2023 YT Industries

Jeffsy Primus 27

A 27.5″ aluminum frame mountain youth bike with upper mid-range components and hydraulic disc brakes.
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MSRP$2,399
Weight33.7 lbs  
FrameAluminum
SuspensionFull, 150 / 150mm
ForkRockShox Lyrik
ShockRockShox Deluxe Select
Wheels27.5″ Aluminum
Drivetrain1 × 12
GroupsetSX Eagle
BrakesHydraulic Disc
SeatpostDropper
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Ride Feel

Based on frame geometry and build specs.

Handling
nimblestable
Jeffsy Primus 27
Other Mountain Youth bikes
Gearing

A bike with lower gearing will be easier to ride up steep hills, while a higher top end means it will pedal faster down hills.

Lowest gear

(climbing)

24 mph

Jeffsy Primus 27

Highest gear

(descending)

Spec Level

Based on build material and quality level of the frame, fork, wheelset, groupset, suspension system, and more.

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Sizing
One Size

5'0" – 5'5"

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Reviews
Bike Perfect
Hands on: 2024 YT Jeffsy Core 5 first ride review – downtube storage, T-type shifting, and one hell of a price tag

Oct 2023 · Jamie Darlow

YT has reworked its Jeffsy trail bike, adding more tech, more price, and better performance

Highs
  • Pedals better when sat down and stood up cranking

  • Frame is sleeker and now comes with internal storage

  • Bikes range from £2,500 up to £5,999 for Core 5

  • Amazing spec on Core 5, with Fox Factory suspension

Lows
  • Costs a bomb for a direct-sales bike

  • Frame storage door could be bigger

Read Review

Pinkbike
First Ride: 2024 YT Jeffsy - Now With Updated Geo & In-Frame Storage

Oct 2023 · Dario DiGiulio

The new Jeffsy stays true to its trail bike roots, with 145mm of rear travel and 29" wheels.

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BikeRadar
YT Jeffsy Core 3 review

Jun 2023 · Tom Marvin

A blast from the past that's still a serious contender

Highs
  • Fun, poppy ride quality

  • Excellent frame details

  • Good value for money

Lows
  • Some pedal bob when you’re trying hard

  • Harsh cockpit

  • Brakes are underwhelming

Read Review

Bikerumor
YT Jeffsy Primus 27 is an Affordable All-Mtn Bike for Shorter Riders

Apr 2023

The YT Jeffsy Primus 27 steps up an affordable 150mm all-mountain bike for riders 135cm to 165cm tall (or 4’5” – 5’5”); priced at $2,399

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Loam Wolf
2023 Budget Bike Roundup: YT INDUSTRIES JEFFSY CORE 2 REVIEW

Feb 2023

Read our YT Industries Jeffsy Core 2 review and see why this versatile, affordable mountain bike is made for rippers and beginners alike. Read the review now!

Highs
  • Best Bang for the Buck

  • Solid Spec

  • Looks the Most Refined

  • Comfortable All-Day Ride

Lows
  • Shift Performance or lack thereof

  • G2 Brake Fade

  • Short Dropper Post

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MBR
YT Jeffsy Primus 24 first ride review - MBR

Nov 2022 · Danny Milner

Those who think the youth of today have it too easy look away now, because this Jeffsy Primus is a kids’ bike at least as cool – if not cooler – than anything you could be buying yourself. And if your youngsters look like they could get serious about their riding this will give them an incredible leg-up, opening up burly terrain and big hits for even the youngest of shredder. Be careful what you unleash…this is one of the best kids mountain bikes out there. Need to know Available in 24-inch and 26-inch wheel versions, though not switchable from one to the other Attention to detail extends to narrow grips, custom shock tunes, tubeless prep and more besides Proper tyres open up serious terrain for proper little riders Super active suspension that actually works, even for smaller kids Virtual Four Link design carried straight over from adult sized Jeffsy range No corners cut on the spec, top quality finishing kit from front to back If you started out mountain biking on a rusty Falcon Sierra or wobbly old Raleigh Activator prepare for a shock at how far kids’ bikes have come. And how quickly a quality bike like this awesome looking YT Jeffsy Primo can unleash the proper ripper in your nipper. At a price. Like anything you get what you pay for, and at first glance you know there have been no corners cut shrinking down YT’s popular all-rounder for a younger generation of riders. And the deeper you dig into the spec the more impressive it becomes, the attention to detail underlining a zero-compromise approach that makes the price actually look relatively reasonable – particularly now it’s been reduced by over £400! It starts with the foundations of a sleek looking and well-finished hydroformed aluminium frame based around YT’s Virtual Four Link design, driving a Manitou McLeod shock with 130mm of rear-wheel travel and a four-stage compression switch to configure it to the terrain you’re riding. This is paired with a burly looking, 130mm travel Manitou Machete JUNIT front end whose Expert Air springing promises a kid-optimised response that’s often lacking in the basic forks found on most 24-inch bikes. Quality SunRinglé Düroc wheels are another welcome sight and save a chunk of valuable rotating and unsprung weight compared with the hefty hoops standard on the Marin 24in Rift Zone Jr we had on test at the same time. True, the Minion DHF/DHR tyre combo is probably overkill for all but bike park riding, but points to YT’s intentions, the fact they turned up already tubeless and with Peaty’s valves another satisfying detail. The relatively small 42t top cog on the SRAM 11-speed cassette is another indicator of the Jeffsy Primo’s gravity focused ambitions, even if the stumpy 155mm SRAM SX cranks will help little legs and are acut above the kind of no-name components often found on kids’ bikes. Quality finishing kit from SDG completes the spec, the dinky saddle, 650mm bars and super skinny grips …Continue reading »

