First Look: YT Jeffsy Primus Is For Riders From 135-165cm (4’5”–5’5”)

Apr 27, 2023
by Seb Stott  
Skills not included.

YT have a new bike out for youths or shorter riders. The Jeffsy Primus 27 joins the Primus 24 and Primus 26, and as the name suggests, it uses larger (27.5") wheels for slightly taller riders. The Primus range is based on the Jeffsy trail bike and shares many of the same features and suspension layout. The three models together are designed to suit riders from 135-165cm (4’5”–5’5”), so it's more than just a kid's bike - the Primus 27 could suit shorter adults.

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There Primus range is divided up by wheel size (24", 26" and 27.5"), and there is only one frame size and spec option for each wheel size. The componentry, suspension travel and geometry are specific to the wheel size and the height/weight of the intended rider. The Primus 24 has 130 mm suspension travel, the 26 has 140 mm and the new Primus 27 has 150 mm at each end. YT suggest they're designed with a gravity bias.

Here's how YT describe the differences:

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JEFFSY PRIMUS 24 (For riders 135cm to 150cm tall)

"The smallest ride in the PRIMUS lineup still packs a punch with 130mm of travel all round. Suspension duties are performed by the Manitou Machete Junit fork and McLeod rear shock – both with custom light weight tunes as well as compression & rebound adjustment. Catering for smaller contact points, the junior specific SDG Slater bars, grips and SDG Fly seat provide improved ergonomics. As well as 155mm Sram X1 cranks, the drivetrain features SRAM NX 11 speed shifting and G2 R brakes with 160mm rotors. Sunringle Duroc 30 wheels keep things rolling with the cult classic Maxxis DHF & DHR II tire combo for increased confidence on the descents."

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JEFFSY PRIMUS 26 (145-160cm)

"The PRIMUS 26 comes in 140mm travel, this time with the Rockshox Reba fork and Deluxe Select rear shock (yep you guessed it- both have custom lightweight tunes). Steering this sender is an E13 base cockpit with ODI grips, and an SDG Bel Air 3.0 saddle rounding up the contact points. The PRIMUS 26 also gets a YT Postman 100mm dropper for little legs too. Drivetrain steps up to SRAM SX 12 speed derailleur with a 11-50T cassette and 165mm cranks, whilst wheels and tires are the slightly bigger version of it’s 24 stablemate."

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JEFFSY PRIMUS 27 (154-165cm)

"New to the PRIMUS platform, the PRIMUS 27 comes in hot with 150mm travel, capable of everything from all-mountain adventures to park bike sessions. Suspension is handled by the MY23 Rockshox Lyrik Base fork with Debonair+ air spring and Rush RC damper, and Deluxe Select rear shock with custom tune. Following on from the Primus 26” the E13 cockpit with ODI grips features here too, along with SRAM’s SX Eagle 12 speed drivetrain and 165mm cranks. Chosen for slightly longer legs, the 125mm YT Postman dropper and SDG Bel Air 3.0 provides seating duties, whilst the 27.5” Sunringle Duroc 35 wheels are wrapped in Maxxis DHF & DHR II tires for go-to grip in all conditions."



Geometry

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Primus 27



Pricing

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The Jeffsy Primus 27 is in stock right now on YT's website.

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Author Info:
seb-stott avatar

