FIRST RIDE: Transition's Sentinel V3 18

Do we all not crave the simplicity of one bike to suffice for most rides? I'll be the first to admit my one-car garage has a couple of hands worth of bikes. But some hide beneath thicker layers of dust than others, and no matter how hard I try, I can only ride one at a time. Maybe it's the minimalist I'm suppressing by owning so many bikes, but I get jazzed up about bikes like Transition's Sentinel. There is just something special about finding the right tool for multiple jobs. The latest Sentinel continues to bleed this ethos but introduces various updates to satisfy the wants of existing Sentinel owners while keeping it competitive in the broad pool of mid-travel bikes. 

Highlights

• 150mm rear wheel travel // 160mm fork
• 29-inch wheels (size XS dual 27.5-inch)
• Mixed wheel compatible
• Full carbon or alloy frame options
• GiddyUp suspension design with updated kinematics
• 64-degree head tube angle
• Size-specific chain stay lengths
• 'Boom Box' internal frame storage (carbon frames)
• UDH equipped (alloy and carbon frames)
• 180mm post mount (223mm max)
• Sizes: XS-XXL
• Weight (size medium): Alloy: 34.4-36.4 lbs (15.58-16.51 kg) // Carbon - 32.9-33.6 lbs (14.92-15.21 kg) // Alloy frame: 9.91 lbs (4.50 kg) // Carbon frame: 7.41 lbs (3.36 kg)
• MSRP: Alloy: $3,299-4,499 USD // Carbon: $4,899-7,899 USD // Alloy frame: $2,199 USD // Carbon frame: $3,399 USD

What's New?

The Sentinel is one of those bikes that has lived through a few versions of what would be considered a trail bike. Or an all-mountain bike. Whatever you want to call it. Initially, it was the longest travel 29er Transition had ever made at a whopping 140mm. This was at the beginning of 29-inch wheels expanding beyond XC bikes, and it helped ring in a new wave of longer-slacker geometry combined with a shorter fork offset. Things that are commonplace today. Transition definitely pushed the needle pretty far forward with the first Sentinel. Two years later, they launched V2 with minor geo and suspension tweaks, 150mm of rear travel, and refreshed the frame aesthetic. More travel was a welcomed change to match the progressive geometry, and subjectively, the shift from swoopy frame curves to straight, sharp tubes elevated the look and cohesiveness of Transition's entire line.

Four years later, the third Sentinel har arrived with updates that keep it at the forefront of modern mid-travel bikes without tainting its do-everything, middle-of-the-product line role. We are definitely in the era of 'refined, not redefined,' but for a bike like the Sentinel, that's a good thing. 

Here are the standout differences from V2 to V3:

Frame Details

Looking at old versus new Sentinel frames side-by-side, it's easy to think Transition is trying to pull a fast one on you when the silhouettes overlap so much. Once a crab-link bike, always a crab-link bike, right? Of course, there are numerous meaningful updates, and with that, a completely new frame.

You wanted it, and now you've got it—the option to run mixed wheels on the Sentinel. All builds will ship with dual 29-inch wheels, and swapping to a 27.5-inch rear wheel simply requires changing the flip chip in the lower shock mount to the 'High' position. 

Travel has remained the same, but riders can now make the Sentinel 160mm front and rear with a longer stroked shock. Before, you could only go the other way, and drop travel to 140mm with a shorter stroked shock. I'm curious how many Sentinel owners tapped into this adjustment in the past. Personally, I wouldn't mind playing around with understroking the bike. The next dual-29-inch bike in Transition's lineup is the Smuggler at 130mm rear and 140mm front, which is less travel than I typically ride. If you're high maintenance like me, the good news is that you can still toss a 57.5mm stroke shock in the Sentinel V3 and get around 145mm of travel.

What's also interesting is that the Sentinel, in its 160mm, MX wheeled form, now bleeds into Patrol territory more than ever before. The Patrol is more aggressive all around and has the potential to sway into mini-DH bike territory. But for everyday riding, I'd be curious to know where the two bikes differ and excel.

Cable routing has changed, and all cables, including the rear brake, are routed through the downtube and chainstay. The only discrepancy is that alloy frames still run the rear brake externally on the chainstay. Carbon frames also route cables out the back of the seat tube just above the bottom bracket. Before, the shifter cable popped out of the downtube near the lower shock mount. This should minimize cable wear around the chainring. 

I have mixed feelings about the rear brake living inside the frame going forward. I get it—it's fashionable and fairly functional. But the simplicity of snipping a few zip ties and swapping brakes instead of having to bleed a line is quickly becoming one of my favorite pastimes. 

