2016 YT Jeffsy CF Comp 1 29

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Review - YT Jeffsy CF 29 from Vital MTB Test Sessions

YT creates a winner with their first trail bike, providing mountain bikers with a lightning fast ride at a price that can't be beat.

Rating: Vital Review
Review - YT Jeffsy CF 29 from Vital MTB Test Sessions

YThas made quite the leap into the suspension bike arena in the last few years. They've had notable freeriders and slopestyle riders before, but now with UCI World Cup Downhill Champion Aaron Gwin and some enduro racers on their side they have really moved into the big leagues with the bikes they have to offer. The Jeffsy 29 is one of their newest offerings, sporting 29-inch wheels and an ultra progressive suspension system they have come to be known for. As their first trail bike, it's designed to be an "everyday" ride. We put it to the test during the 2017 Vital MTB Test Sessions.

Highlights

  • Carbon frame
  • 29-inch wheels
  • 140mm (5.5-inches) of Read More »

YThas made quite the leap into the suspension bike arena in the last few years. They've had notable freeriders and slopestyle riders before, but now with UCI World Cup Downhill Champion Aaron Gwin and some enduro racers on their side they have really moved into the big leagues with the bikes they have to offer. The Jeffsy 29 is one of their newest offerings, sporting 29-inch wheels and an ultra progressive suspension system they have come to be known for. As their first trail bike, it's designed to be an "everyday" ride. We put it to the test during the 2017 Vital MTB Test Sessions.

Highlights

  • Carbon frame
  • 29-inch wheels
  • 140mm (5.5-inches) of rear wheel travel // 140mm (5.5-inches) fork travel
  • Virtual 4-Link suspension design
  • Tapered headtube
  • External cable routing
  • Flip chip adjustable geometry
  • Integrated downtube and chainstay protection
  • Optimized chainstay length between S/M and L/XL frames
  • Press fit BB92 bottom bracket shell (no ISCG tabs)
  • Boost 148mm rear spacing with 12mm through axle
  • Measured weight (size large, no pedals): 28.4 pounds (12.87kg)
  • 2016 MSRP: $4,499 USD // 2017 MSRP: $3,999 USD

The Jeffsy came to us ready to rumble and paired with some of the best parts you can get for the money. The high value promise of YT's consumer direct sales model is undoubtedly one of the biggest reasons for people’s rising interest in the brand, but price certainly doesn’t make the whole bike. Taking cues from YT's other successes, the little details scattered around the Jeffsy make it look like it has been around for a lot longer than it has.

The carbon frame has smooth lines, flush fittings for all suspension bolts, and all pivot bearings are sealed for longevity. The Virtual 4 Link (V4L) suspension design promises independent suspension action and is paired with a 200x57mm RockShox Monarch RT3 shock. Like all of YT's bikes, the progressive suspension system was designed to leave something in reserve for fast and rough sections of trail. The bike's 140mm of travel is actually progressive enough that running a coil shock isn't out of the question.

YT says they've made the "high modular" carbon fiber tube walls "thicker in critical areas to make sure the frame can handle the abuse, and integrated protectors keep the downtube and chainstays out of harm’s way when the action heats up." The polyurethane downtube guard is a bit on the small side, but it's there nonetheless. We also dig the small aluminum plate located just above the cassette on the seatstay to prevent frame damage should the chain derail.

The frame makes use of the new Boost 148 rear axle standard for added wheel stiffness, as well as an easy to use DT Swiss thru axle. It is not 27.5+ compatible, however, as YT doesn't feel plus tires are up to par just yet. There's also no ISCG mounts to be found, although it's possible to use the e-Type front derailleur mount to install an upper chainguide for some extra chain security.

Jeffsy frames use a mixture of internal and external cable routing that is clean and well thought out, with the rear brake remaining entirely external for easy maintenance. Small guides ensure the rear derailleur cable and small portion of internal dropper routing stay quiet inside the frame.

We dig that the bike lacks any proprietary bits save the optional custom "Thirstmaster 3000" water bottle designed to tuck in underneath the shock. Mud clearance is also good, with around 1.5cm of room for the muck to build up with the stock 2.4-inch Onza rear tire.

