Trek added a complex suspension design for the latest Slash and it's otherworldly most of the time, but beware of bending that chain guide!

Product Overview

Overall rating:

Score 8

Trek Slash 9.9 X0 AXS T-Type Gen 6


  • • Perfectly tuned suspension and pedalling performance
  • • Stiff chassis never feels harsh and twangy
  • • Much livelier and more reactive than you’d expect
  • • Consistent and neutral ride feel at all trail gradients and speeds
  • • Rear end easily be set up and adjusted to taste 
  • • Frame adjustability and finish is top drawer
  • • Very quiet and well protected


  • • Upper idler and lower guide design brings potential reliability and durability issues 
  • • Own brand parts like Bontrager wheels and tyres are not to my tastes (although carbon wheels get a two-year warranty)
  • • Very expensive
  • • Reverb dropper won’t be long enough for taller riders


I loved the ride quality of Trek’s latest high-pivot Slash, but a bent idler means I’d have to think long and hard about buying one

Price as reviewed:


With high-pivot suspension, mullet wheels and multi-adjustable frame, the latest Trek Slash is about as modern a bike as you’ll find in 2024. It’s more than just trendy though, this sixth incarnation of the famous enduro sled uses tech borrowed from Trek’s Session DH bike to take on enduro terrain, meaning it should come alive when the trail points down.

Trek’s long travel enduro bike has been around for over a decade and always been closely related to the Session, but this latest iteration is the most radical yet and even more DH-optimised. The new model gets more travel and now boasts 170mm travel at both ends, which should stand it in good stead against the best enduro bikes on the market. 

Trek Slash review

Trek has radically overhauled the Slash, adding mullet wheels, adjustable geometry and of course a high-pivot suspension design

Trek Slash need to know

  • Trek Slash Gen 6 switches to a high-pivot suspension design with upper chain idler and lower guide
  • 170mm RockShox Ultimate suspension with Zeb fork and Vivid Air shock
  • Full carbon frame with downtube storage and multi-adjustability
  • SRAM electronics including T-Type transmission and Reverb AXS
  • Mullet wheels with own brand carbon rims and Bontrager tyres
Photo of the Trek Slash 9.8 mountain bike from the side

The previous generation Trek Slash was a simpler suspension design, had 10mm less travel and 29in wheels… it’s still available in Trek’s range too

Trek’s DH DNA

The burlier outlook, extra complexity and additional 10mm of travel bring with it extra heft, which is presumably why Trek still offers the Gen 5 Slash with 29in wheels as a more traditional enduro bike, one that’s lighter and simpler.

However embedded Trek’s DH DNA is though, to be an effective enduro bike the new Slash still has to pedal and climb efficiently and cope with longer rides. The brand’s engineers have built that capability into the suspension and geometry, and also squeezed in a downtube lunchbox for spares and a BITS steerer tube tool to keep you going, if slashing turns turns into crashing berms.

Typically for one of the bigger bike brands, there is a huge range of models and frames. It comes in full carbon fibre, like this blinged-out 9.9 version that’s the best part of ten grand, as well as multiple aluminium frames starting at the much more affordable price of just over 4k.

Trek Slash review

With a high pivot idler and a lower chain guide pulley, the new Slash needs about a mile of chain to link round

Trek’s high pivot idler design

While the Slash has changed year on year, each generation has proven itself to roll smoothly and possess good tracking under braking. In fact, that’s my impression of a lot of the brand’s bikes, including the Trek Fuel EX, which easily earns its place as one of the best trail bikes around.

So the big question: why has Trek bothered adding the extra complexity and drivetrain complications of a high-pivot suspension design and idler, when the Slash rolls so well anyway? Simple really, the brand was after the rearward axle path engineers covet so badly, which lets the back wheel can move in the same direction as impact forces while riding along.

In theory, this translates to more momentum in rough terrain, fewer hook-ups on square-edged hits and a bike that holds pace and stabilises the rider better in the roughest terrain. With the new Slash having the upper idler mounted to the chainstay rather than the front triangle like on many similar-looking designs, this also affords further options for tuning suspension and ride characteristics.