Highs
  • Looks fantastic. Kid-optimised attention to detail. Suspension actually works. They’ll love shredding the downhills…

Lows
  • …but the climbs will be a drag on those fat Minions. Not cheap. Limited gearing range. Might not last a growing kid very long.

Read Review

off.road.cc
YT Industries Jeffsy 29 Core 3 review

Aug 2022

The YT Jeffsy 29 Core 3 is a very capable all-mountain bike which can handle the rough stuff but is equally at home on flow trails and jumps. While the specification list is solid for the money, it's worth paying extra attention to frame sizing and geometry to get the ride you want. With a longer dropper and some tougher tyres this bike has what it takes to be a real challenger when it comes to the best mountain bikes.

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Beta
The Beta Tests: YT Jeffsy Core 2 29

Dec 2021 · Lydia Tanner

A great value with an appetite for rowdier trails. . 

Highs
  • Incredibly capable

  • Incredibly fun

  • Incredibly versatile

  • Incredible value

Lows
  • Pedal bob had us using the lockout on long climbs

  • Slightly limited water bottle space

  • Could use stronger brakes

Read Review

Geometry
99 Spokes on YouTube99 Spokes on YouTube
Specs
Build
Fork

ROCKSHOX LYRIK BASE, 27.5“ | 150 mm Travel | RC | 100 x 15 mm Axle | Offset 44 mm | Adjustable Rebound, Air Pressure

Travel150mm

Spring TypeAir

Shock

ROCKSHOX DELUXE SELECT, Shock Length: 230 mm | Shock Stroke: 60 mm ≙ 150 mm Travel | Adjustable Rebound, Air Pressure, Custom Tune 0L1230x60mm | R |Custom Tune 0L1| Volume Reducer

Travel150mm

Spring TypeAir

Headset

ACROS AZX-576, High Cap | 2 Spacer 5 mm

Stem

E13 BASE 35, Length 40 mm | 35 mm Clamp | Rise 0° | 6061 AL

Handlebar

E13 BASE 35, Width 760 mm | Rise 20 mm | 9° Back Sweep | 5° Up Sweep | 6061 AL

Saddle

SDG BEL AIR 3.0, YT Custom | Width 140 mm I Lux-Alloy Rail

Seatpost

YT POSTMAN, Ø 31.6 mm | Length 125 mm | Standard-Remote

TypeDropper

Grips

ODI ELITE MOTION V2.1, Lock On

Groupset
Rear Derailleur

SRAM SX EAGLE, 12-speed

Crank

SRAM SX EAGLE, Crank Arm Length 165 mm | 32T | DUB

Shifters

SRAM SX EAGLE, 12-speed

Cassette

SRAM PG1210 Eagle, 11-50T | 12-speed

Brakes

SRAM G2 R, Rotor CENTERLINE Ø front 200 mm / rear 200 mm Adjustable Reach

TypeHydraulic Disc

Wheels
Rims

SUNRINGLÉ DUROC 35, Aluminum Rims 27.5“ | Inner Width 31 mm | Front Hub 100 x 15 mm | Rear Hub 148 x 12 mm

Tires

FRONT: MAXXIS MINION DHF I REAR: MAXXIS MINION DHR II, Front: Tire Size 27.5“ x 2.4 I EXO Casing I 3C MaxxTerra Compound I Tubeless Ready I Rear: Tire Size 27.5“ x 2.3 I EXO Casing I Dual Compound I Tubeless Ready

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Last updated February 24