Those of you that know me are probably aware of my affection for 29” wheels. Or more specifically the marriage of 29” wheels and bikes with rowdy geometry. Naturally, when I got word of the Sentinel, touting boundary-pushing geometry paired with 140mm rear / 160mm front suspension travel, my curiosity was piqued. The not-so-old adage of “longer, slacker, lower” continues to ring true with the Sentinel, but the folks at Transition have executed this in a way that’s a bit different than what we are seeing on virtually every other bike being released these days. Transition is calling it SBG - and no, that doesn’t stand for some silly sexual innuendo as we’ve seen from these guys in the past. This time they clearly mean business, as they have opted for a serious acronym - Speed Balanced Geometry. What does that mean? I’ll get into that, but first, let it be known the Sentinel is one hell of a wild ride, and not one for the faint of heart. Interested? Read on to find out more…

About the Reviewer - Jadyn Welch

• Height: 5'7"
• Weight: 130 lbs
• Years riding mountain bikes: 25
• Bike size tested: small

The quick ‘n dirty features

For those that don’t want to read my thoughts/feedback on this bike, here are the at-a-glance features of the Sentinel:

• All new aluminum frame build, featuring Speed Balanced Geometry
• Metric/Trunnion rear shock
• Boost 12x148mm rear dropout spacing
• Compatible with 29” x 2.5" tires
• Threaded 73mm BB shell
• Internal cable routing for dropper and rear shifter. Rear brake routed externally.
• GiddyUp rear suspension with 140mm travel
• Water bottle cage mount on all sizes, fits full-sized bottle

I don’t like acronyms...what the heck does SBG mean?

Call it whatever you want, it doesn’t really matter. What does matter is the thought process behind SBG, the execution, and how it translates to the trail. As bikes seem to be getting longer’er and slacker’er, we have to question at what point does the bike become cumbersome? Yes, the Sentinel is certainly longer and slacker than what we’re used to seeing from Transition bikes of the past. To be specific, the Sentinel is sporting a massively raked-out 64° head tube angle. Just a couple years ago, that number was pretty much reserved for full-fledged downhill sleds. Naturally, that head angle pushes the front wheel way out there in front of you.

This is where things get interesting. Most 29” suspension forks have a 51mm offset, which means the top crown is offset 51mm forward of the steering axis. Transition have worked with Fox and Rock Shox to build suspension forks with a reduced offset, either 44mm on the Fox 36, or 42mm on the Rock Shox Lyrik. The reduced offset not only helps to reign that front wheel in a bit, but it also affects trail. Trail is a geometry figure, which you may not be familiar with as it’s not typically listed in most geo charts. It can be thought of as the tire contact point trailing behind the steering axis. Less trail equates to faster steering, effectively making the bike feel more nimble, but less stable at high speeds. More trail equates to slower steering, but provides more stability at higher speeds. With SBG, the head angle has been slackened, and the fork offset reduced, effectively providing more trail. The folks at Transition, through lots of real-world testing, believe they have found the sweet spot where the most traction is gained, while not feeling too sluggish.

Acronyms or no acronyms, this bike rips.

My brain hurts...what does all this mean on the trail?

After riding the Sentinel on a variety of trails, I can say for certain that bike is different from any 29’er I’ve ridden. It does seem to provide endless front-end traction - not once did I feel like I was losing my front tire in a corner. The length of the bike took some getting used to for me, as I typically don’t love super long bikes. Compared to my Wreckoning, the Sentinel is about an inch longer in the wheel base. Not a huge difference, but noticeable nonetheless. The bike takes a bit more rider input to handle, especially at lower speeds or on technical climbs. But let’s not kid ourselves - Transition did not build this bike for people who want to spend all day in the saddle pedaling. The Sentinel is going to be your best friend when pointed down the nastiest, steepest, chunkiest crap you can find. My first ride on the Sentinel was on some fairly mellow XC-style trails, and suffice it to say, I wasn’t having a whole lot of fun. I quickly realized I made a mistake though...you wouldn’t bring a trophy truck to a Formula 1 track. Nope. I then took the Sentinel to one of the steepest trails around, and boy oh boy, that’s when the bike truly came to life. The bike simply oozed confidence on everything I could find...super steep rock rolls, chunky steeps, and heck, even some pretty sizable jumps! Not once did I feel like I was overwhelming the bike, nor did I ever feel that I lost control.

We know now that the Sentinel descends like a bat out of hell, but many of you are probably curious at this point, how does the it climb? I’m not going to sugarcoat this - it’s not going to blow any minds on the climbs. That said, the bike does put you in a pretty darn good climbing position, body-wise, which is mainly due to the super steep seat tube angle. The small Sentinel I tested as a 77° seat tube angle, which is a solid 2° steeper than any bike I’ve ridden. It definitely puts your body weight further forward over the pedals, which really does help on those steeper climbs. That being said, those seeking out slow-speed technical climbs are going to need to muscle the bike a fair bit. With that 64° head tube angle, the front wheel can tend to wander. It’s also no secret the Sentinel is a bit hefty. Transition came to the realization that the people riding their bikes tend to push the limits and play hard. The Sentinel (and all of the 2018 SBG bikes) are built to take beating for years on end. They’ve added material to the entire frame to make these things just about as burly as anyone could possibly need. And of course, that all comes at a weight penalty - about a pound heavier than last year’s Transition bikes. Generally speaking, I only noticed the extra weight on the climbs. The bike didn’t feel cumbersome on the descents, and was still perfectly capable of being tossed around at a moment’s notice. While not quite as playful as the Wreckoning, it’s still pretty impressively nimble given the nature of the bike. For those that are still put off by the weight of the Sentinel aluminum frame, we've got good news! Transition will be releasing a full carbon version of this frame very soon, and it will drop the frame weight by a reported 2.5 pounds, which is huge.

Transition made a couple minor tweaks to the suspension kinematics, but it’s still a GiddyUp bike through-and-through. The Sentinel comes stock with a Float DPX2 Performance Elite, which I found to be pretty capable shock overall. Paired up with the Trunnion bearing top mount, the rear suspension feels nearly stiction-free. Bigger riders, and/or those that really push into their suspension hard may want to add one or two volume reducers to make it a bit more progressive. For those interested in other options, there’s not much out there yet - but Fox is slowly embracing more metric/Trunnion shock sizes, so I’m betting we’ll see a Float X2 Factory option coming down the line at some point in the 205x57.5mm size required for the Sentinel. Push is also in the process of unleashing a huge variety of metric/Trunnion ElevenSix shocks for those seeking a coil shock option.

Going down? The Sentinel abides...

Do you want this bike? That depends...

You’ve probably come to your conclusion at this point as to whether or not this bike is for you. If you’re a beginner rider, or just looking for a more well-balanced every day trail bike, then you’re probably better off checking out the Smuggler or the Scout. Those bikes will be a bit easier to handle and maneuver for the less experienced riders, and they’ll be significantly more playful and nimble for the average rider. The reality is, the Sentinel is a downhill bike masquerading in trail bike attire. If gravity is your game, and you’re looking for a flat-out destroyer 29’er, the Sentinel should be on your short list.