YT Jeffsy 29 CF – Trail Bike – Review

YT Jeffsy 29 CF – Trail Bike

Twelve months ago, the Trail bike of the Year in the 29in category was the YT Jeffsy. It’s back again this year and on paper looks every bit as well specced as its predecessor, but a year is a long time in the bike business and there are three new bikes challenging for that coveted crown.

Price-wise the Jeffsy 29 CF is £200 more than anything else in its class, but for the extra dosh you do get a full carbon frame, and that means front triangle, chainstays, seatstays and linkage. It’s nicely finished too and comes with armor at all the pinch points like the down tube, chainstays and BB area. Four sizes are available and to keep the handling balanced across the range, YT uses proportional chainstays — small and medium frames get 435mm stays, large and XL bikes have 440mm.


Last year’s bike came with Fox Performance Elite suspension front and rear but for 2018 YT has switched to a RockShox Pike RCT3 fork and Monarch RT3 shock. Front and rear travel is the same at 140mm, but the fork offset is now 51mm, rather than 44mm, so the bike is a little longer.

On the rear the Jeffsy 29 CF still has adjustable geometry, which is accessed via a flip-chip located on the tip of the seatstay assembly. There are two settings: low/slack or high/steep. You can flip the chip mid-ride but you will need two 5mmAllen keys to do so.

Very few manufacturers bother to fit the bigger 31mm Torque caps to mate with RockShox dropouts. These increase steering precision but the ones on the E13 wheels are loose-fitting so constantly fell off when we tried to get the wheel in and out.


YT bucks the SRAM Eagle trend and fits a Shimano shifter and derailleur with E13’s new 11-speed, 9-46t cassette. This has a whopping 511 per cent gearing range so the jump between the upper and lower gears is bigger than on a SRAM Eagle cluster. Overall, the gearing is higher, though, and combined with a 32t chainring up front, the resulting lowest gear is actually harder to push.

We’d definitely consider swapping to a 30t if you struggle with fitness on the climbs. Following the current trend for more drop, YT has fitted a 150mm E13 TRS dropper post to the size L Jeffsy, but unfortunately, we ran into a sizing issue with the longer post. That’s because increasing the drop makes the post longer overall, but the upper link pivot on the Jeffsy prevents it from inserting all the way into the frame.

On our large test bike there’s about 25mm lower shaft exposed, which means it’s like riding a 170mm post and at full extension we really struggled to reach the pedals. With infinitely adjustable posts, like the RockShox Reverb, you can just drop it a bit to compensate, but the E13 TRS dropper uses three pre-set heights, so we actually had to run the post in the second position and with even more of the lower shaft exposed to get the correct saddle height. YT does offer the Jeffsy 29 CF with a 125mm post, which may be the better option if you’re of average height.


Jeffsy 29 CF is every bit as well dressed as last year’s bike and even comes with a few upgrades like a better fork and rear shock. However, the geometry is starting to look dated — the bike has the shortest reach, the steepest head angle and the highest bottom bracket height for its travel. It’s still nippy and efficient but the sizing is just too short and the fit is compromised by the lack of infinite adjustment in the dropper post.

That’s not the fault of the post, it’s just the two things don’t mesh very well together. The Jeffsy 29 CF has also put on about half a kilo since we tested it last year but that seems to be the case with all bikes that have gone to Boost spacing.


Even though the Jeffsy 29 CF is £200 cheaper than the bike we tested 12 months ago, it still has an amazing frame and fantastic components for the money.

Unfortunately, while the spec has moved on, the ride quality has taken a step back. We felt perched on the Jeffsy 29 CF and it felt more nervous compared to the other three bikes in this test. The issue with the seatpost also put the mockers on a lot of our rides as we were constantly worried about it firing back to full height.

  • Frame: Carbon, 140mmtravel
  • Shock: RockShox Monarch RT3
  • Fork: RockShox Pike RCT3, 140mmtravel
  • Wheels: E13 TRS 29 wheelset, TRS + 29×2.35in tyres
  • Drivetrain: Race Face Turbine 32t chainset, Shimano XT r-mech and shifter
  • Brakes: SRAM Guide RS 200/180mm
  • Components: 35mmTurbine R 780mmhandlebar, Race Face Turbine R 50mmstem, E13 TRS+ 150mm dropper post
  • Saddle: SDG FlyMTN R
  • Weight: 13.75kg (30.3lb)

Rating 8.6/10

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