Given YT's release schedule, we reviewed a 2016 CF Comp 1 model that sold for $4,499 at the time of this test. YT has since released their 2017 lineup, and the same bike now goes for $3,999 with changes to equivalent or better options in the wheel and dropper post departments. Even the paint job is identical. YT offers the bike in a total of four carbon builds ranging from $3,999 to $5,599, and two very affordable aluminum models at $2,599 and $2,999.

Geometry

YT offers riders a ‘low’ and ‘high’ geometry adjustment through the use of a flip chip at the rear shock mount. There are small differences in the settings – 0.7-degrees in the headtube and 8mm of bottom bracket height – but those differences can mean clipping rocks or cleaning technical sections, adding some capability and drifting the way you want, or tweaking things to suit tight and twisty trails better. We measured the bottom bracket height at 339mm in the low setting.

While not an industry first, it's neat to see YT use different length chainstays to maintain a consistent balance between frame sizes. Large and XL bikes see a 5mm increase from small and medium frames.

At 5'8" and 5'10" (1.73 and 1.78m) tall our testers opted for the size large frame with a 445mm reach measurement. YT's sizing is on the smaller end of today's spectrum, meaning a standard medium might not be ideal for someone who typically rides a medium. With a reach of 445mm, the large is just 10mm longer than what is quickly becoming standard for a medium. Riders taller than ~6'3" (1.88m) may find YT's maximum 465mm reach to be a limiting factor.

Suspension Analysis

Using the bike industry's leading linkage analysis software, André Santos, the Youtube suspension whiz, was able to determine a close approximation of the the Jeffsy 29's kinematics for the purpose of this review. These charts provide great insight into several key factors that impact how it rides. Those unfamiliar with these types of graphs should watch André's excellent series of suspension fundamentals videos. The results of his analysis are as follows:

Observations:

  • This is a very progressive trail bike (47%). Thus, 30% sag on shock corresponds to a real sag of 34% at the wheel, resulting in softer initial travel. At the same time, the bottom-out resistance is higher than most trail bikes.
  • Anti-squat values range between 70-80% for a 32-tooth chainring. Considering the smoother initial travel and the relatively lower anti-squat values we can expect a moderate pedaling efficiency. Thus, it’s a good idea to use the shock's pedaling/trail mode for pedally sections. The Jeffsy will pedal relatively well on a 24-tooth chainring for those who have a 2x11 setup (both the 2017 CF 2 and AL 2 models use 2X drivetrains).
  • Given the relatively low amount of anti-squat on the whole travel, the pedal kickback is also lower than most trail bikes.
  • Anti-rise is around 55%, meaning that the suspension is relatively isolated from braking forces.
  • Overall it’s a very progressive trail bike with a moderate pedaling efficiency and relatively low pedal kickback.

How does science meet the dirt? Did our real life ride time confirm the analysis? It's back to Vital's testers to hear how the Jeffsy performed on trail.

On The Trail

Tucson, Arizona's Mount Lemmon served as our test location, interspersing truly wild rock sections with all out speed, lung busting climbs, and slow tech to keep you on your toes. We rode multiple laps on Prison Camp trail to get trial and error out of the way before going to bigger trails like Bug Springs and La Milagrosa. The trails had a mix of fast and tight corners, as well as lots of natural jump options.

In an effort to get the most stability out of the Jeffsy as possible, we chose to set it up in the low geometry setting. Our shorter tester threw on a shorter 35mm stem to bring the total reach down to a comfortable position. With the steep 74.7-degree effective seat tube angle, we felt on top of the bike in a good way and not super stretched out on the size large. While we fit on the bike and felt comfortable, some riders with short legs will either have to be on a shorter dropper post or size down. Our 5’8” tester had to run the seatpost slammed, so pay attention to seat tube length when determining what will work best for you.

We set up the suspension at our standard settings at first, equating to 72psi in the RockShox Pike RCT3 fork for our 175-pound test riders. We set the low-speed compression to four out from full firm in the open setting. Per YT's suggestion, we set the Monarch shock to 30% sag (17.1mm), adjusted rebound to feel, and took off.

