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2021 YT Jeffsy Core 3 29 Bike

Vital Rating: (Outstanding)
2021 YT Jeffsy Core 3 29 (Assault Green)
2021 YT Jeffsy Core 3 29 Bike 2021 YT Jeffsy Core 3 29 Bike 2021 YT Jeffsy Core 3 29 Bike 2021 YT Jeffsy Core 3 29 Bike 2021 YT Jeffsy Core 3 29 Bike 2021 YT Jeffsy Core 3 29 Bike 2021 YT Jeffsy Core 3 29 Bike
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Vital Durability Review - YT Jeffsy Core 3

Not your typical Vital bike test...

Rating: Vital Review
Vital Durability Review - YT Jeffsy Core 3

When YT launched the revised Jeffsy platform in 2019, we were on hand for our First Ride report from the press camp. Since then we've tested the $2,399 Jeffsy 29 Base model and again, found it to be a stand-out performer, especially for the price. When YT released their latest Jeffsy Core offerings earlier this year, that Core label had us grinning. We have a test pilot who is the very type of rider that YT’s marketing efforts embrace. Young, eager to hit massive jumps without much regard for personal safety or equipment, Logan Brown is not the typical product reviewer and would be the perfect punisher to test out just how Core this Jeffsy iteration is.


  • All fun, all the time
  • Capable climber
  • Excellent parts spec
  • Encourages aggressive riding
  • Confident descender for both rocks and jumps
  • A true all-rounder


  • Frame protection quickly peels
  • Seemingly forever sold-out (even before the bike boom)


  • Full carbon frame
  • 29-inch wheels only (alloy has 27.5-inch option)
  • 150mm (5.9-inches) of rear wheel travel // 150mm (5.9-inches) fork travel
  • V4L, Horst Link suspension design
  • Tapered headtube
  • Internal cable routing
  • Five year warranty
  • FidLock, proprietary water bottle
  • DUB Pressfit bottom bracket with ISCG tabs
  • Integrated, rubber molded frame protection on downtube, bb, and stays
  • Clear frame protection in select areas
  • Boost 148 rear spacing with 12mm through axle
  • Measured weight (size large, no pedals): 31.87 pounds (14.45kg)
  • MSRP $4,199 USD


We arranged to have YT send us a Jeffsy Core 3 29er to review, and we eagerly lined up Logan as the pilot. Once it arrived, we turned over the still-sealed box and sent Logan on his way, just as any YT customer would find themselves. Initially, Logan was a bit sad to have a 29er. He figured the 27.5-inch version would be easier to whip, flick and 360. As it turns out, that wasn't an issue. Let’s dig into how this 150mm-travel 29er performed on the trail, at the jump park, and under the abuse of lift-served laps.


For 2021 YT left the Jeffsy alone, only updating the colors and lineup. Moving to a simpler, Core, nomenclature, there are only three trim offerings. The Core 2 is the starting point at $2,999. Riders will get the same alloy frame as the prior Base model which follows identical geometry as the carbon frames. It merits a mention this is the only model offered with a 27.5-inch wheel option. A SRAM NX drivetrain and FOX Performance level suspension take care of the big stuff while DT Swiss M1900 wheels and Maxxis Minion DHRII tires round out things.

Jeffsy Core 2 - Alloy - $2,999

Next up is our test bike, the Jeffsy Core 3 with its carbon frame. 150mm of squish is handled by a FOX 36 Performance Elite fork and FOX DPX2 Performance Elite rear shock. SRAM's venerable 12-speed GX Eagle drivetrain takes over shifting duties and rounds out a kit that should be both durable, and still easy(ish) on the wallet at $4,199.

Our test bike, Jeffsy Core 3 - $3,999

YT's big dog Jeffsy, the Core 4 gives riders FOX Factory versions of the 36 fork and DPX2 shock with a bump to SRAM's X01 Eagle drivetrain. The wheels also get a bit nicer with DT Swiss XM1700s and a star ratchet hub. Those upgrades come with a tab, however, as the Core 4 will set a rider back $5,199.

Jeffsy Core 4 - $5,199

We really took a shine to the Jeffsy Base last year and felt like we had a read on it. Not wanting to go full baller though, we opted for the $4,199 Core 3 build. Every part on this bike should be up for some very heavy use, with no excuses.

SRAM GX Drivetrain

First Impressions

The Jeffsy came right out of the box ready to ride. We slapped on the bars and wheels and it was good to go. This is what we would expect with YT being a direct-to-consumer brand. We cut down the 780mm bars 10mm on each side just to make it a bit more nimble. On the jump lines and flow trails, we rode the YT stiff to get some more pop out of the travel. We were under the 30% sag recommendation, getting the preferred feel closer to the 20% range. The flip-chip was set in the low (slack) position. That put the reach on our large at 470mm, effective seat tube angle, 77 degrees, head angle hits 66 degrees and chainstay length is 435mm for sizes small through large, stretching out to 440mm on XL and XXL sizes.


