The Long Haul

2021 Trek Slash 9.9 XO1 - Full Review

Photos Deniz Merdano (unless noted)
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In this time of heavy EWS interest and influence, it seems that bikes like the Trek Slash, Specialized Enduro, and Santa Cruz Megatower, to name just three, are the flagship off road bikes for these and many other companies. They may not sell the most units world wide, but they seem to get the most attention and these companies devote a lot of engineering horsepower to making them ride as well as possible down UCI DH worthy terrain, without deeply compromising pedalling efficiency. It's a monumental task but 'Enduro' bikes have been making significant leaps forward of late, with geometry in particular, resulting in bikes that do almost everything very well. As luck would have it, these are perfect 'North Shore XC' bikes for many of us, and there's never been a time with as many great bikes to choose from for the challenging terrain many of us like to ride.

The Slash is one such flagship, but unlike much of the competition, Trek has trickled the bike all the way down to moderately sane prices with aluminum models. In fact you can buy a complete Slash for 4500 CAD or 3500 USD, which is hundreds of dollars less than the carbon frame alone with a rear shock (or you could before COVID that is). This complete version, with a set of Bontrager Line Elite 30 Carbon wheels, sells for 11050 CAD or 8500 USD. For more on the complete spec., and a comprehensive price list, check my first look article here.


The sturdy Slash frame combined with the 38mm stanchions on the RockShox ZEB Ultimate fork boosted my confidence heading into rock faces with uncivilized endings. Like this one.

Saying my relationship with the Slash 9.9 XO1 got off to a troubled start would be an exaggeration, but a couple of issues stopped us from taking things to the next level, despite most elements aligning nicely. My most immediate concern was related to the slack actual seat angle. Trek's geometry chart measures the effective seat angle at a thoroughly modern 75.6º* for the 19.5" size large frame in the low/slack position. Unfortunately that only tells part of the story.

*The measuring convention for the effective seat angle is to raise the saddle so the top of the post is level with the top of the head tube and then measure the angle from the centre of the bottom bracket to the middle of the top of the post in relation to the ground while the actual seat angle is the angle of insertion of the seat post


The issues I had with the slack actual seat angle (vs. the effective seat angle) won't affect most riders. If you have disproportionately long legs, but if you do you may need to install a longer dropper and slide your saddle forward a little.

Unlike most manufacturers, Trek is transparent about the actual seat angle, which is listed in the geometry chart as 66.6º, again for the large size in low. Trek should get props for this disclosure, considering many riders may wonder about that angle of the beast, which was the biggest hurdle preventing my warm feelings for the Slash from getting hot. For many riders this won't be a big issue, but if you happen to have long legs in proportion to your upper body, this may be tricky for you as well.

Slash Highlights

  • New longer, lower, slacker geometry with reach numbers growing 30mm on the XL frame in low position and head angle moving from 65.1º to 64.1º
  • Travel increased by 10mm to 170 up front and 160 rear
  • Effective seat angle Increased 2º while actual seat tube angle increases by 1º
  • Upper models equipped with new Rock Shox Super Deluxe thru shaft shock with usable open setting
  • On board storage compartment in down tube for carbon and aluminum models
  • Full length down tube guard protects against debris and truck tailgate damage
  • threaded bottom bracket on all models
  • Knock Block 2 increases steering from 58º to 72º and can be removed without fear of frame damage
  • 34.9 mm post diameter increases strength and can improve longevity and performance of dropper post

Slash Geometry Chart

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Excellent numbers for the most part. Geometry data as reported by Trek.

The slack climbing position was easily remedied by moving the saddle forward on its rails, a little less than an inch. My descending challenges (cornering in particular) weren't so easily compensated for. That slack actual seat angle means the saddle comes to rest further forward than I'm used to at the bottom of the 170mm dropper post, and this was exacerbated by the saddle being pushed forward. The wide rear portion of the saddle was now in line with my both my right knee and my left thigh when I angled the bike with my left-foot-forward stance. This made me feel even more awkward than usual and prevented me from squeezing all the zest out of the trails. A temporary solution was to dismount before the descent and lower the saddle about an inch and a half, and then raise it again for longer climbs. This worked, but I've become so spoiled by droppers that I found it unbearably inconvenient. Fortunately a long term solution for this terrible hardship was at hand. It's shocking how soft I've become.