The last Sentinel came out a few months after SRAM launched its UDH and was not retrofitted with the Transmission Trojan Horse. Transition updated alloy frames after the fact, but not carbon frames. Now, the carbon frame is UDH equipped to keep all you button pushers happy. But rest assured, there is still cable drivetrain routing with both frame materials.

BOOM Box

I'm a fan of internal downtube storage. I'm an even bigger fan of the marketing names brands have come up with to describe a hole in your frame upon which you can store stuff. Transition's party in the woods culture runs deep, and Boom Box is a fitting name for their first in-frame storage solution. While the concept is not new—a latched door covers a hole that exposes the inside of your downtube—placing the opening beneath the water bottle mount makes access much easier. You don't have to work around or remove your bottle and cage to get inside your frame, which can be an extra hassle during trailside repairs. The door is also dead silent.

Internal storage is almost a must on a new bike. And whether you love it or hate it, Transition has at least made a usable, simple design. 

Suspension Design

Not a ton has changed with the kinematics of the Sentinel. The leverage curve is a touch less progressive and more supportive higher in its travel. The leverage ratio starts at around 2.90 and drops to 2.21. V2 started at 2.85 and dropped to 2.13. As a result, overall progression has dropped from 25% to 24%.  

Transition wanted to build on the Sentinel's snappy, energetic demeanor while maintaining control during big compressions. It's not supposed to eliminate every bump, but it has no problem withstanding successive, fast hits. And simultaneously, it delivers an immediate response time to rider input that keeps your average speed high on flatter terrain.

Geometry 

Just like the kinematics, geometry hasn't changed much. The most significant tweaks are the head tube is actually steeper, sitting at 64 degrees (it was 63.6 degrees), and chainstay lengths are now size-specific. Well, mostly—XS has its own chainstay length; small and medium frames share the same length, as do large, XL, and XXL frames. Chainstay lengths have also grown slightly across all sizes. However, size medium and large have the most balanced front-to-rear ratio. Size XL and XXL still have a short rear center relative to reach.

Reach and stack heights are a few millimeters longer and taller across the board but are within what you'd expect by today's standards. The bottom bracket height and drop are both ~4mm higher, and the effective seat tube angle is over a degree steeper. The steeper HTA, higher BB, and steeper STA make the new Sentinel a more enjoyable climber than the outgoing model. 

Of course, you can swap the flip chip to the high position without swapping to a smaller rear wheel. Transition doesn't provide a geometry chart for this configuration, but presumably, most angles get steeper, the BB rises, and the reach grows slightly.

Build Kits

Transition has always done a great job of offering builds with proper components where you want them. The Sentinel V3 is no exception, and you can actually get rolling on it for less money than the V2. Or, if you'd like to build up a bike, the alloy frame retails for the same amount ($2,199 USD), while the carbon frame is a few hundred bucks cheaper (down from $3,699 to $3,399 USD).

A noteworthy component change is the move from SRAM NX and GX to Shimano Deore and XT, as well as from FOX to RockShox suspension. The outlier is the top-of-the-line XO AXS build that uses Transmission and FOX Factory suspension.   

On The Trail

This is a 'First Ride' review because I've only logged two days on the Sentinel V3. However, I owned V1 and spent a day riding V2 before swinging a leg over the new bike. So, I might not be an expert on how the Sentinel has evolved, but I've got an idea of what's made it so popular in the past. Of course, the next few months will give me time to completely assess how the latest iteration has changed while uncovering its strengths, corks, and durability. 

The previous generation Sentinels were all-terrain vehicles because the geo created a balanced, comfortable bike. So I was relieved that Transition left the geometry mostly untouched. I didn't reference the geo chart before starting my first climb, and while I didn't notice the steeper HTA or longer chainstays, the higher bottom bracket and steeper STA were noticeable during the first punchy pitch. It wasn't a massive improvement but a marginal gain. My hips sat over my pedals and I didn't have to reach for the bottom of my pedal stroke like I had done the day prior on V2. The geo changes were less impactful on gradual or bumpy climbs, but the bike still delivered the smooth, quick-moving personality I remember loving about the first generation. I'd place the Sentinel towards the top of my list of 150mm travel bikes I'd spend extended periods of time pedaling. There is little energy lost to suspension movement, and the seated position is relaxed without being inefficient. 

On the way back down, the geometry changes were less significant. A 64-degree head tube angle seems to be the magic number for bikes like the Sentinel. Slack enough to remain stable at speeds, but manageable climbing. Realistically, the change from 63.6 to 64 degrees is minuscule, and I'd bet most riders would struggle to feel a difference. The 448mm chainstays on the size large kept the rear wheel trailing close behind without being too slap-happy in corners. Any longer, and I think it would detract from the Sentinel's playfulness. I'm curious how a 27.5-inch rear wheel will change things. It only reduces the chainstays by 2mm but lowers the BB by 6mm. That's enough of a change that, when combined with a smaller wheel, should elevate the Sentinel's agility quite a bit.

