2021 Trek Slash

2021 Trek Slash

Test Location: Crested Butte, Colorado

Test Duration (so far): 1 day

Size Tested: ML

Build Overview (Trek Slash 9.9 X01):

Wheel Size: 29”

Travel: 160 mm rear / 170 mm front

Blister’s Measured Weight (as built, w/o pedals): 32.25 lbs / 14.63 kg

MSRP: $3,499 – $8,999 ($7,999 as tested)

Blister reviews the 2021 Trek Slash
2021 Trek Slash 9.9 X01
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Review Navigation:  Specs //  Intro //  The Frame //  Suspension & New Shock //  The Builds //  Fit & Geometry //  Initial Impressions //  Bottom Line


Just a couple of years ago, our reviewer Noah Bodman called the 2018 Trek Slash one of, if not the best all-round Enduro bike he’d ridden at that time.

But in the world of mountain bikes, a couple of years feels more like a decade, given how quickly brands have been changing bike geometry, suspension, components, and almost everything else we use to get around on two wheels. The Slash that Noah reviewed had been essentially unchanged since it was released in the 2017 model year, so many people have been eagerly waiting to see what would come next.

Today, Trek provided those people with an answer when they released the all-new, 2021 Slash.

Trek says their two main goals when redesigning the Slash were to (1) “enhance the Enduro race capability of the bike” and (2) “preserve the ultimate Trail rider experience.” We’ll be having a few of our reviewers spending time on the new Slash over the coming weeks and months to really see how this new bike performs and stacks up against the competition.

For now, we’ll dive into what Trek changed on the Slash to accomplish those two goals, how the new bike’s design compares to the rest of the crowded Enduro 29er category, and then provide our initial, first-ride impressions.

The Frame

Aesthetically, the 2021 Slash looks very similar to the previous version, as well as many of Trek’s other bikes. It maintains most of the clean, fairly straight lines throughout the frame and still uses a similar version of Trek’s ABP, 4-bar suspension linkage. That said, there are a lot of noteworthy differences with the newest Slash that might not be obvious at first glance.

First and foremost, the 2021 Slash gives you 160 mm of rear travel and is designed around a 170 mm fork, while the previous version had 150 mm of rear travel and a 160mm-travel fork.

The Slash is still available in either a fully aluminum frame or fully carbon frame, with the two alloy builds designated with a single digit in their name (Slash 7, Slash 8) while the five carbon-frame builds are designated with decimal points (e.g., Slash 9.7, Slash 9.8, & Slash 9.9). However, while the old Slash’s geometry and some of its features differed between the alloy and carbon models, the 2021 Slash keeps pretty much all of the frame features and geometry the same, whether you opt for alloy or carbon. That’s great news for those who don’t feel like going the carbon route.

One of the most exciting new features is the frame’s integrated storage in the down tube, and the fact that it’s standard on both the carbon and alloy Slash. Similar to Specialized’s SWAT box and the down tube on the carbon Trek Fuel EX, the new Slash lets you open a little “hatch” on the down tube so you stash a tube, tool, burrito, or whatever other little items in the frame, and not on yourself.

Blister reviews the 2021 Trek Slash
2021 Trek Slash Down Tube Storage

That little hatch on the down tube also serves as a mounting point for a water bottle cage, and Trek says all sizes of the 2021 Slash will fit a water bottle within the front triangle. Our size ML fits a 20-oz bottle quite easily. Cables are routed internally on both the alloy and carbon 2021 Slash, and they’ve been very quiet so far.

One of the more polarizing features of several Trek bikes is their “Knock Block” system. On the old Slash, this was essentially a keyed headset that prevented the front wheel from turning past roughly 58° to either side. On that bike, the down tube ran straight from the head tube to the bottom bracket, which Trek said let them get a more ideal strength-to-weight ratio from the frame. It also meant the fork could bash into the down tube without the Knock Block system during a crash, an ultra-tight turn, or if you finally decided it was time to learn barspins.

The 2021 Slash features what Trek is calling “Knock Block 2.0.” In its stock configuration, it still prevents the wheel from turning all the way around, but you can now turn the bars 72° to either side, as opposed to 58° on the old version. The 2021 Slash’s new, slightly curvier down tube also means it has enough clearance for the fork’s crown, and given that, Trek made Knock Block 2.0 removable, and it will now work with “standard” stems that aren’t Knock Block specific. Given that there’s no longer a physical conflict with a straight down tube, Trek says the primary purpose of Knock Block 2.0 on the 2021 Slash is to help prevent wear on the top tube and cables from pulling out.

