Dan & Ben review the 2021 Trek Slash

Trek’s flagship enduro pinner, the Slash, is receiving a major and welcome overhaul for 2021. As the spiritual successor to the Remedy 29, the current Slash was released over four years ago. In that time the enduro racing scene has changed considerably. No longer are 29in wheels looked upon with concern and disdain. Nowadays, you’ll be hard-pressed to find an EWS team that isn’t rolling on 29in wheels. As the sport has professionalised, we’re seeing athletes train harder, race times get tighter, and courses that wouldn’t be out of place at a World Cup downhill race. Unlike DH racing though, enduro racers have to back up those race runs over multiple stages, often over multiple days, with hundreds and thousands of metres of climbing between the start and finish. Oh, and they’re regularly racing those trails blind too.

Watch our video review of the 2021 Trek Slash 9.9 here!

Trek Slash overview

Given the evolving demands of enduro racing, enduro bikes need to evolve too. Taking on board these changes, the new Trek Slash has had a 10mm lift in travel at both ends, and now features a 170mm fork matched to 160mm of rear wheel travel. Following requests from Trek’s EWS athletes, it also gets a bit slacker and longer as expected, which is to help it cope with the gnarlification of modern day enduro racing.

All of that is built around a brand new chassis that features in-built storage, a new Knock Block system, and a serious amount of battle armour. Along with the unique rear shock and adjustable geometry, Trek is making use of every tool in its disposal to produce what it says is the fastest and most technically proficient Slash yet.

For the past month we’ve been testing the top-end Slash 9.9 to see how all of those changes play out on the trail, and whether this newly refocussed enduro race bike is now more of a one-trick-pony. Before we get to our ride impressions though, let’s take a detailed look at what sets the Slash apart from its predecessors and its contemporaries.

There’s a new custom shock

At the heart of the new Slash is a unique rear shock that Trek has co-developed alongside the gurus at RockShox. This shock is currently exclusive to Trek for 2021, and it’ll come on all of the Slash models in Australia, bar the cheapest Slash 7.

On the outside, it doesn’t look dramatically different. It’s essentially a Super Deluxe Ultimate shock, which features adjustable air pressure, air volume, rebound and compression damping. On the inside you’ll find the Trek-designed Thru-Shaft damper, along with some magic sauce the two brands have cooked up together.

Why Thru-Shaft?

Thru-Shaft itself isn’t a new technology in itself. Trek first introduced the Thru-Shaft damper design back in 2017, where it debuted on high-end Fuel EX, Remedy and Slash models.

In essence, Thru-Shaft eliminates the traditional Internal Floating Piston (IFP) that is found inside most rear shocks. The IFP is a sealed piston that sits at the base of the shock underneath the oil chamber. The job of the IFP is to separate the damper fluid on one side, from a small nitrogen-charged chamber on the other side.

Why do we need an IFP in the first place? Firstly, that gas-charged chamber is necessary to accommodate fluid expansion as the oil heats up. Secondly, it’s there to handle the change in volume of the oil chamber as the shock is compressed. When the shock is compressed, the main damper shaft is introduced into the oil chamber, and the further it goes in, the more room it takes up. To compensate for that increase in volume, the IFP is able to slide and compress the nitrogen-charged chamber behind it. As the shock rebounds, the IFP then pushes back on the oil chamber.

But in Trek’s Thru-Shaft shocks, there is no IFP. Instead, the damper shaft runs all the way through the oil chamber. And during compression, the damper piston exits the shock completely – you can see the silver rod emerging from the base of the shock as it goes through the travel. Since the damper piston no longer impacts on the volume inside the oil chamber, there is no need for a traditional IFP.

And what about fluid expansion? That’s what the piggyback reservoir is for – it’s a big ol’ thermal compensator that handles the fluid expansion as the oil heats up in the shock.

But in Trek’s Thru-Shaft shocks, there is no IFP. Instead, the damper piston runs all the way through the oil chamber. And during compression, the damper piston exits the shock completely – you can see the silver rod emerging from the base of the shock as it goes through the travel.

The main driver for the Thru-Shaft design is all about reducing stiction and making the shock movement as slippery as possible. A normal IFP uses seals, and those seals need to slide smoothly up and down the the inside of the shock’s stanchion. Because of the high-pressure environment the IFP lives in, it’s likely to experience stick-slip during changes of direction. By removing the IFP entirely, the Thru-Shaft damper reduces stiction and this stick-slip effect, improving the damper’s sensitivity and its willingness to change direction quickly. On the trail, it simply results in a more responsive and buttery-feeling to the rear suspension – something we’ve noted on the Remedys and Fuel EXs we’ve tested in recent years, including our most recent long-term test bike.

