For all of the amazing benefit carbon fiber brings to bicycles and componentry -- we're thinking here of frames, forks, rims, handlebars, seatposts, bottle cages, cranksets, etc, etc -- one area where carbon hasn't been widely adopted has been stems. It's not that there aren't a boatload of carbon fiber stems in the marketplace, but rather it's that carbon doesn't have the reputation for making stems lighter, stiffer, stronger, or better in any measurable way. Its benefit seems to be purely aesthetic -- a carbon stem will match all the other carbon bits on your bike, that's about it.FSA manufacturers carbon fiber stems, but perhaps their very best stem (though not their most exotic or their most expensive) is their OS-99 stem. The OS-99 is the lightest stem in the FSA family, and -- believe it or not -- it's made from 7050 aluminum alloy. The 90mm stem weighs a paltry 103g.Don't let the extreme lightness of the OS-99 give you concerns about durability. FSA manufactures it using a proprietary 3D forging technique that uses slow forging speeds and extremely high pressures to eliminate surface deformation. They carefully control the heat treatment process to ensure ideal crystal growth. The heat treatment is so critical to the finished product, in fact, that FSA documents and inspects every heat treatment session to ensure quality. It might weigh 103g, but it has the toughness of a heavyweight.The forged faceplate has a serrated grip area to securely fix both alloy and carbon fiber handlebars. All sharp edges are radiused to eliminate potential stress risers -- even the washers and counterbores for the Ti bolts are radiused for better stress flow. And the clamping area is diagonally cut to better distribute the clamping load across the steerer tube.The OS-99 is available in lengths from 80mm-130mm. It has an 84 degree rise (a.k.a. +/- 6 degrees), with a clamp stack height of 35mm. The clamp diameter is 31.8mm
a Cross Country Rider
from Soquel, CA
Date Reviewed: March 23, 2012
Strengths: Strong, super light and it looks nice
Weaknesses: None that I could find
I have used this stem on three different bikes in two stem sizes and it holds up nice. It has Titanium hardware and it is really light. My 100mm weighed in at 104 Grams and the 80mm was less than100 grams. It has taken some hard crashes and held up great. I am not a down hiller or big jump rider. Look elsewhere for a heavier, beefier stem if you are.