2025 Transition Sentinel
Wheel Sizes:
- S–XXL: 29’’ front and rear (mixed wheel compatible)
- XS: 27.5’’ front and rear
Suspension Travel:
- Frame: 150 mm (160 mm w/ 65 mm stroke shock)
- Fork: 160 mm
Geometry Highlights:
- Sizes offered: XS, S, M, L, XL, XXL
- Headtube angle: 64°
- Reach (size Large): 480 mm
- Chainstay length (size Large): 448 mm (Carbon), 446 mm (Aluminum)
Frame Material: Aluminum and carbon fiber versions available
Price: Complete bikes starting at $3,299 USD (details in Builds section below)
Intro
The release of the 2018 Transition Sentinel was a bit of a seminal moment in mountain bike design. Sure, it had its flaws (which I’m familiar with — I owned one), but it also was one of the first mainstream examples of combining a truly slack head tube angle, shorter fork offset, long reach, and steep seat tube angle. Despite having just 140 mm of inadequately progressive rear suspension travel, it felt like I could get away with murder on that bike since it was so stable at speed and in steep terrain compared to just about every other Trail bike out there at the time. Transition called that concept Speed Balanced Geometry (or SBG), and while the acronym has become less relevant given the near-ubiquitous adoption of the underlying geometry concept across the bike industry, the influence and importance of that first Sentinel can’t be ignored.
The Sentinel entered its second iteration back in 2021, still positioned at the intersection of Trail and Enduro — and it was Transition’s longest-travel 29er at the time. So it’s been almost 4 years since the last revision, and at long last, it’s here — the third-generation Sentinel. Despite similar intentions to the outgoing bike, the geometry has been revised, in-frame storage and mixed wheel compatibility have been added, and Transition has refined a bunch of the other details, too. Let’s check out what the new Sentinel has to offer.
The Frame
Transition has built its full lineup around a very familiar frame aesthetic that is both contemporary in its angular shapes, while still having a rather traditional four-bar suspension layout. The new Sentinel gets some updated industrial design details, but still very much looks like a Transition. It also still comes in both carbon and aluminum, with both frames sharing nearly all of the same features, and now comes in a whopping six sizes, from XS to XXL.
Like the old one, the new Sentinel gets 150 mm of rear travel matched to a 160 mm fork, though Transition says that it can go up to 160 mm of rear travel with a swap to a longer 65 mm stroke shock from the stock 60 mm one. Transition says that they’ve revisited the Sentinel’s suspension kinematics to offer more support earlier in the travel — a welcome change in my experience, as the high starting leverage rate on their past generation of bikes could feel a bit unsupportive in the first third of the travel. Transition has gone with a 25% progression rate, which should play nice with coil shocks — the leverage curve is as follows:
While the outgoing Sentinel was a 29’’ wheeled affair, Transition now includes a flip chip at the lower shock mount to accommodate either full 29’’ wheels or a mixed wheel setup. Small through XL sizes come with 29’’ wheels as stock and can be switched to mixed as an aftermarket option, while the XS is 27.5’’ front and rear only.
The only feature difference between the Sentinel’s carbon and aluminum frames is that in-frame storage is limited to the carbon option. Transition has added their new B.O.O.M. (Burritos or Other Munchies) Box design, which comes with two gear bags for organization, and there is still an accessory mount under the top tube too. Both frame options include a Fidlock base as a water bottle mount option to maximize bottle size in the given amount of space, though you have to buy the bottle separately. You can of course still run a regular old bottle cage too.
The Sentinel also gets a new, much more substantial chainstay protector, as well as revised cable routing via new bolt-on covers at the head tube, which more securely clamp cables to prevent rattling. Transition has also revised the lower shock mount area on the carbon frame to prevent water and grit from forming a little pond around the shock eyelet, which I affectionately call the “swimming pool” on my Repeater.
