2021 Trek Slash 8 Review: A No-Compromise Ripper Without the Sticker Shock

Fully prepared to slay everything from jump trails to double black diamond downhill runs, the 2021 Trek Slash 8 provides more performance than you could even purchase in a mountain bike five years ago.
Trek Slash 8 review at mountain of the rogue trail oregon
Mountain of the Rogue, Oregon

The new 2021 Trek Slash 8 model will soon be available online and in bike shops near you with an MSRP of $3,999. This aluminum-framed mountain bike is a full-blooded enduro ripper that offers spectacular performance in a low-cost, no-compromise package. No, this isn’t a “budget” mountain bike for riders hoping to pay less than a thousand bucks. Yes, it’s still worth more than my car. But the value that Trek provides in this package is astonishing.

Fully prepared to slay everything from jump trails to white-knuckle, double black diamond downhill runs, this competent steed provides more performance than you could even purchase in a mountain bike five years ago. Can you eke out a little more performance from the $8,000-$9,000 Slash 9.9? Sure, and you’d be paying at least twice as much and not getting nearly twice the performance than the Trek Slash 8.

Still not convinced? Read on.

Trek Slash 8 Geometry

2021 Trek Slash 8 mountain bike review

The Trek Slash has long defined the long-travel 29er category. When Trek purchased the Gary Fisher brand and later subsumed the Fisher bikes into the greater Trek brand, they effectively became one of the pioneering 29er brands along with Niner. Trek was early to the long-travel 29er game, and today they’ve embraced 29-inch wheels from hardtail race bikes to dual-crown downhill sleds. To claim that Trek has nailed long-travel 29er geometry is an understatement.

The Trek Slash 8 frame sports a flip-chip to adjust between high and low geometry positions, but all testing was conducted in the low position. The adjustable frame can provide either a 64.1° or 64.6° head tube angle. For 2021, the seat tube is steeper by 1.9°, with an effective seat tube angle of either 75.6° or 76.1°. The reach is longer this year, measuring 450mm in the size medium, low position, or 456mm in the high position. The total wheelbase on the size medium is 1222mm in the low position or 1212mm in the high position. Chainstays measure 437mm (low) or 435mm (high) across all models. And for even more geo specs across a whopping five different frame sizes with two different geo positions per size, you can visit the Trek website.

Trek Slash 8 Build kit

The build kit makes-or-breaks both the price point and reliability of a mountain bike. Good news for mountain bikers: the value and reliability of components have never been better. While prices of mountain bikes haven’t dropped dramatically (yet), the performance and reliability have both skyrocketed in recent years. This is great news for all mountain bikers, and especially those shopping on a budget.

The Trek Slash 8 is specced with a RockShox Lyrik Select+ fork, RockShox Super Deluxe Ultimate rear shock, SRAM GX 12-speed drivetrain with a 10-52 tooth cassette, SRAM Code 4-piston brakes, a 150mm Bontrager TranzX dropper post, Bontrager Line Comp 30 wheels, a 200mm rotor up front, a 180mm rotor in the rear, a Bontrager XR5 29×2.6″ tire up front, and a Bontrager XR4 29×2.4″ tire in the rear.

The 8 model of the Slash isn’t quite the most affordable model in the line. Trek also offers a more affordable Slash 7 (only $500 cheaper), but there are also three models that are more expensive, at least two of which are offered with multiple build kit options. Consequently, the Slash 8 nails a fantastic cost-to-performance spot in the Trek line.

Trek Slash 8 changes from 2020 to 2021

Changes to the Slash for 2021 include a new suspension layout and all-new rear shock. The new RockShox Super Deluxe Thru Shaft shock is exclusive to the Slash, and comes with a bevy of enhancements. The suspension travel also bumps up 10mm front and rear, for a total of 170mm front and 160mm rear.

The Slash frame now offers integrated storage in the down tube on all models, including the alloy frames. The seat tube is steeper by 1.9°, measuring 75.6° on the size medium in the low geometry position. Seatpost insertion has been increased by 45mm, and the seat tube is now designed for 34.9mm posts. New Bontrager Line Elite dropper posts come specced on Slash models, which are longer and purportedly more reliable than previous models. The reach is longer (450mm in size medium, low position), and the head tube is a degree slacker at 64.1° in the low position. As you can undoubtedly surmise, the frame features a flip-chip to adjust between high and low positions, but all testing will be conducted in the low position.

Photo: Trek

The Knock Block has also been updated to v2.0. For those who haven’t ridden a long travel Trek recently, the Knock Block is a restriction in the headset that prevents the bars, front wheel, and fork from turning completely around, to prevent the frame and cabling from being damaged. The V2.0 increases the turning radius from 58° to 72°, which they label as “more shuttle friendly” for putting over the tailgates of pickup trucks. Despite the Knock Block preventing the fork from turning all the way around, downtube clearance on the new 2021 model is also improved so that component and frame impacts don’t appear to be an issue. However, Trek notes that the Knock Block still keeps the cabling from being ripped out.