Those big wheels are a big part of the Jeffsy’s demeanor, and when combined with a head angle a hair under 67-degrees the YT simply wanted to go fast. We’ve found that a pair of 29-inch wheels makes us feel like we are riding a bike with a degree or two slacker head angle with a little bit more stability and control at speed. In the Jeffsy’s case, the angles and wheels melded together to make for a really fun ride. The chainstays are a cool part of the frame as well. With the front center being a little longer than what we were used to, the slightly longer than today's norm 440mm chainstays helped things feel balanced. A super short back end with a really long front end has left us searching for front end grip and balance in the past, but that wasn’t the case with the Jeffsy. The chainstay and front center measurements complimented each other well, giving us a great feeling of balance. We feel YT's chainstay methodology keeps the handling in check with the broad range of front center measurements. Combined with the 46mm offset fork the bike changes direction incredibly well, and in successive turns we were hooting and hollering as we'd pop out of one into another with the front wheel in the air. Like most 29ers we ride these days, the Jeffsy drifted controllably and had a lot of traction in general.

The bike's incredibly progressive rear suspension creates a ride that is almost immediately responsive to rider inputs.

The Jeffsy loves to go downhill, but not with the smooth, relatively plush feel we thought we’d encounter. That isn’t to say the bike doesn’t handle well, but as it sags into its travel it gets a bit stiffer than most. The bike's incredibly progressive rear suspension creates a ride that is almost immediately responsive to rider inputs. It's not a forgiving ride, that's for certain, and you need to be on top of your game at the suggested 30% rear sag. The firm, responsive feel helps creates bursts of speed when you're able to pump the terrain, and overall you get the impression that it's one fast ride with a pronounced rising rate to keep riders away from bottom out.

Compared to other YT bikes we’ve ridden, the Jeffsy benefits from better terrain feel at the back wheel. The Capra, for example, can feel so plush initially it loses a little bit of feedback. Because this model of the Jeffsy uses a rear shock without a Debonair can and its larger negative air spring volume, small bumps are still communicated, but they don't feel overly harsh thanks to the high initial leverage rate. Medium-sized hits are really felt, however, and the bike exhibits loads of support. It's not a bad thing as the bike didn’t kick back or get slowed down, but you feel them. This is likely not be as pronounced on higher end models using shocks with the FOX EVOL air can.

Combining this trait with the geometry made for a ride that was fun and playful, but also didn’t get out of shape. The big wheels aided in bump absorption via the extra rollover capabilities. We have ridden other short travel 29ers that are responsive, but not the way the Jeffsy is. The Jeffsy is a responsive bike not just in the up and down plane with regards to how the suspension works, but also in the side to side arena. It's a great combination of go for it attitude and save your ass handling. The bike worked really well when pushed hard, encouraging the type of poor decision making that makes mountain biking truly fun.

Through all of our testing we expected the last bit of travel to feel harsh, but it never did. We jumped as far as we could, plopped off drops, and hit g-outs as hard as we dared. Despite being so progressive and having a relatively small air can, you're still able to use all the travel. On multiple instances we blew the o-ring indicator off the shock but never really felt bottom out. You'll find four bands packed inside the shock, offering riders some adjustability if unable to use full travel. Out of curiosity we dropped into the 34-35% sag range, which opened up a bit more off the top traction without fear of bottoming harshly.

If we were to look for a perfect setup, we’d like a rear shock with more adjustment. Luckily it's possible given the standard shock sizing. The RockShox Monarch RT3 shock worked well, but we feel the tunability is limited. As you get deep into the stroke it gets very springy feeling, and adjustable high-speed rebound could be key to toning this down just a hair. The only real option for on trail adjustments are ‘open’ and ‘pedal’ compression modes, as the firmness of the 'lock' mode is only suited to smooth road climbs. We wish there could be a stiffer open setting, which might keep the bike higher up in the travel without pushing so quickly into the stiffer portions of the rear suspension’s rate.

The Jeffsy is a responsive bike not just in the up and down plane with regards to how the suspension works, but also in the side to side arena. It's a great combination of go for it attitude and save your ass handling.