Like the Sentinel V2, I love how the size large distributes my weight over the bike—arms comfortably bent and my hips just behind my heels. The perfect starting position to react to the trail ahead. The 633mm stack isn't the tallest I've ridden for a large frame. However, it's tall enough to create that 'in the bike' feel that makes it easy to settle into corners and remain planted through chatter. 

The main selling point that draws me towards the Sentinel instead of Transition's longer-travel Spire or shorter-travel Smuggler is that it spreads out its strengths without feeling mediocre in any setting. You can take it down the same gnarly trails you'd frequent on the Spire, or rip down flowy single track like you would on the Smuggler. In both instances, the Sentinel holds its own without feeling undergunned or sluggish. I can't say the same about other similar bikes I've ridden, as some try to check so many boxes that they lack any specific strengths.

Somewhere in between steep gnar and smooth XC trails is where the Sentinel shines most. When there is enough chunk to appreciate its travel without getting jostled around, combined with natural rollers and flat lulls that exploit its support and efficiency, the Sentinel is very rewarding. The more energy I put into pumping transitions, pedaling out of awkward turns, or yanking for gaps, the more responsive the bike became. Lowering the leverage rate through the first portion of travel definitely added to the bike's liveliness and efficiency. Having a firm platform to push against made it easy to generate speed and get the wheels off the ground. 

Through rough sections with constant compressions, I did feel the force of impacts more than some 150mm travel bikes I've tested. It didn't completely mute bumps, which I don't think is a bad thing, as it never hindered braking performance or control. It's a trade-off you have to make with a bike like the Sentinel—it might not be as mind-meltingly smooth through successive hits, but it makes up for it with its fast, fun, and playful personality during otherwise boring sections of trail.  

Overall, the Sentinel V3 is not a radical departure from how the V2 performed but a nice evolution. Comparing the new Sentinel to its outgoing self, the key improvements are:

• The steeper seat tube angle makes for a more efficient pedaling position.
• The lower starting leverage rate increases support and speed generation.
• The slight increase in stack and reach builds on the confidence and capability established by the first two Sentinel models. 

Long Term Durability

As I look forward to my long-term testing, I'm excited about a few details on the Sentinel V3. 

Redesigning the lower shock mount and removing the hole that existed there before should keep the lower bushing from wearing as fast. If nothing else, it'll be a lot easier to keep clean.

The ribbed chain slap protector has been silent thus far and is a big improvement over the V2 version. I hate bikes that make noise, but I feel good about the new protector's ability to deaden chain noise going forward. 

I've had good luck with pivot bearings lasting and hardware remaining tight on Transition bikes. As we head into winter, I'll have more opportunities than usual to do some damage on linkage pivots. The GiddyUp design is straightforward to clean and maintain, and I expect the bike to remain creak-free. 

I haven't had the chance to test the waterproofing on the Boom Box door. I don't expect it to be airtight, but I'm hopeful it will keep most moisture from penetrating items inside the frame. 

Lastly, I'm testing the Glacier White colorway. I'm a sucker for white frames, but the hype usually fades after a few months when normal wear and tear reminds me why white isn't the best frame color. The paint job appears resilient, but time will tell. 

What's The Bottom Line?

The Sentinel V3 remains true to its ride-everything identity while improving its climbing efficiency and responsiveness on low-angle trails. Still a capable descender that can hold its own on when things get gnarly, the Sentinel flourishes most on trails that maximize its maneuverability and fast handling. You tack on the new additions of mixed wheel compatibility, internal storage, updated chain slap protection, reworked cable routing, UDH on carbon frames, and a geometry flip chip, and the Sentinel V3 answers the wants of many past owners. Refined, not redesigned, looks pretty damn good.

For more information, please visit transitionbikes.com

View key specs, compare bikes, and review the Transition Sentinal in the Vital MTB Product section.

Reviewed by: Jason Schroeder - Age: 29 // Years Riding MTB: 18 // Height: 6' (1.8m) // Weight: 180-pounds (79.3kg)

A once-upon-a-time World Cup downhill racer turned desk jockey, Jason has spent years within the bicycle industry from both sides of the tape. A fan of all-day adventures in the saddle or flowing around a bowl at the skatepark, he doesn't discriminate from any form of two-wheeled riding. A SoCal native who doesn't spend too much time in any single place, you can find Jason camped out in his van most weekends somewhere on the West Coast.