If there's a design-focused arms race occurring in mountain biking, one needs look no further than Transition as a key protagonist in the current push toward ever-longer and more-aggressive geometry. Case in point: the newly carbon-fibered Sentinel, a 140-millimeter rear travel, 29-inch-wheeled bruiser unapologetically tailored for the steepest and deepest of terrain. The numbers of our size large test bike push the boundaries of sensibility—64-degree head angle, 76.3-degree seat angle, rangy 475-millimeter reach and a whopping 49-inch (1,247-millimeter) wheelbase. Aside from the modest suspension travel, those are the kind of numbers we see with full-on DH sleds.
As such, it should come as absolutely no surprise that the Sentinel is most at home bombing downhill. It does this ridiculously well, straight-lining the roughest, ugliest, sketchiest descents with a supreme confidence that borders on disdain. The suspension, which Transition recommends setting at between 32- and 35-percent sag, hoovers up everything from chattery, small rubble to massive wheel-sucking g-outs and big drops. There is substantial ramp-up toward the end of travel that defies bottom-out, and this aids the meaty Maxxis Minion DHF/DHR II tire combo in flattening any obstacles that might be so unlucky as to appear in the bike's path. An appropriately beefy Fox 36 Float RC2 fork with 160 millimeters of travel further reinforces the Sentinel's gravity prowess. Even the most timid rider will grow some gravity-courage aboard this bike.
One might conclude that such assertive dimensions would maybe come at the cost of playful behavior or ease of cleaning switchbacks, and one would be right. Stable, implacable, hugely capable at speed? Yes. The Sentinel crushes that game. Playful, nimble, agile, sprightly in technical slow going? Not so much. It is a big bike, and while the shift from aluminum to carbon fiber shed some weight, there is no getting around the fact that there's a lot of room between the wheels and it takes a good amount of muscle, or speed, or both, to really get it properly lit up. While the seating position was great for climbing, the suspension wanted to move around during hard efforts and out-of-the-saddle stints, and the bike was happier when a little more pedaling platform was fed through the trunnion-mount Fox DPX2 shock. That's not to say it is a bad climber—it gets up the hill just fine. But don't go thinking this is some light-duty trail bike with a climbing bias. In case we didn't make it obvious, the Sentinel really, really wants to rail downhill.
At a hair under $6,000, with a mostly X01 drivetrain (except for GX chain and cassette), e*thirteen wheels, Race Face bars and stem and a cleanly executed carbon-fiber frame, Transition's Sentinel Carbon hits a good value target and offers a singularly badass avenue to a degenerate life of mountain bike excess.
Q&A with Lars Sternberg, marketing for Transition Bikes
Aside from reducing the fork offset, what are the key elements of Transition’s Speed Balanced Geometry?
Well, there are five key elements we explored and fine-tuned to achieve the ride quality and rider position that is SBG:
1. Frame reach. We identified that we felt our frame sizing to be a little shorter per size than we wanted. Reach is one of the most important frame dimensions to us. It correlates to your two points of contact on the bike—the horizontal distance between where your hands and feet are when standing, which is where all the party happens. So, we lengthened it 18 millimeters per size.
2. Seat-tube angle. There’s no reason the rider should be sitting over the rear wheel with a slack seat-tube angle, which is only exasperated more when you’re ascending. Then add in rear-shock sag and you’re hanging off the back. So, we made the seat-tube angles steeper across the board. This helps center the rider between the wheels when seated and improves rear-wheel traction when going up.
3. Headtube angle. Kick that sucker out. We want slack. But then the front wheel is pretty far out there making it hard to weight it when you’re not pointed straight down.
4. Shorter offset fork. This brings the front axle/wheel more rearward and in an ideal position to make it far easier to apply weight.
5. Shorter stem length. This was one of the last things we tuned with the SBG system. Going from a 50-millimeter to a 40-millimeter stem length as standard dramatically improves the front end feel overall. Having a stem length and fork offset dimension that is similar to one another really makes the handling sing.
Following on from the first question, what do the aspects of SBG translate to as ride characteristics?
I suspect the handling of a SBG bike would be interpreted and translated differently depending on who you ask. Everyone is unique and feels things differently than the way someone else might. This is the beauty of the bicycle, right? There are so many variables that everyone has their own independent experience. Like a little snowflake, ha. That said, in my own words: The whole point of the SBG system is to help the rider get a bit more centered in the bike between the front and rear wheels. As trail bikes have been evolving and getting slacker, increasing in suspension travel and growing in length, we felt that the way the rider interacted with the bike was becoming increasingly rearward-biased. So, we created SBG to achieve better rider-to-vehicle harmony. One of the really cool improvements in ride feel is that the bikes are more nimble at slower speeds, and more stable and confidence-inspiring as your speed increases. I can’t stress this point enough. In my opinion, they have a bit of a chameleon type of character, they do what you want when you want depending on what you’re riding. The front-wheel traction is improved so much that you kind of stop thinking about what it’s doing and focus more on the ride.
Forty nine freaking inches! That’s a helluva long wheelbase, like DH bike long, but the travel is mid-trail bike travel. Do you think you’ve found the upper limit as far as wheelbase length is concerned?
I know, right? In 2008, my size medium IronHorse Sunday’s wheelbase was somewhere in the neighborhood of 45 inches. I raced three DH World Cups and World Championships on this bike that year. Sounds crazy now. This might seem super-weird, but wheelbase figures were somewhat of an afterthought on this project. We developed the bikes by ride feel and honed in the numbers until we were extremely happy with how they performed. We somewhat just let the wheelbase numbers land where they did. One of the big hurdles with this project is educating our customers about the new geometry. It’s easy to pass one of the new bikes off to ride a certain way due to its numbers. I feel these bikes are different products and, as such, need to be looked at differently. A don’t-judge-a-book-by-its-cover sorta thing. Could future bikes end up longer? Why not? We thought our DH bikes were super progressive back in 2008. I remember the same year Gee’s (Atherton) Commencal was ‘insanely long’ at 47 inches. As long as the bikes continue to meet the demands and needs of the riders, anything is possible.
To that end, mid-range travel meets DH geometry, who do you define as the Sentinel’s target rider?
What, a 64-degree headtube angle with 140 millimeters of rear travel? Impossible! Crazy! It won’t work … You could say we took the reverse-mullet approach with the new bikes. Party in the front, business in the back. It’s no secret we like to build bikes that maximize fun, and the SBG bikes are just an evolution of that. We wanted all the bikes to swing way bigger than their travel range, but also to be far more capable on the other end of the spectrum as well. In doing so, you also get a very capable bike that isn’t a beast to pedal around. We have awesome progressive trails out our front door, but we also love to get out and pedal for hours. So, we wanted good functional travel that was complemented by its geometry. The beauty of this approach is there are no travel-adjust levers, lockouts or wild custom shocks needed to have a bike that feels like a 140-millimeter trail bike on the way up, and a 160-millimeter trophy truck on the way down. "Engineered to Party.”