RE:aktiv begone

While the Slash’s new shock carries over the Thru-Shaft concept, one of the big differences is that it no longer uses the RE:aktiv valve on the main damper piston. Instead you’ll find a standard shim valve on the main piston (which differs from an off-the-shelf RockShox shock), which Trek has moved to in favour of more gluey descending-oriented damping performance. While the RE:aktiv damper piston does provide excellent pedalling support, and will continue to be used on the Fuel EX, the new Slash is placing a greater priority on traction and high-speed control, and it’s claimed that a standard shim valve arrangement is the best solution for this application.

The second key difference with the custom Super Deluxe Ultimate shock is found in its damper adjustments. The rebound dial is much smaller and located on the side of the shock, and it now features numbers to assist with tuning. There’s a two-position lever that allows the rider to toggle between open and firm settings.

On top of the lever is a separate adjuster that allows you to tune the low-speed compression damping of the open mode. The blue cam gives you three compression settings: -1, 0 and +1. According to Trek and RockShox, this adjuster is all about fine-tuning the shock’s response to rider inputs, depending on the terrain at hand. So you can firm up the feel of the shock to provide more support for pedalling and riding smoother bikepark type trails, or soften it up for riding steep and rooty trails where you want maximum traction. Consider it as a wet/dry adjuster. Regardless of that setting though, it’s claimed that the shock’s high-speed compression circuit remains completely independent, and it’s in here where Trek and RockShox have been cooking up a little extra special sauce.

The third big difference is in the shock’s air can itself. RockShox states that stiction has been lowered for smoother performance, while the negative spring volume has been increased to create a more progressive spring curve. In fact, it’s claimed to be more progressive than the current MegNeg design, which basically eliminates any need for a MegNeg hop-up. There’s the option to tune with volume spacers too, which we’ll get onto in a bit.

Frame features

Aside from the custom shock, there are big changes afoot in the Slash chassis too. And when we say big we mean it literally – the Slash now takes a 34.9mm diameter seat post. This allows Trek to build a fatter, stronger and shorter seat tube, which provides greater compatibility with long-stroke dropper posts.

To go with it, Bontrager is rolling out a new 34.9mm Line Elite dropper post. The bigger diameter chassis promises increased strength and stiffness, and the post gets a whopping 200mm of travel on the longest option. Internally, the MaxFlow is said to provide faster compression and rebound for slicker performance.

No Super Boost needed

Looking at all the other key mounting points on the Slash frameset, it’s clear that Trek has made a concerted effort to stay away from anything too edgy standards-wise.

While some other brands have adopted the newer Super Boost 157x12mm hub standard for their long travel 29ers, Trek is sticking with the Boost 148x12mm standard that it invented and launched back in 2014. However, by employing the wider 55mm chainline that’s now on offer from both Shimano and SRAM (which pushes the chainring out a further 3mm over a traditional Boost drivetrain), Trek’s engineers say they’ve been able to get all the necessary clearances without having to resort to Super Boost. And they’ve done it too – there’s room for a 34T chainring and a 29×2.5in tyre, even with the Slash’s impressively short 435mm chainstays.

Common sense has prevailed elsewhere too. No longer will you find a press-fit bottom bracket cups. Instead, the Slash gets a 73mm threaded BB shell, which is surrounded by ISCG 05 chainguide tabs.

Common sense has prevailed elsewhere too. No longer will you find a press-fit bottom bracket cups. Instead, the Slash gets a 73mm threaded BB shell, which is surrounded by ISCG 05 chainguide tabs.

The dropouts utilise a SRAM UDH derailleur hanger on one side, and 180mm post-mount brake tabs on the other. For the true gravity enthusiasts, it’s worth noting that the Slash is cleared for use with up to a huge 220mm disc rotor. And while the rear shock is a custom jobby, the size isn’t – most aftermarket metric shocks will fit in its place, including coil shocks.

Secret storage

Brought over from the latest Fuel EX, the Slash now gets integrated downtube storage. What’s impressive is that you’ll get that sane downtube trap door on the alloy frames too. For the alloy Slash, the downtube is hydroformed with a depression around the storage door, before the door is then cut out of the tube. Apparently it’s a very difficult process to achieve on an alloy frame, which is probably why we haven’t seen it on any other brand.