Apart from the B.O.O.M. Box being a carbon-only feature, there’s also a significant weight difference between the carbon and aluminum frames. A Medium carbon Sentinel frame rings in at a claimed weight 7.41 lbs / 3.36 kg, while the Medium aluminum frame is quite hefty at 9.91 lbs / 4.5 kg. The cost difference is $1,200 USD between the two frames, but with the Alloy Deore build ringing in at 36.4 lbs with EXO casing tires in a size Medium, such a substantial weight difference between the two frame materials is worthy of consideration.
Fit & Geometry
The new Sentinel has gotten several revisions when it comes to geometry, and they’re all promising changes in my view. In the stock 29’’ configuration with the flip chip in Low (or the stock 27.5’’ wheel configuration in the case of the XS), Transition has actually made the Sentinel a touch steeper at the head tube — now measuring at 64° rather than the prior version’s 63.6°. That’s not a huge change, to be fair, but I think the 64° suits the Sentinel’s more all-around intentions a bit better. Using a Large as the reference point, reach has increased slightly to 480 mm, the stack is 633 mm, and the bottom bracket drop has reduced slightly to 25 mm from the previous 29 mm.
Swapping to a mixed wheel setup via the High flip chip position makes things a bit slacker. The head tube angle shifts to 63.6°, and a size Large sees the reach tighten up slightly to 476 mm, with the stack increasing to 636 mm.
One interesting detail is the difference in geometry between the Sentinel’s alloy and carbon frames. While I imagine this has to do with the aluminum frame requiring some slightly different tubing placements, there are some notable differences. In the stock 29’’ configuration, the carbon model has a substantially steeper seat tube angle at 78.3° in a size Large, compared to 77.3° with the aluminum version. The carbon frame’s effective top tube length is quite a bit shorter than the aluminum one as a result, at 605 mm in Large compared to the metal bike’s 614 mm.
With the new Sentinel, Transition also offers size-differentiated chainstays, but they are again a bit different by frame material. In the stock 29’’ configuration, a Large carbon frame has 448 mm chainstays, while an aluminum one is 2 mm shorter at 446 mm. Those 448 mm (carbon) and 446 mm (aluminum) chainstays persist on sizes Large through XXL, while the Small and Medium bikes get 442 mm chainstays for both frame materials. The XS has the shortest stays at 436 mm given its diminutive size and 27.5’’ rear wheel.
As a final note, while Transition says you can run either geometry setting at a given wheel size, I’d suspect that things would get a bit too tall and steep with 29’’ wheels in High mode, while mixed wheels in Low mode would be very low and slack.
Full geometry is as follows for all sizes, frame materials, and wheel size options:
The Builds
Transition is offering two aluminum builds and three carbon builds for the Sentinel, along with frame-only options for both materials. Builds are nearly identical across the two frame materials until you get to the top-shelf carbon build.
The base model is the Deore build, which comes with a full Deore drivetrain and four-piston brakes from Shimano. The alloy model gets a RockShox Super Deluxe Base rear shock and a Psylo Gold RC fork, while the carbon build steps up slightly to a Super Deluxe Select rear shock and Lyrik Select fork. The next step is the XT build, which unsurprisingly gets a full Shimano XT drivetrain and four-piston brakes. Suspension is again a RockShox Super Deluxe rear shock and Lyrik fork, and again differentiated slightly by frame material: the aluminum option gets the Select+ models while the pricier carbon build jumps to RockShox’s range-topping Ultimate models.
The lone build with Fox suspension is the XO AXS build, which is offered for the carbon frame only. A Fox 36 Grip X2 Factory fork is matched to a Float X Factory rear shock, with XO Transmission handling shifting and SRAM’s powerful Maven Silver brakes handling stopping duties.
Dropper post lengths are generous across the board, which is great to see — the XS starts at 120 / 125 mm depending on the build, and the XL and XXL sizes reach as high as 230 mm / 240 mm.
Interestingly, each model sticks with aluminum wheels, there are no fancy electronic suspension upgrades on offer, and there’s only one build that comes with electronic shifting. While the range-topping XO AXS build sure isn’t what I would call affordable at $7,899 USD, Transition seems to have kept prices in check while offering balanced and well-chosen builds, with the aluminum XT build being a particular standout on the value front.