Member since Dec 29, 2014
298 articles

139 Comments
  • 219 32
 They should have called it the Jeffsy Epstein for the kide ! nice trails on his island &free candy
  • 88 11
 @RedBurn ....LOL!!! lol and as a reminder...Epstein didn't kill himself Attention
  • 2 1
 Marc, is that you?
  • 25 3
 Jeffsy Saville for the English cohort
  • 3 2
 @tomo12377: I was vaguely aware of Saville until last summer when I watched the Netflix docmentary on him. Wow!
  • 3 0
 Oof! LOL
  • 6 0
 Everyone else pack up and go home.
  • 3 5
 @bman33: Pinkbike is weird. Comments like this reinforce a collective narrative that so to speak, staring down the rabbit hole but not actually advancing.
  • 5 1
 @bman33: if he is actually dead...
  • 2 2
 @PauRexs: Another good twist theory to eplore for sure!
  • 3 5
 @lehott: is good to see this community has advanced so much since ppl was defending 2... Look you Furer... Fauci what he said about masks... Was all a joke!.. an so on an so on!...
  • 2 1
 @lehott: * 2 masks
  • 98 1
 Dear manufactures - stop putting SX on kids bikes, put Microshift
  • 39 1
 Problem is Microshift doesn't have forks/suspesion. SRAM uses those as leverage to 'convince' OEM's to buy the hot pile of sh*t SX is to get a deal on the whole package
  • 38 1
 @bman33: Hmmm...maybe the smaller brands should get together and form a package deal alliance. I'd love to see a Microshift/DVO trim level on new bikes.
  • 47 2
 stop putting SX on k̶i̶d̶s bikes. FTFY
  • 16 1
 @bman33: microshift and xfusion and you'd have a beautiful value package
  • 9 0
 @Aleven: Microsoft, formula, and DVO would be amazing.
  • 9 0
 Given that Manitou/Hayes specifically makes the J-Unit line of suspension and components for groms, they'd be a great match for this.
  • 24 1
 @joebiden: Microsoft would cause your bike to freeze and crash unexpectedly all the fkn time
  • 5 0
 @DizzyNinja: Constant updates and request for a full license....
  • 8 0
 @bman33: Now I'm just picturing Microsoft and the UCI 'working' together.
  • 2 0
 @bman33: check the latest Marin e-bike. SRAM suspension and Shimano drive train.
  • 1 0
 @squarewheel: I refreshing exception, but unfortunately not the rule. Kudos to Marin's OEM spec guy for making that deal happen
  • 2 0
 Why just kids bikes? Put Microshift on all value bikes. I used Advent X in my first build and it's damn flawless.
  • 1 0
 @rbarbier12: or suntour
  • 3 0
 @Aleven: instead of DVO - Formula
  • 1 1
 @DizzyNinja: simply not true, msft delivers quite robust and stable systems, but they would change, relocate or remove essential parts and functionality every 2 months.
Like brakes suddenly requiring multi-factor authentication before every maneuver.
  • 43 1
 While I understand that you essentially get a free SX drivetrain when you spec literally any other SRAM part, down to like, crank bolts, as OE, I am begging product managers to stop taking that deal, especially on youth bikes. SX is objectively poor quality. Poor quality means more time fixing stuff. Parents have little enough time as it is to get their kids stoked on riding, and having a kid on a drivetrain that is simultaneously a boat anchor, and made of cheese, is not a recipe for good times. I know it's a margin hit to spec Deore or Microshift, but for any company that wants to claim it actually cares about growing the sport, I think its a tradeoff that needs to be made. Please stop rewarding bad product with your OEM budget just because it improves the bottom line.
  • 3 0
 Amen
  • 1 0
 This bike with a Pike, light 30mm rims, SLX or GX or even Deore or NX 11-speed, Deore brakes is what would be 12.xx kg and good for light people. I build something like that out of a Liv Intrigue, the pre2023 Cube Stereo 140 in XS or S is an even better base when comparing price, parts, weight, standover
  • 34 2
 They should have used nx 11spd on all their models instead of just using it on the 24” model. I’d rather have nx 11spd than sx 12spd any day.
  • 54 1
 They should have used microshift 10 speed instead. lighter, cheaper, more reliable
  • 8 0
 @rbarbier12: My daughter's Prevelo Zulu 24" just arrived with MicroShift AdventX 10 - 48, I'm eyeing up taking it off and putting it on my bike, it's pretty nice Wink
  • 13 2
 @rbarbier12: deore 11/12 speed is the better choice for both IMO.
  • 8 1
 @rbarbier12: Or Shimano Deore 11 speed (now CUES) 51T so massive range and, oh yeah, more reliable.
  • 2 0
 @chacou: I used the Advent X 10-50 on a gravel/commuter/road build I did a few months ago, and it's been flawless. It's almost as light as my XT and GX 12 speeds on my MTBs, and shifting's been flawless and easy to set up.
Would recommend!
  • 33 3
 Primus sucks.
  • 12 2
 Primus sucks!
  • 6 0
 My Name is Mud!
  • 3 0
 @funkzander: Not to be confused with Bill, or Jack, or Pete, or Dennis
  • 3 0
 Available in Seas of Cheese Yellow.
  • 1 0
 But never came in last...
  • 1 0
 Too many puppies
  • 17 0
 Its a true shame we didnt get a video of Seb trying to ride this bike
  • 23 0
 My first enduro bike (Lapierre Spicy 2011) had the same reach as this (literally) and smaller wheels. I crashed a lot but I could technically ride it.
  • 2 0
 @seb-stott: wild how much bikes have grown in the past decade. I often wonder how us tall folks ever managed
  • 2 0
 @seb-stott: pics or didn't happen
  • 2 0
 Why not Ben?
  • 4 0
 @seb-stott: why are you sending me pics of BMX racing I thought you said it was an enduro bike
  • 3 0
 @nickfranko: mostly cause he was the author the first look. Cathro would be extra funny on these tiny bikes
  • 2 0
 @mtmc99: steve peat 2000's videos look absolutely ridiculous
  • 4 0
 @seb-stott: found a video of you racing on that bike!