The trapdoor itself is identical between the alloy and carbon frames, and it’s the same as what you’ll find on the Fuel EX. A discreet lever opens and secures the latch, and inside the cavity is a soft tool roll that’s designed to hold a spare tube, levers and CO2. The bottle cage is included with the bike, and Trek says every frame size, including the Small, will fit a bottle without drama.

A bonus of the trapdoor design is that it provides you access to the internal gear, dropper and brake lines. The cables and hoses are zip-tied to the underside of the door, which helps to minimise vibration and noise.

Knock Block 2.0

Trek has also updated its headset steering limiter system, called Knock Block 2.0. Addressing our criticism of the previous design, Trek has increased the available steering radius, so you now get 144° of rotation.

What’s interesting though, is that the Knock Block system isn’t actually necessary anymore. That’s because the downtube no longer uses the StraightShot profile of the old frame – it features curves at both ends, which means the fork crown no longer contacts the downtube during a full rotation.

We’re told that the designers decided to keep the Knock Block system as it doesn’t really impact the riding experience, and it helps to protect the brake lines, shift and dropper cables in the event of a bar-spinning crash. If it still bothers you though, the Knock Block can be removed entirely.

Geometry

The Slash’s geometry was no doubt due for an update, and Trek has willingly obliged. However, while the designers wanted to address the needs of Trek’s EWS racers, they also wanted to retain the comfort, balance and agility that made the previous version such a popular and accessible bike.

As such, the head angle kicks back a degree, and the reach has grown by 15-40mm depending on the frame size. The seat tube angle (both actual and effective) has increased by two degrees, which helps to shift the pilot further forward on the bike, without pushing them so far forward as to put excessive weight onto the wrists and arms.

Trek is producing five frame sizes in the Slash, from Small through to X-large. All frame sizes are now built around the same stubby 35mm stem length, which aims to keep the front-end steering consistent regardless of rider height.

Also found on every frame is the familiar Mino Link, which is located in the upper seatstay pivot. The Slash comes set from the factory in the Low position, but flipping the link into the High position will lift the BB height by 7mm and steepen the head and seat angles by 0.5°. Here are lots of numbers for those who want them;

Trek Slash price & specs

If you’re digging the new Slash vibe, you’ll be pleased to know that stock is available as of right now through Trek’s dealer network. In Australia, we’ll see four models come to our shores – two with carbon frames, and two with alloy frames. Additionally, you’ll be able to get a standalone frameset too – Trek Australia will be offering a Slash frameset in both carbon and alloy variants.

Read on for a closer look at each of the four complete bike options, followed by our ride impressions from testing the top-end Slash 9.9 X01.

2021 Trek Slash 9.9 X01

• Frame | OCLV Mountain Carbon Fibre, ABP Suspension Design, 160mm Travel
• Fork | RockShox ZEB Ultimate, Charger 2.1 RC2 Damper, 44mm Offset, 170mm Travel
• Shock | RockShox Super Deluxe Ultimate, Thru-Shaft 3-Position Damper, 230×62.5mm
• Wheels | Bontrager Line Elite 30, OCLV Carbon Rims, 30mm Inner Rim Width
• Tyres | Bontrager SE5 29×2.6in Front & SE4 2.4in Rear
• Drivetrain | SRAM X01 Eagle 1×12 w/X01 30T Carbon Crankset & 10-52T GX Eagle Cassette
• Brakes | SRAM Code RSC 4-Piston w/200mm Rotors
• Bar | Bontrager Line Pro, OCLV Carbon, 35mm Diameter, 27.5mm Rise, 820mm Wide
• Stem | Bontrager Line Pro, Knock Block, 35mm Length
• Seatpost | Bontrager Line Elite Dropper, 34.9mm Diameter, Travel: 100mm (S), 150mm (M/ML), 170mm (L), 200mm (XL)
• Available Sizes | S, M, ML, L, XL
• RRP | $11,499 AUD

