Sunn Kern S1 review

Climbing legend

Our rating 
3.0 out of 5 star rating 3.0
GBP £2,699.99 RRP | USD $4,090.33

Our review

Like a rocket on the climbs, but it’ll burn up on re-entry if the gradient is too steep
Skip to view product specifications

Sunn are synonymous with downhill racing, but gravity machines are just one string to their bow. The Kern uses a downsized pedal-friendly version of their renowned downhill suspension platform to combat gravity, as well as work with it.


Ride & handling:

The bang-on combination of 22.5in top tube, 73-degree seat angle and 90mm stem gives a good position for climbing and singletrack blasting, and Sunn’s 700mm UN bars are a great shape.

For a 140mm (5.5in) travel bike, this is a climbing legend! In the granny ring, pedal input extends the shock, keeping the bike sat up and your power going straight through the back wheel. In the middle ring, a flick of the Floodgate switch on the shock helps keep its rapid ascending trait.

It’s not over light, at 12.5kg (27.6lb), but the stiff frame and efficient suspension makes it climb like a cross-country race whippet. Technical singletrack is executed with the minimum of fuss and maximum speed. The majority of the suspension bulk is between your feet, keeping the centre of gravity super-low and central. Direction changes are intuitive and lightning fast, and give the feeling of a much lighter bike.

The bike is specced with a 68.5-degree head angle – steep for a 140mm (5.5in) travel bike. Our sample measured at 69.1 degrees – way too steep. The effect is an unnerving ride when speed picks up on any descent. We rode with our weight way back, losing steering control, just to stop the front wheel from tucking under in the turns.

The rear suspension copes well with harsh compressions and landings, but suffers in high-speed compression through rock gardens and roots, where it feels like a bike with far less travel. If you’re a true all-mountain rider, the Kern will fall short in its ability to cope with proper steep gnarl. But if you’re a trail centre fan, this could be the weapon of choice. Their well groomed tracks with drops, jumps, berms and stonking climbs is just where this bike excels.

Frame & equipment:

The Kern is neat and unfussy. Reserved hydroforming of the neatly curved down tube and the subtly dipped top tube is pleasingly non-aggressive. A beefy, and sturdily braced, single pivot swingarm houses Sunn’s NCDO modular dropouts. Under compression, the chainstays pull back on the bottom bracket mounted rocker, which actuates the shock. It’s similar to GT’s original RTS suspension design. 


RockShox’s Revelation fork is excellent, particularly in this Dual Air guise. SRAM X.7 shifters and X.0 rear mech shift faultlessly, and Truvativ’s Stylo cranks are solid underfoot. Formula R1 brakes are small on size and weight, but big on power and modulation. SDG’s I-Fly saddle is light and well shaped, but short on padding for all-day epics.

Product Specifications


Name Kern S1 (10)
Brand Sunn

Brakes R1 180/160
Rims Feather 32
Front Wheel UN Feather 32, QR front and rear
Tyres Hutchinson Barracuda 2.1in, Python 2.0in rear tyres
Top Tube (in) 22.5
Weight (lb) 27.6
Weight (kg) 12.5
Shifters X7
Seatpost Alu
Seat Angle 73
Saddle I-FLY
Cassette Sram PG970 9V
Rear Derailleur XO color
Head Angle 69.1
Handlebar ELITIS
Grips/Tape 2 lock On
Front Derailleur SLX
Frame Material Alpha Tubing
Fork RACE 140
Cranks Stylo 3.3 22/32/44
Chain 951
Rear Wheel UN Feather 32, QR front and rear