Blister reviews the 2021 Trek Slash
2021 Trek Slash — Knock Block 2.0

While it ditches the “Straight Shot” down tube of the last version, the 2021 Slash is still touted as being light and strong, with Trek claiming a stated weight of 2450 grams for the carbon frameset (we’re working on confirming which size that weight is for). Our size ML Slash 9.9 X01 weighed in at 32.25 lbs / 14.63 kg without pedals, which isn’t exceptionally lightweight for a high-end, 160/170 mm bike, but also not particularly out of the ordinary for a long-travel 29er.

One cool feature on the 2021 Slash that we don’t see on too many other bikes is its massive down tube protector. Running from the bottom bracket to just a few inches shy of the head tube, the dual-density pad should keep the down tube looking fresh for longer, particularly for people who often shuttle their bikes. And as would be expected, the new Slash also features some protection around the chainstay.

Blister reviews the 2021 Trek Slash
2021 Trek Slash — Down Tube Protection

Speaking of the bottom bracket, the 2021 Slash comes with a BSA 73 one that’s got threads in it, rather than the press-fit BB on the old version. This should equate to less creaking and easier service. The new Slash also gets a larger, 34.9mm-diameter seat tube to accommodate the increasingly popular droppers of that diameter (including the new 34.9 mm Bontrager Line Elite spec’d on the higher-end Slash builds).

The Slash uses 110×15 mm hub spacing up front and 148x12mm out back, which is pretty standard, and Trek says the max rear tire size is 29”x2.5”. Other misc. specs include a rear brake mount that fits 180 mm rotors directly and fit up to 220 mm rotors, the ability to run chainring sizes from 28-tooth to 34-tooth, and stated dropper post insertion depths ranging from 205 mm on a size Small to 310 mm on a size Large.

Blister reviews the 2021 Trek Slash
The 2021 Trek Slash will directly fit a 180 mm rear rotor, and up to a 220 mm rotor

Suspension Design & New RockShox Super Deluxe Ultimate Thru Shaft

The 2021 Slash’s overall suspension linkage is still pretty similar to the previous Slash, using a version of Trek’s 4-bar “ABP” linkage. They’ve been using this general design for years, and a few of our reviewers have particularly been fans of how active the ABP linkage tends to stay under hard braking.

Like the old version, most 2021 Slash builds come with a special version of a RockShox rear shock that features the exclusive-to-Trek “Thru Shaft” design, but again, there are some notable differences.

First, the 2021 Slash’s shocks no longer feature Trek’s special “RE:aktiv” tune, which essentially relied on speed-sensitive damping and was meant to help the shock stay firm during low-speed forces (e.g., pedaling) while opening up during bigger impacts. Trek says they made this change because they felt a shock without the RE:aktiv tune was better suited to the demands of modern, high-speed Enduro races, which are becoming more and more like multi-stage DH races.

Second, several of the 2021 Slash bikes (carbon frameset, 8 build, 9.8 builds, & 9.9 builds) come with a special version of the RockShox Super Deluxe Ultimate, rather than the special RockShox Deluxe RT3 on the old Slash.

Blister reviews the 2021 Trek Slash
2021 Trek Slash 9.9 X01 — down tube protection & Super Deluxe Ultimate Thru Shaft shock

So, what’s so “special” about these shocks? Well, the Thru Shaft design itself is exclusive to shocks on Trek bikes, and was something that Noah really liked about the old Slash’s shock. After swapping between the two, he found the Thru Shaft shock made the bike feel much smoother and more sensitive over small chatter compared to when he swapped to a regular Super Deluxe shock. (Noah already went into a lot of detail regarding Thru Shaft in his review of the old Slash, so I’d check that out if you want to get more into the weeds about how it actually works.)

While Thru Shaft itself isn’t new, the Super Deluxe Ultimate on the 2021 Slash is. Its most notable new, exclusive feature is a 3-position switch (the bright-blue knob on the shock) that’s meant to specifically change how the suspension is affected by rider input (i.e., slower-speed forces created by the rider pushing down on the bike), without affecting damping during higher-speed impacts that come up from the trail. In simpler terms, it lets riders quickly switch between three preset low-speed-compression settings.