2021 Trek Slash 9.8 XT

• Frame | OCLV Mountain Carbon Fibre, ABP Suspension Design, 160mm Travel
• Fork | RockShox ZEB Select+, Charger 2.1 RC Damper, 44mm Offset, 170mm Travel
• Shock | RockShox Super Deluxe Ultimate, Thru-Shaft 3-Position Damper, 230×62.5mm
• Wheels | Bontrager Line Elite 30, OCLV Carbon Rims, 30mm Inner Rim Width
• Tyres | Bontrager SE5 29×2.6in Front & SE4 2.4in Rear
• Drivetrain | Shimano Deore XT 1×12 w/XT 30T Crankset & 10-51T Cassette
• Brakes | Shimano Deore XT 4-Piston w/203mm Rotors
• Bar | Bontrager Line Pro, OCLV Carbon, 35mm Diameter, 27.5mm Rise, 820mm Wide
• Stem | Bontrager Line Pro, Knock Block, 35mm Length
• Seatpost | Bontrager Line Elite Dropper, 34.9mm Diameter, Travel: 100mm (S), 150mm (M/ML), 170mm (L), 200mm (XL)
• Available Sizes | S, M, ML, L, XL
• RRP | $8,999 AUD

2021 Trek Slash 8

• Frame | Alpha Platinum Alloy, ABP Suspension Design, 160mm Travel
• Fork | RockShox Lyrik RC, Charger 2 Damper, 42mm Offset, 170mm Travel
• Shock | RockShox Super Deluxe Ultimate, Thru-Shaft 3-Position Damper, 230×62.5mm
• Wheels | Bontrager Line Comp 30, Alloy Rims, 30mm Inner Rim Width
• Tyres | Bontrager XR5 29×2.6in Front & XR4 2.4in Rear
• Drivetrain | SRAM GX Eagle 1×12 w/Descendent 6K Eagle 30T Crankset & 10-52T Cassette
• Brakes | SRAM Code R 4-Piston w/200mm Rotors
• Bar | Bontrager Line, Alloy, 35mm Diameter, 27.5mm Rise, 820mm Wide
• Stem | Bontrager Line, Knock Block, 35mm Length
• Seatpost | TranzX Dropper, 34.9mm Diameter, Travel: 100mm (S), 150mm (M/ML), 170mm (L), 200mm (XL)
• Available Sizes | S, M, ML, L, XL
• RRP | $6,299 AUD

2021 Trek Slash 7

• Frame | Alpha Platinum Alloy, ABP Suspension Design, 160mm Travel
• Fork | RockShox Yari RC, Motion Control RC Damper, 42mm Offset, 170mm Travel
• Shock | RockShox Deluxe Select+, 230×62.5mm
• Wheels | Bontrager Line Comp 30, Alloy Rims, 30mm Inner Rim Width
• Tyres | Bontrager XR5 29×2.6in Front & XR4 2.4in Rear
• Drivetrain | SRAM NX Eagle 1×12 w/Descendent 6K Eagle 30T Crankset & 11-50T Cassette
• Brakes | SRAM Guide T 4-Piston w/200mm Rotors
• Bar | Bontrager Line, Alloy, 35mm Diameter, 27.5mm Rise, 820mm Wide
• Stem | Bontrager Line, Knock Block, 35mm Length
• Seatpost | TranzX Dropper, 34.9mm Diameter, Travel: 100mm (S), 150mm (M/ML), 170mm (L), 200mm (XL)
• Available Sizes | S, M, ML, L, XL
• RRP | $5,299 AUD

Testing the 2021 Trek Slash 9.9 X01

With its metallic orange paint job, the Slash 9.9 X01 bares a resemblance to the distinctive Tiger Mica colour of Holden’s VU Commodore SS ute. We’d say the finish is just a tad classier here though, and indeed the Slash impressed as soon as it was pulled out of the box. It wasn’t too much of a strain to do so either – this big travel 29er tips the scales at a respectable 14.56kg.

That’s with the tyres setup tubeless, and we’ve gotta give props to Trek for the fact that the bike arrives genuinely tubeless ready – TLR strips and valves are pre-installed, and two bottles of sealant are included. Just remove the valve cores, squirt in the sealant, inflate and away you go. Nice!

Being the poshest model that comes to Australia, the Slash 9.9 X01 comes decked out with plenty of high-end toys including the new RockShox ZEB Ultimate fork, SRAM X01 Eagle shifting, powerful Code RSC disc brakes, and a 170mm travel dropper post on our Large test bike. There’s plenty of carbon to be found too – the crank arms, handlebars and rims are all made of plastic-fantastic.