Trek Slash review

Tried and tested ABP still in use on the Slash, the rear pivot is concentric to the axle placement, it’s said to free up the suspension under braking

While the high-pivot aspect might be all-new, plenty of typical Trek touches remain, including ABP (Active Braking Pivot) rear suspension. This sees the chain and seat stays rotating directly around the Boost rear axle on a concentric pivot. It’s also now T-Type compatible for SRAM’s latest electric drivetrains where the rear mech mounts directly to the frame.

Trek Slash review

Trek’s OCLV carbon uses a higher proportion of carbon fibres to resin than normal, to increase strength and reduce weight

OCLV carbon fibre

Trek is one of the few brands still developing some carbon technologies in-house in the States, including the OCLV (Optimum Compaction Low Void) carbon layups. It’s used this approach for years to better compress carbon layers and purge fillers for increased frame strength and impact resistance. Many riders will be glad it’s also stuck with older features like a 73mm BSA threaded bottom bracket with ISCG05 tabs and cable routing that swerves the headset entry many bigger brands are adopting. Trek’s internal cable solution is very neat, totally mutes tube rattle and also allows more space inside the chassis for the down tube’s internal frame storage.

Trek Slash review

Trek’s still happy to punch holes in its head tube on the Slash , and we’re also pretty pleased with that as it means no weird headset cable routing

To further dampen noise and improve chain stability, there’s a chunky, sculpted chainstay protector and a metal guard plate on the interior of the stays where the chain can potentially slap and rub against the carbon. These stays can also fit fat rubber and offer good mud clearance and a mud guard, and there’s more protection behind the BB and under the downtube where removable plastic guards defend against rock strikes and shuttle damage. This 9.9-level carbon frame also has the Knock-Block feature so you don’t bash the fork crowns into the downtube, a magnesium rocker link to save weight and even an impact-resistant laminate under the paint for extra durability.

Trek Slash adjustable geometry

The Gen 6 Slash comes with a 170mm fork that gives a slightly slacker 63.3° head angle, but it’s also rated for up to 190mm fork if you want to go full ‘noughties freeride’ and slack it out further. Trek has your back too if you just want to adjust the head angle without changing the fork, by offering adjustable headset cups aftermarket. There’s even more adjustability in a lower shock mount that allows a switch to 29in wheels from the smaller rear MX wheel format (which is what plenty of Trek’s enduro athletes are already doing; presumably to gain extra rolling speed for competing at UCI EDR events).

Trek Slash review

Geometry adjust is via a flip chip on the lower shock mount, you can also buy an aftermarket angleset to tweak the head angle independently

A 77° seat angle is pretty much spot on for climbing without being too steep to pedal longer distances in comfort, and across a broad range of sizes (including a M/L that will be in the sweet spot for plenty blokes around the 175-178cm mark). The Slash’s chainstays grow in length from just under 430mm on the M to almost 440mm on the XL. Reaches range from 448mm to a rangy 513mm across the same spread, and while the 351mm static BB height sounds reasonably tall, it doesn’t feel at all high when you’re actually riding.

Finally, the lower shock mount also has a further special trick for tweakers where you can flip the leverage rate between less or more progressive. Riding with less ramp up (like I did) offers a plusher feel and a smoother and more supportive mid-stroke, and flipping it to more progressive is for when you’re riding fast, hitting big features and don’t want to bottom out. The more progressive setting also lets you switch to running a more linear coil shock.

High pivot suspension

Controlling the Slash’s travel are a tried and trusted RockShox Zeb fork and the brand’s newer Vivid Ultimate Air shock. The top-level Zeb has the Charger 3.0 damper, Buttercups and 170mm of travel; the exact same amount controlled by the (also top-level) Vivid Air. The 38mm legged Zeb is a totally sorted and very stiff fork many riders might have experience with already, but the Vivid will be new to most (and me) and I found out it’s a very impressive bit of kit.

