My particular challenge with mountain biking right now is that once I go mountain biking, which I recently did for the first time in a while, it's quite seriously all I want to do. So fun. So. Fun.
Anyhow, this post is about wheels and not my ever precarious cycling missions, so let's jump in. Buying mountain bike wheels is a pain in the butt. Selling them can be a pain in the butt. Stocking parts with which to build them is close to hopeless. In addition to the multiple diameters that rims use, there's a huge range of widths in play, and people are quite specific about which widths they prefer.
In road/cross/gravel, there's basic consensus that an internal rim width of something around 21- or 22mm is ideal for 700c, and slightly wider is the go for 650b. As we've discussed before, the biggest gravel tires for 700c are going to be in the 42mm range, and you want the ratio of tire width to rim width to be a bit bigger with the wider tires (for suspension and rim protection) where the more road oriented tires work better with more even tire to rim width. Since you're more likely to use 42- to 47mm (ish) tires with 650b for gravel, it makes sense to have a slightly wider rim to support a proportional tire to rim width ratio. From there it's just a question of which depth works for you, and there's enough space for our RCG36 and GX24 to have a nice market volume, with the more road-dedicated upcoming Cafe Racer 46 and more cross gravel oriented 28mm rims (did I just say that out loud?) also seeing enough demand to have an easy place. This in addition to all of the outstanding alloy rim options (still love them, yup!) that work so well for road, cross and gravel with both 650b and 700c tires.
In order for us to offer the weight and impact resistance advantages of carbon at a price premium that doesn't make us gag in our mouths a bit and think it's just not worth it, there needs to be that market gravitas. Buying rims for the road/cross/gravel segment in the bulk that allows us to keep them in stock at reasonable cost without locking up an undue amount of dough to do it is easy. The lower market volume and higher specificity of mountain bike requirements makes it harder. For good or bad, the cost of missing out on some sales because we do a 28mm carbon mtb rim and you need one that's 29mm is less painful than having tons of cash tied up in inventory that takes forever to turn. With alloy rims, this isn't an issue since we're able to order rims at wholesale on demand.
As much as we'd love to go full hammer down and do some carbon mtb builds, it's a a struggle to settle on "the right" width. I'm personally using i28mm rims with a 700c rim weight right around 435g that seem pretty awesome. They save almost all of 100g versus an alloy rim of similar specs, while being plenty stiff (always a bit of a nebulous thing) and really strong and impact resistant. At somewhere around a 40% premium to an equivalent alloy build, they're compelling enough that if you were considering an $875 alloy build, there's a good case to be made for choosing carbon. If you're considering a $2000 carbon build, these probably have some notable advantages apart from the significant cost differential (better rims maybe, better hubs almost certainly, plus build quality). And we can be price equivalent to anywhere else you might get a build with these rims. It's just tough to commit to getting the few dozen sets we need to in order to make all that math work, without knowing if the specs hit the sweet spot for a broad enough market.