The “0” setting is supposed to be the baseline, general-trail-riding setting that you’d use in most cases. The “–” setting decreases the amount of low-speed compression, which Trek says makes more sense on steeper and rougher trails where the rider’s weight is biased more toward the front of the bike, and not the rear. Then the “+” setting adds more low-speed compression, meant for smoother, flow-style trails where you want a more supportive platform for pushing into berms and off jumps.

Blister reviews the 2021 Trek Slash
RockShox Super Deluxe Ultimate Thru Shaft

This new 3-position switch is not a “climb” switch or a lockout lever — the Super Deluxe Ultimate Thru Shaft has a separate, 2-position lever that you can use to fully lock out or fully open the shock. The lockout lever is situated directly over the 3-position switch on the shock.

Aside from that new 3-position LSC adjustment, the Super Deluxe Ultimate Thru Shaft on the 2021 Slash also features a larger, tunable negative air spring, which is meant to make the shock more progressive and supportive near the end of its travel, without losing the small-bump and mid-stroke sensitivity supposedly offered by the Thru Shaft design. You can also add volume spacers to both the negative and positive air springs to fine-tune the shock, though the Super Deluxe Ultimate Thru Shaft comes stock without any spacers inside.

RockShox also tweaked the positioning of the dials and switches on the Super Deluxe Ultimate Thru Shaft, putting them on the left side for easier access and they also added numbers to the single rebound-adjustment dial to make it easier to know what setting you’re on.

Now, I just used a lot of words to talk specifically about the exclusive Super Deluxe Ultimate Thru Shaft shock that comes on most of the 2021 Slash builds. However, many people will be happy to know that you can still fit several other shocks on the Slash, including the 2021 Fox Float X2, 2021 Fox DHX2, Fox DPX2, RockShox Super Deluxe Coil, and most inline shocks without piggyback reservoirs. Trek says the regular, non-Thru-Shaft Super Deluxe won’t fit due to where its lockout lever is placed. They say that the leverage ratio of the new bike is progressive enough that most coil shocks are compatible, though I’d recommend checking with them just to be sure you won’t have any clearance issues with the coil shock you’re considering.

Trek is talking a pretty big game about this new Thru Shaft shock, so we’re very curious about (1) how well it’ll live up to Trek’s various claims, (2) how useful the new 3-position LSC switch actually is, and (3) how it compares to other downhill-oriented air shocks that don’t feature Thru Shaft, but that do feature more finely adjustable compression and rebound settings.

The Builds

As of publishing this First Look, the 2021 Slash is available as an alloy frameset ($2,199), carbon frameset ($3,999), or in 7 full builds ranging from the $3,499 Slash 7 to the $8,499 Slash 9.9 XTR.

For all of the carbon builds, you can also customize the color / paint of the frame through Trek’s Project One program, which adds $500 to the cost.

At $3,999, the Slash 8 in particular seems like a pretty solid deal: you get the special Thru Shaft shock, RockShox Lyrik RC fork, full SRAM GX drivetrain, and SRAM Code R brakes.

We’re testing the high-end Slash 9.9 X01 build, which leaves little to be desired for the price of $7,999.

Blister reviews the 2021 Trek Slash
2021 Trek Slash 9.9 X01

Here’s the quick rundown on some of the Slash 9.9 X01 build highlights:

  • Fork: RockShox ZEB Ultimate
  • Rear Shock: RockShox Super Deluxe Ultimate Thru Shaft
  • Drivetrain: SRAM X01
  • Brakes: SRAM Code RSC
  • Wheels: Bontrager Line Elite 30 carbon
  • Front Tire: Bontrager SE5 2.6”
  • Rear Tire: Bontrager SE4 2.4”
  • Dropper Post: Bontrager Line Elite 34.9
  • Handlebar: Bontrager Line Pro carbon

Geometry & Fit

Like every other new bike in recent memory, the 2021 Slash is longer, has a slacker head tube angle, and a steeper seat tube angle than its predecessor. With that said, the changes are not quite as drastic as you might expect, given some of the radical bikes released in the past year. And that seems in line with Trek’s goals of improving racing capabilities while maintaining more general trail-riding performance.

