Go to any mountain bike race and you're bound to see a whole slew of Stan's rims. Their Crest, Arch, and Flow rims have always been popular with wheel builders. Mountain biking tends to place a premium on high quality, durable hubs, while it's traditionally turned rims into something of a consumable especially in places like New England where you can have your choice of rocks or bigger rocks.
In the past couple of years, RaceFace (aka Easton) has been making big inroads with their ARC rims. Beautifully made, somewhat more substantial (stiffer and heavier) than Stan's rims, and available in a range of widths, they've become quite popular.
Both companies just released (Stan's just today, although it's been on background for a short time) carbon versions of their component rims. Stan's starts off with the Crest and Arch, which are as always aimed toward XC (Crest) and Trail/All Mountain/Enduro (Arch). RaceFace's ARC Carbon is 31mm wide internal, which is definitely in the wider side of town and more appropriate for tires in the 2.5" and wider range.
So why the about face on carbon? It's all about use case and value proposition (and thus not an about face). Properly done carbon is quite good off road with disc brakes. Without needing to deal with brake heat, you can use more resilient resins, which decreases the likelihood of impact cracks. Both Stan's and RaceFace are onto this, with Stan's stating that their Crest and Arch carbons can deflect 10mm without damage. Alloy rims can do a lot of stuff, but they can't do that. Hookless bead designs help, too, both in strength and reliability of manufacturing. Go to sticker company sites and you will actually see copy in their carbon disc brake rim sections about how they use high temp resins, which is the opposite of what you want in a disc brake rim. Stan's and RaceFace are serious about matching the product to the application here.
There's also a weight benefit. 29" Alloy Crest rims are about 370g each, with the carbon rims knocking about 45g/rim off of that. Stan's also claims a notable lateral stiffness increase in carbon over alloy, which I don't doubt (alloy Crests have never been the world's stiffest rims). So you increase durability while decreasing weight and increasing stiffness, for the tradeoff of price. How you prioritize each of these pieces is up to you, which leaves November able to respond to your priorities with an appropriate build. As always, our infinite array of custom configurations lets you choose your favorite hub and spokes for the job, and they get hand built here by us.
Builds with our usual suspect hub and spoke combos will go up in the MTB section over the next couple of days, with availability of all of these new builds starting next month.