Carbon fiber. We see it on frames. We see it on saddles. We see it on handlebars, seatposts and wheelsets. We don't see this material on stem's much though. Ever wondered why?
Sure there are carbon stems out there. They tend to fall into two camps though. Carbon laminated ie coated over alloy or full carbon construction stem that is usually heavier than their alloy counterpart.
Unlike parts on a bicycle such as seatposts where the measurable amount of stress and movement placed on it is rather one dimensional in nature, a stem's movement is a lot more variable in nature. It needs to be stiff in almost all directions. Think about how cornering loads up your stem. Now think about when you get out of the saddle and wring your handlebars to sprint. Think about how you hop over a pot hole. The deflection and stress you place on your stem is hugely variable. This raises certain challenges in construction to produce a product that is both light/stiff in all directions of deflection or rather to produce a product that is different enough it can be considered an improvement over an aluminium stem.
If a typical lightweight alloy stem weighs in at around the 110-120g range pre tuning (ie titanium bolts) then the MCFK stem certainly hits the mark in-terms of justifying it's entry price weight wise. Starting at 77g it is a whopping 30% lighter dependent on length.
From a riding perspective the MCFK stem is fairly unique. One of the first things you notice is how buttery it feels. It feels very much like when you upgrade from a set of alloy handlebars to a set of carbon. Bumps are smoothed over and small vibrations are further minimised. Carbon construction here has the same effect as it does on seatposts or handlebars providing an excellent vibration damper to mute unwanted road chatter. This also means that you corner better because you are further isolated from bumps mid corner.
You do notice that even though it feels soft to ride, it certainly isn't missing stiffness. When comparing this stem to other stems of comparative weight, it is markedly stiffer in all directions. In fact it is probably one of the stiffest stems possible, if you factor in stiffness to weight ratio. There is a little bit of a twang in the stem as you load it up which is fairly unique to carbon stems and something that makes riding out of the saddle interesting.
Installing the MCFK stem involves slightly more effort vs a traditional stem. Due to the opening on the stem, you may have to unravel a little bit of your bar tape as the stem will not slide over the clamping zone of your handlebar directly. The stem can be installed by inserting it around the handlebar at a narrower point and then sliding it into the middle of the clamping zone. The stem was constructed like this as a feature so that the stem covers more of the clamping zone around the handlebar to ensure a better and safer interface. Finally the stem has a fairly long stack height so adequate steerer length is necessary for installation.
If you are in the market to upgrade your alloy stem but still want to keep within the sub 100g mark, the MCFK is an interesting proposition for stem options. You do pay more but you receive the holy trinity of comfort/weight/stiffness and in this case, it is a very balanced stem in terms of performance.