We switched to the high geometry setting while climbing once and for a short winding descent. It didn’t make that much of a difference, but it was positive nonetheless. If riders want the most crank clearance the ‘high’ mode would be a good option. As it sits in the ‘low’ position we had very few instances of crank spiking, so we kept the geometry there to gain the most stability in rough sections. Note that there is a slight change to the leverage curve when switching geometry modes, and it may be necessary to readjust the shock pressure after a change.

At all times we were surprised at the bike's relatively lightweight feel. Sure, it comes with a high end parts spec and wasn’t a tank on the scale at 28.4-pounds (12.87kg), but it felt even lighter on the trail. With suspension that let us move the bike around and a wheel/tire combo that rolled fast and accelerated easily, the Jeffsy was always up for a race among friends. Even when sprinting, we felt the 29-inch wheels didn't hinder us. The suspension was neutral enough that we kept traction and didn’t get knocked off line.

Not all of our time on the Jeffsy was spirited though, as we did slog up some hills in search of fun. The climbs gave us enough saddle time to find one of our few complaints. We wished the Jeffsy had a slightly lower gear than what it did. With big wheels and a 32-tooth chainring, we were sometimes left looking for another shift. This is by no means a deal breaker, it's a matter of cadence and personal preference. Moving to a smaller chainring will also help the bike edge closer into that ideal anti-squat range.

When we were climbing and wanted to get up the hill as quickly as possible, the Jeffsy did a commendable job. Traction was good and our body position was great considering the long wheelbase. It allowed us to make adjustments easily. For example, if we were grinding up a steep section and needed more rear wheel traction, we could lean back just a little without the front coming off the ground. The head angle was also just steep enough that the front wheel didn’t wander. While there is some suspension movement when pedaling, the Jeffsy was a better climber than we thought it would be. It's excellent in general. All you need is some power.

Build Kit

YT build kits are some of the best around, especially for the price. A unique thing about the entire YT brand is the lack of ‘house brand’ parts. The bar, stem, seatpost, wheels and saddle are all tried and true brands, which we appreciate. The only thing that seems to be somewhat ‘in house’ are the Sensus Lite grips given the brand's connection with Cam Zink. The grips are fantastic, thin, and comfy. Grips don’t make a bike though, but they sure did comfort our hands after long days in the saddle.

We had minimal gripes about the other parts, which is something we're rarely able to say. We experienced zero flats, had an easy time adjusting the controls, and could take our minds off of everything other than the ride - that’s how it should be.

At this price point, most bikes come with a lower end FOX 34 or RockShox Pike RC fork. The Jeffsy CF Comp 1 (now called the CF 1 in 2017) comes with the top of the line RockShox Pike RCT3. The ability to tune the low-speed compression and also have a separate pedaling mode was a bonus. Tuning was easy and familiar, which was especially important when we added Bottomless Tokens to the fork to match the progressiveness of the back end. The 140mm travel fork comes stock with two tokens, but three or four balance better with the rear.

The Onza tires were a unique choice, no doubt added to the YT line because of the team affiliation with Aaron Gwin and the YT Mob. While the 2.4-inch width tires were on the large side of things for this type of bike and looked like they would be beasts to lug uphill, the tires rolled fast and felt lighter than they appeared. Traction was good and we had zero issues with folding casings. The corner knobs do give way a bit too easily in high load turns, however, so ultimate cornering bite isn't quite up to par with market leaders.

The tubeless DT Swiss M1700 wheelset was also a nice bit of bling on this build and proved to be problem free for the duration of our rides. We didn't manage to put any dents or wobbles in it and appreciated the quick engagement and stiffness. While a bit on the narrow side, the rims held the tires well, were light, and proved to be durable. For 2017 YT has move to e*thirteen's TRS+ wheels, which we feel will compliment the bike even better.

SRAM brakes are a fairly standard inclusion on many bikes these days, but the RSC version on the Jeffsy was a welcome addition. The ability to adjust pad engagement felt like a bit of luxury compared to the standard Guide R brakes typically included on bikes in this price range. Power was good thanks to the 200 and 180mm rotors and modulation was just fine. We appreciated the added power over smaller rotors when slowing down.