The cockpit on the YT felt right at home. This is a super solid bike in which one should feel comfy doing some big drops or hucks. The handlebar setup is clean, and SRAM's Matchmaker system kept the YT Postman dropper lever and GX shifter neatly tucked away. With the seatpost extended, the bike is ready for the climbs. Rider position may be a bit more over the front with a 50mm stem, but not so much that traction suffered on the steep stuff. With the 150mm Postman dropper slammed, the seat sits quite low, making it nice for over-the-seat tricks and getting weight over the back wheel on the descents. Other than making sure the flip-chip was in low and a slight shave of the handlebars, the Jeffsy Core 3 was pretty close to perfect out of the box.



On the Trail

Our YT Jeffsy saw all kinds of action during testing. Of course, we took it out to the foothills for plenty of trail riding. We also had some sessions at the jump park, as well as some lift-served downhill laps. Over the past months, it became our do-everything bike.

The Jeffsy is nimble and lively on the trail. Our tester has an affinity for 27.5s, and the Jeffsy’s feel of being more on top of the bike, rather than submerged in the bike, brought to light just how playful wagon wheels can be.



After experimenting with different configurations, the Jeffsy Core suited our jump and bike park riding preference with a firmer suspension setup. When set up in the 30% range, the bike soaked up the small and mid-sized trail hits quite well. That said, we preferred the stiffer settings to embrace the Jeffsy's more aggressive nature and while providing that extra pop for jibs and jumps. The FOX DPX2 is a reliable performer for most trail bikes. We did find that speeding up the rebound gave a more lively feel to the rear end and helped propel the bike when boosting sharkfin booters and hopping out of corners. Despite our firm settings, the bike kept its composure under braking and blitzing through the chatter.


Pedaling the Jeffsy uphill was an easy task. The balanced rider position was fantastic. When we got to really steep sections, the rear tire maintained its grip, and the bike just motored up the grade. We never felt the front end wander and appreciated the "trail" intent of this bike's nature.


If there was a standout characteristic of the Jeffsy, it would be fun. Downhills are always the best part of the ride and this bike just takes it to a new level. We found that in areas with steep jumps like the Boise Bike Park, the Jeffsy Core 3 carried speed and was still able to get loose; throwing it sideways and even spinning 360s. Although it took a little while to find the balance point, once we did, the Jeffsy would manual for days. We felt the Jeffsy handled both chunky sections and fast, flowy trails equally well. This 29er ate everything we put in front of it.

Parts Check

The build spec on our bike was fantastic. SRAM's GX Eagle drivetrain is a strong performer and worked awesomely. We did explode the rear derailleur on a rock, but that was our fault, not SRAM's. After a new hanger and derailleur, we were back on the trail with no more issues.


Fork - Our favorite component on this bike would be the FOX 36 Performance Elite fork. It was plenty stout for our abuse and gave us the adjustability we needed. Whether it was downhill laps at the gravity park or boosting really steep lips, the FOX fork did its job well.

Brakes - The SRAM G2 R brakes felt solid out of the box. Even on longer descents, they held their own. After a few weeks of riding, however, the rear brake got a little spongy. We did a quick brake bleed and it firmed right back up without a flinch throughout the rest of the test.


Wheels - The only weak piece of spec was the DT Swiss rear hub with its 3-pawl engagement. In sprints or powering out of corners, slapping gears, we noticed a delay and slam before driving forward. Because the Jeffsy is such a charger on the downhill, something small like this really stood out to us when we did have to put the power down. The M1900 rims, however, stayed strong and true regardless of endless attempts to ruin them with berm slaps and sideways landings.



Frame - It was a little ironic that the only thing to show immediate wear was the frame protection. The clear protective kit that YT includes started to peel off fairly quickly. We know this stuff is supposed to protect the paint but it has to stay on the bike to do that. Riders will want to get their own protective kit straight away.


What's the Bottom Line?

After a couple of months of some very hard riding, the YT Jeffsy Core 3 held its own, and we were impressed with the versatility of this 150mm-travel 29er. With only some peeling stickers, it seems the Jeffsy is up for the care-free nature of its target demographic. Should they become available sometime soon, we would once again give the YT Jeffsy two thumbs up.