[The geometry of the new Slash, as well as the new Pivot Switchblade and now-fairly-old Rocky Mountain Instinct BC, actually kickstarted an interesting conversation around Blister pertaining to the current status and future of mtb geometry, which we’ll be posting later today on our Bikes & Big Ideas podcast.]

The old Slash wasn’t the longest option in its class when it was first released, the 2021 Slash also isn’t truly pushing the limits in terms of length, and that’s something several of us are actually quite excited about.

Depending on the size of the frame, the new Slash’s reach is 15–41 mm longer than the last iteration, with a size M coming in at 450 mm, an ML coming in at 469 mm, and a size L coming in at 486 mm. Compared to, say, Commencal’s new Meta TR and Meta AM, the Slash’s reach numbers sit slightly on the more conservative side, though they’re pretty much in line with bikes like the newest Transition Sentinel and Norco Sight.

Compared to the last version, the 2021 Slash’s head angle gets slacker by a degree, sitting at 64.1° in the Low setting and 64.6° in the High setting of its “Mino Link” flip chip (the bike comes stock in the Low setting). While we’re seeing more bikes in this class with sub-64° head angles, the new Slash’s head angle seems relatively standard for Enduro bikes these days.

Blister reviews the 2021 Trek Slash
Trek Slash — Mino Link Geometry Flip Chip

Combined with chainstays that didn’t change much (2 mm longer at 437 mm in the Low setting), all of that adds up to a longer, but not extremely long wheelbase: 1222 mm for a size M, 1243 mm for a size ML, and 1264 mm for a size L.

Just looking at the old Slash and comparing it to newer bikes, the most obvious difference in its geometry is probably its seat tube angle. With a 73.6° effective seat tube angle and 64.3° actual seat tube angle, the old Slash looks very different than the numerous bikes of today with seat tube angles approaching (or even reaching) 80°.

The 2021 Slash’s seat tube still has a significant “kink” in it, keeping its actual seat tube angle quite slack at 66.6°, but its effective angle has gotten almost 2° steeper, with Trek claiming 75.6° with the saddle height at 750 mm. That’s still notably slacker than a lot of bikes these days, and given the very slack actual angle, this may still present some issues for people who need to run very long droppers. But we’re curious to see just how noticeable that seat tube angle actually is.

All in all, the new Slash features pretty much all the geometry changes you’d make if you wanted to make a bike more stable at speed and in steep terrain, and more comfortable on steep climbs. Other brands have taken those changes even further and others have been more conservative, with the new Slash sitting roughly around the middle of the pack for a bike in this class.

As for sizing / fit, the 2021 Slash adds an “ML” size to the lineup, which will be great news to people like me and Noah, who were split between the fairly large sizing gap between the M and L sizes on the old Slash. With reach numbers ranging from 425 mm on a size S to 516 mm for a size XL, the 2021 Slash should work for a wide range of riders. Like most bikes (but increasingly, not all), the 2021 Slash’s chainstay length is the same across all sizes, which may be something to consider for riders at the upper and lower end of the sizing spectrum, but having equal-size chainstays across all sizes is still pretty much the norm these days.

For reference, here’s the full geo chart for the 2021 Slash:

Blister reviews the 2021 Trek Slash
2021 Trek Slash Geometry (click to expand)

Initial On-Trail Impressions

We received and built up the Slash 9.9 X01 yesterday, so I’ve only been able to get one day on it so far. Rest assured that our other reviewers will be spending far more time on the bike in the future, but for now, I’ll just go over the things that did quickly stand out.

On the uphill, the 2021 Slash’s suspension felt like it fell into the “great traction, not super efficient” category. There was a noticeable amount of pedal bob, particularly when out of the saddle — not as wallow-y as the 2019 Specialized Enduro 27.5 or Stumpjumper, but not as firm as the Revel Rail. I quickly found myself preferring to lock out the shock for the smoother sections of climbs, but when I left it open, I did appreciate the noteworthy lack of wheel slip on very loose, chunky sections. For reference, I’m 5’8”, 155 lbs / 173 cm, 70 kg and had the rear shock’s sag set around 27% and the fork’s around 16%. I kept the shock’s 3-position LSC adjustment in the middle “0” setting most of the time, with one exception that I touch on below.