Full build details are as follows:
- Drivetrain: Shimano Deore
- Brakes: Shimano Deore M6120 (203 mm rotors)
- Fork: RockShox Psylo Gold RC (160 mm)
- Shock: RockShox Super Deluxe Base
- Wheels: WTB ST i30 rims, Novatech hubs
- Dropper post: SDG Tellis (XS: 125 mm, S: 150 mm, M: 170 mm, L: 200 mm, XL/XXL: 230 mm)
- Drivetrain: Shimano XT
- Brakes: Shimano XT M8120 (203 mm rotors)
- Fork: RockShox Lyrik Select+ (160 mm)
- Shock: RockShox Super Deluxe Select+
- Wheels: DT Swiss M 1900 Spline 30
- Dropper post: OneUp V3 (XS: 120 mm, S: 150 mm, M: 190 mm, L: 210 mm, XL/XXL: 240 mm)
- Drivetrain: Shimano Deore
- Brakes: Shimano Deore M6120 (203 mm rotors)
- Fork: RockShox Lyrik Select (160 mm)
- Shock: RockShox Super Deluxe Select
- Wheels: WTB ST i30 rims, Novatech hubs
- Dropper post: SDG Tellis (XS: 125 mm, S: 150 mm, M: 170 mm, L: 200 mm, XL/XXL: 230 mm)
- Drivetrain: Shimano XT
- Brakes: Shimano XT M8120 (203 mm rotors)
- Fork: RockShox Lyrik Ultimate (160 mm)
- Shock: RockShox Super Deluxe Ultimate
- Wheels: DT Swiss M 1900 Spline 30
- Dropper post: OneUp V3 (XS: 120 mm, S: 150 mm, M: 190 mm, L: 210 mm, XL/XXL: 240 mm)
- Drivetrain: SRAM XO Transmission
- Brakes: SRAM Maven Silver (200 mm front / 180 mm rear rotors)
- Fork: Fox 36 Grip X2 Factory (160 mm)
- Shock: Fox Float X Factory
- Wheels: DT Swiss XM 481 rims, DT Swiss 350 DEG hubs
- Dropper post: Fox Transfer Factory (XS: 120 mm, S: 150 mm, M: 180 mm, L: 210 mm, XL/XXL: 240 mm)
Frame-only options are available in both carbon and aluminum, both with a RockShox Super Deluxe Ultimate rear shock. The more affordable aluminum option costs $2,199 USD, and the carbon one costs $3,399 USD.
Some Questions / Things We’re Curious About
(1) How does the Sentinel’s on-trail personality compare to other bikes in the highly competitive 150–160 mm travel, and does it fall more on the Trail or Enduro side of the spectrum?
(2) Given some not-so-subtle differences on paper between the carbon and aluminum models in both weight and geometry, how different do they feel in practice?
Bottom Line (For Now)
The new Sentinel may not look radically different from the old one, but Transition has found a lot of opportunities for refinement on the new bike. The result is a bike that could likely check a lot of boxes for a lot of people — but that of course can only be judged for certain by how it rides. We will have a new Sentinel headed our way shortly, and we will report back once we can get some time on it.
Flash Review: Our Initial On-Trail Impressions
BLISTER+ members and those who purchase our Digital Access Pass can check out the Flash Review below to read our initial on-trail impressions. Get our Digital Access Pass to view all our Flash Reviews and Deep Dives, or become a BLISTER+ member today to get access to that and a LOT more, including the best worldwide Outdoor Injury Insurance, exclusive deals and discounts on skis, personalized gear recommendations from us, and much more.
Flash Review: Transition Sentinel V3
Update 1.13.2025: We’ve got a bunch more time on the new Transition Sentinel, and our impressions have evolved. Check out our latest thoughts.
Blister’s Flash Reviews and Deep Dives are accessible to those who purchase one of our paid subscriptions
To get our comprehensive Deep Dives and our initial, unfiltered reports on new gear, become a member and receive many other services, deals, and discounts.
If you’re already an active member, please log in.
(If you’re already logged in and a member in good standing and seeing this message in error, please refresh this page in your browser.)