Trek Slash review

The Vivid Air seems to deliver the kind of plush ride normally reserved for heavier coil shocks

Delving into the Slash’s design, moving the main pivot higher (but not as high as some) also impacts on the suspension in other ways; most notably by increasing the distance between rear axle and front chain ring as the suspension cycles. This can be seen as a negative, because it ups pedal kickback (chain growth), which can feed back into the rider as harshness and inhibit free suspension movement.

Trek has therefore had to engineer an upper pulley wheel (and further complicated chain retention solutions) to negate the effect and retain the benefits of a high main pivot. Essentially, by routing the chain around an idler pulley and controlling the distance between the axle and the high main pivot, the brand can better control any pedal kickback.

On top of this, because the upper idler is mounted to the Slash’s chainstay rather than the main triangle, it also moves relative to the BB and the rear cassette as the suspension cycles. As I understand it, this provides independent control of the anti-squat and chain growth (or shrinkage) outside of axle path and other suspension properties and allows precise tuning of how the bike responds under pedal power and body weight inputs like pumping.

Trek Slash review

The the idler mounted to the rear triangle rather than the seat tube Trek says it can better manipulate the suspension performance

If you’re still taking all this in, as well as this high-pivot set-up, Trek’s still uses its familiar, wraparound, ABP rear axle pivot I mentioned that also helps control anti-rise by partially rotating as the bike reacts to braking forces on the suspension (and how much it wants to extend under braking).

Yes, all this lot together definitely adds complexity, but you’d have to assume it gives Trek’s engineers a potent formula for tuning suspension characteristics exactly how they want it, which is another reason beyond the high-pivot’s bump swallowing rearward axle path capabilities they were keen to go with this design.

Trek Slash review

SRAM Code SLR brakes are brilliant, with power and control in equal measure from the 200mm rotors


For the best part of ten grand, it’d be reasonable to expect not to have to change a single bit of Trek’s 9.9 level kit, but sadly that’s not the case here; especially if you want to be able to keep up with the Slash’s exceptional DH performance.

The worst culprits on the spec sheet are own brand Bontrager tyres that just don’t have enough grip and stability. I’m not sure what’s happened with them as Bonty rubber used to be decent when I tested them five years or so ago. Maybe all the other brands have just come on in leaps and bounds since?

Trek Slash review

Bontrager tyres feel “scary and pingy”, two things you really don’t want on a gnarly descent

The 2.5in wide Bontrager SE 5 and SE6 combo have a decent-looking tread, but the 120tpi casing lacks damping and protection and is far too flimsy for a bike with this much DH capability. Worse still, the rubber feels scary and pingy on wet rocks and roots, to the extent I had to change them out after a day’s riding in the Alps and had a night and day better experience on some new Michelin tyres. Trek’s top enduro racers like Hattie Harnden obviously feel the same and are running Continental tyres with the logos blacked out to race at World Cup level, so you’ll have to spend nearly £150 extra too if you want to charge downhill with maximum confidence.

It doesn’t help grip and control either that Bontrager’s own Line Pro 30 carbon wheels (using the same OCLV tech as the chassis) are very much at the old-school ride feel end of carbon wheels. With a rapid pick up, there’s a razor sharp and quick-to-accelerate vibe a bit like older Enves, but this makes them edgy and harsh on rocky terrain and the Line Pros lack the extra compliance and tracking engineered into the best modern mountain bike wheels. I wound off half a turn of spoke tension on every spoke and added a bit more comfort, but did end up with one nipple on the rear unwinding.

Trek Slash review

I loosened the spokes slightly to get the wheels to feel softer and more compliant

I can’t comment on the feel of the carbon in Trek’s own one-piece bar/stem combo, as a previous tester had cut it down too narrow for me, but it definitely looks cool and is very lightweight if the shape suits you. These one-piece combos don’t make it easy to change stem length or bar shape independently if you don’t like it though.