www.instagram.com/reel/CourS9GNUm3
  • 2 0
 @seb-stott: Well at least you have the brake levers pointed straight down
  • 2 0
 This video of Cathro on a tiny Orange 5 is probably comparable! www.youtube.com/watch?v=_TwXsyUeGkQ
  • 2 0
 @Woody25: hahaha, this is exactly what I wanted. Big man tiny bike is always great for laughs
  • 11 0
 If your kid rides this bike after a big rainstorm, he'll be saying "My Name is Mud"
  • 11 0
 Shake Hands with Beef...wait no, Bike
  • 11 0
 Wynona's Big Brown Bike?
  • 9 1
 These are great bikes for smaller women looking for a bike with good standover. My 5 ft tall wife rides a 26 inch Jeffsy.
  • 7 14
flag sorrymissjackson (Apr 27, 2023 at 8:32) (Below Threshold)
 So there are no small men? I think I've seen a few.
  • 1 0
 What's the standover height on that?
  • 1 1
 My 5' tall GF is selling her Transition Patrol. She doesn't want to though, just lack of space.
  • 3 0
 I agree. The lack of appropriate reach numbers on mountain bikes is absolutely ridiculous! As a middle-age man who is 5’4.5” I really struggle to find a new mountain bike that actually fits me. If I could get a longer dropper post and have improved suspension kinematics on my 2015, Transition Patrol, I would rock that bike forever!
  • 3 0
 My wife is 4'11" and can ride her XS juliana rubion just fine. Pretty similar reach numbers at 405mm to the 397 on the 26in YT. The rubion does have 27.5in wheels though, and 160mm of travel. Would be interested to compare stand over heights, but YT doesn't list them. Not sure why YT doesn't just make the Jefsy in an XS instead of adding an entirely different line.
  • 1 0
 @mark-chandler: I can post later. I have multetted her bike, so it's a little less than stock.
  • 1 0
 @XTRider: Can she put her feet flat on the ground?
  • 2 0
 @bctrailblazer68: Yes. She can stand over the top tube.
  • 1 0
 Only the frame, the parts suck
  • 1 0
 @fageltron: This is why I will probably be buried with my Banshee Spitfire V2. As a 5'3 female with a comically short torso, I'd have to put the stem on backwards on most new "small" frames to be able to reach the bars. Plus, I have zero complaints about the V2's kinematics or geometry, and after 5 years of incremental upgrades, I'd have to spend $7k to get something meaningfully lighter or better spec'd. No thanks.
  • 10 2
 With how much the industry wants to kill the 275 and smaller, i'm surprised it's not 29 both wheels.
  • 5 0
 ST is to long and won't allow for good seatpost insertion...some many get this is wrong on the smaller bikes ruining them. For reaches under 440/445 ST should be no more than 380mm and allow for proper insertion of at least 245mm. Yeti, Ibis, SC, Norco, Revel...they all get this, why can't the rest of the industry?!
  • 3 0
 I wonder if bike companies even have people shorter than 5'6" testing their size small bikes before production?
  • 2 0
 @otterchaos: I suspect not often
  • 9 0
 Can’t wait for the Specialized equivalent, the Stumpyjumper
  • 5 0
 A year ago, I sadly joked that soon people like me would buy children's bikes. And so it happened. Jeffsy Primus suits me. Amazing. I am 35 years old and I will buy children's things again.
  • 3 0
 I'm thinking about it. I want a 26" bike that has a bit more travel than a slope/dj bike since it would suit my local trails and be a blast. All the old bikes in this wheel size have tall seat tubes or wheel/fork compatibility issues.
  • 6 2
 A 432mm chainstay is not for shorter riders. My Ibis Mojo 4 has a 425mm chainstay. Also, it needs an uninterrupted seat tube so it can take longer dropper posts.
  • 4 0
 Agreed - this sizing especially the ST is garbage
  • 1 0
 Agreed. When your CS is longer than the reach it's never a great combo.
  • 5 0
 AYO DASH W***IS YOUR EEWINGS ARE AT THE SHOP DUDE
  • 5 0
 Those cranks lengths are a big fail.
  • 5 1
 Reach still 422 mm, equal to or nut much smallert than many current size smalls. That checks out.
  • 3 0
 Too big for my 5' GF.
  • 2 0
 But not 29 wheels.
  • 1 0
 Pivot offers xs sizing that's pretty on point
  • 3 0
 @JSTootell: I'm assuming you meant the bike. It says it's for 4'5" to 5'5" so that puts her right smack dab in the middle.

It's interesting though that the Jeffsy 29 geo chart says a small is for 5'1" to 5'5". And that's with 29" wheels.
  • 2 0
 @uphill-blues: 410 is about as long of a reach as she can manage. Depending on stack that is still a stretch.
  • 2 0
 Yeah, what the heck?
422 reach and 432 CS.
Imagine a 150cm/5' woman who doesn't want 26", this only adds... irrelevant options.
My gf will stay on her 2017 strive XS...