BikeYoke to the rescue. I needed a longer post to compensate for the saddle position when lowered and I was sent a prototype Revive Max from BikeYoke in Germany. It's a 34.9 post that has an upper tube diameter of 28mm, while the competition uses one diameter for all sizes; 25mm. BikeYoke's new lever is a beauty as well. Photos - Cam McRae


The saddle isn't quite slammed all the way forward on the rails, but it's close. This was an excellent position for me when climbing. My main issues with body position related more to the saddle in its lowest position.

I published a 2-Minute Expert piece with Stefan "Sacki" Sack of Bikeyoke about his contention that all droppers should be 34.9, for strength and durability, and since Trek agrees, this was my chance to try out his theory. As luck would have it, Sacki was working on a 225mm drop post using the Revive Max platform, to determine feasibility and gauge interest. Most droppers have the same 25mm inner post diameter for every size, but Bikeyoke uses a 28mm inner for their 34.9mm posts with everything else scaled up similarly.

The 225mm post is a few millimetres high when fully inserted and fully extended, but that's easily remedied from the saddle. At first it seemed a little too low at the bottom as well, on rare occasions when I was seated, but I've got used to that now and have grown quite fond of having all that space at my disposal. One minor side affect is that I can now quite easily give my ass a knobby massage on steeps or going off drops. Once I became aware of this I adapted easily and it rarely happens now.


While the carbon bar unquestionably felt too stiff, I was surprised by how much more compliant and comfortable the aluminum replacement felt.

The other adjustment I made was to swap out the Bontrager carbon bar, for an uncut 750mm Bontrager aluminum bar I happened to have. The original carbon bar was 820mm wide before I cut it. This is excellent for the rare clydesdale/orangutan mixes out there, but a bar that is adequately strong at that width turned out to be unbearably stiff at 750mm, my preferred cut.* I didn't expect much difference but it was shocking how much better the bike felt with the aluminum bar, making me question why we carbon bars ever became a thing.

*Why aren't more bars engineered for specific widths, so the stiffness could be tuned more accurately for those of us who prefer having our hands closer together?

With both issues solved I really began to charge on the Slash. To be clear, I mean charge compared to my usual performance, and my aging compadres, and not compared to say, Sam Hill. Lately, despite the snow and rain, and occasionally thanks to dry and frozen conditions, I've been knocking off a few moves I've never done before. I rode two rock faces I'd never attempted just last week, and I've also been doing some modest gaps I've never had the nerve to send previously.


I lost count of the number of drops, rock faces and gaps I've successfully navigated for the first time on the Slash, but it's likely into the double digits. I've been backing away from several of them for years and there aren't many better feelings on the bike than knocking moves off that list.

Suspension Set Up and Performance

I've grown particularly fond of the damping characteristics of the rear shock on the Slash; the Trek-specific ThruShaft version of the Rock Shox Super Deluxe Ultimate air shock. In the past I've sometimes found that I can set up a shock to work on lower angle, low speed tech trails, without heavy impacts like those on Mt. Fromme, or the faster, steeper and more demanding trails on Mt. Seymour, but rarely have I been able to nail settings for both mountains/trail conditions without tweaking my damping.* With this shock I've found settings that feel great on both mountains without twisting a single dial or changing air pressure.

*I'm generalizing about the trails on both mountains and there are lines on each that don't fit my categorizations


Conditions have been variable lately but ridiculously fun as well.

There's one section of trail I used to notice this on in particular, near the end of a long steep and technical descent. All of a sudden things open up and speeds double, with moderately sized impacts coming in rapid succession. I've rarely managed to set up a rear shock so it works well with the slower steep line as well as this section that's more like a downhill track, but the Slash with the ThruShaft devours it with no fuss at all.