Finally, the new Slash has a “full length, dual-density downtube guard for additional protection and shuttling.”

Specs: Trek Slash 7 vs. Trek Slash 8

Trek Slash 7 cheaper model
Photo: Trek

Compared to the Slash 8, where does the Slash 7 cut costs? Unfortunately, almost everywhere.

The Trek Slash 7 comes with a cheaper RockShox Yari RC fork and a RockShox Deluxe Select+ rear shock. The downgrade on the rear shock is especially notable, as Trek has integrated a slew of fabulous proprietary technology into the Slash 8’s rear shock. In fact, the Slash 8 shares the exact same rear shock with the $8,000+ expensive Slash 9.8 and 9.9 series bikes, meaning the 8 provides an excellent suspension value. More on the rear shock below.

The drivetrain on the Slash 7 gets downgraded to SRAM NX (substantially heavier than GX), and the brakes also get downgraded to SRAM Guide T (not nearly as well-acclaimed or reliable as the Codes). 

In sum, that’s a huge performance loss for a mere $500 in cost savings. If you’re deciding between a Slash 7 and a Slash 8, it behooves you to scrape together an additional $500 for the upgrade. What do you think they invented credit cards for, if not for buying mountain bikes that you can’t afford?

IRL: Tech trails and proprietary suspension

Trek Slash 8 handling tech trails
Marty’s Trail, Ashland, Oregon. Photo: Peter Schnelle

The Slash 8 is a no-holds-barred downhill shredder of the first degree. When pinning downhill, I found the Slash to feel centered and confident in all situations. The slack front end tracked wonderfully at speed, and the short chain stays made for a supremely flickable and manual-able rig. The top-tier suspension is also required to provide this world-class gnar-gobbling performance, and Trek steps up to the table with some of the best suspension components on the market, even at this mid-range price point.

The Slash’s 160/170mm of suspension is more than enough to soak up even the roughest and gnarliest of rock gardens and drops. I found myself loving the RockShox Lyrik Select+ fork. The fork reacts quickly with very little stiction, providing a supple yet supportive ride quality. I found myself running the fork in a very plush setting that still supported well in the end stroke, even without any tinkering with air volume tokens.

The RockShox Super Deluxe Ultimate rear shock is a fantastic piece of engineering that performed superbly throughout my test. The shock includes an easy-to-understand low-speed compression adjustment dial to tailor how the open mode performs. The shock can be set to a Zero (middle) setting or a plus or minus position for additional or reduced compression. This is in contrast to a three-position “Open, Trail, Climb” design found on many Fox shocks. But when you are ready to climb, the shock lever flips to closed, providing a fully locked out rear end.

Trek Slash 8 shock rebound adjustment
Photo: Trek

The shock also includes a unique numeric rebound adjustment that displays a numbered indicator to show you where the rebound is currently set. This makes tweaking your rebound much easier and much more transparent than the old method. Gone are the days of counting clicks in a rebound dial and doing some quick math to figure out where the dial should start, and then adjusting from there. The numeric indicator will also help you change your rebound quickly and reliably on the fly. For instance, you could settle on a preferred rebound setting for standard trail riding and a much faster setting for high-speed bike park riding, switching between the two depending on what your day has in store.

The Super Deluxe Ultimate rear shock includes additional proprietary technology developed by Trek in conjunction with Rock Shox. One of the most notable features is the Thru-Shaft design, which isn’t brand-new to Trek but is still a notable feature of the Slash compared to other brands. Here’s how Trek explains it:

Rather than a separate IFP chamber for compressed air, ThruShaft employs a solid column of oil, a single damper piston, and a rod that exits the bottom of the shock during compression. This design maintains a constant oil volume within the shock thus eliminating the need for an internal floating piston and the complexity and lag that comes with it.

Trek Slash 8 super deluxe ultimate rear shock proprietary suspension
“1. Main damper shaft 2. Main piston 3. Solid column of oil with no gas charge 4. Internal floating piston and gas charge. 5. Secondary damper shaft.” Photo: Trek

So what does this mean to the rider? How does this tech impact the Slash’s performance on the trail?

“The main benefit with thru-shaft is how quickly the shock’s able to react and track the terrain,” according to Jason Lindenberg, a Suspension Technology Engineer at Trek. This quick reaction is a direct result of the reduced stiction from removing the IFP. “You’re basically reducing the lag in that system’s response,” Lindenberg continued.

“Anecdotally, the biggest comment that I heard from a lot of people who rode that shock back to back [with a standard shock] is that the grip over chattery stuff is a lot better, just because the shock could react to that stuff a lot faster,” said Ross Rushin, MTB Product Marketing Coordinator. “Personally where I notice it the most is seated pedaling over real choppy stuff. I notice that my back wheel is sticking to the ground more—I’m not getting bounced up as much,” she continued.

I love seeing brands work to break through barriers by developing innovative technology. Not content to wait for a new stock shock to be released by Rock Shox or Fox, Trek has taken the initiative by working diligently over the past several years to develop and improve this innovative design.