We had a few minor skipping issues with the SRAM X1 drivetrain, but overall it worked well and the RaceFace narrow/wide chainring never dropped a chain. As mentioned before, we would recommend going to a 30-tooth chainring if you want to make the most out of the Jeffsy’s climbing ability. Going larger, like found on the SRAM Eagle drivetrain equipped builds, will reduce pedaling efficiency. Interestingly, we often found ourselves in too easy of a gear after rough sections and rolling terrain - a testament to the Jeffsy’s superb trail speed.

We enjoy trails a lot more when we can focus on what's coming up instead of what’s going on with the bike, and are pleased to say we didn’t get distracted by any rattles or loose sounding bits and pieces. The Jeffsy could do with a slightly softer chainstay and seatstay protector to cut down on chainslap noise, but that is really minimal. The protectors do a great job of saving the frame, but they aren’t as quiet as some of the other bikes we’ve ridden.

Long Term Durability

We have no concerns above normal wear and tear with the Jeffsy. The Onza tires work decently well and roll fast, but we'd be surprised if they last long given their medium ground between a semi-slick and full knobby. We also haven’t had the best luck with the press fit bottom brackets as far as durability and noise, so only time will tell with the Jeffsy. The bike is backed by a three year warranty (five in the US) and crash replacement program.

What's The Bottom Line?

The YT Jeffsy is a great choice for lots of riders. It can move around tight sections with ease, has great straight line stability, and maintains excellent speed, often creating it where others bog down. It isn’t the smoothest, but what you lose in mid-stroke plushness you gain in the Jeffsy’s fun, playful and responsive nature. If you want to go fast, pump the terrain, and have a great all around bike, this 29er is worth a try at whatever price point you can muster.

Visit www.yt-industries.com for more details.

Vital MTB Rating

  • Climbing: 4 stars - Excellent
  • Descending: 4 stars - Excellent
  • Fun Factor: 4.5 stars - Outstanding
  • Value: 5 stars - Spectacular
  • Overall Impression: 4.5 stars - Outstanding

Bonus Gallery: 20 photos of the 2017 YT Jeffsy CF Comp 1 29 up close and in action


About The Reviewers

Steve Wentz - Age: 32 // Years Riding MTB: 20 // Height: 5'8" (1.73m) // Weight: 178-pounds (80.7kg)

"Despite what it looks like, I'm really precise and calculated, which I'm trying to get away from. I'm trying to drop my heels more and just let it go." Steve is able to set up a bike close to perfectly within minutes, ride at close to 100% on new trails and replicate what he did that first time over and over. He's been racing Pro DH for 14+ years including World Cups, routinely tests out prototype products, and can squish a bike harder than anyone else we know. Today he builds some of the best trails in the world.

Brandon Turman - Age: 30 // Years Riding MTB: 16 // Height: 5'10" (1.78m) // Weight: 175-pounds (79.4kg)

"My current riding joys include pulling up hard and hucking test bikes into poor landings and techy sections with reckless abandon, then seeing how they react upon landing." Formerly a Mechanical Engineer and Pro downhill racer, Brandon brings a unique perspective to the testing game as Vital MTB's resident product guy. He has on-trail familiarity with nearly every new innovation in our sport from the past several years and a really good feel for what’s what.

Which reviewer resembles you the most? Don't miss our Q&A with the testers for more insight about their styles and preferences.

About Test Sessions

For five years a dedicated crew of Vital MTB testers have been bringing you the most honest, unbiased reviews you'll find anywhere. This time around we rode 2017's most exciting trail, all-mountain, and enduro bikes on a wide variety of rowdy trails in Tucson, Arizona. Reviews can be accessed 24/7 in our Product Guide. Test Sessions was made possible with the help of Arizona Cyclist. Tester gear provided by Troy Lee Designs, Specialized, Five Ten, ZOIC, Sombrio, Race Face, and EVOC. All photos by Lear Miller.