Putting the power down, SRAM’s latest T-Type transmission with a 10-52t cassette is pretty rock solid and shifts without ever skipping a beat, plus the latest adjustable POD shifter design is the first time I’ve really felt 100% natural with thumb position on SRAM’s electronic shifting since it launched. Basically, after a week in Italy riding every day, it felt weird to use mechanical shifting again, which is testament to POD ergonomics.

One other neat drivetrain aspect is the new solid and stiff XO1 cranks being 165mm for extra ground clearance. These pedal the chain through Trek’s idler and lower MRP guide that demands a longer chain and while it’s unlikely you’ll need to replace it considering SRAM’s top-tier chains are very durable and smooth, the Gen 6 Slash still uses one standard 126-link chain in all sizes except the extra-large, which needs 128-links.

Unfortunately, I did have a significant drivetrain issue with the AXS XO1 T-Type rear mech. It handled getting bashed and scratched like a champ, but the AXS battery got knocked clean off the back (presumably by trail debris) and lost forever somewhere in a forest. Luckily, I’d brought a spare battery away, but this could be a major problem for a race result or holiday with how the battery is mounted exposed at the back and held by a small plastic tab (that snapped on this one). This is clearly an issue SRAM is aware of too, it’s now moved the battery up and inside the mech body on the newer (heavier) GX Eagle T-Type mech for better security.

Trek Slash review

Trek Slash certainly looks the business, with sizing and geometry big enough for almost all riders and trails


The Trek Slash is something of a flawed genius (no Scott pun intended here). It has DH levels of calmness on the descents and actually feels great on the climbs too. The extra complexity of the high pivot suspesnion design and – more importantly – the idler did cause problems though, as you’ll see…


I’ll keep this short and sweet and say Trek’s done a fantastic job with this aspect. Contrary to any expectations of excessive drivetrain drag and a soft feel under power, the latest Slash feels smooth, spritely and efficient. Whether sprinting along the flat or smuggling cranks out of tight corners, the Slash feels positive and also has the enviable ability to crawl up the steepest sections while supporting rider weight evenly and never losing traction or wheel-spinning.

I’ve not ridden them all, but this is still the most efficient pedalling high-pivot bike I’ve tried, even with the big 19t upper idler, X-Sync chainring, lower guide idler and that massive T-Type mech and 10-52t cassette. The chain is quiet and smooth rolling, the suspension never really wallows or bobs on the downstroke and Trek has engineered in just the perfect amount of bite for slippery or loose surfaces like creeping up over little roots or rocks. I reckon the new T-Type SRAM drivetrains helps with this aspect too by being super smooth, stiff and perfectly lined up, so I can’t comment if this efficiency aspect would quite so good with lower tier kit on board.

Even though there’s a sharpness to power delivery comparable to many lighter non-high-pivot rigs, I did find the active back end benefits a bit from flipping the Vivid Air into the locked position for longer climbs on tarmac or smooth gravel fire roads where you don’t need that super-active first touch.

The Slash’s seated climbing position is just about perfect too (within a couple of mm of rail tweaking for personal preference) and not too far forward to be uncomfortable on more flowy terrain or long undulating liaison pedals, which can be an issue with steeper seat angled enduro rigs overly optimised for winching straight up steeps to come back down the same hillside.

Trek Slash review

Smooth trails or rocky steeps, the Slash has the performance and composure to add speed and control


The Gen 6 Slash is marketed around its posh high-pivot suspension design, but it’s not the first thing you notice when riding the bike. Instead it’s the floaty comfort I imagine you’d get riding on moon dust. (I’m not convinced there’ll be trails in space in my lifetime though.) There’s less of a trapdoor feel to the rear end where impacts fall into the suspension equivalent of a black hole and more an isolating. What’s great about it is how the back end is soft and smooth, yet manages to avoid any of that flaccid, bogged-down feel that can make it harder to manual and pump for speed on many similar-looking designs.

Not being a total plough bike isn’t to say either the rear suspension isn’t super active tracking the ground. You can basically achieve anything from comfy sofa cushion to bondage taut with the dials on the new Vivid, and the shock seems to change direction seamlessly and do it all like a very classy piece of kit. As well as the wide adjustment window, RockShox’s DH air shock genuinely feels like a coil spring on ripple hits or little sharp edges in terms of muting trail feedback.