I've stumbled upon settings for the Slash that seem to keep me in the sweet spot at all times. I'm easily able to ride the biggest moves on my list without bottoming the front noticeably, and while the rear shock's fun meter is frequently, quite literally off the chart, I haven't noticed a hard bottom out that I can remember in the rear either. The Slash is an incredibly well-sorted platform and the work both Trek and Rockshox have put into dialling in the ThruShaft shock to match the leverage ratio and other kinematics of the bike, have paid off handsomely.


The Slash doesn't soak up drops to flat as well as the Santa Cruz Nomad, (few bikes do) but it remains composed upon re-entry.

My settings differ a fair amount from Trek's suspension calculator's recommendation, which is 56 PSI up front with 9 clicks of rebound (this is also what RockShox recommends) and 185 PSI in the rear with 5 clicks of rebound. I have the Zeb Ultimate set up with 66.5 PSI and rebound 10 clicks out, while HSC is at 4 clicks and LSC at 14, while the Super Deluxe Ultimate ThruShaft is at only 166 PSI with the 3 position compression in the + position and 9 clicks of rebound. This is based on my weight being 165 lbs all geared up, which is likely pretty close. My rebound settings are a little faster than they would be in summer to compensate for cold starts. The difference in set up may be explained by my affection for the North Shore's plentiful steep terrain, which puts most of my weight on the fork for long periods.


The 3-position low-speed compression adjustment is easily adjusted on the fly and operates independently from the high speed circuit, which isn't adjustable. I've been running a little less than recommended pressure but using the highest (+) damping setting. If you'd like to sit a little deeper in your travel, just pull and twist to the 0 or – settings. Photo - Cam McRae

If I was experiencing any limitations I'd change things a little but I'm using all the fork travel only in 'oh shit' situations but every millimetre at the rear regularly. I've been feeling confident on both high and low speed terrain, with one minor exception. I may try a little less low speed rebound in the rear on my next ride because large steps at low speed have been feeling a little harsh, making me suspect the rear shock isn't returning quickly enough. (Because it can't be my fault)


My affection for the Rockshox Zeb remains undiminished.

The Zeb fork seems to be getting better over time. I've continued to fine tune my settings a little and spring pressure has increased marginally, but overall, nailing the settings on the Zeb has been ridiculously easy. I continue to appreciate the tall ride height that reserves deep travel movements for impacts that call for them, and the stiff chassis keeps boosting my confidence in rowdy situations or when tipping into a rockface or steep section at a sharp angle.


This wasn't a happy discovery. The tool still works, and some oil has kept everything deploying smoothly, but who doesn't hate rust?

Frame Details and Durability

I've come to appreciate the comprehensive frame protection on the Slash even more over time. If I lift the bike into my truck, when there is a thick coat of mud on the downtube, I feel a little glow of satisfaction knowing my tailgate pad won't be scraping that gritty residue into the paint. A full length guard protecting the underside of your frame makes excellent sense and I hope other manufacturers will go that direction.

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At first I assumed a terrible design error was responsible for the placement of a pair of cables and the rear brake line in the opening of the storage hold. Closer examination revealed an early production assembly error. Photos - Cam McRae


Once properly configured it became much easier to get things in and out of the hatch, and to use both the upper and lower voids in the down tube.

The integrated storage in the head tube is welcome and useful, but unfortunately not sealed against the weather or post ride cleaning. Everything I'd stored in the downtube was soaking when I last looked, 24 hours after the last ride and the mini tool has become quite rusty. It still works and a little oil has kept things moving well, but I hate rust on my bikes. I also found it a little challenging to get the tool roll in and out of the hatch because of the unconcealed brake, rear derailleur and dropper lines blocking the edge on the drive side of the opening, reducing the usable width of the door. Closer inspection revealed this to be an assembly error and now the cables and line are tucked away tidily.


