What to Look for in a Carbon Mountain Bike Rim

Carbon bicycle rims have come a long way over the years. Once known for being harsh, brittle, and very stiff, today’s rims offer peak performance, comfort, and are often more durable than aluminum counterparts. Manufacturers have worked on balancing rims so that they are built to perform, while still providing an enjoyable ride-feel in an ongoing battle between stiffness and compliance.

The refinement of carbon mountain bike rims has resulted in an abundance of options, each filling a different niche for different types of riders. Mountain bikes have bellowed into many refined categories such as XC, Downcountry, All Mountain, Trail, Enduro, and Downhill. As the field expands, so have the rim options to match the needs of each type of ride style. What we’re left with is a list of rims that perform exceptionally well, but can be difficult to narrow down for the individual rider. While there is no “best” rim, there are benefits from different options that can pair up with how you ride, and what you need out of a rim.

For this comparison, I’ll be looking at some of my favorite carbon rim options, all available to build in our custom wheel build form. There are many more options, but after building wheels for some serious riders, I can vouch for their craftsmanship, durability, and company support. These options represent carbon rims for bikes in the all-mountain/enduro category.

Rim Profile

One of the most important factors on how a rim rides is the cross-section profile. Tracking trends, we’ve been seeing rim profiles becoming wider and flatter, which has a significant impact on vertical compliance. Vertical compliance results in the feeling that a rider experiences when traversing over rocks and rough terrain. A rim that is more vertically compliant will absorb more of the hard hits, producing a smoother ride feel.

Vertical compliance also affects how a rim tracks over uneven terrain. An overly stiff rim will resist conforming to an impact, leading to a ping-pong effect that can make it harder to hold a line. On the opposite end, a rim that is too compliant will feel “noodly” and will absorb more of the weight being forced upon it. Finding the balance for your ride-type is important in this aspect.

Most companies produce different rims for different disciplines. These line up with the ride styles of the discipline, and the toughness required to hold up to ride demands. Typically XC rims will be lighter, narrower, and lower spoke counts while Enduro rims are built up to handle impacts and drops.

The image above shows the cross-section between the previous generation of ENVE’s M6 all-mountain rim, and their current generation. You’ll notice the new rim design is almost 6mm shallower, creating more radial compliance which allows the rim to flex vertically under load. This can soften impacts and make for a smoother ride.

Having a flatter rim will also make it less stiff laterally, which can impact efficiency while pedaling, and flex while cornering or biking over techy sections. For this reason, ENVE beefed up the rim bead and connecting areas so that it still keeps its performance characteristics and balanced handling.

Looking at some of the other rim choices, you can see the different approaches taken by manufacturers. While ENVE and We Are One opt for flatter and wider rims, Astral and Raceface’s options are taller, but with less material. Hardtail riders will likely appreciate a rim that’s more vertically compliant, while those riding a super plush full suspension may desire to stiffen up their ride with a more angular rim.

Internal Rim Width

The rims in the above image all represent wheels that could be used all-mountain/enduro type bikes. These bikes typically ride best with tires in the 2.3-2.6″ range. The most important factor for pairing a rim to tire size is the rim’s internal width, measured from bead to bead. This profile determines how the tire will sit on a rim – the wider the internal width, the flatter the tire profile will be. Flatter profiles can help with traction, especially while cornering, while a rounder tire profile can be more efficient when pedaling on straightaways.

This characteristic is shown in ENVE’s M6 rim, which has front and rear-specific rim widths. The front M6 rim has a 32mm internal width with a 29mm rear rim. This helps with traction on the front tire, helping to lock into corners and dirt, while the rear width creates a more round tire profile, excellent for acceleration and rolling resistance.

Generally speaking for mountain bike rims, an internal width of 27mm-29mm (XC) will be best for 2.1″-2.35″ tires, a 30mm-32mm (Downcountry/All Mountain) will be best for 2.35″-2.6″ tires, and 33-36mm (Enduro/Downhill) will be best for 2.6″-2.8″ tires.

Spoke Count & Spoke Choice

Spoke Count

With a handbuilt wheel, we’re able to create strong and stable wheels with most common hole counts. For carbon mountain bike wheels, 24 hole or 28 hole is standard for XC, while 28 hole or 32 hole is typical for all-mountain and enduro.

One thing to keep in mind is that while more spokes makes the wheel stronger, it also makes the wheel significantly stiffer. For people riding long distances at a time, or lighter riders, lower spoke counts can sometimes make sense over maximum spoke counts. As mentioned above, compliance is also a factor for traction – an overly stiff front wheel can be harsh and springy compared to a lower spoke count wheel. Custom wheelsets can be a great option for riders who want to mix-and-match with a stiff and strong rear wheel, but a more compliant front wheel.

Bigger riders, or bikepackers who carry a lot of gear will likely benefit from a custom built wheel with a higher spoke count. The added weight of camping gear can add extra stress to the wheel which can cause premature spoke fatigue. It can also stress the wheel in a way that changes the performance characteristics that the wheel was designed for. Most rim manufacturers offer options for higher spoke count rims for this reason so that wheelbuilders can select the details for the individual rider.

Spoke Choice

Spoke choice is also an important factor in building a custom wheel. Round, double-butted spokes offer strong builds that are easiest to source replacements for, and are the easiest to maintain and true down the line. They are also laterally stiffer than comparable bladed spokes. DT Swiss competition spokes are our go-to for a reliable, decently light and affordable spoke.

Bladed spokes have many performance advantages but come with some considerations. They’re most noticeable for aerodynamic advantages at high speeds – which is not as significant of an advantage for mountain biking. Additionally though, they do produce a more radial stiff wheel which is an important factor for acceleration and power transfer in the wheel. For this reason, you can use a lighter spoke than a comparable round spoke and get similar performance advantages. Bladed spokes do come at usually ~twice the price of round spokes, and in my experience are harder to maintain and source if the wheel does go out of true.

My current favorite spoke for mountain bike wheel builds is the DT Swiss Revolite spoke. It has a fluted design that’s somewhere between bladed and round. This combines the advantages of being lightweight, and achieves the characteristics of lateral stiffness of a round spoke and the radial stiffness of a bladed spoke. This increases the durability of the spoke since it is not flexing under stress as often, yet keeps the performance characteristics of a bladed spoke.

There are several factors to consider when building up a custom wheel, but it is truly the best way to achieve a wheelset that ticks all the boxes for you as a rider and your ride styles and goals. Take a spin on our custom wheel builder to see what options are possible and don’t hesitate to reach out for recommendations and real-rider experiences on the different rim and spoke options.