Trek Slash review

There’s more travel at the back end now, but you can make the Slash feel any way you want it – taut and fast or squishy and comfy

Part of the reason for this is the clever ‘Touchdown’ design inside that bypasses the compression damping for the first 10% of the travel. This provides extra sensitivity off the top to stay connected with the floor, but then deeper in the travel, the Slash back-end controls and damps impacts of any size with a muted calmness and still feeds back plenty trail information, rather than just feeling limp and lifeless.

Every single Vivid adjustment parameter is meaningful and noticeable too, so the Slash can be set to feel impressive everywhere from isolating tiny stones and broken surfaces right through to supporting rider weight landing huge drops on rock slabs or slamming deep hollows and compressions.

Before I get too carried away praising the shock, this sense of smooth continuous support is a part of Trek’s neutral and predictable system, and it carries over into the way it pedals and pumps too. Whatever gear you’re in, there’s a rounded platform to push into when cranking to generate momentum and no surging/dipping cycles or bobbing as you pedal harder or at higher cadences.

Trek Slash review

The RockShox Zeb doesn’t have the newest 3.1 damper inside, but it’s still plenty plush enough to match the back end

The rear suspension is also well balanced with the stiff Zeb fork so the bike keeps you centred even in really rowdy terrain or hard cornering g-forces. It’s further enhanced by a well-damped and smooth carbon chassis that never feels harsh in your hands and feet. I’d argue that (much like the best frames, including the Specialized Enduro or the Atherton AM170 I also really rate) Trek’s carbon frame can hold any line through the rough stuff, yet has zero twanginess and never jars the rider unexpectedly or flexes erratically.

Atherton S170

I loved the feel of the Atherton S170, just like the Slash you can set it up easily for the bike park, Alpine steeps or anything in between

In terms of steering and handling, the Slash is also very neutral, but with way more err, slash, than you’d expect turning sharply, so you can really ping and flick in and out of turns. This means it’s more reactive than some bikes that iron out everything in their way and can get a bit wallowey in corners. This attitude extends to the way it jumps and I found you can really carve up jump faces and pop off lips without it ever feeling soggy, even when you have it set up for a very pitter-patter feel at the rear tyre.

One of the best Slash traits is not having any sense of the front end coming light mid turn either, like I’ve experienced on some MX high pivot bikes where rider weight distribution shifts as the bike gets loaded in the corners. In fact, support against body language and inputs through your feet feels just about perfectly balanced against bump swallowing. The Slash keeps working under braking and the rear tyre keeps on tracking above and beyond what you’d expect, so you can brake later and more effectively. Whether this aspect is due the ABP pivot or not, it’s hard to say, but it helps give the bike extra traction on steep trails, so you’re confident attacking on super steep sections.

Trek Slash review

I found the MRP chain guide and lower jocket wheel just too exposed and flimsy, it left me high and dry up a mountain

A Slash too far

So far, so good then, but while the Slash’s ride quality is totally dialled, despite this bike being set up by the factory race team mechanic, I had some serious issues; in particular with chain security and durability of the idler and lower guide set up. And when Trek’s £9,000+ machine left me stranded up a mountain in a way that couldn’t happen on a normal bike, it’s a tough pill to swallow for this much cash.

Riding down a loose rocky trail in Italy, one of two things happened; either a rock got flicked up by the front tyre and ‘punched’ the lower MRP guide or a rock got sucked into the guide from the rear tyre. The resulting impact bent it inwards at 90-degress and wrote off the lower guide and jockey wheel. The lower guide could either be better protected by a bigger clamshell bash guard or it needs a thicker aluminium plate, so it’s hard to bend in the first place.

The aftermarket MRP replacement I used did have a thicker backplate than Trek’s original, so perhaps Trek uses a thinner material to save your frame at the expense of the guide. How you set up this lower idler with a gap of 10-24mm from the bottom of the chainstay to the top of the lower roller affects performance too.