Trek Slash 8 riding at white rabbit in ashland oregon
White Rabbit, Ashland, Oregon

Throughout my test, the Rock Shox Lyrik Select+ and Super Deluxe Ultimate were so plush and so capable that I didn’t have time to seek out the genuinely insane tech-gnar need to push the Trek Slash to its limit. Despite blasting through several substantial rock gardens and dropping down near-vertical rock rolls, the Slash didn’t even blink. I needed to seek out trails with much more extended gnar, all of which were unfortunately in the process of being buried under the snows of early winter. 

Suffice it to say, I don’t think there’s a technical obstacle that the Slash will balk at. If anything, the only question is whether or not you’ve properly tuned the suspension for your weight, riding style, and the type of trail you’re on. And even on the affordable Slash 8, this fantastic suspension provides plenty of tunability to do just that.

IRL: Jump trails

Trek Slash 8 review jump trails oregon
Mountain of the Rogue, Oregon

Despite the wagon wheels and the relatively heavy weight of 33.15lbs, I found the Trek Slash 8 to be equally at home on flow trails as on tech. Due to the early winter timing of my test and the trails available to me in Southern Oregon, I had better access to jump trails than I did to tech trails. And the Slash blew me away in this application!

I found myself launching tabletops on the Slash more confidently than I have on any bike this year. Boosting big(ish) air (for me) felt natural, with plenty of pop springing from the Slash, even with the substantial suspension fully open. I may have had the best results on booters.

On the Trek Slash 8, I finally cleared several long doubles and low, fast gap jumps on a few of Ashland’s flow trails after many tries this year. The stability of the bike and the confidence it inspired helped me to rail into several booters at high rates of speed, sending long-distance launches to narrow sniper landings with confidence. The first time I cleared one particular gap was a massive fist-pump moment. I had tried it numerous times before, feeling like I should be able to make it, and the Slash enabled my final success!

IRL: Climbing

Trek Slash 8 climbing at blue diamond trail nevada
Blue Diamond, Nevada

First, let me note that this is a long-travel rig that isn’t designed for climbing, which makes its favorable climbing characteristics that much more notable.

Yes, the 33-pound weight might look bad on paper, but the Trek Slash 8 climbs so spryly it belies the reading on the scale. The 75.6° seat tube angle (in the low position) provides a fantastic pedaling position for steep climbing, dramatically outshining the weight penalty. For more on this, be sure to read staff writer Matt Miller’s excellent article.

I tested the Slash 8 with the stock tires instead of my preferred tires with Double Down Maxxis casings, and the lightweight Bontrager XR4 tire on the rear no doubt helped with the perceived quickness on the climbs. However, the XR4 felt under-gunned even on moderately-technical terrain, so if you’re going to punish the Slash on true double black diamond gnar, you’ll need to upgrade at least the rear tire. More rear tire weight will negatively impact the bike’s quickness on the climbs.

This is the first bike I’ve tested with the 10-52 Eagle cassette. Yes, that jump into the 52-tooth big cog is downright massive and the shift never feels great (an intermediate gear would be much appreciated), but having such a low bailout gear is a godsend when trying to climb steep terrain on a 33-pound, 170mm enduro bike. I also really appreciated the 30T stock chainring—the same size ring that I chose to pair with my own personal 10-50 cassette. Many bike companies are still speccing a 32T chainring stock (see the Jamis Hardline I recently tested), but trying to grind a big bike up a steep mountain is tough work. So thanks Trek, I appreciate the help.

Finally, the full-lockout on the rear shock is helpful to tame the 160mm of rear travel. Unfortunately, at the $3,999 price point, the Lyrik model specced doesn’t come with any sort of lockout. The Lyrik bobbed considerably when climbing out of the saddle, which was made all the more noticeable by how incredibly stiff the rear end is. This only encourages seated climbing, which is, of course, the most efficient. 

If the Trek Slash 8 build does make any compromise, it is on the lack of lockout on the Lyrik. But for a downhill-oriented enduro ripper, that’s a very modest compromise all things considered.

Final thoughts

Trek Slash 8 pedaling blue diamond trail nevada
Blue Diamond, Nevada

When you boil this exhaustive analysis down, here’s the essence that you’re left with.

The 2021 Trek Slash 8 is an aggressive, long-travel bike that’s designed specifically for shredding high-speed downhill trails. Whether those trails are filled with rocks or with jumps, this long-travel 29er will excel on that advanced terrain. It has also been thoughtfully designed to help riders pedal it uphill without too much pain.

At just $3,999, this bike provides astonishing performance and reliability for the price. From speccing a unique shock with proprietary technology found on bikes that are literally double the price, to an array of high-quality budget-friendly components, this aluminum-framed ripper isn’t keen on compromises. Instead, it removes the excuses that you hear from some keyboard warriors that claim, “I’d be a pro rider, if only I had a better bike.”

In 2021, a “better bike” is now available in a reasonably-priced package, and its name is the Trek Slash 8. Get rid of your excuses—buy this bike.