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Specifications

Product YT Jeffsy CF Comp 1 29
Model Year 2016
Riding Type Trail
Rider Unisex
Sizes and Geometry
S, M, L, XL View Geometry
Size S M L XL
Top Tube Length 571mm 592mm 616mm 637mm
Head Tube Angle 66.9° Low, 67.6° High 66.9° Low, 67.6° High 66.9° Low, 67.6° High 66.9° Low, 67.6° High
Head Tube Length 90mm 95mm 110mm 115mm
Seat Tube Angle 74.7° Low, 75.3° High 74.7° Low, 75.3° High 74.7° Low, 75.3° High 74.7° Low, 75.3° High
Seat Tube Length 400mm 440mm 480mm 520mm
Bottom Bracket Height 32mm Drop Low, 24mm Drop High 32mm Drop Low, 24mm Drop High 32mm Drop Low, 24mm Drop High 32mm Drop Low, 24mm Drop High
Chainstay Length 435mm 435mm 440mm 440mm
Wheelbase 1132mm 1154mm 1178mm 1205mm
Standover
Reach 405mm 425mm 445mm 465mm
Stack 605mm 610mm 623mm 628mm
Frame Material Carbon Fiber
Frame Material Details High Modular Carbon Fiber, V4L Virtual 4-Link Rear Suspension, Down Tube/Seat Stay/Chainstay Protection
Rear Travel 140mm
Rear Shock RockShox Monarch RT3 Air Shock, High Volume Air-Can, 3 Position Compression (Open/Pedal/Lock), External Rebound, 7.875"x2.25"/ 200mmx57mm
Fork RockShox Pike RCT3 Air Fork, Solo Air, Charger RCT3 Damper Cartridge, 3-Position Compression (Low/Mid/Firm), Low-Speed Compression, Rebound, Tapered Steerer, 15x100mm QR Thru Axle
Fork Travel 140mm
Head Tube Diameter Tapered
Headset Acros AIX-326, IS41;28,6 | IS52;40, Low Cap, Sealed Headset, Industrial Bearings
Handlebar Race Face Turbine, 760mm x 20mm Rise x 8° Backsweep x 5° Upsweep x 35mm Clamp
Stem Race Face Turbine, 35mm Clamp, 50mm (S/M), 60mm (L/XL)
Grips Race Face Love Handle, Double Lock-On
Brakes SRAM Guide RSC, 4-Piston Caliper, Tool-Free Reach Adjust, Tool-Free Contact Point Adjust, SwingLink Lever, DOT 5.1, SRAM Centerline 200mm / 180mm Rotors
Brake Levers SRAM
Drivetrain 1x
Shifters SRAM X1, 11-Speed
Front Derailleur N/A
Rear Derailleur SRAM X1, 11-Speed, Type 2.1, Aluminum, Cage Lock, Black
ISCG Tabs No
Chainguide N/A
Cranks Race Face Turbine, 175mm
Chainrings 32 Tooth Direct Mount
Bottom Bracket Race Face BB92
Pedals N/A
Chain SRAM PC1130, 11-Speed with PowerLock
Cassette SRAM XG 1150, 11-Speed, 10-42 Tooth
Wheel Size 29"
Rims DT Swiss M1700 Spline 29" Wheels
Hubs DT Swiss M1700 Spline 29" Wheels, 15mm x 100mm Thru Axle Front / 12mm x 148mm Thru Axle Rear
Spokes DT Swiss M1700 Spline 29" Wheels
Tires FRONT: Onza Ibex, 29"x2.4", 55a, FRC 120, Kevlar/Fold
Rear: Onza Ibex, 29"x2.4", 55a, FRC 120, Kevlar/Fold
Saddle SDG Circuit Ergonomic Construction, CroMo Rails
Seatpost RockShox Reverb Stealth, Internal Cable Routing, S: 390mm/125mm Travel, M/L/XL: 440mm/150mm Travel
Seatpost Diameter 31.6mm
Seatpost Clamp Standard
Rear Dropout / Hub Dimensions 148mm x 12mm DT Swiss QR Thru Axle
Max. Tire Size
Bottle Cage Mounts Yes
Colors Snow White/Rawr, Rawr/Jet Black
Warranty Three Years
Weight 28 lb 6 oz (12870 g)
Miscellaneous
Price $4,499
More Info

YT Website