Speaking of, both the front triangle and back end are crafted from Trek’s OCLV Mountain carbon fibre, with a magnesium rocker link being the only main metal component of the frame. It leads to an impressively low weight – including the rear shock and hardware, Trek says you’re looking at just 3.12kg for a carbon Slash frame. It’s quite a bit lighter than the alloy version, which is claimed to weigh 4.32kg.

Fit & sizing

We chose a Large size Slash to suit our 181-183cm tall testers. Dan; an accomplished enduro racer who currently rides a Specialized Stumpjumper EVO Carbon in the S3 size. And Ben; a downhiller reborn as an XC/trail pinner who rides a Large-size Trek Top Fuel.

Two different perspectives from two different testers. Dan; an accomplished enduro racer who currently rides a Specialized Stumpjumper EVO Carbon in the S3 size, and Ben; a downhiller reborn as an XC/trail pinner who rides a Large-size Trek Top Fuel.

Both riders were quickly at home with the Slash and its healthy 486mm reach, despite the very short 35mm stem. However, the huge 820mm ape-hangers didn’t last long and were soon chopped down to a more tree-friendly 780mm.

The saddle was also slid as far forward on the rails as it could go. With the saddle height set at 770mm, the seat angle measures out pretty close to the claimed 75.7° (in the Low geometry position). Sliding the saddle forward for our long-legged testers helped steepen it closer to 78°.

There were few complaints in the fit department – the Bontrager Arvada saddle is excellent, and the lock-on grips are nice and tactile, without being offensively so. They do use dual locking clamps, and while the outer collar is smoothly tapered, you can still feel it underneath your gloves if you run your hands wide on the bars. That said, the metal ends have proven to be much more durable than single-locking grips that have rubber ends.

Setting up the Slash

Kudos to Trek for its brilliant suspension setup calculator, which provides a reliable baseline for getting the fork and shock setup for your weight. Combined with the anodised sag gradients on the ZEB fork and Super Deluxe shock, setting up the Slash is made that much easier. We followed the recommendations for our 80kg testers, and both the pressures and rebound settings were pretty much spot on. For reference, Trek recommends 30% sag on the shock and 15% for the fork when sitting stationary on the bike.

There is further tuneability to be had with volume spacers. The ZEB comes with a single Bottomless Token inside, and that suited us fine. The rear shock comes with zero tokens inside, and that also worked well. However, you can add one volume spacer to the shock’s negative spring to make it more linear. Conversely, you can add up to three volume spacers in the shock’s positive spring if you want more progression. That’s probably something only the heaviest of riders will investigate, since the Slash has quite a progressive spring rate to begin with – we never experienced a harsh bottom-out with the stock settings.

Does it get any smoother than this?

Easily the standout attribute of the new Slash is just how plush and controlled the suspension is. We were expecting that from the ZEB Ultimate, as we’ve already tested it separately. It’s a banging fork, with superb suppleness, huge torsional rigidity and steering accuracy that makes it an excellent match for the Slash’s capabilities. It’s the rear suspension that really blew us away though, with a level of off-the-top sensitivity that sees the shock ease into its travel the moment you push down on the saddle.

That activity plays out all the way through the travel too. Trek says the Thru-Shaft damper design eliminates the ‘nose’ of a standard IFP design, and we can believe them. So little force is required to get the shock moving, and it changes direction seamlessly, offering faster reactivity under both compression and extension. Whether it’s copping a square-edge rock at speed, cornering over off-camber washboard bumps on a fast fireroad descent, or skimming across more granular terrain on a loose traverse, the back end maintains a high level of contact with the terrain, boosting grip and confidence levels.

Previous Thru-Shaft shocks have proven to be slippery performers, but now that Trek has ditched the RE:aktiv valve in favour of a more conventional shim stack valve, it’s taken that damping performance to a new level. It’s bloody impressive stuff.

Thanks to the extremely active and supple suspension performance, the Slash is hugely stable in rough terrain. Sure the geometry is dialled, but it’s the suspension on this bike that really encourages you to push hard in technical terrain, knowing the bike will stay composed and stable. It’s a fine example of a bike that rides well beyond the numbers in a geometry chart.

It’s not just a monster truck

From first impressions, our testers initially thought the Slash would be more of a point-and-plow kind of bike. Sure, you can totally ride this way with confidence and let it steamroll down the trail. But where it surprised most was its inherently playful nature. The short chainstays definitely contribute in this regard, and while the shock is extremely sensitive, your feet don’t get lost in a gooey pile of over-damped syrup. That’s the new air spring at play, which delivers fantastically usable mid-stroke support. That responsive attitude encourages you to get creative, try different lines and gap sections of trail.

