I’ve been running the Transition Sentinel Carbon as my primary trail bike for two seasons now. During this time, I’ve worn parts out, ridden a number of epic destinations, and a variety of setups were experimented with. What follows is an update with my experiences owning the bike in the form of a long term review.
Two years ago when the Sentinel was released, the long and low geometry concept was still taking off, and Transition was one of the brands leading the curve. I initially was drawn to the Sentinel as it sold me on the notion it could be that “one bike” – the holy grail of the mountain bike that can do it all: handle and descend like a downhill bike, but then capably climb back up hills. A 29er that charges like a DH bike sounded awesome.
Assembling the Sentinel
The Sentinel is a great looking frame and I’m fond of the aesthetic. I’m also a fan of the threaded bottom bracket as they’ve always run trouble-free in comparison with press-fit options, which can be hit or miss at times with tolerances.
As is becoming the norm with carbon bikes, the frame includes a downtube protector and a chainstay protector. Adding additional frame protection is highly recommended as well, which has come to be expected when investing in a carbon fiber frame. At 6.61lbs with a rear shock, it is light for a bike in its class and saves a good amount of weight over its alloy counterpart.
I had planned to source all the components for the build separately but at the time, forks with the 44cm offset were not yet readily available. I’m a Shimano rider, but I ended up popping for the GX build kit just so I could have the bike and assemble it right away and ride. The Sentinel with the GX kit and the Carbon frame lists for $5k.
Ideally, I would have gone with the Fox 36 on the front end, but it wasn’t available at the time, so I elected to go with the Rockshox Lyrik which has proved to be a solid performing option.
The build kit included SRAM drivetrain and brakes as well as a Rockshox Reverb seat post. I already have two Reverbs sitting under my workbench that need rebuilds so I took a pass on the Reverb. I’m a big Shimano fan, so and XT group was installed; however, I needed to source an HG freehub body so I ran the stock Eagle GX 12-speed drivetrain for a few weeks while I was waiting.
Choosing the frame size
Choosing what size frame to go with was a sticking point I really struggled with before pulling the trigger on the frame. At 5’10”, I fall right in the middle between the medium and large frame recommendations. Coming off a size medium Evil Following with a 415mm reach, the medium was considerably longer than what I had been riding. Although the Following felt short, the recommended large size seemed huge. I was uncomfortable with the idea of having a bike that long, and ended up chatting with Lars at Transition to get his take; with his blessing, I elected to go medium.
Two years into riding the bike, I still feel ok about the choice of the medium. I’ve run both a 50mm and 40mm stem to experiment with the fit. Since then, I’ve also had the opportunity to roll around on size large Transition frames. Now that I have a second trail bike in rotation with 27.5″ wheels, I feel like a large would differentiate the two bikes more clearly, and give the Sentinel more “plow-factor.”
These days sizing decisions look to be influenced by three factors: Head tube and seat tube angle, reach, and wheelbase being 3 of the main factors coming into play. With the long wheelbase, the large would be more stable at speed but that 1247mm wheelbase could be a bit of a bear on steep trails with tight turns. As I’ve added a more nimble 27.5″ long term test rig in rotation, I have a bike dedicated for steep and tight.
On the trail
It’s nice when a bike lives up to expectations. In the past, I’ve changed out my rides regularly. Sometimes I’m simply looking for the next cool thing to check out, or there are a few things I wish were different. That’s never happened with this bike. Not only is the Sentinel the most capable and versatile trail bike I’ve owned, but it really can do it all. Two years in, I have no desire to go through the efforts to replace it with something new and shiny, though the aftermarket link from Cascade Components really has caught my attention.
I’m a fan of the 140mm/160mm travel concept – depending on the build, the bike can hang with shorter travel trail bikes on the climbs and party with long-travel enduro steeds on the descents. Long travel 29ers could easily feel like a giant plow bike, but for a 29er as capable as it is, it is still relatively jumpy and poppy on flow trails. Admittedly not as lively as a bike with 27.5″ wheels, but it’s a different kind of fun. If the features are scaled up to near DH level proportions and speeds, its right on.
I’ve ridden the bike in bike parks, from our local hills to the Whistler bike park and the bike simply shines regardless of where you take it. Well – mostly. In Moab, when playing on the skatepark style terrain, I found myself wishing for smaller wheels; to be fair though, I felt the same when riding Utah on the Following, which is already a more nimble bike.
When it comes to suspension tuning, I’ve found the rear end to be a bit too linear, which can make set up a challenge. I can set the bike up to rail the turns or to take big hits, but it can’t quite handle both. I recently added a volume spacer to the rear and stiffened it up a bit, but now the back end doesn’t hug the ground as well as it once did. The aftermarket link claims to resolve those issues…
I have zero complaints on the Lyrik fork, though I should probably do my lower leg servicing a bit more frequently.