Trek Slash review

Setting up the lower guide is a tricky balancing act, get it just right and you’re flying though

Rotating the guide clockwise increases chainwrap on the chainring, counters lower chain growth and offers better chain retention and rotating the guide further from the frame will improve the overall performance and smoothness of the Transmission system. But, obviously, it’s hard to get any of this or the alignment dead right if you’ve twisted the guide just riding down a rough rocky trail.

Also, once the MRP guide was bent out of line, I had to run a home-made roller guide while awaiting a replacement. I then had multiple issues with the upper idler stuffing the chain between the jockey and the frame that required an allen key each time to claw it free again. None of which was exactly ideal. Trek has now designed a rolling revision to make the teeth on the upper idler longer and help stabilise the chain, but my test bike didn’t have that yet to check if it makes a big difference or not. Either way, if the same thing happened to you during a race or holiday, it would be a terminal problem and while you might be able to ride with a shortened chain and no lower idler, I didn’t try this and suspect it wouldn’t exactly help with chain retention.

Yes, this lower idler caused me a big issue, but so far I have thousands of metres descending on the replacement without any problems and I’ve kind of forgiven the Slash a bit as it’s so much fun to ride. It’s a bike with all the safety and security of a big super enduro bike that can really truck on calmly through proper chunky terrain. But it’s still very easy to ride fast and maintains a load of the sensory stimulation of a ‘regular’ 160mm-ish enduro bike if you set it up a little bit tighter and firmer, which all means it can offer a lot of positives to a lot of riders.

With smooth, continuously-supportive suspension and extra smoothness off the top, the DH performance is a cut above most rivals though and Trek’s overall frame feel, adjustability and handling are all also top notch.

Trek Slash review

Bend it even slightly, and the MRP jockey wheel and guide won’t keep your chain on reliably

The elephant in the room though is this is only with the Slash working as intended, and the added complexity of the high-pivot design introduces extra potential issues that caused headaches in testing and could for you too in the unpredictable world of enduro riding and racing in natural terrain.

I also wasn’t a fan of some of the Bontrager components, including the stiff carbon wheels and flimsy tyres, so, while the new Slash’s ride quality is up there with the very best enduro bikes, I’d find it hard to part with this much of my own hard-earned cash for this 9.9 model.

Trek Slash review

Trek Slash: when it’s good, it’s really good


While the latest Trek Slash’s looks radical on paper, it’s actually one of the most well-rounded and balanced enduro bikes once you’re on the trails and basically feels much like a ‘normal’ bike. It's blisteringly quick and composed on the descents, and climbing is effifient, spritely even. There are some issues though, the spec isn't absolutely nailed, as I'd expect from a bike that's nearly £10,000, and the idler proved itself unreliable during my testing period.


Frame :Trek OCLV carbon HP w/internal storage
Shock :RockShox Vivid Air Ultimate 170mm travel
Fork :RockShox Zeb Ultimate Charger 3 170mm travel
Wheels :Bontrager Line Pro 30 carbon w/Rapid Drive 108 hubs. Bontrager Team Issue tyres 29in x 2.5in front SE6 and 27.5 x 2.5in rear SE5 w/Core Strength sidewalls
Drivetrain :SRAM XO Eagle Transmission, SRAM XO AXS POD Ultimate, T-Type DUB crank 165mm, XO Eagle rear mech and 10-52t cassette.
Brakes:SRAM Code SLR 4-pistoon w/ 200mm 6-bolt rotors F&R
Components :RockShox Reverb AXS 170mm dropper, Bontrager Arvada saddle, Bontrager RSL integrated bar stem w/35mm equivalent stem length and 820mm wide bar
Weight :16.2kg (35.7lb) 
Sizes :M, M/L, L, XL
Size Ridden:18.5in (Medium/Large)
Rider Height:176cm
Head angle:63.3°
Seat Angle:73°
Effective seat angle:77.4°
BB height:350mm (MX setting)
Front Centre:821mm
Seat tube:420mm
Top tube:606mm