size) compared to the Gen 1 bikes. Which puts the frame right on the 2kg mark that most serious racers would consider the competitive ceiling. Racers will also be pleased to hear you can fit a 38 tooth chainring and the bike comes with two carbon bottle cages fitted as standard.

Trek Supercaliber SLR 9.9 XX AXS Gen 2

Two bottle cages gives the Supercaliber versatility when it comes to longer distance racing.

Trek is still sticking with its extra wide PF92 bottom bracket as it says the stiffness to weight gains from the bigger tube junctions are too good to ignore. The bottom bracket height also raises 10mm to reflect the increased travel and the main pivot position also comes up 10mm in relation to the BB to increase the anti-squat, so the bike pedals better too.

Trek Supercaliber SLR 9.9 XX AXS Gen 2

RockShox has taken over the baton for building the integrated IsoStrut shock.


The heart of the Supercaliber’s 80mm rear suspension is Trek’s unique IsoStrut design. This is essentially a small RockShox SIDLuxe based shock hidden inside a 38mm diameter alloy tube (IsoStrut) that bolts into the top tube at both ends. Then the carbon seat stay head forms a larger tube that slides along the IsoStrut on a bushing borrowed from the RockShox ZEB fork; it has 38mm diameter legs. 

The slider then connects to the inner shock through a slot to stop it rotating, so the whole unit acts as a structural frame member. Hence the increased stiffness.

Trek Supercaliber SLR 9.9 XX AXS Gen 2

Last lap sprints can be powered up with just a twist of the wrist.

Despite claims of it being lighter, the IsoStrut element alone without the seat stay head, bushings etc. is over 100g heavier than a standard SIDLuxe shock. Talking to the Trek design team during testing they assured us that achieving similar stiffness from a conventional linkage system like that seen on the 120mm travel Top Fuel, would incur a significant weight penalty. 

Trek Supercaliber SLR 9.9 XX AXS Gen 2

RockShox SID SL fork is light, supple and racy.

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.

Trek Supercaliber SLR 9.9 XX AXS Gen 2

SRAM AXS shifter pod brings accurate gear changes.


As the model name suggests, there’s a full SRAM XX AXS drivetrain 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 here though. 

Trek Supercaliber SLR 9.9 XX AXS Gen 2

No modern race bike would be complete without a one-piece bar and stem.

Brakes are SRAM’s lightest Level Ultimates with 4-piston calipers. Fox provides the 2-position Transfer SL dropper post which offers a 240g saving over the RockShox Reverb AXS wireless equivalent.

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. 

It’s worth noting that reduced ‘official’ tyre clearance on the SID SL forks mean the 9.9 SLR is the only Supercaliber to come with 2.2in not 2.4in versions of the new Saint-Anne RSL XR tyres. Actual clearance seems fine though, so for most of the test we ran our 2.35in Maxxis Rekon Race control tyres.

Trek Supercaliber SLR 9.9 XX AXS Gen 2

Gen 2 Supercaliber is 1.5º slacker in the head tube and has 20mm more travel than Gen 1.


It might come with a dropper post and the potential to fit a 120mm fork, but the Supercaliber is clearly an XC race thoroughbred dedicated to on course performance not off piste play.

The high degree of anti squat means the suspension compresses less the more power you put in. That’s amplified by the ‘Open’ compression damping mode on the IsoStrut shock being tuned to match the ‘Pedal’ mode on 3 position SIDLuxe shocks. Here, firm equals fast.

Trek Supercaliber SLR 9.9 XX AXS Gen 2

The Supercaliber is not just an accomplished climber.

And while we’re not fans of the wider PressFit bottom bracket from a bearing replacement point of view, it is part of the reason the frame feels very stiff under power. The IsoStrut design clearly plays a part too. Sure, the frame is heavy for an 80mm travel bike, but the 9.75kg (21.5lb) overall bike weight is highly competitive. 

The result is a very positive, ego boosting pedal response that’s fantastic for charging out of corners, putting the boot into other riders on climbs or sprinting away from real or imaginary start lines. Although we rarely used it even on smooth climbs, twisting the TwistLoc remote instantly turns the shock and fork solid for maximum effort attacks or just zero movement psychosomatic efficiency. 

Trek Supercaliber SLR 9.9 XX AXS Gen 2

Loose terrain needs careful power inputs.

Higher anti squat figures inevitably mean the back end is easier to spin out on loose or slippery surfaces if you’re not paying attention. However, it also gives you very clear feedback of what’s happening under the rear wheel so you can meter out power in relation to traction from the fast rolling rather than high traction rubber. 

Once the ZEB bushing in the IsoStrut beds in, this takes around ten hours, the shock is supple enough to respond quickly and fluently to random jank and roots. The tyres are also sturdy enough to stay supportive at lower pressures rather than pinging around. That means while the baseline bike feel is a firmly progressive race tune, it’s much smoother and more connected than a hardtail or the Specialized Epic WC. Fatigue levels are greatly reduced too and any speed gained on rougher terrain is easy to sustain too.

Trek Supercaliber SLR 9.9 XX AXS Gen 2

Trek Supercaliber deserves to be in the racing spotlight.

After switching to the wider rubber the Supercaliber also impressed on more challenging descents and technical sections. It can’t shrug off bigger hits or be ridden as ignorantly as the best 120mm travel XC bikes, but it feels controlled and confident enough to ride aggressive lines fast and accurately if you’re on the ball. The fact the Supercaliber comes with a dropper post as standard makes a world of difference to how confidently most riders will be able to ride it straight away too.


The Supercaliber has a lot of radical shock and frame features but get it on track and it feels like a really sorted, conventional race bike. Where the stiff frame, progressive suspension and increased anti squat all boost ego when you’re putting the effort in. With only 80mm frame travel, it’s definitely firm on bigger, rougher terrain, but it’s predictable and controllable so you don’t have to back off. It’s also comfortable enough that you don’t get beaten up.  At 9.75kg (21.5lb) the overall package is very competitive and performance is excellent. The inclusion of a dropper post is a definite win when it comes to modern XC courses too, although we’d like wider tires and a power meter at this price.


Frame:OCLV SLR carbon, 80mm travel
Shock:RockShox/Trek IsoStrut SIDLuxe
Fork:RockShox SID SL Ultimate, 110mm travel
Wheels:Bontrager Kovee RSL, Bontrager Saint-Anne RSL XR 29x2.2in tyres
Drivetrain:SRAM XX SL Eagle 34t, 175mm chainset, SRAM XX SL AXS T-Type derailleur and shifter pod, SRAM Eagle XS-1299 10-52t cassette
Brakes:SRAM Level Ultimate 4-piston, 160/160mm rotors
Components:Bontrager RSL Integrated OCLV Carbon 750mm, bar and 80mm stem, Fox Transfer Factory SL 125mm post, Bontrager Aeolus RSL saddle
Sizes:S, M, M/L, L, XL
Weight:9.75kg (21.5lb)
Size tested:L
Rider height:
Head angle:67.5°
Seat angle:71.5°
Effective seat angle:74.5°
BB height:327mm
Front centre:735mm
Down tube:
Seat tube:460mm
Top tube:620mm