I know it's a niche. But when a brand goes and and tries to fill it... Well, please try at least?
  • 1 0
 Hummm
I think 24 and 26 versions are good options for young shredder.
But 27,5 version make no sense for me.
It is a marketing niche.
If your height is above 1m60 you can buy an adult version in 27,5 ou 29....
For information, my mates and me ride in enduro with 27,5 bikes (SC Nomad, Canyon Strive, Commencal Meta AM) and we ride as fast and hard than 29er.
Very fine sizing with all wheel size is a bit too much for me
  • 4 0
 26 ain't dead!
  • 3 0
 So it's a XXXL from 5 years ago
  • 2 0
 Dear bike manufacturers, what we need is small person Ebikes, WITH headset routing ASAP
  • 2 0
 All comments about kids bike and I am here thinking can I ride it being 165 cm tall. xD
  • 2 0
 Looks like the kind of bike that never did win no chequered flags but never did come in last.
  • 2 0
 All those cranks are still too long. Instead of 155/165/165 they should be 130/140/150mm.
  • 1 1
 The BMX Background is giving way to a bunch of kids with lyrics. Marketing is an unstoppable beast. I'm not throwing shade, but I loved growing up on a bmx bike.
  • 1 0
 You can ride your BMX around the neighborhood anytime you want as a kid. You need mommy and daddy to take you to the nearest trails to ride this.
  • 2 1
 I don't care about the YT bikes at all, but i love that it's called the Primus. Primus (the band) is amazing.
  • 3 0
 Primus sucks
  • 2 0
 Refreshing lack of cable tourism.
  • 1 0
 The author didn’t like my Jeffsey game. Frown
  • 1 0
 155 cranks for 135 kids: ridiculous!
  • 1 0
 you have a 135mm kid?
  • 2 0
 Too Many Puppies…
  • 1 0
 The 26" wheel one would be fun in a full size too.
  • 2 0
 Cranks are too long
  • 1 0
 If you love your kid, don't let them ride an SX groupset
  • 1 0
 Just need this in an EEB format, and my wife would be riding one
  • 1 0
 Have kids. Swear a lot around them. Tell us in 25 years how they turn out
  • 2 1
 Probably not on stock .
  • 2 0
 The 26" is already sold out.
  • 1 0
 Never was. I bought an XS 27.5 rift zone for my kid.
  • 1 0
 @fruitsd79: just checked the homepage, they ship latest may 18th in the us and are in stock in germany
  • 1 0
 @MilkyWayne: well I bought in 2021.
  • 1 0
 @fruitsd79: and you mean it was out of stock for two years? sorry but I doubt that
  • 4 6
 I'm not bying 3 expensive bikes for my kid in 3 years, they should've made asjustable geo so that bike could grow with the kid
  • 6 0
 Start a bike company and make that perfect bike. "One size fits all" has always been the best approach right?
  • 1 0
 Buy it too big and hand it down. Get a few years out of it. I'm glad YT is making these. Great youth slalom bikes when the reach no longer complies with the 2025 norms whatever they are.
  • 2 0
 Polygon has some great options where you can upsize the wheels as your kid grows.
And for less $$$
  • 2 0
 @bman33: no but other companies do a better job of making their bikes adapt as kids grow.
Besides, isn't that was the comment section for? To armchair quarterback every decision made by every bike company?
  • 4 0
 @BarryWalstead: In my experience the adjustable kids bike are almost all junk if a kid really rides the bike. Buy a bike that fits the kid and will last, then sell it and upgrade. Most good kids MTB's hold their value and are easily sold. I am sure that doens't fit everyone, but my approach to kids bikes
  • 1 0
 @bman33: well these specific bikes literally didn't exist a few years ago so maybe we have gotten to a better place. Several even have adjustable geometry to account for the wheel size change.

How were they junk?
  • 1 1
 Translation: THEY SHOULD HAVE MADE THE IDEA THAT I NOW HAVE AFTER SEEING THEIR PRODUCT
  • 2 0
 @BarryWalstead: Yup, my 8 year old daughter has a Polygon 24" wheel bike. She is borderline big enough for it but it will last her years. Plus, it is pretty decent out of the box so I can always throw parts at it as she needs (like, ditching the long reach brake levers and Gripshift).
  • 1 0
 Looks like a Yeti
  • 5 6
 Not cool to have F-bombs in an ad for youth.
  • 1 2
 never understood how swearing hurts kids.
  • 1 2
 Jeffsy primus 26 rear end on a large Jeffsy 27 plez..... 29 is dead
  • 1 2
 This is how bikes should be fitted. Not by frame size but by wheel size.
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