The light and durable DT Swiss XMC 1200 wheels.

What Goes Round and Round

The DT Swiss XMC1200 Spline carbon wheels are clad with Onyx Ibex tires. Initially, I was concerned about the wheels because of how incredibly light they are, even calling YT to confirm that Howie was riding them. He reassured me, and I’ve also had zero issues after a lot of abuse. The hubs are tiny and spokes amazingly small, adding minimal weight to a package that continues to perform exceptionally well. I’d prefer a wider wheel (~34mm internal) on the bike, but the XMC1200 wheels would be my choice for longer rides.

The tires were the first item to be changed out on the bike. It is now clad in a Minion DHF 2.5”-DHRII 2.4” combination. There were no clearance issues. Though this selection compromises on weight, it works well for my riding style.

Climbing and Pedaling

The Jeffsy’s light weight and pedaling position make climbs less painful. Those characteristics have really helped me put power down while reducing fatigue. The sitting position is fairly relaxed. I’d describe the stack versus reach to be moderate, striking a nice pedaling positions compromise between upright and aggressive.

Enjoying the woods. Photo by Ale Di Lullo

While pedaling on flat or uphill terrain, I played with the different shock settings. Even when fully open, there was minimal pedal bob. For sustained fire roads, I take all the help I can get and lock out the shock. For most riding, the middle setting was a good compromise to retain traction. The progressive ramp up gets the rider to a fairly strong spring rate quickly, so Jeffsy is supportive even when totally open. That really helps for technical obstacles, where more dynamic force is required. One comment regarding the Float DPS shock. Many shocks have a climb switch which firms up the low speed compression damping, but this one nearly locks it out. Think seriously stiff, which I loved for pedaling on smooth surfaces, but when the terrain is the least bit rough, the middle setting was preferred.

A flip chip is present to increase bottom bracket height and slightly steepen the head tube angle. This is accomplished via lengthening the seatstays slightly at the shock mount. The high setting is something I tried once, but it has remained in the low position the rest of the time. If low speed technical rocks were common on my rides, placing ground clearance at a premium, I’d consider it. Other than that, the low setting is preferred.

The stock 32T chainring is a bit steeper than many ride on a 29er with 1x setup. (I generally choose 30T.) But the bike’s weight combined with pedaling performance made it reasonable and that 32t is still on there.

Launching down the trail. Photo by Ale Di Lullo

Hard pedal strokes initially got the nose a tad light, but finding an optimal pedaling position is intuitive. Part of the reason for those nose lifts is the reduced fork offset. That places the front wheel a tad farther back relative to the steerer axis, and is also why the rider needs to keep their weight low and back in turns at speed. This atypical 29er fork offset has a few effects on the riding experience. First off, it reduces the “long nose” feel that some 29ers have when turning in tight terrain at slow speeds. With more offset from the steerer axis, tire contact point offset from centerline increases as the bars are turned, helping to initiate the lean, bringing the nose around quickly. At speed, this also increases the radius slightly from what is expected, running wider at corner exit and takes a little while to retrain yourself.

Round and round you go. Photo by Ale Di Lullo

The Jeffsy is incredibly fun, even on flat terrain, which is not something I can typically say about a bike. Hard pedaling jets it forward, and the riding position plus short chainstays make it very easy to get centered over the rear wheel — and do manuals. There are very few times I ride the Jeffsy in a straight line, frequently recalling memories from Lee McCormack’s clinic I attended many years ago. The Jeffsy lets you feel how much power is possible from flat ground pumping.

One characteristic unique to some riders (think Sasquatch with size 13 feet) is chainstay-heel clearance. I quickly rubbed the protective sticker off the left chainstay, but haven’t scratched through the finish itself. Smaller feet should not have an issue.

Going Down

When gravity becomes a partner rather than adversary, the Jeffsy really gets fun. Combine its active, athletic riding position, dropped seat, short chainstays and progressive geometry, and you can utilize every ounce of your body weight to jet forward.

The 150mm dropper post worked with zero issues during our test. Some people experience issues with the Reverb, which is often the result of hanging the bike by its saddle while the post is dropped. Don’t do that. As mentioned earlier, I’d prefer an under-bar left-hand lever.

The author and Jeffsy Comp 1, in their happy place. Photo by Ale Di Lullo

For riders accustomed to a ~160mm travel bike, a riding style shift is needed to maximize enjoyment of the Jeffsy. Use the terrain to smooth your path rather than blasting straight through it. The 29er wheels reduction of impact angles plus the suspension geometry’s supportiveness allows the rider to really boost off small features, flying over nasty sections. Add those items together and you’ll be flowing with more speed than expected.

Departing takeoffs, Jeffsy is very composed, not bucking the rider. The Fox dampers are owed a nod here for controlling rebound nicely. For descents, I generally ran with the shock open, occasionally just leaving it in the middle setting. You’ll have more flight time than on many other bikes because of how effectively the rider can put weight down on lips, plus the Jeffsy’s light weight makes it easy to pilot. Landings were very friendly, rarely bottoming out. Given the amount of travel, I did avoid huck-to-flat features, simply to reduce overall abuse to the bike. The Jeffsy had zero issues with larger jumps and step downs with transitions.

Flying. Photo by Ale Di Lullo

The Fox Float 34 fork worked without issues, just requiring a volume reducer to prevent bottom out during low speed events, even with the compression damping closed. Some flex was present, but I’m on the heavy end of the rider spectrum, so that was expected. It was also the only item on the bike which makes noise (squoosh squoosh). For most riding, I left the FIT4 damper in the medium setting, occasionally changing to open for wet conditions. On my personal Jeffsy, I swapped the 34 for a FOX Float 36 fork, a setup I absolutely love.

One item I was very happy to find on the Jeffsy was a water bottle holder. It might sound like a small detail, yet the disparity between riding with water on your back versus not is huge, especially for sub-2-hour spins. YT made a custom bottle holder and bottles for Jeffsy. Sadly, it is a location where a water bottle holder fits, but is not retained. The bottle went flying out on the second left-hand berm and needed to be secured with a strap.

The author and Jeffsy Comp 1, coming at ya. Photo by Ale Di Lullo

The SRAM Guide brakes have worked with zero issues, just a bit of noise when they get wet. My personal preference is Shimano, but I found zero faults after riding this bike for about four months. Zero bleeds were required. The combined Race Face/SRAM drivetrain performed similarly, generating no complaints outside a few dropped chains, which would be prevented by an upper chain guide. Most of the drops were before getting the suspension fully dialed, upping spring pressure a tad. Since then, only muddy conditions have caused chain drops.

The DT Swiss XMC1200 wheels and hubs have performed incredibly. As noted earlier, their inner width is a tad narrow for personal preference, yet their incredibly light weight makes up for it. They needed to be slightly trued once, which is less than most wheels I’ve ridden. The hubs have held up with zero issues. Engagement is reasonably fast, noise is moderate, and their size is miniature.

The author’s test Jeffsy out exploring.

Bottom Line

The Jeffsy wants a rider to pilot it, flying over terrain, finding flow. Of the bikes on the market now, the Jeffsy is the one I purchased and ride 75% of the time. The reason I select an alternative bike is when terrain will include a lot of high speed roots and rocks. The Jeffsy can handle rough terrain, but when it is sustained, the bike will be deep its travel, reminding you about the high effective spring rate that progressive geometries provide (bottomless, becoming very firm). Riders, especially larger and stronger ones, can generate an incredible amount of power. Jeffsy is my berm slayer — and the bike I take exploring.

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