The finish on the Trek Slash has managed to withstand worst case scenario abuse and come out shining. Photos - Cam McRae


Putting money into durable paint will make riders happy over the long term. Well - this rider at least.

The paint and clear coat on the frame has been a highlight. There are very few scratches or blemishes in even high wear areas and the gloss continues to glisten everywhere. The chain stays are only little bit dull from heel rub. It's pretty clear that Trek has put a lot of effort into these details with the rider's experience in mind.


The Slash loves carving semi circles.


Fast; that's my number one comment about the aptly named Slash. It's easy to pump it up to speed even in surprisingly rough situations, and it carries that velocity easily as well. The well-honed suspension and kinematics make it easy to get light on the pedals and let the bike float beneath you. I've found myself staying in contact with riders who used to drop me easily lately and generally having a blast on the Slash. And thus far, every time I think I've gotten in over my head, the bike has kept me out of trouble.

Setting up early for corners reaps rewards measured in Gs and traction is so good, inside lines I've never considered have become options. The stiff Bontrager wheels undoubtedly contribute to these qualities, along with the Bontrager SE4/SE5 tire combo. The combo could be accused of being a little portly though, depending on rider weight and trail savagery. The rear with the SE5 29 x 2.6 tire weighs 2180 grams without a rotor while the rear weighs 2100 shod with an SE4 29 x 2.4.


A few of the moves that used to scare the hell out of have become almost automatic on the Slash.

Compared to...

At times it feels like I've been testing slightly different versions of the same bike, for years. For that reason the Kona ESD, the Santa Cruz Tallboy, and to a much lesser extent the odd eMTB, have been a nice break. What I'm getting at is that many of the things I've said about other bikes, notably the Yeti SB150 for this example, apply to the Slash. They ride differently, that's certain, but many of my overall impressions line up quite closely. Like the SB150, the Slash is more speeder than star cruiser, or if you prefer, more elvish than orcish, at least within this category. The Trek however is closer to the middle of that characterization. The Slash is a little less nimble than the 150, and it requires bolder inputs to change course, but both bikes are adept at getting up and over obstacles, swapping lines, and flopping from left to right in tight, quick, corners. The Trek frame has a stiffer, more robust structure, particularly around the head tube and in the rear end, which is sometimes better but sometimes not, at least for my stature. This likely explains why the Slash generally feels a little more stable at speed in rough terrain (along with the extra 10mm of travel in the rear).

The SB150 is an incredible climbing machine, but the Slash is no anchor. I could get up all the bumpy single track sections I find challenging on the Slash, but at a slightly lower success rate than I do on the Yeti. Rear wheel grip is excellent and the tweaked riding position was very comfortable while allowing me to put down power efficiently. Without a doubt setting up the Fox Factory X2 rear shock is a more challenging proposition compared to the Super Deluxe, particularly the 2021 variant. I wouldn't hesitate to pedal the Slash long distances, but given the choice I'd choose lighter wheels and possibly tires for the job.


Final Analysis

Despite a few minor pecadillos, most that were relatively easily dealt with, this is one hell of a capable trail smasher. The Slash is a bike that quiets my inner demons and has me diving into sections I thought I'd be walking down until I trade my bike for a cane. And because it keeps going well, that confidence continues to build and the list of moves I have been too chicken to try, gets shorter and shorter. With some help from this orange and black beauty, I'm having more fun on the bike than ever. And yes, I may have said that last year as well.

If you like to ride aggressive terrain in something of a hurry, or against the clock, the Slash should undoubtedly make your shortlist. It's a shining example of how fun, capable, and dare-I-say transcendent, a modern enduro bike can be, even if your budget is reasonable.

More on the Trek Slash
Cam McRae

Height - 6'/183cm (mostly legs)

Weight - 170lbs/77kg

Inseam - 33"/84cm

Ape Index - 0.986

Age - 57

Trail I've been stoked on lately - Lower Digger

Bar Width - 760mm

Preferred Reach - 485-500mm (longer with 27.5 wheels than 29)

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+6 Cam McRae Mammal Metacomet Zero-cool Andy Eunson Dan

Why don't we have some kind of bar stiffness measurement? Clearly people of different heights and weights will have different experience of bar stiffness. Yet there is no objective measurement for comparison, never has been.


