2023 YT Industries

Jeffsy Primus 24

A 24″ aluminum frame mountain youth bike with high-end components and hydraulic disc brakes.
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Manufacturer Price

Weight27.8 lbs  
SuspensionFull, 130 / 130mm
ForkManitou Machete JUNIT
Wheels24″ Aluminum
Drivetrain1 × 11
GroupsetNX, X1
BrakesHydraulic Disc
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Based on frame geometry and build specs.

Jeffsy Primus 24
Other Mountain Youth bikes

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


19 mph

Jeffsy Primus 24

Highest gear


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One Size

4'5" – 5'0"

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Price History
Singletrack World
YT Jeffsy Core 4 review

Mar 2024 · Ben Haworth

The YT Jeffsy Core 4 is a bike that arrives in a box that is not quite perfect out of the box. BUT... there is loads of potential here.

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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

  • 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

  • Costs a bomb for a direct-sales bike

  • Frame storage door could be bigger

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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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YT Jeffsy Core 3 review

Jun 2023 · Tom Marvin

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

  • Fun, poppy ride quality

  • Excellent frame details

  • Good value for money

  • Some pedal bob when you’re trying hard

  • Harsh cockpit

  • Brakes are underwhelming

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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

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!

  • Best Bang for the Buck

  • Solid Spec

  • Looks the Most Refined

  • Comfortable All-Day Ride

  • Shift Performance or lack thereof

  • G2 Brake Fade

  • Short Dropper Post

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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 »

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

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

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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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99 Spokes on YouTube99 Spokes on YouTube

MANITOU MACHETE JUNIT, 24“ | 130 mm Travel | 110 x 15 mm Axle | Offset 42 mm Adjustable Rebound, Air Pressure


Spring TypeAir


MANITOU MCLEOD, Shock Length: 190 mm | Shock Stroke: 40 mm ≙ 130 mm Travel 4-way Adjustable Compression, Rebound, Air Pressure


Spring TypeAir


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


SDG JR, Length 40 mm | 31,8 mm Clamp | Rise +/-3°


SDG SLATER, Width 650 mm | Rise 20 mm | 8° Back Sweep | 5° Up Sweep


YT Custom | Width 122 mm


YT POSTMAN V2, Ø 31.6 mm | 100 mm | Std. Remote I Adjustable drop 20 / 10 / 5 mm




Rear Derailleur

SRAM NX, 11-speed


SRAM X1, Crank Arm Length 155 mm | 30 T | DUB


SRAM NX, 11-speed


SRAM PG1130, 11-42T | 11-speed


SRAM G2 R, Rotor CENTERLINE Ø front 160 mm / rear 160 mm Adjustable Reach

TypeHydraulic Disc


SUNRINGLÉ DUROC 30, Aluminum Rims 24“ | Inner Width 26 mm | Front Hub 110 x 15 mm | Rear Hub 148 x 12 mm | Freehub HG


FRONT: MAXXIS MINION DHF I REAR: MAXXIS MINION DHR II, Front: Tire Size 24“ x 2.4 I EXO Casing I 3C MaxxTerra Compound I Tubeless Ready I, Rear: Tire Size 24“ x 2.3 I EXO Casing I Dual Compound I Tubeless Ready

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Last updated May 25