I didn’t have any complaints about the Slash’s seat tube angle being too slack, though I admittedly tend to be a bit less sensitive to / particular about that than some other folks. The main thing I noticed on the uphill in terms of geometry was that the 2021 Slash does feel like a pretty long and slack bike in tight and / or steep sections. Compared to the shorter and steeper size Medium Specialized Enduro 27.5 and size Large Rocky Mountain Instinct BC I’ve been riding, the size ML Slash’s front wheel felt more difficult to keep planted in steep spots and it required more physical input on my end to maneuver the bike over / around obstacles. This didn’t come as any surprise to me, and at least so far, seemed like nothing out of the ordinary for a bike with the Slash’s geometry.

As I think should be the case with a bike like this, I immediately started loving the Slash more and more as soon as I got to head downhill. Compared to those two bikes I just mentioned, the Slash felt notably less prone to getting knocked off-line. And despite it being a totally new bike to me, I very quickly felt comfortable carrying as much, or very likely more speed than I would have on those other bikes. I even started trying some new, small gaps that I wouldn’t normally attempt on those bikes, because of how solid and generally confidence-inspiring the Slash felt. The fact that the Slash is more stable is no shocker, but I do think the seemingly non-existent adjustment period I had is noteworthy.

Blister reviews the 2021 Trek Slash
Luke Koppa on the Trek Slash, Strand Hill, Crested Butte, Colorado. (photo by Eric Freson)

The standout characteristic of the Slash on that first day was how calm and well-damped the entire bike felt while riding pretty fast through rocky and rooty sections. Both the ZEB up front and Super Deluxe Thru Shaft out back did a great job of muting out small and medium-sized chatter — and that was after simply setting sag and guestimating compression / rebound settings while pedaling around the trailhead. I think some of that damped feel might also come from the Slash 9.9 X01’s carbon Bontrager rims and bar, but it’s too early to say for sure. The smooth, almost “deadened” (and very quiet) ride of the Slash 9.9 X01 kind of reminded me of a 2019 Specialized Enduro 29 I rode with an Ohlins coil shock, Roval Traverse carbon rims, CushCore inserts, and DH-casing tires. I also noticed the Slash’s ABP linkage living up to the claims about it and doing an above-average job of maintaining traction while on the brakes in chunky stretches.

The Slash was definitely the most fun on the faster, straighter sections of the trail, and I did feel like I was wishing for a slightly more responsive pedaling platform on lower-angle, flowier sections. I briefly flipped the shock’s 3-position LSC switch from the “0” mode into the “+” mode and the difference was subtle, but definitely noticeable — it felt slightly firmer while pedaling and pumping, but I wouldn’t call it a night-and-day difference, at least for now.

Blister reviews the 2021 Trek Slash
Luke Koppa sharing the trail with some friends on the 2021 Trek Slash, Strand Hill, Crested Butte, Colorado. (photo by Eric Freson)

I’m eager to hear what our other reviewers think, but after spending a very brief amount of time on it, the new Slash seems like it could very well live up to Trek’s goals of making a capable Enduro race bike that still maintains some of the accessibility and versatility of more general “Trail” bikes.

Some Questions / Things We’re Curious About

(1) Trek is putting a lot of emphasis on the Slash’s new Super Deluxe Ultimate Thru Shaft shock, but what specific upsides / downsides does it really offer compared to other shocks on the market?

(2) The new Slash is a fairly long and slack bike, but not the absolute longest or most slack. So will it be able to match the race-pace stability of longer / slacker bikes in its class, and could it do that while maybe offering a more maneuverable, manageable ride at slower speeds?

(3) After a very quick initial setup and ride, the Slash’s front and rear suspension already feel very promising. But once we’re able to spend more time playing with the settings, could we get even better performance on the down, and / or efficiency on the up?

Bottom Line (For Now)

The 2021 Trek Slash brings with it many of the updates we’d expect of a new, long-travel 29er: it’s longer, has a slacker head angle, and a steeper seat tube angle than its predecessor. But it also offers several interesting features absent from many other bikes, like a unique shock, sleek, internal frame storage, lots of frame protection, and it also gives customers more freedom to tinker than the last version, due to fewer proprietary part limitations. 

Our initial impressions of the bike — particularly its suspension and intuitive overall ride — are quite positive so far. A few of our reviewers will be putting in a lot of time on the new Slash over the coming weeks and months, so stay tuned for updates.

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