+2 Cam McRae Pete Roggeman

"This is excellent for the rare clydesdale/orangutan mixes out there"

I feel seen.  

Honestly, this is still a good thing, because not everybody rides in places where trees that predate our own existence are perilously close to the trail.  I also feel like larger softer grips are a perfectly adequate way to compensate for bar compliance, but again, large hands, and I struggle to find grips where my fingertips aren't colliding with the base of my hands when squeezing


So 820s work for you? But nobody makes grips that fit?


+1 Cam McRae

I run 810's, so far I've found that gloves 100% of the time along with Sensus Disisdaboss grips (for the lateral coverage) has worked best, but I want to see what Cam Z's latest grip (iirc Lyle signature) has for more circumference, because I think that's going to be my preferred answer.
What I've found is that thicker grips can do a lot for bar compliance and fatigue management, which is why I don't see bikes shipping with massive bars that need cutting down is necessarily problematic (or at least less so than shipping with 780 or 750mm bars that are immediate take-offs for somebody my size).


+1 AJ Barlas

Sensus Meaty Paws.


+2 Cam McRae Dan

Ordered a 9.8 in January, supposed to at be in June - July. Maybe it's just the aluminum models that are super delayed?



Well, ordering a bike and having it arrive in June or July is most people's definition of super delayed. Mine too. I get antsy having to with for shipping to the store! I guess it's not as bad as some time in 2022 for the Slash 8s...


+1 Cam McRae

The new Slash is such a sick bike. I love how stiff and burly the bike feels. It was very confidence-inspiring and just begged to be ridden hard. My biggest gripe was the seat tube angle. I have 35 inch inseam and run a long seat post. I only wish they were available. I was shopping the new Slash along with a few other bikes and I eventually chose the 21 Stumpjumper Evo. Partly due to the fact I could actually buy one.


+1 Trent Blucher

First time I've ever heard the same complaint I'm experiencing with seat too far forward.  Started feeling my seat even when slammed with a 200 dropper when I moved to a Megatower.  Couldn't figure out why.  The slacker real seat angle slightly impact the real vertical drop from my ass but I came to the same conclusion:  the seat is too far forward.  Yes I could move the seat back on the rails but that would impact my effective STA at pedaling height which I don't want to do.

For me it's enough of an issue that I'm switching frames to one with a steeper actual STA.



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+1 Pete Roggeman

I owned the 2012 then the 2017 Slash and it's funny how similar comments come to mind as I noticed Cam's giant eyeballs in the pictures and I remember the same feeling on stuff going way too fast and saved by this fine piece of technology!

+1 Pete Roggeman

LOL. They are indeed quite large. Undisguised terror.


+1 Pete Roggeman Dan 4Runner1

The new Slash is an amazing bike.... good luck finding one in 2021...


Even the higher priced models? I know that anything under 5K is impossible to find around here but I thought upper end bikes were a little easier to find.


+1 Cam McRae

There will be a few floating around for sure but orders placed today for a 9.9 have a late August ETA or 250 days if you want Project 1 colours.    Its all over the map... Trek is doing a good job though in the grand scheme of the bike industry ATM.



Interesting that you briefly discuss the stiff and heavy stock wheel/tire combo, but all the photos are of ENVEs. Curious as to whether a wheel swap changed the ride much? What does that say about the wheel spec? Also curious about your impressions of the ENVE rims to compare against my own.



Would you buy a Slash if you were 185cm with a 90-91cm inseam? 🙂



Encouraging writeup! I am going to upgrade from my '18. Looking forward to a geo update, and a bit more oil volume out back. Plus snack storage! Question is will my handy folding saw fit in that spot? I see the under-TT bosses are no longer available on the Slash. (That's where I lashed my saw.)


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