It’s also a really fun bike to slide around and let the rear hang out when things get loose, giving it a character that is often lost in long travel enduro race bikes. We found the Slash very composed in the air, with the generous travel and progressive end-stroke providing a cosseting return to earth. You can get away with a lot of mistakes while riding this bike, and have an absolute riot doing so.

But where it surprised most was its inherently playful nature. The short chainstays definitely contribute in this regard, and while the shock is extremely sensitive, your feet don’t get lost in a gooey pile of over-damped syrup. That’s the new air spring at play, which delivers fantastically usable mid-stroke support. That responsive attitude encourages you to get creative, try different lines and gap sections of trail.

Given how big and slack it is, we were also really impressed with the Slash’s climbing ability, particularly when things got rough and technical. The buttery shock performance keeps the rear tyre digging for traction, and the low-slung top tube gives you room to manoeuvre. Add in the low gearing from the 30T chainring and 52T sprocket out back, and there’s some serious grunt on offer for muscling your way up choppy ledges, roots and blown-out moto ruts.

The active suspension does mean you’re best to stay in a seated position on smoother climbs though. Stand up to mash the pedals, and Bob will join the party. There’s always the lockout lever, but our testers only ever used it on the road or the smoothest of fireroad climbs – it’s too firm for actual trail riding, and it’s low down enough that it’s a pain to regularly switch back and fourth between smooth and rough sections.

You can tighten things up by flipping the low-speed compression dial into the firmer +1 position though. And because the shock is so supple, it’s possible to run slightly higher pressures to lift the ride height, without sacrificing that much small-bump sensitivity. Flipping the Mino Link into the High position will also help with climbing performance by steepening the effective seat tube angle, while getting you a bit more pedal clearance too.

So stealthy, so quiet!

Modern bikes are getting very good at dampening out noise, but there’s always something that ruins the serenity. Rattly brake pads, a flappy cable, a creaky bearing. Not the Slash though – our test bike developed no play, and no noise all throughout the test period. Just blissful, quiet performance with the sound of tyres rumbling through the forest.

On that note, we love how well thought out the protection on this bike is. The gear cable is shielded underneath a thick chainstay guard, which is textured to dampen chain slap. There’s another strip of rubber on the inside of the drive-side seatstay to eliminate chain contact, and Trek has even put a metal plate below the disc calliper to prevent the rotor from scratching the paint. Brilliant!

This bike is seriously quiet, thanks to carefully managed cabling and a plethora of body armour designed to dampen chain slap and rock strikes.

Those who ride on trails with lots of loose rock will know the importance of downtube protection. It only takes one rock kicked up by the front wheel to lay a crack in a lovingly engineered carbon downtube – we know, it’s happened to us enough times on other bikes. On the Slash, the underside of the downtube is almost entirely covered by two thick, rubber-lined armour plates. As well as giving greater rock strike protection, the extended coverage is also useful for hoisting your bike over the back of a tailgate on shuttle day. The big plastic armour plates are screwed into the frame, so it’s possible to replace them, or remove them if you desperately want to show off more of the Commodore SS paint job.

As well as giving greater rock strike protection, the extended coverage is also useful for hoisting your bike over the back of a tailgate on shuttle day.

The MRP chainguide with its lower bash plate is another handy addition, and the scratches and dings it’s collected from many trail missions attest to its worth. As for the Knock Block? Our testers never noticed it was there, so we’d be happy to leave it in place. It does mean you could trim the cables and brake line to be quite short to neaten up the cockpit, without fear of them being ripped out in the event of a crash.

What could be improved?

Despite Trek’s talk of keeping things balanced and approachable on the Slash, we do think the designers could have gone a lick steeper on the seat tube angle. We’re also not talking about going vertical – an extra degree would do nicely. The Slash is slightly steeper than the Fuel EX (75.6° vs 75°), but because the Slash has more travel and a more active suspension design, the dynamic seat angle is more affected on the climbs as the shock sinks into its travel.

Yes, a steeper seat angle pushes more weight onto your hands. And yes, it’s generally less comfortable for rolling along on more intermediate terrain. But a bike of this travel is generally going to be ridden on bigger and steeper terrain, where horizontal bimbling is less of a consideration.