About the Tester

Logan Brown - Age: 21// Years Riding: 1 year MTB, 8 years BMX, 18 years Moto // Height: 5’11” (1.8m) // Weight: 155-pounds (70.3-kg)

Despite riding downhill for a few years at 15 it was never something I really got into until recently. With a long history in 2-wheeled sports, I picked up MTB relatively quickly. In my short year I have a nice grab bag of tricks and I would like to say I know how to get rowdy and have a good time on a bicycle. I used to be against the climbing aspect of MTB but with my testing of bikes that are well equipped for the climb, I have come to love it. MTB has quickly taken over my life. When I have no plans I'll ride 2-3 times in a day just to put a smile on my face. I currently ride dirt jumpers and all kinds of trail/ DH bikes. It has been awesome learning tricks on the DJ and taking them to the big bikes.


Product YT Jeffsy Core 3 29 Bike
Model Year 2021
Riding Type Enduro / All-Mountain
Rider Unisex
Sizes and Geometry
SM (low, high), MD (low, high), LG (low, high), XL (low, high), XXL (low, high) View Geometry
Size SM (low, high) MD (low, high) LG (low, high) XL (low, high) XXL (low, high)
Top Tube Length 572mm 593mm 615mm 638mm 660mm
Head Tube Angle 66.0°, 66.5° 66.0°, 66.5° 66.0°, 66.5° 66.0°, 66.5° 66.0°, 66.5°
Head Tube Length 100mm 105mm 110mm 120mm 125mm
Seat Tube Angle 77.0°, 77.5° 77.0°, 77.5° 77.0°, 77.5° 77.0°, 77.5° 77.0°, 77.5°
Seat Tube Length 400mm 415mm 435mm 460mm 485mm
Bottom Bracket Height 32mm drop, 24mm drop 32mm drop, 24mm drop 32mm drop, 24mm drop 32mm drop, 24mm drop 32mm drop, 24mm drop
Chainstay Length 435mm 435mm 435mm 440mm 440mm
Wheelbase 1174mm 1196mm 1218mm 1247mm 1269mm
Reach 430mm 450mm 470mm 490mm 510mm
Stack 618mm 622mm 627mm 636mm 640mm
* Additional Info Geometry adjustable via flip chip in rear shock mount.
Wheel Size 29"
Frame Material Carbon Fiber
Frame Material Details High modular carbon fiber, PA 66 down tube protection, rubber seatstay and chainstay protection, chainsuck plate at rear dropout
Rear Travel 150mm
Rear Shock FOX FLOAT DPX2 Performance Elite, 3-position adjust, high/low-speed compression adjust, high/low-speed rebound adjust, 210mm x 55mm
Fork FOX FLOAT 36 Performance Elite, GRIP2 damper, 44mm offset
Fork Travel 150mm
Head Tube Diameter Tapered, 1.125" top, 1.5" bottom
Headset ACROS AZX-576, High Cap
Handlebar e*thirteen Plus 35, 35mm clamp diameter
Stem e*thirteen Plus 35, 50mm length, 35mm bar clamp
Grips ODI Elite Motion V2.1, lock-on
Brakes SRAM G2 R, SRAM CenterLine 200mm rotors
Brake Levers SRAM G2 R, adjustable reach
Drivetrain 1x
Shifters SRAM GX Eagle, 12-speed
Front Derailleur None
Rear Derailleur SRAM GX Eagle, 12-speed
Chainguide None
Cranks Truvativ Descendant 7K Eagle DUB, 175mm length
Chainrings Truvativ Descendant 7K Eagle, 32 tooth
Bottom Bracket SRAM DUB, PressFit
Pedals None
Chain 12-speed
Cassette SRAM GX Eagle XG-1275, 12-speed, 10-52 tooth
Rims DT Swiss M 1900 Spline wheelset, 30mm inner width
Hubs DT Swiss M 1900 Spline wheelset, 110x15mm Boost front, 148x12mm Boost rear with XD driver
Spokes DT Swiss M 1900 Spline wheelset
Tires Maxxis Minion DHR II, Dual Compound, EXO, TR, 29" x 2.4"
Saddle SDG Bel Air 3.0, YT Custom, 140mm width
Seatpost YT Postman Dropper
Seatpost Diameter 31.6mm
Seatpost Clamp Single bolt
Rear Dropout / Hub Dimensions 148x12mm Boost
Max. Tire Size
Bottle Cage Mounts One inside front triangle
Colors Assault Green, Black Magic
Warranty 5 years frame, 2 years components
Weight 31 lb 11.9 oz (14,400 g)
Miscellaneous • V4L (Virtual 4-Link) rear suspension
• Internal cable routing with internal tubes
• Geometry adjustable via flip chip in rear shock mount
• Weight given for size SM set up tubeless, without pedals
Price $4,199
More Info

YT Introduces the New Jeffsy Core Range (press release)

YT Website

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