Reynold TRS Carbon Wheels upgrade
Wheels and tires go a long way towards customizing a bike for the local terrain. When a Reynolds Carbon review set of wheels arrived on loan, it brought about a dramatic change to the bike’s personality. Before, it was a capable 29er trail crusher; the lighter wheels added serious pep to its setup.
Instead of just tolerating the climbs and slugging up hills, it felt much more spry. The lower rotating weight was noticeable everywhere, and instead of manhandling the bike or having to add additional setup time into corners, it was considerably more responsive.
It also allowed me to add some serious meats in the form of high-volume, big-lugged WTB tires. (see: WTB 2.5″ Vigilante, 2.4″ Trail Boss and Judge: Beast Mode Engaged) The light rims cancel out much of the weight of the burly tires, effectively neutralizing the additional weight of the heavier rubber.
In fact, the only time I didn’t love the light wheels was on excessively rocky trails. When riding the Top of the World trail in Whistler, the wheels were stiffer than they needed to be, and I held back a bit as I was concerned with durability. I also have a tendency to run a bit more pressure in my tires than most in order to prevent rim strikes and to protect the wheels — even on loaner wheels. Carbon wheels are plenty strong for most riding, but extremely rocky trails can put a lot of wear and tear on rims.
Fortunately, I have two sets of wheels available for the Sentinel, and I’ve since dedicated a set of wheels towards the desired riding experience. The Reynolds Carbon TRS wheels are now equipped with lighter, 2.35 tires for a lighter, trail/all-mountain go setup, with the heavier stock wheels shod with the burly WTB rubber for gravity-fed runs and shuttles.
The Sentinel with the lighter carbon wheelsets and XT clip-in pedals comes in at just over 30lbs. I think with a bit more swapping I could get her to tip under the 30lb. mark.
Long term maintenance
It’s a good idea to regularly clean and inspect the frame and paint for chips and damage to avoid any surprises. I’m pleased to state that the protective tape I applied has done its job so far. There’s a point on the chainstay that lacks protection and the paint has been chipped away. I’ve made it a regular point to check in on this area regularly as a catastrophic failure could be a big deal, especially if I was on a big ride in the backcountry or on a road trip.
Shimano XT Four Piston Brakes Upgrade (vs Two Piston)
I demand a lot of performance from my brakes and shifting; thanks to product support from Shimano for our coaching activities I had a fresh XT drive train on hand. After the first season of riding, I swapped in a new drivetrain and 4-piston XT brakes as well as a handlebar for a full refresh.
I’ve always felt that XT two-piston brakes had ample stopping power, especially when paired with a 200mm rotor in the front and a 180mm in the rear. That was until I went 4-piston, and now I don’t think I can go back.
For some time, I’ve avoided 4-pot brakes. Many of the previous iterations of four-piston brakes were great initially but then became a bigger maintenance issue down the road with two sets of pistons and seals to keep clean and maintain.
That said, the newest iterations of the Shimano four-piston brake simply rule. I heart these brakes more than anyone should, and anyone that puts them down will receive permanent opposition.
I just received a new Shimano 2020 12-speed group and am looking forward to bolting it up. Unfortunately, I don’t have a Microspline freehub body on hand for both wheelsets, so I may just bolt on the newest 4-piston XT Brakes for the time being and save the 12-speed group for when I build up a new 27.5 rig once we emerge in a post-pandemic world.
At two years the suspension and pivots have been holding up with major concerns. They’re not as smooth as they once were, but I’m not feeling serious grinding or play. With a few loaner bikes available, I didn’t ride the Sentinel as much during the winter months, sparing the frame and pivots some wear and tear. When the bike does get dirty, I take my time washing things by hand.
After a recent ride, I came to the realization that the fork action felt a bit crappy, and after doing some calculations I’m guessing I have somewhere around 100 hours of riding logged. This means I missed the 50-hour fork lower leg service point so the first thing I did after this revelation was to pull the lower legs and service them.
While the seals were on the dry, I was pleased to see the stanchions were holding up with no apparent wear, so it looks like I caught it in time. The next time I pull the lower legs I’ll plan to replace the seals, unless I encounter leaks or seeping before then.
Cause for concern?
I do have one area where I have started noting a cause for concern. The FSA headset has developed a creak.
When I was learning my way through the new jump trail, Johnny Royal, there were a few instances where my speed wasn’t adequate resulting in my coming up short. AKA, I cased the crap out of a few jumps.
