FSA don’t bill the 1-1/4in version of their OS-120 stem as a cyclo-cross specific item but they may as well do since it’s practically purpose-built for the job, especially for racers on carbon steerer tubes.
The key is the included aluminum shim, which steps the steerer diameter down to the 1 1/8in standard and lends a grippier and more solid clamping surface than bare carbon.
This makes gradually loosening headsets (as a result of gradually slipping stems) on rough terrain a thing of the past, and the shim’s offset slot is very effective at preventing crimping too.
The forged alloy extension and body is sufficiently stout, and the four-plate alloy faceplate lends extra security on the handlebar end – both good things to keep at the back of your head as you’re remounting at top speed after a set of barriers.
However, all that extra clamping power does have a cost as our 100mm-long sample weighs a comparatively heavy 175g.
While there are heaps of other stems out there that are far lighter, not many work quite as well for this specific application (though Syntace’s similarly shimmed – but more expensive – F119 comes to mind). Skip it if you haven’t had headset issues but this might be the answer to your prayers otherwise.