That being said, the Bontrager Arvada saddle has a usefully long clamping area on its rails, and our testers were able to get into a comfortable position with the saddle slammed all the way forward. The top tube length is quite long on this bike, so the cockpit never felt too cramped even with the saddle in that position.

The takeaway point? The seat angle ain’t a dealbreaker – there’s adjustment there, so use it if you want to get your hips further the cranks. And if you really want to prioritise climbing performance, then you can always flip the Mino Link into the High geometry position.

The Slash is the third Trek we’ve tested with downtube storage, and thankfully this one didn’t have the rattling issues of the last bike. It’s fundamentally a great idea, and the included tool roll is a nice touch – just make sure you use a lightweight inner tube, as a standard tube won’t leave you any room to fit tyre levers or CO2.

On that note, the width of the trapdoor is quite a bit narrower than a Specialized SWAT door (40mm vs 52mm). That 12mm difference makes it quite a bit trickier to fit bulkier items and XL burritos, so it takes a bit more thought and creativity for packing your haul.

While we’re throwing ideas into the wishing well, it’d be great to see the Slash 9.9 come with Bontrager’s new BITS tool system inside the fork steerer tube. That way you could more easily ditch the backpack, knowing that you’ve got all the basic tools and spares with you, hidden in the bike.

Component highs & lows

Overall the Slash 9.9 X01 has impressed us with a great overall package. The suspension, brakes, drivetrain, wheel and tyre combo all support its nature of being a hard-charging bike.

The rear shock is super impressive, being really smooth and supple with no discernible stiction. This translates to amazing small bump response. Coupled with the equally smooth new RockShox ZEB, once set up the bike feels stupendously plush and balanced. When air-sprung forks and shocks are this good, we’re not sure why you would choose heavier, and less adjustable coil suspension.

The Bontrager Line Elite 30 wheels were also a standout. These have recently been redesigned with a new carbon rim profile that’s said to be almost twice as strong as its predecessor. And we’re happy to report that they’ve withstood many jarring interactions with square edge rocks, and are still in one piece. Weighing in at 2,071g, they’re a couple hundred grams more than the Line Pro 30 wheels we have on test separately, but they do get more readily available J-bend spokes, and they still feature the super buzzy Rapid Drive 108 hubs. They also get that 2-year crash replacement deal, if you do manage to toast a rim.

The Bontrager Line Elite 30 wheels are a standout, and the SE5/SE4 tyre combo have been equally impressive, with great grip and decent rolling resistance.

The Bontrager SE5/SE4 tyre combo was equally impressive, with great grip and decent rolling resistance. The rear tyre does look a bit minimal and comes in quite light on the scales at just 919g (the front tyre is 1,059g), but it held up really well in some chunky terrain, suffering a single tiny cut in the sidewall that was easily sealed with a plug. If this were our bike, we’d be putting an insert into the rear tyre anyway.

The Line Elite dropper post seems marginally quicker in action compared to Bontrager’s previous droppers, but it’s still a ways off the light and smooth action of a Fox Transfer or BikeYoke Divine. The lever shape is good though, and overall it’s performed without hassle. We’ll be interested to see how it fares after a full season of abuse.

Flow’s Verdict

The new Trek Slash is one mighty impressive bike. It packs a load of punch, with the big chassis, newly slackened geometry and burly parts spec working up a thirst for high-speed drama. Its punch is delivered inside a velvety smooth glove though, thanks to the outrageously plush suspension that brings comfort, poise and control to the most chundery of trails. Paired to the superb ZEB up front, this bike just oozes confidence.

As descending really steep and gnarly shit has become the raison d’être for the modern enduro bike though, we were worried that Trek would turn the Slash into a pro-only machine. Our doubts proved unfounded though, and that is indeed the biggest surprise of this bike.

Yes it’s a 29er with 170/160mm of travel and a 64° head angle, and it’ll absolutely steamroll the trail if you let it. But it isn’t a tank. It’s comfortable, reasonably efficient, and it actually climbs technical stuff well. We’d have no qualms taking it on bigger all-day missions.

It’s also playful, chuckable and willing to get airborne. And it’s this all-round competence makes the Slash much more versatile than we expected. We had a blast riding this bike, even when the many of our rides might not have warranted such a big travel bike. But when there are so few downsides, we kept asking ourselves; why wouldn’t you want that extra travel?