Since then, my bike has developed a bit of creaking in the headset. In all the time I’ve been mountain biking, I’ve only had a few frames fail on me. Both failures were at the head tube, with the frames cracking. Bottom line – its a cause of concern for me. I’ve pulled the headset apart a few times now, cleaned and applied fresh grease, and reassembled it, and each time that seems to address the issue but eventually the creak has returned.
It’s not an ongoing creak, but it does come up. As I like to do a lot of nose wheelie pivots to initiate down switchback turns, that force seems to not agree with the front end.
I finally decided to swap the headset out with the premium offering from Cane Creek: the 110. When pressing in the cups the top was a snug fit. However, the bottom cup, while still seeming to be a good fit, went in rather easily, so it has become a cause of concern, especially since the frame seems on the light side compared to other frames.
Having spent some time with the new headset, I’m occasionally still hearing a bit of noise from that front end that makes me nervous, especially when plowing through rock and root gardens with g-outs and that hard hit. Knowing how thin the material is on the headtube of this bike does make me a bit nervous.
That said, Transition is known for good warranty coverage. However, I’m two years into three years of coverage, and acutely aware of it. On the upside, they also have a good crash replacement policy.
Two years later: re-evaluating the versatility of the Sentinel
At two years of ownership, I’ve logged about 1,000 miles of riding on the Sentinel. It would be more if it was my only bike, but much of my riding takes place on demo bikes, loaners, and review bikes, but in the last few months, I’ve returned to the Sentinel to re-evaluate my thoughts on the bike.
There are two things about the bike I would change. One, the rear suspension is too linear to work in all riding conditions. Switching back and forth between test/ review bikes made this take longer to correctly identify, and adding a volume spacer wasn’t enough to fully address the shortcoming. If I set it up to stick to the ground in rough turns, it bottoms out on large features like big drops. On the upside, the aftermarket link looks to be the optimal fix for this problem.
Two. Sizing. I’m now used to longer bikes, and that 450mm reach that once felts like a big change, now feels like it could be longer. I’d happily swap my medium out for a size large now.
I’ve been wanting to get back to doing more epic all-day trail rides, and have toyed with the thought of getting a shorter travel 120mm 29er trail bike platform for this application. I would definitely size up from a medium for long distance rides.
However, I felt the Sentinel deserved a crack at this – after all, it only has 20mm more travel in the rear than a lot of “down country” frames.
In addition, it comes in at a competitive weight in comparison to 120mm frames. A lot of 120mm travel frames are overbuilt to the same standard as the 150mm travel equivalent. I can’t justify spending $3,000 on a new frame that might perform marginally better on the climbs. (plus I just spent $3,000 to buy a motorcycle.. gotta love the moto comparison with MTB pricing, right)
I’m still a big of this bike, and when I am ready to add another bike to the quiver, I’d rather get back into a new 27.5″ rig to mix things up. <update: now I have an additional 27.5″ trail rig, a down country bike is on my list>
Two years following the release of the Sentinel, and there are a lot of competitors on the market with geometry inline with SBG. That said, the Sentinel still holds its own.
Transition has discounted complete bikes on their website leading many to speculate a newer model is on its way. <update: the new model is here and looks to have addressed every niggle and shortcoming, plus the warranty has been extended to lifetime. Also, my predictions below were almost spot on>
If I was to bet on it, I’d bet that not too much will change – I’m guessing small incremental increases in reach (as well as the degree steeper SA) to match the new Scout could be on the way. (I hope the longer headtube would happen as well personally) Some are speculating a 160mm version of the bike is coming, but more travel it would lose what makes the Sentinel special unless it is accompanied by a new Smuggler release with 130mm travel to split the difference. With the new Scout offering 150mm travel with a different shock, this seems like a direction Transition may go, along with the new design aesthetic, with the sharper, more angular lines of the carbon molds.
It remains to be one of the bikes I enjoy riding the most and would strongly recommend it for anyone looking for a versatile capable ride with 29″ wheels. While I initially thought the SBG geometry was aggressive and too much for some riders, riding this bike has become second nature, and I imagine others would acclimate to it as well. While the Sentinel can feel like a lot of bike for riders in areas without a lot of elevation or that log a lot of fast-paced miles, for the wide range of trail experiences we have here in the Pacific Northwest the bike checks a lot of buttons, especially with the second set of wheels available to expand on its capacity.
After two seasons of use, the resale value of a bike starts to drop considerably but I have no desire to replace the bike, which in my book speaks volumes.
Check it out at Transitionbikes.com
Note: Shortly after we posted our long term review, the updated 2020 model dropped with a number of changes. The crew has already spent some time on the bike — find out what they thought here.