Rotor S1 stem review

Super-light stem with clever bolt technology

Our rating 
4.5 out of 5 star rating 4.5
GBP £79.00 RRP | USD $174.00

Our review

Ultralight weight with surprisingly rigid feel but special bolts require care in installation
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Rotor made a name for itself with its eponymous cranks and elliptical reference Q-Rings but lessons learned in the development of its latest Ágilis crankset, namely its unique Double Thread Technology (DTT) hardware, have steered the company into the lightweight components direction.


The DTT bolts resemble basic set screws except that each end uses a different thread pitch. Mating parts are essentially pulled together by their respective threads so there’s no head on the bolt and less localized clamp pressure so the parts no longer have to be reinforced there. Once assembled, the DTT bolt also acts as a sort of reinforcement rod (think rebar). According to Rotor, its DTT concept reduces overall component weight, improves stiffness and reliability, and even increases clamping torque.

One thing is for certain: our Rotor S1 sample stem is seriously light, weighing just 112g in a 120mm x ±7.5° x 31.8mm size. Moreover, its oversized dimensions also impart a notably more rigid feel than most other comparably lightweight stems we’ve tested in recent memory and the DTT hardware design makes for a decidedly sleek and graceful appearance (check out the faceplate). Overall quality was excellent, from the precision of the machining work and laser etching to the durability of the anodized finish.

Inexperienced mechanics will want to take some care during installation, though, as using the DTT system isn’t entirely intuitive. The concept does seem to work as advertised but there’s a definite procedure to the operation and it’s relatively easy to do incorrectly. The aggressive extension machining also doesn’t leave much surface area to grab on to slippery carbon handlebars so be sure to have some friction paste on hand (we now use the stuff on all carbon clamp surfaces anyway).


Otherwise, Rotor’s new S1 has emerged as one of our favorite ultralight stems, bearing all of its intended lightweight goodness with little compromise that we can find. A slightly beefier SX model with a four-bolt faceplate is just about ready, too, and Rotor will also launch a lightweight S1 seatpost with DTT technology in the near future. Considering the S1 stem marks Rotor’s first foray outside of cranks and chainrings, we’d say there are likely more good things to come.

Product Specifications


Name S1 stem
Brand Rotor Bike

Weight (g) 109
Length (mm) 120
Stem Rise 7.5
Cap Bolts 2
Colour Black
Available Colours Black Black/Red
Steerer Size 1 1/8
Clamp/Bar Size 25.4 31.8
Material Aluminium
Bike Use Cross-Country Road
Stem Length/Reach Options 100mm 110mm 120mm 130mm 90mm